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Onions are a cool-season crop that requires a long growing season to produce high quality bulbs and good yields. Medium to light loam soils with good drainage are best suited for onion production. Onions have limited root systems so irrigation is essential, especially in dry years. Weed control is also critical and difficult, and on most farms is the most limiting factor in onion production. Onions bulb according to day length and only long-day and intermediate-day types are recommended for New England. VarietiesBunching Sets
Sets
Yellow Storage Types Reds
Reds
Sweet Spanish Types
Spacing and SeedingStart transplants in late February or early March, 10 to 12 weeks before setting in field. Direct seed onion in spring as soon as soil can be worked. Plant three to four rows per bed, 9” to 18” between rows and 3” to 4” apart within rows for transplants. Spacing will determine bulb size. For direct seeding, aim for a stand of six to nine plants per foot. This can be increased to 9 to 12 plants per foot if double shoe precision seeders are used. This requires 5 to 6 lb of seed per acre (about 1/2 oz per 100 feet of row). Some growers are finding success using black plastic mulch on raised beds. LimeApply lime according to soil test results to maintain soil pH at 6.5 to 6.8. Onions and leeks do not tolerate acid soil, especially in early growth stages. If the magnesium level is high, a lime high in calcium (calcitic lime) should be used to maintain a high calcium level.FertilizerLess nitrogen fertilizer will be needed if manure or legume sod was plowed down (see nitrogen credits). However, these sources may result in high soil nitrogen levels late in the season. Excessive nitrogen late in the season from any source can delay maturity and reduce storability of onions.Onion flavor is determined by cultivar type, temperature and irrigation, and sulfur fertility. Growers wishing to produce mild-flavored onions for retail sale should choose mild cultivar types, irrigate regularly up to harvest, and maintain soil sulfur levels between 35 to 55 lb/A. Excessive sulfur levels in soils or fertilizers will increase pungency Sprout InhibitionFor onions to be stored until mid-November or later, maleic hydrazide (1 1/3 gal of Royal MH-30/A in a minimum of 30 gal/A) should be applied when about 50% of the tops are down, the bulbs are mature, the necks are soft and five to seven of the leaves are still green. See the label for detailsHarvestLate, hard, pungent varieties with good skin retention are preferable for winter storage. Undercutting several days before harvesting can improve keeping quality. It is best to undercut when most of the plants have two leaves that are still partially green. Allowing leaves to completely dry down before undercutting can result in excessive skinningTo develop best skin color, onions should be cured for two weeks at temperatures between 75°F to 80°F and 70% to 80% relative humidity. After curing, lower temperature gradually to as near to 32°F as practical without freezing. Storage temperature should not be lowered too fast, but should follow the average monthly temperature. Cooling too rapidly, followed by a few warm days, can cause condensation of moisture, resulting in bulb staining, sprouting and decay. Maintain storage relative humidity at 65% to 70%.
Weed ControlNOTE: For the herbicides listed below, one product trade name and formulation is provided for each active ingredient (common name) as an example of rates, days to harvest (dh), REI, and special instructions. In many cases there are other products available with the same active ingredient. Please see Table 17 and Alphabetical Listing by Trade Name for more information on products with the same active ingredients. Stale Seedbedglyphosate (Roundup 4S): 1 to 5 qt/A (REI 12h, Group 9). See Stale Seedbed Technique. paraquat (Gramoxone Inteon* 2S): 2.0 to 4.0 pt/A (REI 12h, Group 22). See Stale Seedbed Technique.Seeds, Sets, or Transplants Preemergencebensulide (Prefar 4E): 5 to 6 qt/A (REI 12h, Group 8). Incorporate by shallow cultivation or irrigation. Grass control only; should be supplemented with cultivation or another registered herbicide for broadleaf control. Do not plant non-labeled crops to treated land for 120 days. DCPA (Dacthal) 75WP: 10 lb/A (REI 24h, Group 3). Preemergence. Apply to weed-free soil. Good control of most annual grasses; fair on redroot pigweed, lambsquarter, and purslane. Can be reapplied at layby at up to 14 lb/A on weed-free soil.pendimethalin (Prowl 3.3EC): 1.2 to 3.6 pt/A (45 dh, REI 12h, Group 3). DRY BULB ONIONS ONLY. Apply overtop when onions have two to nine true leaves but prior to weed emergence. Seeds or Transplants Postemergenceclethodim (Select 2EC): 6 to 8 oz/A (20 dh, REI 24h, Group 1). Apply to actively growing grasses. See label for grass height and herbicide rate. Always use a crop oil concentrate at a rate of 1 gal/100 gal spray mix. See both container label and any supplemental label available from dealer. fluazifop (Fusilade DX): 6 to 16 fl oz/A (45 dh, REI 12h, Group 1). For grass weed control only. Apply to actively growing grass weeds (see product