Weeds Pages
| Herbicide | Amount per acre | REI‡ | PHI‡ | |
|---|---|---|---|---|
| (Example trade name) | (hours) | (days) | ||
| Not all registered pesticides are listed. The following are listed alphabetically. When choosing a pesticide, consider information relating to environmental impact, resistance management , the pesticide's properties, and application timing. Tank mixes may be necessary to achieve desired control; see the Susceptibility of Weeds to Herbicide Control for information on specific weed control. Always read the label of the product being used. | ||||
| PREPLANT | ||||
| A. | GLYPHOSATE | |||
| (Roundup PowerMAX) | Label rates | 4 | 14 | |
| WSSA MODE-OF-ACTION GROUP NUMBER1: 9 | ||||
| TIMING: Can be used before planting or after planting, but before the crop emerges. | ||||
| COMMENTS: Registered for preplant use in onions (dry bulb and green), garlic, leek, and shallot. A nonselective, foliar herbicide applied before planting to pre-made beds to kill emerged weeds. Consult the label for specific recommendations on particular weed species. Do not apply to weeds stressed for moisture or weeds with significant dust. For perennial weeds, allow 7 days after application before cultivating. | ||||
| B. | METAM POTASSIUM*§ | 174–360 lb a.i. | ||
| (K-Pam HL) | 30–62 gal | See label | NA | |
| WSSA MODE-OF-ACTION GROUP NUMBER1: 26 | ||||
| TIMING: Preplant only | ||||
| COMMENTS: Registered for use in onion, garlic, and leek. This fumigant is effective against nightshade and many other weeds. Beds must be free of large clods and the soil should be moistened by rainfall or irrigation before application. Applications are made using a spray blade cutting 2 to 3 inches below the soil surface, depending on soil moisture. Disc hillers follow directly behind the spray blade to form a 3- to 6-inch soil cap over the treated area. Other methods of application include shank and drench application. Fumigants such as metam potassium are a source of volatile organic compounds (VOCs) but are minimally reactive with other air contaminants that form ozone. | ||||
| C. | METAM SODIUM*§ | 159.75–319.5 lb a.i. | ||
| (Vapam HL) | 37.5–75 gal | See label | NA | |
| WSSA MODE-OF-ACTION GROUP NUMBER1: 26 | ||||
| TIMING: Preplant only | ||||
| COMMENTS: Registered for preplant use in onion, garlic, and leek. This fumigant is effective against nightshade and many other weeds. Beds must be free of large clods and the soil should be moistened by rainfall or irrigation before application. Applications are made using a spray blade cutting 2 to 3 inches below the soil surface, depending on soil moisture. Disc hillers follow directly behind the spray blade to form a 3- to 6-inch soil cap over the treated area. Other methods of application include shank and drench application. Fumigants such as metam sodium are a source of volatile organic compounds (VOCs) but are minimally reactive with other air contaminants that form ozone. | ||||
| D. | PARAQUAT* | 0.625–1 lb a.i. | ||
| (Gramoxone SL 2.0) | 2.5–4 pt | 24 | Garlic: 200 | |
| Onion: 60 | ||||
| WSSA MODE-OF-ACTION GROUP NUMBER1: 22 | ||||
| TIMING: Either before planting or after planting, but before the crop emerges. | ||||
| COMMENTS: Registered for preplant use in garlic and direct-seeded onions. A nonselective foliar herbicide that kills emerged weeds. Any crop plants exposed to the spray will be killed, even germinating seed in the crook stage. No residual soil activity. Faster acting on warm, sunny days. | ||||
| POSTPLANT | ||||
| Before crop and weeds emerge, loop stage (when specified) | ||||
| A. | BENSULIDE | 5–6 lb a.i. | ||
| (Prefar 4-E) | 5–6 qt | 12 | NA | |
| WSSA MODE-OF-ACTION GROUP NUMBER1: 8 | ||||
| TIMING: Either preplant or postplant, preemergence. | ||||
