NOTE: For the disease control products listed below, a product trade name and formulation are provided for each active ingredient (common name) as an example of rates, preharvest interval (PHI), restricted entry interval (REI), and special instructions. In many cases, there are other products available with the same active ingredient. Please see Table 26 and Fungicides and Bactericides Alphabetical Listing by Trade Name for more information on products with the same active ingredients.

The symbol ^OG   indicates a product is listed by the Organic Materials Review Institute (OMRI) as approved for use in organic production. See Organic Certification section for more detail.

The most common controls for leek and garlic diseases include the use of disease resistant cultivars and pathogen–free seed and bulbs, and cultural practices such as crop rotation and crop residue management that restrict the pathogen. 

Damping-off and seed rot (Pythium and Rhizoctonia)

Avoid excessive soil moisture by improving soil drainage or by utilizing raised beds. Seed and soil treatments with fungicides are a recommended practice.

• azoxystrobin (Quadris F): 0.4 to 0.8 fl oz/1000 row ft; PHI 0d, REI 4h, Group 11. See label for application methods and restrictions
• fludioxonil (Maxim 4FS): 0.08 to 0.16 fl oz/100 lb seed; REI 12h, Group 12. Does not control Pythium and Phytophthora. 
• Gliocladium virens strain GI-21 (Soilgard) OG:  see label for rate. Labeled for Pythium damping-off as pre-plant or at planting, See label. 
• mefenoxam (Ridomil Gold SL): 0.5 to 1.0 pt/A; REI 48h, Group 4. Labeled for Pythium  damping-off as pre-plant or at planting. See label. 
• metalaxyl-m [mefenoxam] (Apron XL):  0.085 to 0.64 fl oz/100 lbs seed; REI 48h. Gorup 4. Seed treatment for Pythium damping-off. 
• Psuedomonas chlororaphis strain AFS009 (Howler EVO) OG: see label for rate; PHI 0d,  REI 4h, Group BM02. May be used in greenhouses. See label for application methods and rates. 
• thyme oil (Guarda):  see label for rate; PHI 0d, REI oh. Group NC. See label for application methods and rate. 

Downy Mildew (Peronospora destructor)

During extended periods of cool, humid weather, this disease can be highly destructive, causing losses in both yield and bulb quality. Practice a 3- to 4-year rotation. Plant in well-drained soil and orient rows in the same direction as prevailing winds. Avoid overhead irrigation. A regular program of fungicide spraying based on climatic conditions and disease forecasts should be followed.

• ametoctradin plus dimethomorph (Zampro): 14.0 fl oz/A; PHI 0d, REI 12h, Groups 45 and 40.
• azoxystrobin (Quadris F): 9.0 to 15.5 fl oz/A; PHI 0d, REI 4h, Group 11.  Do not make more than one application of Quadris before alternating with fungicides that have a different mode of action.
• azoxystrobin plus chlorothalonil (Quadris Opti): 2.4 to 3.7 pt/A; PHI 14d, REI 12h, Groups 11 & M05. See label for tank mix precautions. 
• copper hydroxide (Kocide 3000): 0.75 to 1.5 lb/A; PHI 0d, REI 48h, Group M01. Do not apply in a spray solution having a pH less than 6.5 or tank mix with Aliette.
• dimethomorph (Forum): 6.0 fl oz/A; PHI 0d, REI 12h, Group 40. Forum must be applied as a tank mix with another fungicide with a different mode of action.
• famoxadone & cymoxanil (Tanos):  8.0 oz/A; PHI 3d, REI 12h, Groups 11 & 27. Must be tank mixed with an appropriate contact fungicide with a different mode of action. Do not alternate or tank mix with other Group 11 fungicides. 
• fenamidone (Reason 500 SC): 5.5 fl oz/A; PHI 7d, REI 12h, Group 11. Do not alternate with other Group 11 fungicides.
• mefenoxam plus chlorothalonil (Ridomil Gold Bravo SC): 2.5 pt/A; PHI 14d, REI 48h, Groups 4 & M05. 
• pyraclostrobin (Cabrio EG): 12.0 oz/A; PHI 7d, REI 12h, Group 11. Do not make more than one application of Cabrio before alternating to a fungicide with a different mode of action. Do not rotate with Quadris or Cabrio.