label for susceptible stage). Add 1 gal crop oil concentrate or 1 qt nonionic surfactant per 100 gal of spray. Dry bulb onions only. oxyfluorfen (Goal 2 XL): For postemergence control at 2 to 4 oz/A (REI 24h, Group 14) when applied postemergence to seeded onions that have at least three true leaves. For transplanted onions apply the same rates within two days after transplanting. Multiple treatments at the aforementioned rates may be applied. Do not use a surfactant. Do not tank mix. Two to three days of sunny weather should precede treatment to reduce the likelihood of crop injury. Dry bulb onions only. pelargonic acid (Scythe 4.2): 3% to 10% (REI 24h, Group 27). Use a 3-5% solution for annual weeds (4-6 oz/gal water), a 5-7% solution for biennial and perennial weeds (6-9 oz/gal water), and 7-10% solution for maximum burndown (9-13 oz/gal water). Delivery rate for boom applications should be 75 to 200 gal spray solution/A; complete coverage of weed foliage is essential. Use a DIRECTED/SHIELDED SPRAY; contact with crop will cause injury. For hand-held equipment, spray to completely wet all weed foliage but not to the point of runoff. Repeat applications as necessary. Tank mixes are allowed with this product. These include tank mixes with glyphosate (Roundup), sulfosate (Touchdown), and residual herbicides. See label for complete details. sethoxydim (Poast 1.53EC): 1.5 pt/A (30 dh, REI 12h, Group 1). Apply with crop oil concentrate at 2 pt/A. Apply to actively growing weed grasses (see product label for susceptible stage of growth). Insect ControlNOTE: For the insecticides listed below, one product trade name and formulation is provided for each active ingredient (common name) as an example of rates, days to harvest (dh), REI, and special instructions. In many cases there are other products available with the same active ingredient. Please see Table 20 and Alphabetical Listing by Trade Name for more information on products with the same active ingredients. CutwormsCaterpillars hide under the soil surface adjacent to the plant during the day and feed on leaves after dark. For best results, make application between midnight and dawn while cutworms are feeding aboveground. Synthetic pyrethroids may work best during cool spring weather. All synthetic pyrethroid restricted use (*) insecticides listed to control thrips on onions are also registered to control cutworm on this crop. See cutworms in the Pepper and Tomato (Outdoor) sections for more information on the black and variegated cutworms. Bacillus thuringiensis aizawai (XenTari): 0.5 to 1.5 lb/A (0 dh, REI 4h, Group 11). Must be ingested; apply in evening before larvae are actively feeding and direct sprays to base of stem. Use high rate at cool temperatures. OMRI listed. lambda-cyhalothrin (Warrior*): 2.5 to 3.8 oz/A (14 dh, REI 24h, Group 3A). methomyl (Lannate* LV): 3 pt/A (7 dh, REI 48h, Group 1A). For green and dry onions. Add wetting agent to improve coverage. For black and variegated cutworm only. zeta-cypermethrin (Mustang*): 2.4 to 4.3 oz/A (7 dh, REI 12h, Group 3A). Onion MaggotInfestations may reduce young plant stands, cause plants to wilt and yellow or damage bulbs. There are three generations each year. Effective control of the first generation (mid-May-June), which causes the most destruction, and minimizing mechanical and chemical damage to onions throughout the season, will reduce or eliminate damage by later generations. Harvesting with a potato digger causes less damage than undercutting onions. In smaller plantings, removing culls from the field immediately after harvest will reduce overwintering populations. Gathering culls into deep piles will limit reproduction to surface layers and reduce populations more than deep plowing or harrowing after harvest. If harrowing after harvest, wait until frost to limit bulb damage and winter survival. Granular or soil drench insecticide applications are the most effective. Soil Application: cyromazine (Trigard OMC): (60 dh, Group 17). Seed treatment for onion maggot control. Treated seed must be purchased. See rotational crop restrictions on label. diazinon (Diazinon* AG500): 2 to 4 qt/A broadcast and incorporate just before planting (7 dh, REI 24h, Group 1B). Will not control organophosphate resistant onion maggots. Foliar Application for adult flies: gamma-cyhalothrin (Proaxis*): 1.9 to 3.2 oz/A (14 dh, REI 24h, Group 3A). Adults only. lambda-cyhalothrin (Warrior*): 1.9 to 3.2 oz/A (14 dh, REI 24h, Group 3A). Adults only. malathion (Malathion 57EC): 2 1/2 to 3 pt/A (3 dh, REI 12h, Group 1B). permethrin (Pounce* 25WP): 6.4 to 19.2 oz/A (1 dh, REI 12h, Group 3A). For dry bulb onions only. zeta-cypermethrin (Mustang*): 2.4 to 4.3 oz/A (7 dh, REI 12h, Group 3A). Onion ThripsOnion thrips range in color from yellow to black and are only 1/16” in length. They spend the winter as adults in crop remnants, alfalfa, wheat, greenhouses and weeds along the border of crop fields. Thrips have rasping mouth parts which they use to tear open plant cells and feed on inner juices. Feeding occurs in protected areas between leaves. Damage may appear as silver lines, white patches, tip dieback and curling, slowed growth, reduced bulb size