| COMMENTS: Registered for use on bulb onions, garlic, and shallot, but recommended only for onions in California. Requires irrigation for activation. See label for optimal soil temperature and salinity conditions for preventing crop damage. Effective on annual grasses and on a broadleaf species such as knotweed, pigweed, and purslane. | ||||
| B. | ETHOFUMESATE | 0.5–1 lb a.i. | ||
| (Ethofumesate 4SC) | 16 fl oz (coarse soils) 32 fl oz (medium or fine soils) |
12 | NA | |
| WSSA MODE-OF-ACTION GROUP NUMBER1: 8 | ||||
| TIMING: General preemergence application. | ||||
| COMMENTS: Registered for use in garlic, dry bulb onions, and bulb shallot. Requires rainfall, sprinkler or furrow irrigation for activation. | ||||
| C. | FLUMIOXAZIN | 3.06 oz a.i. | ||
| (Chateau SW) | 6 oz | 12 | NA | |
| WSSA MODE-OF-ACTION GROUP NUMBER1: 14 | ||||
| TIMING: Must be applied within 3 days after planting for preemergence use. | ||||
| COMMENTS: Registered for use in garlic only. Weed control improves with rainfall or irrigation. | ||||
| D. | GLYPHOSATE | |||
| (Roundup PowerMAX) | Label rates | 4 | 14 | |
| WSSA MODE-OF-ACTION GROUP NUMBER1: 9 | ||||
| TIMING: Can be used before planting or after planting, but before the crop emerges. | ||||
| COMMENTS: Registered for use in garlic, leek, onion (dry bulb and green), and shallot. A nonselective, foliar herbicide applied to beds to kill emerged weeds. Consult the label for specific recommendations on particular weed species. Do not apply to weeds stressed for moisture or weeds with significant dust. For perennial weeds, allow 7 days after application before cultivating. | ||||
| E. | OXYFLUORFEN | |||
| (Goal 2XL) | Garlic: 1 pt Transplanted onion: 0.5–2 pt |
48 | 60 | |
| WSSA MODE-OF-ACTION GROUP NUMBER1: 14 | ||||
| TIMING: For transplanted onions, apply immediately after transplanting before weeds emerge. For direct-seeded garlic, apply after planting and before crop emergence. For all other crops, do not apply until after crop emerges (see CROP ESTABLISHED). | ||||
| COMMENTS: Postplant, preemergence application registered for use in direct-seeded garlic and transplanted (NOT direct-seeded) dry bulb onions. In a ground application, apply in a spray volume of 40 to 60 gallons per acre for thorough weed coverage. This will also help avoid injury to the crop. Activated by rainfall or irrigation. | ||||
| F. | PARAQUAT* | 0.5 lb–1 lb a.i. | ||
| (Gramoxone SL 2.0) | Bulb onion: 2–4 pt Seeded onion and garlic: 2.5–4 pt |
24 | Onion: 60 | |
| Garlic: 200 | ||||
| WSSA MODE-OF-ACTION GROUP NUMBER1: 22 | ||||
| TIMING: Either before planting or after planting, but before the crop emerges. Any crop plants exposed to the spray will be killed, even germinating seed in the crook stage. | ||||
| COMMENTS: Preemergence use registered for seeded onions, bulb onion, and garlic. No residual soil activity. Faster acting on warm, sunny days. | ||||
| G. | PENDIMETHALIN | 0.475–1.52 lb a.i. | ||
| (Prowl H2O) | Garlic: 1.5–3.2 pt Onion: 1–3 pt (see Special Labels) |
24 | 60 | |
| WSSA MODE-OF-ACTION GROUP NUMBER: 3 | ||||
| TIMING: For dry bulb onions, registered as a delayed preemergence herbicide (75% onion radical emergence) for kochia control in Lassen, Modoc, Shasta, and Siskiyou counties under a special label (EPA SLN No. CA-150008, Exp. Oct. 31, 2020). For dry bulb, direct-seeded onions, also registered statewide for application at the loop stage under a special label (EPA SLN No. CA-060029). For garlic, general postplant, preemergence application. | ||||
| COMMENTS: Preemergence application registered for use in garlic and dry bulb onions (see onion specifications above). Application rates depend on soil type. Requires rainfall or irrigation for activation. | ||||
| CROP ESTABLISHED | ||||
| A. | BROMOXYNIL | Onion: 0.25–0.375 lb a.i. Garlic: 0.375–0.5 lb a.i. |
||
| (Brox 2EC) | Onion: 1–1.5 pt Garlic: 1.5–2 pt |
24 | Onion: 0 | |
| Garlic: 112 (60 in muck soils) | ||||
| WSSA MODE-OF-ACTION GROUP NUMBER1: 6 | ||||
