From: Brian Lo Newsgroups: rec.gardens Subject: FAQ: More on Onions II Date: Wed, 1 Mar 1995 14:57:29 -0800 ONIONS - PEARL, SET & BOILER Allium cepa Onion bulb size is influenced by a number of factors. Variety, plant density, photoperiod and temperature are several important ones. Small bulb onions are usually produced in the Northwest by using techniques that capitalize on the onion's response to day length, plant density and temperature. Pearl onions are short-day varieties grown under the Northwest's long-day summer conditions and planted at very high plant popula- tions to produce the necessary yields. Onions for "sets" or "boiler" produc- tion may be short, intermediate, or long-day types also grown at high popula- tions and using planting dates that capitalize on optimum warm summer tempera- tures at bulbing. Technically, all onions are "long-day" plants, in that bulbing begins as day length increases. Short-day varieties are those requiring only 10 to 12 hours of day length for bulbing to occur. These are grown in southern states generally below the 35 th. parallel, and are not suitable for bulb production in the northwest, except as pearl or boiler varieties, or for over-winter production. Temperatures and light intensity and light quality (red:far red) can modify onion bulbing response. High temperatures and bright days can "compen- sate" for some day length, causing onions to bulb sooner than they would otherwise. Overcast, cool temperatures, delay bulbing. Time of bulbing is an important factor in determining onion bulb size. Early bulbing contributes to small bulb size, with delayed bulbing resulting in larger size. Selecting the correct variety for your production area and understanding the climatic and other environmental factors that affect its performance is extremely important. VARIETIES Pearl or cocktail onions: Crystal Wax (also known as White Bermuda), Eclipse (L303), Barletta (or White Pearl), White Mexican (or El Toro). All these are short-day varieties that bulb shortly after emergence to produce the desired bulb size at the lattitudes of Pacific Northwest production areas. Set onions: Generally long day varieties such as Stuttgart, Yellow Ebenezer, Yellow Rock, White Ebenezer, and Red Weathersfield are used. Boiler onions: Small bulbs (1-1 3/4 inches) of any of the varieties listed above may be used. When planting specifically for boilers, Southport White Globe or the yellow types such as Stuttgart, Australian Brown or Yellow Ebenezer are commonly used. SEED COMPANIES Asgrow Seed Company, POB 5038, Salinas CA 93915 Crookham Co. Caldwell, ID 83606 Ferry-Morse Seed Co. POB 4938, 555 Codoni Ave. Modesto, CA 95352 Harris Moran Seed Co. 3670 Buffalo Rd. Rochester, NY 14624 Petoseed Co. Inc. POB 4206, Saticoy, CA 93303 Sunseeds, 2320 Technology Pkwy. Hollister, CA 95023 Zenner Bros. Seed Co., Inc. 1311 S.E. Gideon St. Portland, OR 97202 SOIL TEMPERATURE The optimum temperature range for germination is 48 to 90 F. March and April plantings in western and central Oregon and late February to April in eastern Oregon and the Columbia Basin. SOILS In western Oregon, onions are grown on peat soils or silt loams and sandy loams. For pearl or cocktail onions, soils must be friable to allow rapid mechanical separation of onions from the soil at harvest. Loamy sands or similar sandy soils are best. SEEDING Onion seed numbers approximately 9,500 per ounce. These onions are all direct seeded at high seeding rates using specially designed planters that allow for uniform scattering of the seed and close spacings between rows. This is usually done using gangs of planters mounted on multiple tool bars. Depth of seeding has an effect on bulb shape since the onion stem plate (the base of the onion bulb) forms at the point where the seed germinates. Shallow planting results in flatter bulbs, while deeper seed placement results in taller, and sometimes top-shaped bulbs. Plant density also has an effect on onion shape, with onions tending to be taller at high density. When round onions are desired at the high densi- ties used for pearl onions, use varieties that tend to be flat-round in the southern U.S. production areas where they are normally grown as fresh market bulb onions. All these onions are spring seeded. Onions may be seeded as soon as the land can be made ready, but April is considered ideal. Seeding should be completed by May l in Eastern Oregon and May 5 in Western Oregon. Pearl onions are seeded at 80 to 110 lbs of seed per acre depending on the size distribution of the onions desired. The lower densities provide a higher percentage of "boiler" size onions. A Planet Jr. seeder plate number 23 to 26 will provide approximately 80-110 lbs of seed per acre on a total broadcast basis, at a planting speed of about 3 MPH. To accomplish total broadcast plantings, gangs of planters are mounted on several tool bars in a staggered arrangement and 4 inch scatter shoes are used to cover the desired bed width. Onions for sets are seeded at about 55-75 lbs. per acre. Distribute seed in a wide band so that plants are approximately 1/2 inch apart. Uniform distribution of seed is important in obtaining good yields and size distribu- tion. When planting in rows, growers in western Oregon use custom built planting units that meter six rows at a time. These are spaced to plant 18 rows accross a 40 inch bed. These planters use metering units such as those used in dispensing granular materials. These are fitted with flexible tubes that direct the seed to scatter shoes mounted on Planer Jr. or similar seeder frames. When planting primarily for boiler onions, a seeding rate of about 20 to 30 lbs. per acre is used. Seeds are 3/4 to 1 inch apart. They may be planted as described for pearl or set onions above. FERTILIZER Western Oregon Mineral Soils: A soil test is the most accurate guide to fertilizer requirements. Good management practices are essential if optimum fertilizer responses are to be realized. These practices include use of recommended varieties, selection of adapted soils, weed control, disease and insect control, good seed bed preparation, proper seeding methods, and timely harvest. Because of the influence of soil type, climatic conditions, and other cultural practices, crop responses from fertilizer may not always by accurate- ly predicted. Soil test results, field experience, and knowledge of specific crop requirements help determine the nutrients needed and the rate of applica- tion. The fertilizer application for onions should insure adequate levels of all nutrients. Optimum fertilization is essential for top quality and yields. NITROGEN (N): N rates of 80-100 lbs/A should be broadcast and worked into the seedbed before planting, using fertilizers such as ammonium sulfate, 16-20-0 or a mixed fertilizer containing sulfate sulfur. Caution, when mild-flavored onions are desired, reduce sulfur applications to the minimum recommended for proper plant growth since sulfur applications have been shown to increase onion pungency (see sections on "sulfur" below). If necessary, additional nitrogen may be applied during the growing season. Sidedressed nitrogen applications or nitrogen applied in irrigation water can be an effective means of providing supplemental nitrogen to the crop during the season. DO NOT use aqua or anhydrous ammonia in sprinkler irriga- tion. Shallow incorporation of high rates of topdressed or broadcast fertiliz- er N can seriously reduce onion stands. Nitrogen liquid fertilizer formulations having herbicidal effects: AN-20, Ammonium Thiosulfate and mixtures of these two materials can be used in a number of crops. Monocarbamide Dihydrogensulfate (Monourea sulfuric acid) is used in Alliums such as onion, shallots, leeks and garlic. The amount of nitrogen per gallon