Purple Blotch (Alternaria porri)

Practice long rotations with unrelated crops and practices that reduce hours of leaf wetness however possible, i.e., with increased plant spacing. Promote good airflow and good drainage. Rotate Fungicides. Use of a single fungicide throughout the growing season is not recommended.

• azoxystrobin (Quadris F): 6.0 to 12.0 fl oz/A; PHI 0d, REI 4h, Group 11. Do not rotate with other Group 11 fungicides.
• azoxystrobin plus chlorothalonil (Quadris Opti): 1.6 to 3.2 pt/A; PHI 14d, REI 12h, Groups 11 & M05. See label for tank mix precautions. 
• azoxystrobin plus propiconazole (Quilt): 14 to 27.5 fl oz/A; PHI 14d, REI 12h, Groups 11 & 3.
• Bacillus amyloliquefaciens strain D747 (DoubleNickel 55^OG): 0.25 to 3.0 lb/A; PHI 0d, REI 4 h, Group BM02. Disease suppression only. For improved control; mix or rotate with a chemical fungicide. 
• boscalid (Endura): 6.8 oz/A; PHI 7d, REI 12h, Group 7.
• chlorothalonil (Bravo Weather Stik): 1.5 to 3 pt/A; PHI 7d, REI 12h, Group M05. When disease is present, use the higher rate.
• copper hydroxide (Kocide 3000): 0.75 to 1.5 lb/A; PHI 0d, REI 48h, Group M01. Do not apply in a spray solution having a pH less than 6.5 or tank mix with Aliette.
• cyprodinil (Vanguard): 5.5 oz/A; PHI 7d, REI 12h, Group 9.
• cyprodinil plus fludioxonil (Switch 62.5 WDG): 11.0 to 14.0 oz/A; PHI 7d, REI 12h, Groups 9 & 12.
• difenoconazole plus benzovindiflupyr (Aprovia Top): 10.5 to 13.5 fl oz/A; PHI 7d, REI 12h, Groups 3 & 7. No more than 2 sequential applications before alternating to a non-Group 7 fungicide.
• difenoconazole plus cyprodinil (Inspire Super): 14.0 to 20.0 fl oz/A; PHI 7d (dry bulb); PHI 14d (green), REI 12h, Groups 3 & 9. Apply in sufficient volume to achieve thorough coverage. 
• famoxadone plus cymoxanil (Tanos):  8.0 oz/A; PHI 3d, REI 12h, Groups 11 & 27. Must be tank mixed with an appropriate contact fungicide with a different mode of action. Do not alternate or tank mix with other Group 11 fungicides. 
• fenamidone (Reason 500 SC): 5.5 fl oz/A; PHI 7d, REI 12h, Group 11. Do not alternate with other Group 11 fungicides.
• fluxapyroxad plus pyraclostrobin (Merivon Xemium): 4 to 11 fl oz/A; PHI 7d, REI 12, Groups 7 & 11.  For best results, begin applications before disease onset.
• penthiopyrad (Fontelis): 16.0 to 24.0 oz/A; PHI 3d, REI 12h, Group 7.
• polyoxin D zinc salt (VEGGIETURBO 5%SC) OG: 6.5 to 13.0 fl oz/A; PHI 0d, REI 4h, Group 19.
• potassium phosphite plus chlorothalonil (Catamaran): 4.0 to 7.0 pt/A; PHI 14d, REI 12, Groups P07 & M05.
• propiconazole (Tilt): 4.0 to 8.0 fl oz/A; PHI 0d, REI 12h, Group 3. 
• pyraclostrobin (Cabrio EG): 8.0 to 12.0 oz/A; PHI 7d, REI 12h, Group 11. Do not exceed six applications or 72 oz/A. Do not rotate with other Group 11 fungicides.
• pyraclostrobin plus boscalid (Pristine):  10.5 to 18.5 oz/A; PHI 7d, REI 12h, Groups 11 & 7.
• pyrimethanil (Scala SC): 9.0 to 18.0 fl oz/A; PHI 7d, REI 12h, Group 9.
• tebuconazole (Orius 3.6F): 4.0 to 6.0 fl oz/A (for dry onion); PHI 7d, REI 12h, Group 3.