and yields, or result in plant death. Populations are favored by hot, dry weather. Plants are most sensitive when bulbs are forming and still small. Heavy rain or overhead irrigation can lower populations quickly. Lacewing larvae, pirate bugs and predatory thrips are important natural enemies. Reduce populations by cleaning up crop residue after harvest to limit overwinter sites. Do not plant onions near alfalfa, clover, cucurbits or Brassica crops that can harbor large populations of thrips, which may migrate to onions when these crops are cut or harvested. Beauveria bassiana (Mycotrol O): 8 to 32 oz/A (0 dh, REI 4h, Group 22). Thoroughly cover foliage. Takes 7 to 10 days after application to see control. OMRI listed. pyrethrin (PyGanic EC5.0): 4.5 to 18 oz/A (0 dh, REI 12h, Group 3A). OMRI listed. spinetoram (Radiant SC): 6 to 10 oz/A (1 dh, REI 4h,Group 5). spinosad (SpinTor 2SC): 4 to 8 oz/A (1 dh, REI 4h, Group 5). Suppression only. zeta-cypermethrin (Fury* 1.5EC): 3.2 to 4.2 oz/A (7 dh, REI 12h, Group 3A). Begin applications when pest first appears. See restrictions on label. MitesBulb mites are favored by mechanical injury, disease, cool soil temperatures, and soils with high organic matter content. Control onion diseases, avoid adding manure and use fallow periods to eliminate crop residue. In smaller plantings, removing culls from the field immediately after harvest will reduce overwintering populations. Dark plastic mulch will increase soil temperatures and control mites. Disease ControlNOTE: For the products for disease control listed below, one product trade name and formulation is provided for each active ingredient (common name) as an example of rates, days to harvest (dh), REI, and special instructions. In many cases there are other products available with the same active ingredient. Please see Table 22 and Alphabetical Listing by Trade Name for more information on products with the same active ingredients. Botrytis Leaf BlightAvoid close planting and orient rows in the direction of prevailing winds. Do not plant on poorly-drained areas. Remove cull piles and practice crop rotation. Avoid excessive nitrogen fertilization as this increases canopies and susceptibility. Plant less susceptible cultivars. Irrigate early in the day to reduce leaf wetness periods. Apply fungicides based on a disease forecast system (BOTCAST). Incorporate crop residues after harvest. azoxystrobin (Quadris): 9.0-15.5 fl oz/A. (0 dh, REI4h, Group 11). boscalid (Endura): 6.8 oz/A. (7 dh, REI 12h, Group 7). Begin application prior to disease development. Use higher rate and shorter interval when disease pressure is high. Do not make more than one application of Endura before alternating with a fungicide with a different mode of action (FRAC group). Neck Rot (Botrytis)Primarily a storage disease. Do not apply nitrogen late in the season and avoid high density planting. Undercut bulbs to promote drying. Allow the tops to dry completely and have tight necks before topping. Avoid condensation on bulbs during storage. Maintain storage environment at 32°F to 33°F and 70% to 75% relative humidity. Fungicides applied to control Botrytis blight may also decrease neck rot. Downy Mildew (Peronospora)The fungus overwinters in infected bulbs or sets and on other host plants, in cull piles, and in fall-seeded onion. Only a few spores are needed to initate an epidemic. Eliminate cull piles, volunteer onion plants, and wild Allium species. Apply fungicides when mildew is present in the area and weather favors disease increase based upon a disease forecasting system (DOWNCAST). Practice a three- to four-year rotation. Plant only on well-drained land. copper hydroxide (Kocide 3000): 0.75 lb/A. (0dh, REI 12h, Group M1). Can cause phytotoxicity to leaves. Do not apply in a spray solution having a pH less than 6.5 or tank mix with Aliette. fenamidone (Reason SC): 5.5 fl oz/A. (7 dh, REI 12h, Group 11). Do not make more than one application of Reason before alternating to a non-Group 11 fungicide. fluopicolide (Presidio): 3-4 fl oz/A. (2 dh, REI 12h, Group 43). A tank mix with a fungicide wih a different mode of action is required by label. fosetyl-Al (Aliette): 2 to 3 lb/A (7 dh, REI 12h, Group 33). Apply at first sign of disease; reapply at 7- to 14-day intervals. fluopicolide (Presidio): 3-4 fl oz/A. (2 dh, REI 12h, Group 43). A tank mix with a fungicide with a different mode of action is required by label. pyraclostrobin plus boscalid (Pristine): 18.5 oz/A (7 dh, REI 12h, Groups 7 & 11). For suppression only. Rotate with a downy mildew fungicide with a different mode of action. Purple Blotch (Alternaria porri, Stemphylium vesicarium)Purple Blotch can be caused either fungus alone or both fungi together. Avoid Sweet Spanish onion because they are extremely susceptible. Plow under crop residues after harvest. Rotate with non-hosts. Select sites and practice irrigation to enhance rapid drying of foliage. Apply fungicides as canopy becomes more dense and leaf-wetness periods increase. chlorothalonil (Bravo Ultrex): 1.4 to 2.7 lb/A (7 dh, REI 12h, Group M5). When disease is present, use the higher rate. |
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