of material, the rate at which it is applied, and the phyto-toxicity of the material determines what crops these can be used on. Monocarbamide Dihydrogensulfate (Monourea sulfuric acid) is also sold as an herbicide under different trade names (see below). ALWAYS FOLLOW THE LABEL WHEN USING THIS MATERIAL AS AN HERBICIDE. All of these materials, when applied at the proper time and manner have the added benefit of ancillary control of many small (less than 3 inches) broadleaf weeds such as groundsell, pineapple weed, shepherdspurse, mallow, pigweed, hairy nightshade chickweed and many others. Poor, or no control is obtained on lambs quarters, purslane, henbit, black nightshade, knotweed, sow thistle, malva goosefoot and grasses. When using these nitrogen sources in foliar applications, follow cau- tions listed. Severe crop injury may occur if cautions are not observed. General cautions that apply to nitrogen liquid fertilizer formulations are: * Apply to onions only after the first true leaf is as tall as the flag leaf and before onions are 8 inches tall. * Do not apply within 4 days of a period of cool, cloudy or rainy weather, or if free water is present on the leaves. * Discontinue application if spray droplets do not roll off or "bead- up" on the leaves. This indicates a deficiency of adequate waxy cuticle, and may be a temporary condition due to rapid growth, cloudy or rainy weather, or more seriously, the lack of adaptability of the variety. * Do not apply within 4 days after a foliar pesticide has been applied, or with any wetting agent. * Use large nozzles to minimize misting. AN-20 fertilizer formulation: This is a manufactured 20-0-0 formulation (containing 20% N) that may be applied at 50 to 70 gallons of product per acre as a foliar spray. This form- ulation weighs 10.55 lbs per gallon and contains 2.11 lbs N/gallon of product and would provide approximately 100 to 140 lbs N/acre (but some N is lost through volatilization). Do not irrigate for 48 hours after application, but irrigate then to move the fertilizer into the root zone. When this treatment is used, subsequent nitrogen side dressings may be reduced by a portion of the amount of N applied in the treatment. Note: Mixtures of An-20 and Ammonium thiosulfate (usually 1:1) can be made which will reduce the amount of nitrogen applied, provide some sulfur (if AN-20 only would have been applied, and reducing the sulfur if only Ammonium thiosulfate were to be used), and be as effective as either material alone. Application rates are still held at 50 to 70 gallons of the mixture per acre. Note: This formulation is different from a solution that could be prepared by dissolving ammonium nitrate in water. Such a solution would not have the same concentration or herbicidal effect. Also, To prevent crop injury, follow the cautions listed above. ***** Ammonium thiosulfate: This is a manufactured 12-0-0-26 formulation (containing 12% N and 26% sulfur) and weighs 9.33 lbs per gallon. It may be applied at 50 to 70 gallons of product per acre as a foliar spray. This solution contains 1.12 lbs nitro- gen and 2.4 lbs sulfur per gallon of product and would provide approximately 55 to 75 lbs N/acre (some N may be lost through volatilization). At the application gallonage mentioned, about 150 to 168 lbs of S are also applied. Do not irrigate for 48 hours after application, but irrigate then to move the fertilizer into the root zone. When this treatment is used, subsequent nitrogen side dressings may be reduced by a portion of the amount of N applied in the treatment. Note: Mixtures of An-20 and Ammonium thiosulfate (usually 1:1) can be made which will reduce the amount of nitrogen applied, provide some sulfur (if AN-20 only would have been applied, and reducing the sulfur if only Ammonium thiosulfate were to be used), and be as effective as either material alone. Application rates are still held at 50 to 70 gallons of the mixture per acre. Also, To prevent crop injury, follow the cautions listed above. ***** Monocarbamide Dihydrogensulfate (Monourea sulfuric acid) 15-0-0-16 (n-pHuric or ENQUIK): This product is also registered as an herbicide to be applied at 10 to 30 gallons of product per acre as a foliar spray. FOLLOW THE LABEL INST- RUCTIONS WHEN USING IT AS A NITROGEN SOURCE OR AS AN HERBICIDE. It weighs 12.65 lb/gallon and contains 1.9 lbs of nitrogen and 2.0 lbs sulfur per gallon of product. It is most generally used at about 15 to 20 gallons per acre pro- viding approximately 28 to 38 lbs of N per acre (but some N is lost through volatilization). Apply in sufficient water to get good foliar coverage (approximately 1:1 dilution). Do not irrigate for 48 hours after application, but irrigate then to move the fertilizer into the root zone. When this treatment is used, subsequent nitrogen side dressings may be reduced by a portion of the amount of N applied in the treatment. CAUTION: This solution is corrosive, and can injure skin and damage spray equipment. Use proper safety precautions and suitable spray equipment (stainless steel). Also, To prevent crop injury, follow the cautions listed above, and FOLLOW ALL LABEL INSTRUCTIONS. ***** PHOSPHORUS (P): Phosphorus is essential for vigorous early growth of seedlings. If the OSU soil test Apply this amount of for P reads (ppm): phosphate (P2 O5) (lbs/A): 0-40 170-200 40-100 140-170 over 100 100-140 POTASSIUM (K): All K should be applied and worked into the seedbed before planting. Onions require medium levels of available soil potassium. The K soil test is based on K present in the surface soil (0-12"). If the OSU soil test Apply this amount of for K reads (ppm): potash (k2 o) (lbs/A) 0-100 150-200 100-200 100-150 200-350 50-100 Over 350 0-50 MAGNESIUM (Mg): When the soil test value is below 1.0 meq Mg/100g, broadcast 20 to 25 lb Mg/A and work into the seedbed before planting. If deficiency symptoms appear, spray with 10 lb Epsom salts in 100 gal water/A. Mg can also be supplied in dolomite, which is a liming material and reduces soil acidity to about the same degree as ground limestone. Dolomite should be mixed into the seed bed in the fall. BORON (B): No consistent responses of onions to the application of B have been observed in western Oregon. Where the soil test for B is below 0.25 ppm growers may wish to make a trial application of 2 lb B/A. Too much B fertili- zer can be highly toxic and suggested rates of B application should not be exceeded. B should be evenly distributed over the field and not banded. ZINC (Zn): The application of Zn has increased the yield of onions where soils have been deficient. When the soil test for Zn is below 2 ppm broadcast 10 lb Zn/A before planting or include 3-4 lb Zn/A in the fertilizer band. A broadcast application of 10 lb Zn/A should supply Zn needs for 2 or 3 years. OTHER NUTRIENTS: Responses of onions to nutrients other than those discussed in this guide have not been observed in western Oregon. LIME: Onions are classified as being "very sensitive to soil acidity" when grown on mineral soils. Lime applications should be considered when mineral soil pH is 6.0 or below. Lime should be mixed into the soil in the fall for best results. Keep mineral soil pH between 6.0 and 6.8. For acid soils low in magnesium (Mg) (less than 1.0 meq Mg/100 g of soil) 1 Ton/A of dolomite lime can be used as a Mg source. Dolomite and ground limestone have about the same ability to neutralize soil acidity. Western Oregon Muck Soils: A soil test is the most accurate guide to fertilizer requirements. Good management practices are essential if optimum fertilizer responses are to be realized. These practices include use of recommended varieties, selection of adapted soils, weed control, disease and insect control, good seed bed preparation, proper seeding methods, and