| TIMING: For onion, chemigate or apply by ground when onions have 2 to 5 true leaves, and only apply it if the onion leaf cuticle has a waxy appearance. For garlic, may be applied any time after emergence before the crop is twelve inches tall. Weeds should not exceed the 4-leaf stage. | ||||
| COMMENTS: Postemergence use registered for garlic and dry bulb onions only. Very good for control of shepherd's purse, mustard species and Russian thistle. Very effective for control of small broadleaf weeds. If applied to plants with thin cuticles, bromoxynil can cause severe crop injury. Foliage needs to be dry at the time of application. Other conditions can lead to crop injury; consult label before application. Can be used in sequence with oxyfluorfen; use lower rates than those listed in tank mixes. | ||||
| B. | CLETHODIM | 0.068–0.2425 lb a.i. | ||
| (Select Max) | 9–32 fl oz | 24 | 45 | |
| WSSA MODE-OF-ACTION GROUP NUMBER1: 1 | ||||
| TIMING: Apply only after crop has 2 or more true leaves. | ||||
| COMMENTS: Labeled for use on dry bulb onion, garlic, and shallot. Controls annual bluegrass in the 2- to 3-leaf stage as well as other annual grasses and some perennial grasses. Do not apply through any type of irrigation system. Always apply with a crop oil concentrate. Rate differs for annual and perennial grasses. | ||||
| C. | DIMETHENAMID | 0.5625–0.9843 lb a.i. | ||
| (Outlook) | 12–21 fl oz | 12 | 30 | |
| WSSA MODE-OF-ACTION GROUP NUMBER1: 15 | ||||
| TIMING: Apply only after the crop has more than 2 true leaves. If applying to fields infested with yellow nutsedge, apply before nutsedge emerges. | ||||
| COMMENTS: Registered for use in garlic only. Provides control of yellow nutsedge and broadleaf weeds. Most effective when activated by sprinkler irrigation, rainfall, or mechanical incorporation. Amount per acre may be split into two applications rather than one (see label for specifics), but do not exceed a total maximum of 21 fl oz per acre in a single growing season. Maximum rate per season also depends on soil type and organic matter (see label). Use lower rates on coarse-textured soils and higher rates on medium- and fine-textured soils. | ||||
| D. | ETHOFUMESATE | 0.5 a.i. | ||
| (Ethofumesate 4SC) | 16 fl oz | 12 | 30 (+/-2) | |
| WSSA MODE-OF-ACTION GROUP NUMBER1: 8 | ||||
| TIMING: General postemergence application. | ||||
| COMMENTS: Registered for use in garlic, dry bulb onion, and bulb shallot only. Requires rainfall, sprinkler irrigation or furrow irrigation for activation. Controls a variety of broadleaf and grass weeds. | ||||
| E. | FLUAZIFOP-P-BUTYL | |||
| (Fusilade DX) | Label rates | 12 | 45 | |
| WSSA MODE-OF-ACTION GROUP NUMBER1: 1 | ||||
| TIMING: General postemergence application. Safe to the crop. | ||||
| COMMENTS: A selective, foliar herbicide for control of grasses in dry bulb onions and garlic. Effective at controlling small, annual grass seedlings and some perennial grasses. Later growth stages of annual grasses are more difficult to control. Not effective on drought-stressed grasses or on certain species (e.g., annual bluegrass, foxtail, sprangletop). | ||||
| F. | OXYFLUORFEN | 0.12–0.25 lb a.i. | ||
| (Goal 2XL) | Label rates | 48 | Onion: 45 | |
| Garlic and onion grown for seed: 60 | ||||
| (GoalTender) | Label rates | 48 | Onion: 45 | |
| Garlic and onion grown for seed: 60 | ||||
| WSSA MODE-OF-ACTION GROUP NUMBER1: 14 | ||||
| TIMING: In bulb onion only, GoalTender may be used at the 1st true leaf stage under a special local needs label (EPA SLN CA-070006); note that this use is not allowed on onions grown for seed. Otherwise, both Goaltender and Goal 2XL can be used after the onion crop (except crop grown for seed) has 2 fully developed true leaves under the regular label. On onions grown for seed, either product may only be applied when the crop has at least three true leaves. In garlic, either product may be applied when the crop is at least 12 inches tall. Apply when susceptible weeds are in the 2- to 4- leaf stage and actively growing. | ||||