White Rot (Sclerotium cepivorum)

Avoid planting in infested fields. Destroy infected plants and spot treat the surrounding soil around the plants with fumigants. Warm season production of host crops may greatly reduce sclerotial inoculum. Practice crop rotation. Soil fumigation may provide partial control. In general, neither fungicides nor fumigation have provided consistent, reliable, full-season control of white rot. Hot water treatment of seed can reduce the potential to spread white rot sclerotia. Winter flooding and soil solarization can reduce the number of viable sclerotia. White rot symptoms are less severe on leeks compared with related plants.

Disease Control

NOTES:  For the insecticides listed below, one product trade name and formulation is provided for each active ingredient (AI) as an example of rates, preharvest interval (PHI), restricted entry interval (REI), and special instructions. In many cases, there are other products available with the same AI. Please see Table 27 and Insecticides Alphabetical Listing by Trade Name for more information on these insecticides.

The designation (Bee: L, M, or H) indicates a bee toxicity rating of low, moderate, or high. See the Protecting Honeybees and Native Pollinators section for more details.

The symbol * indicates a product is a restricted use pesticide. See Pesticide Safety and Regulations for more details.

The symbol ^OG   indicates a product is listed by the Organic Materials Review Institute (OMRI) as approved for use in organic production. See Organic Certification section for more details.

Allium Leafminer (Phytomyza gymnostoma)

The Allium leafminer (ALM) is a relatively new invasive pest species associated with many allium hosts. The ALM is a true fly species. It was first detected in Lancaster County, PA in 2015. Currently the distribution of the fly is limited within New England. However, the northern expansion of the fly has been rapid with several positive identifications in MA in 2019.

Within the Northeast, ALM populations exhibit two flights per season. These flights are separated by a summer aestivation (“summer hibernation”) period that often precludes the fly from causing significant damage in crops grown and harvested during the summer months (i.e. garlic and bulb onions). The first flight (overwintering population) begins in mid-to-late April, ending in May. The second flight does not begin until September and typically extends into early October. Female flies will make multiple punctures on leaves with their ovipositor (apparatus for laying eggs) that leaves a distinct line of easily visible white dots. These oviposition “scars” are the primary diagnostic indicator for the presence of the pest. Eggs are laid singly inside of leaves where the oviposition marks are made. When ALM eggs hatch, larvae enter the leaves and actively “mine” the plant tissue. After several days, larvae move towards the center and base of plant. After several weeks of active feeding, larvae typically pupate near the base of the plant within the foliage or may exit the plant and pupate in the soil. 

The most vulnerable allium hosts plants tend to be those plants harvested during the early spring and fall (primarily leeks and scallions). The removal of infected host plants and other allium residues from earlier harvested alliums is an important practice for reducing potential outbreaks in fall allium crops. Insect exclusion netting or other types of row covers can effectively exclude ALM flies if securely applied before the second flight begins. Foliar chemical applications have also been shown to be effective for reducing ALM damage. 

abamectin (Agri-Mek* SC): 1.75 to 3.5 fl oz/A; PHI 7d, REI 12h, Bee: H, Group 6. Make 2 consecutive applications then rotate to a different mode of action. Make at least 2 consecutive applications of another mode of action before making additional Agri-Mek SC applications. Insect control can be reduced if used with a sticker or binder type product.

azadirachtin (Azatin O^OG): 6 to 16 oz/A foliar or drench, 6 to 16 oz/100 gal in greenhouses; PHI 0d, REI 4h, Bee:L, Group un. When using lower rates, combine with adjuvant for improved spray coverage and translaminar uptake.

cyantraniliprole (Exirel): 13.5 to 20.5 fl oz/A; PHI 1d, REI 12h, Bee:H, Group 28. Use with an adjuvant to maximize efficacy. Spreading and penetrating adjuvants can cause negative crop response.

cyromazine (Trigard): 2.66 oz/A; PHI 7d, REI 12h, Bee: H, Group 17. Apply when leafminers first appear. Do not apply more than 6 times or 1 lb/A per calendar year.

dinotefuran (Scorpion 35SL): 5.25 to 7 fl oz/A foliar, 8.75 to 10.5 fl oz/A soil.; PHI 1d, REI 12h, Bee: H, Group 4A. Do not apply more than a total of 10.5 fl oz/A per season. Higher water volume provides improved control. Do not apply to vegetables grown for seed. 