timely harvest. Because of the influence of soil type, climatic conditions, and other cultural practices, crop responses from fertilizer may not always by accurate- ly predicted. Soil test results, field experience, and knowledge of specific crop requirements help determine the nutrients needed and the rate of applica- tion. The fertilizer application for onions should insure adequate levels of all nutrients. Optimum fertilization is essential for top quality and yields. NITROGEN (N): See also the comments in the section "western Oregon mineral soils - nitrogen regarding "liquid nitrogen fertilizer solutions having herbicidal effects" as you consider nitrogen applications on western Oregon muck soils. N rates of 60-80 lbs/A should be broadcast and worked into the seedbed before planting, using fertilizers such as ammonium sulfate, 16-20-0 or a mixed fertilizer containing sulfate sulfur. Caution, when mild-flavored onions are desired, reduce sulfur applications to the minimum recommended for proper plant growth since sulfur applications have been shown to increase onion pungency (see section on "sulfur" below). If necessary, additional nitrogen may be applied during the growing season. Refer also to the section above "western Oregon mineral soils - nitrogen" regarding "liquid nitrogen fertilizer solutions having herbicidal effects" as you consider nitrogen fertilization. PHOSPHORUS (P): P is essential for vigorous early growth of seedlings. If the OSU soil test Apply this amount of for P reads (ppm): phosphate (P2 O5) (lbs/A): 0-40 120-150 40-100 80-120 over 100 60-80 POTASSIUM (K): K should be applied and worked into the seedbed before planting. Onions require medium levels of available soil potassium. The K soil test is based on K present in the surface soil (0-12"). If the OSU soil test Apply this amount of for K reads (ppm): potash (k2 O) (lbs/A): 0-100 150-200 100-200 100-150 200-350 50-100 Over 350 0-50 MAGNESIUM (Mg): When the soil test value is below 1.0 meq Mg/100g, broadcast 20 to 25 lb Mg/A and work into the seedbed before planting. If deficiency symptoms appear, spray with 10 lb Epsom salts in 100 gal water/A. Mg can also be supplied in dolomite, which is a liming material and reduces soil acidity to about the same degree as ground limestone. Dolomite should be mixed into the seed bed in the fall. BORON (B): No consistent responses of onions to the application of B have been observed in western Oregon. Where the soil test for B is below 0.25 ppm growers may wish to make a trial application of 2 lb B/A. Too much B fertili- zer can be highly toxic and suggested rates of B application should not be exceeded. B should be evenly distributed over the field and not banded. ZINC (Zn): The application of Zn has increased the yield of onions where soils have been deficient. When the soil test for Zn is below 2 ppm broadcast 10 lb Zn/A before planting or include 3-4 lb Zn/A in the fertilizer band. A broadcast application of 10 lb Zn/A should supply Zn needs for 2 or 3 years. COPPER (Cu): Muck soils tend to be deficient in Cu and "fix" Cu. If Cu has not been applied for 3 years , apply 15-25 lb Cu/A to the soil before planting, OR two foliar applications of 1-2 lb Cu in 100 gal water /A may be applied to onion leaves. Soil Cu applications need not be repeated every year. The best indi- cator for copper is leaf analysis. Consider copper applications when leaf copper levels are below 4 ppm. OTHER NUTRIENTS: Responses of onions to nutrients other than those discussed in this guide have not been observed in western Oregon. LIME: Experimental work on the muck soils of western Oregon has shown that onions will produce good yields over a fairly wide range of muck soil acidity. Lime applications should be considered when the soil pH is 5.5 or below. Keep muck soil pH between 5.6 and 6.0. The liming rate is based on 100-score lime. A lime application is ef- fective over several years. If the OSU soil test Apply this amount for pH reads: of lime (Tons/A): below 5.0 4-5 5.0-5.5 2-4 over 5.5 0 Lime should be mixed into the soil in the fall. For acid soils low in magnesium (Mg) (less than 1.0 meq Mg/100 g of soil) 1 Ton/A of dolomite lime can be used as a Mg source. Dolomite and ground limestone have about the same ability to neutralize soil acidity. Do not apply lime when the muck soil pH is above 6.0. Decreased yields have resulted in Willamette Valley experiments when liming raised the soil pH to 6.5. Eastern Oregon Mineral Soils: NITROGEN: See also the comments in the section "western Oregon mineral soils - nitrogen regarding "liquid nitrogen fertilizer solutions having herbicidal effects" as you consider nitrogen applications on eastern Oregon mineral soils. Onions require a good supply of available N however excess N applica- tions can result in late maturity and large necks that are difficult to cure, soft onion bulbs, and poor storage quality. Sidedressed nitrogen applications or nitrogen applied in irrigation water can be an effective means of providing supplemental nitrogen to the crop during the season. DO NOT use aqua or anhydrous ammonia in sprinkler irriga- tion. Shallow incorporation of high rates of topdressed or broadcast fertiliz- er N can seriously reduce onion stands. Excessive nitrogen available to onions, particularly later in the season (mid-July), can delay onion maturity and make field curing of onions more difficult. The amount of N fertilizer required depends on the nitrogen carry-over from the previous crop and the amount and type of residue to be plowed under. The amount of residual N in the soil varies considerably. A soil test for nitrate-N (NO3-N) helps in evaluation the N carry-over from the previous crops in the case of mineral soils with organic matter content below 2%. Soil samples for NO3-N should be taken in the spring prior to the appli- cation of N fertilizer. Soil samples should be taken from the 0-12 inch soil depth. OSU soil test results for N are reported in ppm. One ppm N in a 12 inch depth of soil equals about 4 lbs N/acre. Nitrate-N Soil Test (ppm) (in 12 inch depth) N application (lbs/A) 0 150 10 125 20 100 30 75 over 30 75 PHOSPHOROUS (P): Onions require relatively high levels of available P. The P soil test is based on P present in the surface soil (0-12"). If the OSU soil test Apply this amount of for P reads (ppm): phosphate (P2 O5) (lbs/A): 0-5 170-200 5-10 140-170 10-15 110-140 15-20 80-110 Over 20 50-80 POTASSIUM (K): Onions require medium levels of available soil potassium. The K soil test is based on K present in the surface soil (0-12"). If the OSU soil test Apply this amount of for K reads (ppm): potash (k2 o) (lbs/A) 0-100 150-200 100-200 100-150 200-350 50-100 Over 350 0-50 SULFUR (S): Onions require relatively high levels of available S. Sulfur fertilizer requirements will vary with soil texture, leaching losses, and S content of the soil. S is frequently contained in fertilizers used to supply other nutrients such as N, P, and K and may be present in irrigation water, which can be tested for S content. Plants absorb S in the form of sulfate. Fertilizer materials supply S in the form of sulfate and elemental S. Elemental S must convert to sulfate in the soil before the S becomes available to plants. The conversion of elemental S to sulfate is usually rapid for fine ground (less than 40 mesh) material in warm, moist soil. Elemental S should be applied the year preceding the crop, using finely ground material. A soil test for sulfate-S is not recommended if elemental S was applied the preceding year. If S levels in the soil are not known, apply 40-60 lbs S/A. Caution, when mild-flavored onions are desired, reduce sulfur applications to the minimum rate recommended for proper plant growth since sulfur applications have been shown