From: Brian Lo Newsgroups: rec.gardens Subject: FAQ: Onions Greens Date: Wed, 1 Mar 1995 14:56:42 -0800 GREEN BUNCHING ONIONS Bunching onions are produced from thickly planted white onion varieties of Allium cepa and more recently also from the non-bulbing Allium fistulosum species. Interspecific varieties are represented by the variety Beltsville Bunching. VARIETIES Allium cepa types - for early crop: White Lisbon, White Knight, South- port White Globe, White Spanish Bunching. A. cepa x A. fistulosum types: Beltsville Bunching. A. fistulosum types - non-bulbing; resistant to pink root and botrytis leaf blight; cold hardy; for later crops and for overwintering: Ishikura, Tokyo Long White, Hishiko, Japanese Bunching, Tokyo Bunching. For trial: Kincho (reported tolerant to high temperatures). Red bunching onion: Santa Clause, "Ishikuro" type, but with rose-red stem that can add color to salads. Red color intensifies with colder weather. SEEDING AND GERMINATION Green onion seed numbers approximately 9,500 per ounce. Use high quality fungicide treated seed. Since onion seed has poor useful longevity (less than 2 years), unless stored under ideal conditions. Germination will occur at temperatures from 46 to 86 F. with the optimum at over 60 F. Seeding rates for bunching onions depends on the spacing between rows. Approximately 10 to 15 lbs of seed are used at about 15 inch spacing, but at the closest spacings up to 25 lbs of seed per acre may be needed. SEED COMPANIES Abbott & Cobb Inc. POB F307, Feasterville, PA 19047 Asgrow Seed Company, POB 5038, Salinas CA 93915 American Takii Inc., 301 Natividad Rd. Salinas, CA 93906 Champion Seed Co. 529 Mercury Lane, Brea, CA 92621-4894 714/529-0702 Crookham Co. Caldwell, ID 83606 Dakota Seed International Inc. POB 5467, Saginaw, MI 48603 Elsoms Seeds Ltd. Spalding, Lincolnshire, England PE11 1QG Ferry-Morse Seed Co. POB 4938, 555 Codoni Ave. Modesto, CA 95352 Harris Moran Seed Co. 3670 Buffalo Rd. Rochester, NY 14624 Nickerson-Zwaan Seed Co. POB 1787, Gilroy, CA 95021 Petoseed Co. Inc. POB 4206, Saticoy, CA 93303 Rio Colorado Seeds, Inc. 4701 Gila Ridge Road, Yuma AZ 85365 Sakata Seed America Inc. Morgan Hill, CA Scottseed. 4876 N. Road H. Vale OR 97918 503/473-3246 Shamrock Seed Co., Inc. POB 4443 Salinas, CA 93912 Sluis & Groot of America Inc. 124 Griffin Street, Salinas, CA 93901 Stokes Seeds Inc. POB 548, Buffalo, NY 14240 Sunseeds, 2320 Technology Pkwy. Hollister, CA 95023 Thompson & Morgan Inc. POB 1308, Jackson, NJ 08527 W. Osborne Seed Co. Int'l. 1679 Highway 99 South, Mount Vernon, WA 98273 Zenner Bros. Seed Co., Inc. 1311 S.E. Gideon St. Portland, OR 97202 SOILS A pH of 5.3 to 6.0 is suitable for organic soils but a pH of 6.5 to 7.0 is preferred for mineral soils. When the pH is below the range considered suitable, lime should be applied and incorporated thoroughly to a depth of 6 in. or more. Lime should be applied in the fall or as early in spring as possible. A late summer green-manure crop of oats, plowed down or worked in, before the ground becomes too wet to work is beneficial. An application of ammonium nitrate when the green-manure crop is being turned in will help break down the material. FERTILIZER A soil test is the most accurate guide to fertilizer requirements. The following recommendations are general guidelines. Prior to transplanting or seeding broadcast and incorporate the follow- ing: Nitrogen: 50-70 (N) lb/acre. Add other nitrogen as needed to keep tops green and vigorous under different temperature and rainfall conditions. It may be necessary to side-dress the crop with an additional 75-100 lb/acre of nitrogen. 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) broad-leaf 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 * Direct the spray to the base of the crop with wide, low nozzles, or use crop shields whenever this can be done while still obtaining complete coverage of the weeds. 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 formulation 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 (ENQUIK or n-pHuric): 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. ***** Phosphate: 145-155 (P2 O5) lb/acre. Potash: 150-170 (K2 O) lb/acre. THE EARLY CROP The early crop may be clump-seeded, 5-6 seeds per cell, in flats and grown to transplant size in plant-houses, green-houses, or cold frames. When ready the seedlings are planted in clumps in rows which are 12 to 15 inches apart. LATER CROPS Seed as soon as the soil can be worked. Four to 7 rows, 12-15 inches apart, are seeded to each set, or bed. Use a scatter shoe to plant a band 2-4 inches wide and seed 35-50 plants per foot of row. Approximately 6-8 lbs. of seed may be needed per acre for direct-seeding. IRRIGATION Onions are shallow-rooted. Maintain the top foot of soil at 65-70% of field capacity or more. In western Oregon 12-15 inches of water may be necessary for a 60 to 70 day crop. HARVESTING, HANDLING AND STORAGE Harvest should begin when onions are 1/4 to 1/2 inch in diameter at the base. There should be at least 2 inches of white shank. Onions are hand pulled and bunched with 6-9 onions held together with rubber bands. Pulling is usually done without undercutting. Bunching is usually done in the field. Field boxes are moved to the processing sheds within two to three hours of being harvested. The onions are run through a washer/cooler machine which automatically washes them in a 33 to 35 F water bath. Green tops are usually trimmed to 12 inches. In some cases harvested onions are bunched in the packing shed. Chilling the wash water removes