Isaria fumosorosea Apopka Strain 97 (PFR-97 20% WDG^OG): 1 to 2 lbs/A; PHI 0d, REI 4h, Bee: M, Group M.

pyrethrins (Pyganic EC5.0II^OG): 4.5 to 17 oz/A; 0.25 to 0.50 oz/gal, 3 gal/1000 sq ft in greenhouse for backpack sprayers; PHI 0d, REI 12h, Bee: M, Group 3A.

spinetoram (Radiant SC): 6 to 10 oz/A; PHI 1d, REI 4h, Bee: M, Group 5. Efficacy improves with the addition of an adjuvant. Do not make more than 2 consecutive applications of Group 5 insecticides. Do not make more than 5 applications per year per crop.

spinosad (Entrust SC^OG): 3 to 6 oz/A; PHI 1d, REI 4h, Bee: M, Group 5.

Leek Moth (Acroleopiosis assectella)

Though leek moth feed upon most cultivated alliums, leeks are the most preferred and susceptible host species. Because garlic and onions are generally harvested for their bulbs, leek moth feeding damage tends to be less of a concern in these crops, as even moderate damage to the above-ground foliage typically does not lead to significant reductions bulb size or yield.

There are three flight periods of leek moth per season. The first flight (the overwintering generation) begins in mid‐late April, ending in mid‐May. The second flight period (the first generation) begins in mid‐June, ending in early to mid‐July. The third flight period begins in late July, ending in mid‐to late August. Although leek moth activity slows down after the last flight period, the damage can still develop on remaining allium vegetables, especially leeks, in the field. These larvae are considered to be the third generation and become the overwintering adults or pupae.
Eggs are laid singly on lower leaf surfaces whenever night temperatures are above 50-54°F.  Females lay up to 100 eggs over a 3-4-week period. After hatching larvae begin to burrow into the stem and move towards the center of the plant where young leaves are formed. In onions, leek moth larvae enter the hollow leaves and continue to feed on the inner cuticle of the leaf leading to the characteristic “window-paning” damage. After several weeks of active feeding, larvae exit the foliage and initiate pupation on the outside of leaves. Pupation lasts about 12 days, depending on weather conditions. 

Pre-harvest strategies: For smaller plots, insect exclusion netting can be an effective strategy for reducing leek moth damage by directly reducing exposure to egg laying female moths. Chemical applications are typically well-suited for larger growing areas and are best applied 1-2 weeks following peak moth flights, which can be monitored using traps baited with pheromone lures. In addition, research has shown that the timely release of the parasitoid wasp, Trichogramma brassiceae, can significantly reduce leek moth damage in leeks and other alliums. 

Post-harvest strategies: The primary concern for garlic and onion growers is the potential damage that may occur during post-harvest curing and/or storage. Damage during curing and storage is generally the result of larvae being brought into the storage area following harvest. A simple low-risk strategy for reducing the prevalence of leek moth larvae in these areas is to remove as much of the foliage as possible prior to curing. This “topping” strategy leaves larvae in the field where they no longer can access the bulbs. Research has also shown that topping prior to curing or storage does not affect bulb quality or shelf life.

Bacillus thuringiensis kurstaki (Dipel DF^OG): 0.5 to 2 lb/A; PHI 0d, REI 4h, Bee: L, Group 11. Must be ingested. Apply in evening or early morning, before larvae are actively feeding. Adherence and weather-fastness will improve with use of an approved spreader-sticker. Use high rate at cool temperatures. Bt may be unlikely to provide adequate control by itself due to the mining behavior of leek moth larvae. 

lambda-cyhalothrin (Warrior* II): 0.96 to 1.60 oz/A; PHI 14d, REI 24h, Bee: H, Group 3A.

methomyl (Lannate* LV): 3 pt/A; PHI 7d, REI 48h, Bee: H, Group 1A. For green and dry onions. Add wetting agent to improve coverage. Begin application before populations reach 3 to 5 thrips per plant.

spinetoram (Radiant SC): 6 to 10 oz/A; PHI 1d, REI 4h, Bee: M, Group 5. Thorough coverage is essential. Efficacy improves with the addition of an adjuvant.

spinosad (Entrust SC^OG): 3 to 6 oz/A; PHI 1d, REI 4h, Bee: M, Group 5. 