to increase onion pungency. Onion pungency is also strongly dependent on the variety being used. Elemental S is a strong acidifier. S in the sulfate form can be applied at planting time. ZINC (Zn): An application of Zn is suggested when the Zn soil test value is below 0.8 ppm. Where Zn is required, either 10 lb/A of Zn should be broadcast and worked into the soil prior to planting or 3-4 lb/A of Zn should be banded with the fertilizer at planting time. An application of 10 lb Zn/A should supply Zn needs for 2 or 3 years. To correct Zn deficiency during the growing season, thoroughly wet plants with a solution containing 1 lb Zn in 50-100 gallons of water. Banding an acidifying fertilizer such as ammonium sulfate can reduce Zn deficiency. Zn deficiency is most likely to occur on calcareous soils where land leveling has exposed a calcareous subsoil. OTHER NUTRIENTS: Responses of onions to other nutrients and lime have not been observed on mineral soils in eastern Oregon. IRRIGATION Onions are shallow-rooted, and require a constant supply of moisture. Maintaining moisture near the surface, at the onion stemplate is important in root generation. Onion roots generate at the stemplate only when moisture is present. Proper moisture management is important in alleviating pink root problems, general root health, and therefore bulb growth vigor. Excessive irrigation causes nitrogen movement beyond the root system and reduces nitrogen available to the plants. Soil type does not affect the amount of total water needed, but does dictate frequency of water application. Lighter soils need more frequent water applications, but less water applied per application. HARVESTING, HANDLING, CURING, AND STORAGE Although small in size, yields of pearl onions can be about 20 tons/acre when the correct plant population and other cultural practices are realized. Harvesting begins after tops have fallen and dried thoroughly. Beds of pearl onions intended for processing are topped using flail choppers or mowers just prior (about 24 hours) to digging the onions. This allows the tips to dry yet does not allow the onions to green or scald. In western Oregon, "set" onions may be harvested and temporarily stored without removing the tops. Tops are removed prior to packaging. When tops are not to be removed, "set" onions are undercut and allowed to cure in the field. Undercutting us accomplished in such a way as to lay the tops over the windrow to protect the onions from sunscald. "Set" onions must not have been treated with sprout inhibitors commonly used in bulb onion production. When pearl onions are harvested for processing, they are undercut to remove as much of the root system as possible and harvested using specialized equipment designed specifically for pearl onion production. Harvesters lift the entire bed and convey the onions over closely spaced rod conveyers to bins or bulk trucks for transport to the processing plant. Onions intended for storage should be adequately cured in the field, in open sheds, or by artificial means before or in storage. Adequate curing in the field or in open sheds may require 2 to 4 weeks, depending on the weather. The best temperatures are 75 to 90 F. STORAGE (modified from USDA Ag. Handbook #66): Pearl, set and boiler onions may be held in either common or cold storage. Storage quality is influenced by cultivar and by the conditions under which they are grown. Onions are damaged by freezing, the damage appearing as water soaked scales when the thawed onions are cut. Onions only slightly frozen may recover with little perceptible injury if allowed to thaw slowly and without handling. Store at 32 F and 65 to 70 % relative humidity. The temperature and humidity requirements for onion sets, used primarily as planting stock for early green onions, as well as pearl and boiler onions are essentially the same as those for large dry onions. Because of their small size, these onions tend to pack closely, so they should not be placed into deep piles. They are usually held in ventilated storage in shallow, slatted trays rather than in bags or crates. Set onions are handled in mesh or Kraft paper bags for marketing. Low relative humidity and low temperature are important to keep the sets sound and dormant and free from sprouting and rooting. At humidities much above 70 % and at warmer temperatures (40 to 50 F), more of the sets will sprout, develop roots and decay. Onion sets should be stacked to allow good air circulation. A storage life of 6 to 8 months is possible for good quality sets. Onions should not be stored with other products that tend to absorb odors. They may be stored with garlic. Set onions are handled in mesh or Kraft paper bags for marketing. Low relative humidity and low temperature are important to keep the sets sound and dormant and free from sprouting and rooting. At humidities much above 70 % and at warmer temperatures (40 to 50 F), more of the sets will sprout, develop roots and decay. Onion sets should be stacked to allow good air circulation. A storage life of 6 to 8 months is possible for good quality sets. Onions should not be stored with other products that tend to absorb odors. They may be stored with garlic. PEST CONTROL FOR ONIONS, PEARL, SET & BOILER THE PESTICIDES LISTED BELOW, TAKEN FROM THE PACIFIC NORTHWEST PEST CONTROL HANDBOOKS, ARE FOR INFORMATION ONLY, AND ARE REVISED ONLY ANNUALLY. BECAUSE OF CONSTANTLY CHANGING LABELS, LAWS, AND REGULATIONS, OREGON STATE UNIVERSITY CAN ASSUME NO LIABILITY FOR THE CONSEQUENCES OF USE OF CHEMICALS SUGGESTED HERE. IN ALL CASES, READ AND FOLLOW THE DIRECTIONS AND PRECAUTION- ARY STATEMENTS ON THE SPECIFIC PESTICIDE PRODUCT LABEL. USE PESTICIDES SAFELY! Wear protective clothing and safety devices as recommended on the label. Bathe or shower after each use. Read the pesticide label--even if you've used the pesticide before. Follow closely the instructions on the label (and any other directions you have). Be cautious when you apply pesticides. Know your legal responsibility as a pesticide applicator. You may be liable for injury or damage resulting from pesticide use. WEED CONTROL Cultivate as often as necessary when weeds are small. Proper cultiva- tion, field selection and rotations can reduce or eliminate the need for chemical weed control. THE WEED TREATMENTS LISTED BELOW ARE TAKEN FROM THE PACIFIC NORTHWEST WEED CONTROL HANDBOOK, AND ARE FOR INFORMATION ONLY. CONSULT PRODUCT LABELS FOR CURRENTLY LEGAL REGISTRATIONS, RATES, AND COMPLETE INSTRUCTIONS. WEED MANAGEMENT GENERAL STRATEGY Onions are a noncompetitive crop with short, vertical leaves that fail to form a canopy that suppresses weeds. Weeds are managed with selective herbicides combined with frequent cultivation. Winter cover crops or crop rotations enhance both soil and weed management. ______________________________________________________________________________ STALE SEEDBEDS FOR VEGETABLE PRODUCTION Stale seedbeds are sometimes used for vegetable production when other selec- tive weed control practices are limited or unavailable. The concept depends on controlling the first flush of emerged weeds before planting or emergence of the crop followed by minimal soil disturbance which reduces subsequent weed flushes during establishment of the crop. Following establishment, other weed control practices including cultivation or use of other herbicides can be used. 1. Prepare a seedbed, preferably 2 to 3 weeks before planting to achieve maximum weed seed germination near the soil surface. Soil temperatures and moisture must be reasonable or results will be erratic. 2. Plant the crop with minimum soil disturbance. Otherwise, new weed seed will be exposed to favorable germinating conditions. 