COMMENTS: Registered for use in garlic, dry bulb onions, and onions grown for seed (see above row for stage-specific uses allowed for each crop). In a ground application, apply in a spray volume of 40 to 60 gallons per acre for thorough weed coverage. This will also help avoid injury to the crop. GoalTender is less active as a burndown herbicide, is most effective on young weeds, and causes less damage to crop foliage than the 2XL formulation. It will control some small annual grasses postemergence. In dry bulb onions, GoalTender may be tank-mixed with other pesticides such as bromoxynil, but such tank mixes must only be used on older onions with well developed cuticles to avoid unacceptable crop injury. Unacceptable injury may occur if applied to small onions without adequate cuticle development, and in conditions such as after cloudy or rainy weather. Follow the label closely to avoid crop injury when tank mixing. |
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| G. | PENDIMETHALIN | 0.71–1.52 lb a.i. | ||
| (Prowl 3.3 EC) | 1.8–3.6 pt | 24 | 60 | |
| (Prowl H2O) | 1.5–3.2 pt | 24 | 60 | |
| WSSA MODE-OF-ACTION GROUP NUMBER1: 3 | ||||
| TIMING: Prowl H2O may be applied to onion and shallot between the 2- and 6- true leaf stages, and applied to garlic when the crop has 1 to 5 true leaves. Prowl 3.3EC may be applied when garlic, onion, and shallots have between 2 and 6 true leaves. | ||||
| COMMENTS: For use on garlic, shallot, and bulb onion. Chemigate or incorporate with sprinklers or a heavy furrow irrigation. Controls many broadleaf weeds and annual grasses. Application rates depend on soil type, with lower rates for coarse-textured soils and higher rates for fine-textured soils; do not use on muck soils. | ||||
| H. | SETHOXYDIM | 0.19–0.28 lb a.i. | ||
| (Poast) | 1.0–1.5 pt | 12 | 30 | |
| WSSA MODE-OF-ACTION GROUP NUMBER1: 1 | ||||
| TIMING: Postemergence, when grasses are actively growing. Safe to the crop. | ||||
| COMMENTS: Registered for use in garlic, leeks, both green and bulb onions, and shallots. A selective, foliar herbicide for control of grasses. Effective in controlling small, annual grass seedlings and some perennial grasses. Later growth stages of annual grasses are more difficult to control. Not effective on drought-stressed grasses or on certain species (e.g., annual bluegrass, sprangletop). | ||||
| LAYBY | ||||
| A. | PENDIMETHALIN | |||
| (Prowl H20) | Coarse soil texture: 1.5 pt Medium texture: 2.0 pt Fine soil texture: 3.2 pt |
24 | 60 | |
| WSSA MODE-OF-ACTION GROUP NUMBER1: 3 | ||||
| TIMING: May be applied to onion and shallot between the 2- and 6- leaf stages, and garlic between the 1st and 5- leaf stages. | ||||
| COMMENTS: Registered for use in garlic, bulb onion, and bulb shallot. Controls many broadleaf weeds and annual grasses. | ||||
| PREHARVEST | ||||
| A. | GLYPHOSATE | |||
| (Roundup PowerMAX) | 22–44 fl oz | 4 | 30 | |
| WSSA MODE-OF-ACTION GROUP NUMBER1: 9 | ||||
| TIMING: After the last irrigation and before removing the top of the crop. | ||||
| COMMENTS: Registered for preharvest use only in onions and garlic grown for processing (dehydration), for suppression of nutsedge and field bindweed, under a Special Local Needs label (SLN No. CA-170011, expires August 31, 2022). Apply by ground sprayer equipment only. In addition to nutsedge and bindweed, also effective at drying down nightshade. Avoid contact with the crop; otherwise severe damage may occur. | ||||
| ‡ | Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest. |
| * | Permit required from county agricultural commissioner for purchase or use. |
| 1 | Group numbers are assigned by the Weed Science Society of America (WSSA) according to different modes of action. Although weeds may exhibit multiple resistance across many groups, mode-of-action numbers are useful in planning mixtures or rotations of herbicides with different modes of action. |