Onion Maggot (Delia antiqua)

For more information on this pest and for cultural and biological controls, see onion maggot in the Onion section.

diazinon (Diazinon* AG500): 2 to 4 qt/A; REI 3d, Bee: H, Group 1B. Broadcast and incorporate just before planting. Will not control organophosphate-resistant onion maggots. DO NOT make more than one application per year.

Onion Thrips (Thrips tabaci)

Thrips are favored by hot, dry weather. 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 overwintering sites. Do not plant leeks near other Alliums (onion family) or alfalfa, clover, cucurbits or brassica crops that can harbor large populations of thrips, which may migrate to leeks when these crops are cut or harvested. Begin applications when damage is first noticed. Repeat applications at 7- to 10-day intervals. Use a shorter interval in hot, dry weather. Use a spreader-sticker for better coverage. Apply in early evening, using high pressure and 100 gal water/A for best results. See onion thrips in the Onion section for more information.

acetamiprid (Assail 30SG): 5 to 8 oz/A; PHI 7d, REI 12h, Bee: M, Group 4A.

Beauveria bassiana (Mycotrol ESO): 0.25 qt to 1 qt/A; PHI 0d, REI 4h, Bee: L, Group UN. Treat when populations are low and thoroughly cover foliage. Takes 7 to 10 days after the first spray to see control. Repeat applications may be needed.

Burkholderia spp. strain A396 (Venerate XC^OG): 2 to 4 qt/A; PHI 0d, REI 4h, Bee: M, Group UN. Suppression only.

Chromobacterium subtsugae strain PRAA4-1 (Grandevo^OG): 2 to 3 lb/A; PHI 0d, REI 4h, Bee: M, Group UN.

deltamethrin (Delta Gold*): 1.5 to 2.4 oz/A; PHI 1d, REI 12h, Bee: H, Group 3A.

dinotefuran (Venom): 3 to 4 fl oz/A foliar, 5 to 6 fl oz/A soil; PHI 1d foliar, 21d soil, REI 4h, Bee: H, Group 4A.

imidacloprid (Admire Pro): 14 oz/A; PHI 21d, REI 12h, Bee: H, Group 4A. Soil applications only.

kaolin (Surround WP^OG): 25 to 50 lb/A or 0.25 to 0.5 lb/gal; PHI 0d, REI 4h, Bee: L. Suppression/repellence only. Good coverage into plant crown is essential. Generally compatible as a tank mix with other insecticides.

malathion (Malathion 57 EC): 1.5 to 2 pt/A; PHI 3d, REI 24h, Bee: H, Group 1B.

pyrethrin (PyGanic EC5.0^OG): 4.5 to 17 oz/A; 0.25 to 0.50 oz/gal, 3 gal/1000 sq ft in greenhouse for backpack sprayers; PHI 0d, REI 12h, Bee: M, Group 3A.

spinetoram (Radiant SC): 6 to 10 oz/A; PHI 1d, REI 4h, Bee: M, Group 5. Thorough coverage is essential. Efficacy improves with the addition of an adjuvant.

spirotetramat (Movento): 5 oz/A; PHI 7d, REI 24h, Bee: M, Group 23. Must be tank-mixed with a spray adjuvant with spreading and penetrating properties to maximize leaf uptake and sytemicity. Don't use sticker adjuvants. Controls immature stages, may also reduce adult fertility.

zeta-cypermethrin (Mustang*): 2.88 to 4 oz/A; PHI 7d, REI 12h, Bee: H, Group 3A.

Insect Control

NOTES: For the herbicides listed below, one product trade name and formulation is provided for each active ingredient along with preharvest interval (PHI), restricted entry interval (REI), resistance management group number, and example of rates and special instructions. In many cases, there are other products available with the same active ingredient. However, not all products with the same active ingredient are registered for use in a crop. Always check the product label to be sure that the crop is listed before using. 