3. Just before or after planting but before crop emergence, treat the field by flaming or with herbicide to kill all germinated or exposed weeds. Weed Treatment Active Ingredient Per Acre and Application Comments ------------------------------------------------------------------------------ Flaming Use liquid propane or similar fuel-burning equipment to quickly sear the weeds, but not consume them with flame. ------------------------------------------------------------------------ paraquat 0.625 to 0.94 lb ai/A Gramoxone Extra (see remarks) Restricted-use pesticide. Do not ingest or inhale spray mist. Wearing protective face shields, respirators, and clothing is advised. Apply during or after planting, but before crop emergence. Add a nonionic surfactant or crop oil concentrate according to label specifications, taking care to avoid anionic formulations that react in the tank to form insoluble precipitates. Exposed crop plants will be killed. Do not apply preplant or preemergence to soils lacking clay minerals, such as peat, muck, pure sand, or artificial planting media. (Acts as contact; absorbs energy produced by photosynthesis forming peroxides that disrupt living cells.) ------------------------------------------------------------------------ glyphosate Consult Labels Roundup Roundup RT (E. Washington and Idaho only) or Honcho + nonionic surfactant Apply to actively growing weeds either preplant in conjunction with site preparation or preemergence crops listed on the label. Consult label for specific rates, times of application, and perennial species control- led. Generally 1 to 1.5 lbs ai/A should be used for annual weeds, while perennial weeds require higher rates. Addition of a surfactant or ammonium sulfate improves activity when weeds are stressed. Do not apply more than 8 lbs. ai/A per year, nor plant nonlabeled crops within 12 months following application. (Inhibits production of 3 amino acids and protein synthesis.) ______________________________________________________________________________ ONIONS--MINERAL SOILS Weed Treatment Active Ingredient Per Acre and Application Comments ------------------------------------------------------------------------------ bensulide 3 to 6 lb ai/A Prefar (spring planted bulb onions only) Idaho, Oregon and Washington special local needs (SLN-ID840011 and OR840041 and WA880015) only. Apply 3 lb rate in fall in 10-12 inch band and bed-up by throwing soil from furrows over the sprayed band, or broadcast 6 lb rate and incorporate before bedding up in the fall. In spring, drag-off bed tops with spiketooth harrow being careful not to expose soil beneath the treated layer. Plant in center of beds. (Inhibits roots of seedlings). ------------------------------------------------------------------------ DCPA 6 to 9 lb ai/A Dacthal Apply after planting to moist soil surface before weeds and onions emerge. In eastern Oregon when rainfall is sparse, shallow incorpora- tion using a nailboard has improved weed control. Results are improved with overhead irrigation immediately following application. Consult label for planting sensitive crops within 8 months. (Inhibits mitosis). ------------------------------------------------------------------------ oxyfluorfen 0.12 to 0.25 lb ai/A Goal Causes skin irritation--Wear protective gear. Apply postemergence to onions with 2 fully developed true leaves while broadleaf weeds have less than 4 true leaves. Multiple treatments may be required as new weeds emerge, but do not exceed 0.5 lb ai/A. Use a clean sprayer and do not mix with oils, surfactants, or other agricultural chemicals. Do not apply to onions under any stress. Slight leaf curl may occur and young plants sometimes become prostrate on the soil surface for 1 to 2 days, but yields have not been reduced. Do not apply within 60 days of harvest. (Acts as a selective contact that disrupts cell membranes). Special local needs (SLNOR-910026 and WA-910012) allows irrigation through sprinkler irrigation systems. Read and follow label instruc- tions precisely regarding irrigation interval and all chemigation specifications to minimize environmental hazards. ------------------------------------------------------------------------ monocarbamide 10 to 30 gal product/A dihydrogensulfate Enquik Apply in sufficient water volume for full coverage when first true leaf is as tall as flag leaf. Repeat applications may be necessary. Do not apply in presence of free moisture or within 5 days after a foliar pesticide application. Repeat as required until crop is 8 inches tall; then direct sprays between rows. Do not apply to green onions after they reach 8 inches to avoid scarring. Adjust fertilizer rates for nitrogen and sulfur. (Acts as contact). ------------------------------------------------------------------------ bromoxynil 0.25 to 0.38 lb ai/A Buctril Do not ingest or inhale spray mist and prevent contact with skin. Wearing protective face shields, respirators, and clothing is advised. For use in Idaho and east of the Cascades in Oregon and Washington only. Apply in 50 to 70 gal water for thorough coverage when onions have 2 to 5 true leaves. Apply on sunny days when plants are dry and humidity is low. Do not apply west of the Cascades or when the protec- tive waxy cuticle on onion leaves may be thin or damaged. Application can be preemergence but irrigation or rainfall within 2 days of applica- tion may result in crop injury. Do not add adjuvants. Injury can some times occur even under ideal conditions. (Precise action unknown; acts as a selective contact that disrupts cell membranes). ------------------------------------------------------------------------ paraquat 0.625 to 0.94 lb ai/A Gramoxone Extra A restricted-use pesticide. Do not ingest or inhale spray mist. Wearing protective face shields, respirators, and clothing is advised. Apply before, during, or after planting, but preemergence to crop to control emerged weed seedlings only. Add a nonionic surfactant or crop oil concentrate according to label specifications, taking care to avoid anionic formulations that react in the tank to form insoluble precipi- tates. Preharvest interval is 60 days. (Acts as contact; absorbs energy produced by photosynthesis forming peroxides that disrupt living cells.) ------------------------------------------------------------------------ sethoxydim 0.19 to 0.28 lb ai/A Poast Identify susceptible grasses and apply at optimum growth stage listed on the label. Add 2 pints/A nonphytotoxic crop oil concentrate to improve leaf absorption. Erratic control often occurs when grasses are stunted or stressed from drought, high temperatures, or low fertility. Resis- tant grasses include annual bluegrass and all fine fescues, whereas quackgrass can be suppressed. Do not apply within 30 days of harvest, nor exceed 4.5 pints/A per season. (Inhibits fatty acid production, cell membranes, and new growth.) ______________________________________________________________________________ ONIONS--MUCK OR PEAT SOILS Weed Treatment Active Ingredient Per Acre and Application Comments ------------------------------------------------------------------------------ oxyfluorfen 0.12 to 0.25 lb ai/A Goal Causes skin irritation--Wear protective gear. Apply postemergence to onions with 2 fully developed true leaves while broadleaf weeds have less than 4 true leaves. Multiple treatments may be required as new weeds emerge, but do not exceed 0.5 lb ai/A. Use a clean sprayer and do not mix with oils, surfactants, or other agricultural chemicals. Do not apply to onions under any stress. Slight leaf curl may occur and young plants sometimes become prostrate on the soil surface for 1 to 2 days, but yields have not been reduced. Do not apply within 60 days of harvest. (Acts as a selective contact that disrupts cell membranes). ------------------------------------------------------------------------ monocarbamide 10 to 30 gal product/A dihydrogensulfate Enquik Oregon special local needs (SNL-OR850029) label. Apply in sufficient water volume for full coverage when first true leaf is as tall as flag leaf. Repeat applications may be necessary. Do not apply in presence of free moisture, nor within 3 days after a foliar pesticide ap- plication. Do not apply to green onions after they reach 8 inches to avoid scarring. Adjust fertilizer rates for nitrogen and sulfur. (Acts as contact). ------------------------------------------------------------------------ sethoxydim 0.19 to 0.28 lb ai/A Poast Identify susceptible grasses and apply at optimum growth stage listed on the label. Add 2 pints/A nonphytotoxic crop oil concentrate to improve leaf absorption. Erratic control often occurs when grasses are stunted or stressed from drought, high temperatures, or low fertility. Resistant grasses include annual bluegrass and all fine fescues, whereas quack- grass can be suppressed. Do not apply within 30 days of harvest, nor exceed 4.5 pints/A per season. (Inhibits fatty acid production, cell membranes, and new growth.) ------------------------------------------------------------------------ paraquat 0.625 to 0.94 lb ai/A Gramoxone Extra A restricted-use pesticide. Do not ingest or inhale spray mist. Wearing protective faceshields, respirators, and clothing is advised. Apply before, during, or after planting, but preemergence to crop to control emerged weed seedlings only. Add a nonionic surfactant or crop oil concentrate according to label specifications, taking care to avoid anionic formulations that react in the tank to form insoluble precipi- tates. Preharvest interval is 60 days. (Acts as contact; absorbs energy produced by photosynthesis forming peroxides that disrupt living cells.) ______________________________________________________________________________ ONIONS-SPROUT INHIBITION Weed Treatment Active Ingredients Per Acre and Application Comments ------------------------------------------------------------------------------ maleic hydrazide 2 lb ai/A Royal MH-30 Apply when bulbs are fully with soft necks and 5 to 8 green leaves, or when approximately 50% of the tops have fallen, but are still green. Should be applied at temperatures below 80 to 85 F to avoid crystaliz- ation on leaf surfaces. Use of a spray adjuvant is suggested in arid regions west of the Rocky Mountains. Avoid early sprays before maturity to reduce spongy onions. Do not treat seed onions. ______________________________________________________________________________ ______________________________________________________________________________ INSECT CONTROL Proper rotations and field selection can minimize problems with insects. THE PESTICIDES LISTED BELOW ARE TAKEN FROM THE PACIFIC NORTHWEST INSECT CONTROL HANDBOOK, AND ARE FOR INFORMATION ONLY. CONSULT PRODUCT LABELS ARE CURRENTLY LEGAL REGISTRATIONS, RATES AND COMPLETE INSTRUCTIONS. Insect and Description Control, Active Ingredient Per Acre --------------------------------------------------------------------------- Cutworms and Armyworms Lannate - 0.45 to 0.9 lb Different species Bacillus thuringiensis - 1 to 2 Small to large larvae that chew qt. Use a spreader-sticker to holes in bulbs and leaves. enhance control. Phosdrin - 0.25 to 0.5 lb Climbing cutworms only. permethrin - 0.1 to 0.3 lb --------------------------------------------------------------------------- Brown wheat mite Petrobia latens Small, light tan to brown active mite. Damages leaves. --------------------------------------------------------------------------- Bulb mites soil fumigation Rhyzoglyphus sp. Small, white mites capable of causing damage to developing bulbs and intro- ducing pathogenic fungi. Damage can continue in storage. -------------------------------------------------------------------------- Onion thrips azinphosmethyl - Thrips tabaci 0.5 to 0.75 lb Adults are small, pale yellow to malathion - 1 to 2 lb light brown in color with feath- ery wings. Young are pale yel- Phosdrin - 0.5 lb lowish-green and wingless. They feed on onion foliage and diazinon - 0.5 lb cause it to become white, kill- ing the tops and reducing Penncap-M - 0.5 lb Apply yields. only to dry onions. Do not use on green onions. WARNING: Microencapsulated methyl parathion (Penncap-M) should never methyl parathion - 0.5 to be sprayed on blooming weeds in 0.83 lb onion fields or adjacent fields. If misused, this formulation is permethrin - 0.15 to 0.3 lb especially hazardous to honey bees and other pollinating insects be- Metasystox-R - 0.75 lb Use cause of its strong tendency to only on Spanish bulb onions. contaminate pollen. Vydate L - 0.25 to 0.5 lb Note: Dasanit applied in the seed Do not harvest tops. furrow for onion maggot control sup- presses thrips populations in the Lannate - 0.45 lb early season. This may allow growers to reduce foliar sprays. Oregon, Idaho, and Washington only, 24 c. Caution: Dasanit may reduce onion stands in sandy/light soils. --------------------------------------------------------------------------- Onion maggot diazinon - 2 to 4 lb Delia antiqua Dyfonate - 1 lb Use Dyfonate Adult is a fly, pale to dark gray only where organic matter in color, less than inch in exceeds 10 percent. size. Larvae are legless, blunt white maggots that kill seed- diazinon - 1 lb lings and damage bulbs of Furrow applications only. older plants. malathion - 1.5 to 2 lb Lorsban 4E - 0.034 lb ai/1000 row ft. Apply as in-furrow treatment on direct-seeded dry bulb onions only. Lorsban 15G - 0.034 lb ai/1000 row ft. Apply as in-furrow treatment on direct-seeded dry bulb onions only. --------------------------------------------------------------------------- Pea leafminer diazinon - 0.5 lb Liriomyza huidobrensis Larvae of tiny fly. Mine in leaves. When abundant, cause leaves to wither from tip downward. --------------------------------------------------------------------------- Wireworms diazinon - 3 to 4 lb Limonius spp. Telone II - preplant Brown, jointed larvae of click beetles. Kill young plants, Telone C-17 - preplant weaken older ones. ______________________________________________________________________________ ______________________________________________________________________________ DISEASE CONTROL Proper rotations, field selection, sanitation, spacings, fertilizer and irrigation practices can reduce the risk of many diseases. Fields can be tested for presence of harmful nematodes. Using seed from reputable seed sources reduces risk from seed born diseases. THE PESTICIDES LISTED BELOW ARE TAKEN FROM THE PACIFIC NORTHWEST DISEASE CONTROL HANDBOOK, AND ARE FOR INFORMATION ONLY. CONSULT PRODUCT LABELS FOR CURRENTLY LEGAL REGISTRATIONS, RATES AND COMPLETE INSTRUCTIONS. ONION -- BASAL ROT Cause: Fusarium sp., soilborne fungi. Symptoms: Yellowing, wilting, and lack of vigorous growth. Red-brown rot where roots are attached to the base. The rot and discoloration usually affect all of the base and upwards into the scales. Sometimes a weft of mycelium develops over the surface of the base or between the affected scales. Rot may progress in storage under situations where elevated moisture levels exist. Infection is often associated with pink root, maggots, or other insect injury. ~Control: 1. Protect plants from insect, fertilizer, or other injury. 