field and ambient heat from the onions. They are then immediately packed, 4 dozen bunches to a paraffin coated box, containing about 11-12 pounds of onions. STORAGE (Quoted from USDA Ag. Handbook #66): Hold green onions at 32 F and 95 to 100 % relative humidity. Green onions (scallions) and green shallots are quite perishable and are normally marketed promptly. They can be stored 3 to 4 weeks at 32 F if moisture loss is prevented. Crushed ice spread over the onions aids in supplying moisture. Packaging green onions in perforated polyethylene film also will aid in preventing moisture loss. Storage life at 50 F for green onions is only about 1 week. Higher temperatures favor more rapid yellowing and decay of the leaves. Vacuum cooling is effective for removing field heat, but the onions should be wetted first and packed in polyethylene-lined cartons to minimize moisture loss. For maximum storage, a controlled atmosphere of 1 % oxygen with 5% carbon dioxide at 32 F should allow 6 to 8 weeks storage. However, the green onions must be properly packed in waxed cartons or poly-lined containers. The freezing point of green onions is about 30 F. PACKAGING Green bunching onions are commonly packaged in cartons holding 4 dozen bunches weighing 11-12 lbs. and iced to weigh 25-29 lbs, or in larger wire- bound crates weighing a total of 47-54 lbs. PEST CONTROL FOR GREEN BUNCHING ONIONS 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 Time of Application ------------------------------------------------------------------------------ DCPA 6 to 9 lb ai/A Dacthal Apply after planting to moist soil surface before weeds and onions emerge. In eastern Oregon and Washington when rainfall is sparse, shallow incorporation 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). ------------------------------------------------------------------------ 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. ------------------------------------------------------------------------ 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 protective waxy cuticle on onion leaves may be thin or damaged. Application can be preemergence, but irrigation or rainfall within 2 days of application may result in crop injury. Do not add adjuvants. Injury can sometimes 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 pre- cipitates. 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 ------------------------------------------------------------------------------ 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, or within 3 days after a foliar pesticide application. Do not apply to green onions after they reach 8 inches to avoid scaring. 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 growt stage listed on the label. Add 2 pints/A nonphytotoxic crop oil concentrate to im- prove leaf absorption. Erratic control often occurs when grasses are stunted or stressed from drought, high temperatures, or low fertil- ity. Resistant 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.) ------------------------------------------------------------------------ paraquat 0.625 to 0.94 lb ai/A Gramoxone Extra A restricted-use pesticide. Do not ingest or inhale spray mist. Wear- ing 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.) ______________________________________________________________________________ ______________________________________________________________________________ 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 FOR 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 light malathion - 1 to 2 lb brown in color with feathery wings. Young are plae yellowish-green and Phosdrin - 0.5 lb wingless. They feed on onion foliage and cause it to become white, killing diazinon - 0.5 lb the tops and reducing yields. methyl paration - 0.5 to WARNING: Microencapsulated methyl 0.83 lb parathion (Penncap-M) should never be sprayed on blooming weeds in onion Lannate - 0.45 lb fields or adjacent fields. If misused, this formulation is especially hazard- permethrin - 0.15 to 0.3 lb ous to honey bees and other pollinating insects because of its strong tendency Pyrellin - 1 to 2 pt to contaminate pollen. --------------------------------------------------------------------------- Onion maggot ethion 5G - 0.4 to 2 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 Use for adult control. diazinon - 2 to 4 lb preplant broadcast --------------------------------------------------------------------------- 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 varities: `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. Use Allium fistulosum varieties that are resistant. 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 rotation restric- tions. --------------------------------------------------------------------------- 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 Histroy), 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 1.5 to 2 ai/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. Ridomil/Bravo - See cautions under downey mildew. Rovral WP--Tolerance 0.5 ppm. Do not apply within 4 days of harvest. Copper: Exempt. --------------------------------------------------------------------------- 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 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 prepared 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 or questions to your County Extension Agent or Dr. N. S. Mansour, Department of Horticulture, Oregon State University, Corvallis, OR 9733l. --------------------------------------------------- ---------------------------------------------------