See section on Soil Fumigation Outdoors. Proper use of Vapam can provide control of most weed species.

Stale Seedbed

See Stale Seedbed Technique.

• glyphosate (Roundup Power Max): PHI 14d, REI 4h, Group 9.
• pelargonic acid (Scythe): PHI 1d, REI 12h, Group 0.

Preemergent Herbicides (before weeds germinate)

• dimethenamid (Outlook): PHI 30d, REI 12h, Group 15. Apply 8-21 oz/A per application, up to 2 applications allowed per year, a minimum of 14 days apart. Do not exceed 21 oz/A per year. Use the lower rate on sandy soils and the higher rate on silt and clay soils. Apply to garlic that has at least 2 fully expanded true leaves or significant crop damage may occur. If applying to transplants, do not apply until transplants are in the group and have had several days to recover.
• pendimethalin (Prowl H2O): PHI 30d, REI 24h, Group 3. Apply up to 2 pt/A per application, up to 2 applications allowed per year, a minimum of 30 days apart. Do not exceed 4 pts/A per year. Apply to the soil surface after planting but before crop emergence, or after crop emergence when leeks are at the 2- to 3-leaf stage, or at both timings. Emerged weeds will not be controlled.

Postemergent Herbicides (after weeds germinate)

• carfentrazone-ethyl (Aim EC): REI 12h, Group 14. Apply 0.5-2 oz/A per application, multiple applications allowed per year. Do not exceed 6.1 oz/A per season. Can be applied as a preplant burndown no later than 30 days before planting by seed. Can also be applied to row middles of emerged crops with hooded sprayers to control emerged weeds. Prevent any spray from contacting the crop, or injury will occur.  For best results, make application to actively growing weeds up to 4” tall and rosettes less than 3” across.
• clethodim (Select Max): PHI 14d, REI 1d, Group 1. Apply 6-32 oz/A per application, up to 4 applications per year (or 2 if using 32 oz/A), a minimum of 14 days apart. Do not exceed 64 oz/A per year.  Apply to actively growing grasses. Add 0.25% v:v nonionic surfactant (1 qt/100 gal of spray).  Can also be applied as a spot-spray by mixing 0.33-0.66% (0.44-0.85 oz/gal) Select Max and 0.25% v:v nonionic surfactant (0.33 oz/gal).  Spray to wet, but do not allow runoff of spray solution.
• glyphosate (Roundup Power Max): PHI 14d, REI 4h, Group 9. Apply 10 oz to 3.1 qts/A per application, multiple applications allowed per year. Do not exceed 5 qts/A per year. Rate based on target weed species. Can be applied during fallow intervals, prior to planting or transplanting, at planting, or before crop has emerged. Could cause injury when applied prior to transplanting or direct-seeding into plastic mulch. Remove residual product from plastic mulch with a 0.5” of water through irrigation or rainfall prior to planting.
• pelargonic acid (Scythe): PHI 1d, REI 12h, Group 0. Apply a 3-10% solution (3-10 gallons per 100 gallons of spray). Rate based on target weed species. Apply in 75-200 gal/A of spray or with a spot sprayer until foliage is wet but not to the point of runoff. Repeat applications as necessary. Can apply for vegetative burndown during site preparation, prior to crop emergence from soil, as a directed and shielded spray during crop growth taking care to avoid contact with foliage and green tissue of crops, or after harvest.
• sethoxydim (Poast): PHI 30d, REI 12h, Group 1. Apply up to 1.5 pt/A per application, multiple applications allowed per year, a minimum of 14 days apart. Do not exceed 3 pts/A per year. Apply to actively growing grasses. Use with crop oil concentrate (2 pt/A) or methylated seed oil (1.5 pt/A). Note that crop oil can cause injury under hot and humid conditions. Can also be applied as a spot-spray by mixing 1-1.5% (1.3-1.9 oz/gal) Poast and 1% v:v crop oil concentrate (1.3 oz/gal). Spray to wet, but do not allow runoff of spray solution.

Weed Control