2. Rotate crops use well-drained soil. 3. Some soil chemicals have been tried but at present none are being recom- mended. In a test in Malheur County, the following varieties had less basal rot when compared to a number of other varieties: `Golden Cascade', `Cima', `Oro Grande', and `Cashe'. Other onion varieties described as tolerant but not tested in Oregon are `Bronze Reserve', `North Star', `Sassy Brassy', and `Sentinel'. --------------------------------------------------------------------------- ONION -- DOWNY MILDEW Cause: Peronospora destructor, a fungus. This organism survives the winter on infected plants or on old onion plant material in the field. Symptoms: Bluish, downy spots appear on the leaves. Plants may be dwarfed, distorted, and pale green. Spots develop first with a water-soaked appearance, later taking on a purplish shade. In dry climates, the leaf spots may be white in appearance. As the spots enlarge, often girdling the leaves, a whitish mold develops on the surface of the spot, later turning black. Secondary leaves may develop on infected plants, retarding normal bulb development. Plants are not often killed, but bulb quality is poor and often spongy. ~Control: 1. Avoid poorly-drained soils. 2. Practice a 3-year crop rotation where possible. 3. Destroy onion plant refuse and cull piles. 4. Eradicate perennial onions or wild onions. 5. There are no resistant varieties of the types grown in Oregon. 6. Spray with one of the following: a. Mancozeb (dry onions only) at 1.6 to 2.4 lb ai/100 gal/A. b. Maneb at 1.6 to 2.4 lb ai/A. c. Ridomil MZ58 at 1.5 to 2 lb product/A. d. Ridomil/Bravo 8l W at 1.5 to 2 lb product/A. e. Fosetyl-Al (Aliette) at 1.6 to 2.4 lb ai/A. f. Fixed copper. Residues: Mancozeb - Tolerance 0.5 ppm. Do not apply within 7 days of harvest. Do not apply to exposed bulbs. Maneb - Do not apply more than 16.8 lb ai/A/season. Do not apply within 7 days of harvest. Fosetyl-Al -- Do not apply within 7 days of harvest. Ridomil/Bravo 81W - Do not apply to dry bulb onions within 7 days of harvest or to green onions within 21 days of harvest or more than 4 times on green onions. See product label for rota- tion restrictions. --------------------------------------------------------------------------- ONION -- NECK ROT Cause: Botrytis allii, a fungus. This organism survives the winter on dead plant parts in the soil and on infected bulbs. The most common causes for severe losses are (1) use of excessive amounts of nitrogen which delay maturity of the crops, (2) irrigation and/or rainfall late in the season, (3) inadequate or improper curing, and (4) improper storage. Symptoms: The organism appears on maturing bulbs just prior to harvest and during harvest, with infection occurring through the neck tissue or through wounds in the bulbs. Frequently infection enters the neck as a result of topping the onions prior to proper drying of soft susceptible top tissues. The fungus moves rapidly into the succulent onion bulb in the neck region, producing a water-soaked appearance. Yellow discoloration often appears. Between the onion scales a gray mold develops, later producing small, black bodies (sclerotia) which develop as a solid layer around the neck. Ultimately the bulbs break down to a soft mass, and secondary infections follow. ~Control: The tops should be allowed to mature well, and the onions should then be lifted or undercut. If normal dry weather prevails, the onions should then cure on the ground for 6 to 10 days. Bruising and mechanical injury in topping and storing should be kept to a minimum, and the onions should be stored in well-ventilated houses at temperatures of 32 F or just slightly higher. Higher temperatures should be used when humidity cannot be held below 75 percent RH. There are no fungicides that consistantly control neck rot even though EPA has granted several labels for this use. --------------------------------------------------------------------------- ONION -- NEMATODE (Stubby Root) Cause: Paratrichodorus allius. An ectoparasitic nematode that overwinters in the soil. The largest populations of nematodes and conspicuous plant symptoms occur during cool, damp springs. Symptoms: Roots are extremely short with yellow to brownish cast plants are stunted usually in spots in the field. ~Control: 1. Telone II at 4.5 to 36 gal/A (follow label recommendations). Fumigate in the fall. OR 2. An in-furrow spray of 1.5 to 2 gal Vydate L (broadcast basis) in 20 to 50 gal of water or .75 to 1 gal Vydate L (broadcast basis) as an in-furrow drench in 100 to 150 gal of water are usually adequate to control the problem. In situations with extremely high nematode presence, two or three postemergence applications may be made. See label--Oregon only (SLN OR 810033). Residues: Telone II. Preplant soil treatment. Seal soil for 7 to 14 days then aerate 1 week for each 10 gal/A applied--longer in case of heavy rains or temperatures below 60 F--until the odor of the fumigant is gone. Do not treat extremely heavy soils. Do not apply near living plants. Considered to be a nonfood use. Soil fumigants. If fall fumigation is done, beds will be free of fumigant by spring planting. Vydate. Limit 14 days before harvest. Such late applications will not be effective in any case. Sampling: Stubby-root nematodes are migratory ectoparasites (see Nematodes- Life History), and are found only in the soil. Before planting crops suscep- tible to stubby-root nematodes, soil samples should be taken with sufficient lead time to implement management procedures if necessary. If this is soil fumigation, it may be several weeks before crops can be planted. Fall sampling for crops to be planted the following spring is an excellent strate- gy. For diagnosis, submit both soil and onions containing roots. --------------------------------------------------------------------------- ONION -- PINK ROOT Cause: Pyrenochaeta terrestris, a fungus. This fungus may live in the soil saprophytically for several years. Symptoms: The disease may appear either in young seedlings or later throughout the growth of the onion. There is a yellowing of roots followed by a pinkish-colored root development. These take on a bright-pink shade and die. New roots produced thereafter become diseased and also die. As this process continues through the growing season, the bulbs lack normal development and are reduced in size and vigor with stunted tops. ~Control: 1. A crop rotation in which onions are planted only every 5 years will reduce the severity of infection however, some plants will be invaded by the fungus. 2. Use adequate fertilizer, irrigation, cultivation, etc., to stimulate rapid bulb growth. 3. Some partially resistant varieties of the sweet spanish type are avail- able. 4. Preplant soil fumigation with Telone C-17 is effective in control of the disease on mineral soils at the rate of 5.1 to 41 gal/A. Not effective on peat soils. Note: Fall fumigation is more effective than spring. 5. The varieties `El Capitan', `Avalanche', `Bullseye', `Bravado', `Merit', `Durango', `Yula', `Armada', `Valdez', and `Fiesta' were bred for resistance. `Yellow Globe Danvers' types are resistant. Caution: Since the fumigation must be done prior to planting, it is important that the planting row be directly over the fumigated soil when only the planting row is treated. Variations of a few inches can cause complete loss of control. Not effective on peat soils. --------------------------------------------------------------------------- ONION -- PURPLE BLOTCH Cause: Alternaria porri, a fungus. The organism overwinters on dead, diseased onion trash in the field and on infected bulbs. Infection often follows injury caused by other fungi, e.g., Botrytis, or by sand or dust during windstorms. The spores require rain or persistent dew to cause infection. The optimum temperatures are 77o to 81o F. Almost no infection occurs below 55 F. The disease is sometimes severe in irrigated onion growing areas of eastern Oregon. Symptoms: On the leaves a small, water-soaked area develops, which soon turns brown. As the spot enlarges, zones may appear, and it turns purplish. White margins often encircle the purplish centers. When the weather is moist, the surface of the spot usually becomes covered with a brownish-black, powdery fungus growth. Leaves with large spots turn yellow and are blown over by the wind. Infection of the leaves may be noticed by the presence of leaf spots very soon after infection has occurred, sometimes within 2 days. Bulb decay may occur during and after harvest. It shows first as a watery rot starting around the neck and is particularly noticeable because of the yellowish to wine-red discoloration in the neck region. As the fungus moves through the onion tissues, they dry and take on a papery texture toward the outside. `Sweet Spanish' onions are very susceptible to purple blotch. ~Control: The disease does not occur in Oregon with sufficient frequency to warrant an annual spray program. Spraying as soon as the disease occurs will prevent further spread of the disease. The variety `Fiesta' has tolerance. Other control practices which will reduce losses are: 1. Destroy old onion pulp piles. 2. Handle and harvest with care, destroying any diseased onions. 3. Proper curing of bulbs in field--lift and allow to dry several days before topping. Spray: Mancozeb (dry bulb onions only) (Dithane M-45, Manzate 200)--1.6 to 2.4 lb ai/100 gal/A. Bravo 720 at 1.5 to 3 pt/a (2 pt maximum) on dry bulb onions in sufficient water to cover. Maneb at 1.6 to 2.4 lb ai/A. Do not apply more than 16.8 lb ai/A/season. Do not apply within 7 days of harvest. Ridomil/Bravo 8l W l.5 to 2 lb/A. Rovral WP--1.5 lb/A in 50 to 100 gal of water. Spray fixed copper. Several formulations and products are available. See product labels for rates. Tolerance: Mancozeb (dry bulb onions only)--Tolerance 0.5 ppm. Do not apply within seven days of harvest. Do not apply to exposed bulbs. Maneb--Tolerance 7 ppm. No time limitation. Bravo 720--Tolerance 5 ppm on green onions, 0.5 ppm on dry bulb onions. Do not apply within 14 days of harvest (green onions) or 7 days of harvest (dry onions). Do not apply more than three times per season on green onions. Do not apply to sweet spanish onions except in Idaho and Oregon. Ridomil/Bravo - See cautions under downey mildew. Rovral WP--Tolerance 0.5 ppm. Do not apply within 4 days of harvest. Copper: Exempt. --------------------------------------------------------------------------- ONIONS -- RUST (Seed Onions Only) Cause: Puccinia asparagi, a fungus. The fungus actually survives on asparagus which commonly grows wild along ditch banks of irrigated areas in southern Idaho and eastern Oregon. Symptoms: The uredial stage attacks the onion leaves and seed stalks. Light yellow to orange or reddish, powdery pustules develop. With pustules enlarge- ment, the leaves or seed stalks become girdled. The affected tissues at and above the girdling turn yellow and die prematurely, thus reducing seed yield. ~Control: Destroy wild asparagus or spray the asparagus and adjoining onions with mancozeb. Residues: See under Onion--Purple Blotch. --------------------------------------------------------------------------- ONION -- SEED TREATMENT Aids in control of smut, seed decay, and damping-off. Thiram-- or 2 t/lb or 1 lb product for 10 lb seed for smut. --------------------------------------------------------------------------- ONION -- SMUT Cause: Urocystis cepulae, a fungus. This fungus survives saprophytically in the infested soil for several years. It attacks only members of the onion family including onion, leek, and Welsh onion. Symptoms: The disease appears first in the stems of the young plant as it emerges. Infected areas have a raised blisterlike appearance near the ground level. These rupture to expose black powder masses of spores. Numerous seedlings are killed during the emergence period, and those which live produce distorted bulbs having darkish streaks and numerous smutty lesions. ~Control: 1. Pelleted onion seed using Thiram with a methocel sticker has been used in some areas. Such pelleted seed is applied at the rate of 5 lb/A. 2. Small onion sets and young onion plants may be set out in infested soil without apparent danger of infection. 3. Control smut by an in-furrow drench at seeding of mancozeb or Maneb at 2.4 lb actual/A (29,000 linear feet of furrow). --------------------------------------------------------------------------- ONION -- STINKING ROT (soft rot) Cause: Unknown species of Pseudomonas and Erwinia. Symptoms: First symptoms appear in late June. Either the inner or outer whorl of leaves, but usually not both, become flaccid and rapidly change from green to white to brown and collapse to the ground. Soon the disease progresses to the apparently unaffected parts, with water-soaking and collapse following. After collapse of the foliage a watery, foul-smelling liquid exudes from the bulbs. Further spread of the disease is reduced by warm, dry summer weather. Slightly affected plants may recover, but usually are distorted and chlorotic. Bulbs infected late in the season may appear, but decay during storage. The disease does not spread from bulb to bulb in storage. This disease has been widely distributed in western Oregon onion-growing areas, and occurs in Oregon and Southwestern Idaho onion-growing areas. There is a lower incidence of this disease in furrow or rill-irrigated fields. ~Control: 1. Some control can be obtained by using water from deep wells, rather than from ditches. 2. Reduce mechanical injuries during cultivation and weeding. 3. Thoroughly cure onions before storing. --------------------------------------------------------------------------- ONION -- WHITE ROT Cause: Sclerotium cepivorum, a fungus. The fungus can remain viable in the soil for many years without the presence of the host--probably as long as 8 to 10 years. Other hosts include garlic, leek, shallot, and other allium sp. Symptoms: The leaves of a diseased plant decay at the base, turn yellow, wilt, and topple over. The older leaves collapse first. Roots are rotted and the plant can be easily pulled up. Fluffy mycelium may be present on the remaining roots and bulb. Affected bulbs may become watery and the outer scales cracked as they dry and shrink. Small (1/50 inch) sclerotia are formed in affected parts of the bulb and on the surface, often around the neck. The sclerotia are smaller and rounder than those of Botrytis (the cause of the neck rot dis- ease). ~Control: Idaho law forbids the import of sets, bulbs, or other material infected with white rot. Avoid the movement of contaminated soil or machinery into clean fields. Treatment of heavily infected areas of organic soils with 400 lb of methyl bromide/A tarped has been useful in reducing inoculum in infested fields. Spray 2 lb of Ronilan 50 WP in a 4- to 6- inch band in 400 gal. of water/A or in a 2- to 4- inch band in 100 gal of water/A over the seed row. Apply at least 2 more applications of 2 lb. of Ronilan 50 WP in 100 gal of water/A at 4-6 week intervals. Residues: Ronilan--Do not apply more than 10 lbs. Ronilan/A in one crop season. Do not apply within 18 days of harvest. Do not apply through any type of irrigation system. ______________________________________________________________________________ ______________________________________________________________________________ --------------------------------------------------- --------------------------------------------------- This information was adapted by the Oregon State University Extension Service from Oregon and Pacific NW publications as well as other vegetable production guidelines from public institutions in the U.S. and Canada. These guidelines are intended as a general guide for Oregon commercial vegetable producers. Address comments and questions to your County Extension Agent or Dr. N. S. Mansour, Department of Horticulture, Oregon State University, Corvallis, OR 9733l. ---------------------------------------------------