How to Manage Pests

UC Pest Management Guidelines

Herbicide		Amount/Acre	R.E.I.+	P.H.I.+
(trade name)			(hours)	(days)
When choosing a herbicide, consider information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
PREPLANT
A.	METAM SODIUM*	50–75 gal	48	—
	(various products)
	COMMENTS: Beds must be free of large clods and the soil should be moistened by rainfall or irrigation before application. Soil temperatures should be between 40° to 90°F at the 3-inch depth. Broadcast rate is 50–75 gal /acre but if only the planted row is to be treated, reduced rates can be used depending on the number of rows to be planted/bed. Applications are made using a spray blade cutting 2 to 3 inches below the soil surface, depending on soil moisture. Disk hillers follow directly behind the spray blade to form a 3- to 5-inch soil cap over the treated area. After 7 to 14 days, depending on the rate applied, the soil caps are removed and allowed to air. The label requires a 14-day interval between application and planting. Avoid moving untreated soil into the banded area. This treatment is effective against nightshade and many other weeds. 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. Fumigate only as a last resort when other management strategies have not been successful or are not available.
B.	PARAQUAT*	0.625–1 lb a.i.
	(Gramoxone Inteon)	2.5–4 pt	12	200
	WSSA MODE OF ACTION GROUP NUMBER1: 22
	COMMENTS: A nonselective foliar herbicide that kills emerged weeds. Can be used 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. No soil residual activity. Use the lower rate on small broadleaf weeds, the higher rate on larger weeds and grasses. Highly toxic if ingested; wear protective clothing. Faster acting on warm, sunny days. For use on seeded onions and garlic.
C.	GLYPHOSATE	1–4 lb a.i.
	(Roundup)	1–4 qt	12	—
	WSSA MODE OF ACTION GROUP NUMBER1: 9
	COMMENTS: A nonselective, foliar herbicide applied before planting to pre-made beds to kill emerged weeds. Allow 3 days after treatment before planting. Use the lower rate for annual grasses and weeds, the higher rate on perennial weeds. Consult the label for specific recommendations on particular weed species. Do not apply to weeds stressed for moisture. For perennial weeds, allow 7 days after application before cultivating.
AT PLANTING
A.	DCPA	4.5–10.5 lb a.i.
	(Dacthal) 75W	6–14 lb	12	—
	MODE OF ACTION: WSSA MODE OF ACTION GROUP NUMBER1: 3
	COMMENTS: Apply at planting to control annual grasses and some annual broadleaf weeds. DCPA can be sprayed directly over transplants without injury. In sandy loam soils, maximum preemergence rate of 10 lb/acre is recommended.
POSTPLANT
Before crop and weeds emerge
A.	ETHOFUMESATE
	(Norton) 4 SC	16–32 fl oz	12	30 (+/-2)
	MODE OF ACTION: WSSA MODE OF ACTION GROUP NUMBER1: 8
	COMMENTS: For use on onions. Apply preemergence. Use lower rates on coarse-textured soils and higher rates on fine-textured soils for preemergent applications. Do not exceed 48 fl oz on coarse-textured soils and 96 fl oz on fine-textured soils in one season.
POSTPLANT
Crop established
A.	DCPA	4.5–10.5 lb a.i.
	(Dacthal) 75W	6–14 lb	12	0
	MODE OF ACTION: WSSA MODE OF ACTION GROUP NUMBER1: 3
	COMMENTS: For use on onion. Apply after planting to clean cultivated soil when crop has 4–5 leaves to prevent weed germination. Incorporate with irrigation water, not mechanically. Make band application, except from Aug 1 to Dec 31 when several counties are exempt from this requirement; see label for details. Good control of annual grasses and some annual broadleaf weeds. See label for plantback restrictions. In sandy loam soils, maximum preemergent rate of 10 lb/acre is recommended.
B.	BENSULIDE	4 lb a.i.
	(Prefar) 4E	4 qt	12	0
	WSSA MODE OF ACTION GROUP NUMBER1: 8
	COMMENTS: Registered for use on bulb onions and garlic, but recommended only for onions in California. Do not incorporate by mechanical methods.
C.	DIMETHENAMID	0.5625–0.9843 lb a.i.
	(Outlook) 6 EC	12–21 fl oz	12	30
	MODE OF ACTION GROUP NUMBER1: 15
	COMMENTS: Provides yellow nutsedge and broadleaf weed control. Apply at second true leaf stage of onions but before nutsedge emerges. Do not exceed a total maximum of 21 fl oz/acre in a single growing season. Use lower rates on coarse-textured soils and higher rates on fine-textured soils.
D.	PENDIMETHALIN	0.5–1.5 lb a.i.
	(Prowl) 3.3 EC	1.2–3.6 pt	24	60
	(Prowl H20) 3.8F	1–3 pt	24	60
	WSSA MODE OF ACTION GROUP NUMBER1: 3
	COMMENTS: For use on garlic, shallots, and bulb onions. Apply after planting garlic, incorporate with sprinklers or a heavy furrow irrigation. Will control many broadleaf weeds and annual grasses. The two formulations of pendimethalin have different application timings: Apply Prowl 3.3 EC between 2 to 6 true leaf stage (shallots/onions) and 1 to 5 true leaf stage (garlic). Prowl H20 has a Special Local Needs registration and can be applied at the loop stage in direct-seeded dry bulb onions. 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.
E.	PENDIMETHALIN	0.618–1.237 lb a.i.
	(Prowl) 3.3 EC	1.5–3 pt	24	60
	(Prowl H20) 3.8F	1–3 pt	24	60
	WSSA MODE OF ACTION GROUP NUMBER1: 3
	. . . PLUS . . .
	OXYFLUORFEN	0.25 lb a.i.
	(Goal) 2XL	1 pt	48	Onions: 45; Garlic: 60
	WSSA MODE OF ACTION GROUP NUMBER1: 14
	COMMENTS: For tank mixes, observe all directions for use on all labels, and employ the most restrictive limits and precautions. Never exceed the maximum a.i. on any label when tank mixing products that contain the same a.i.
F.	BROMOXYNIL	0.25–0.375 lb a.i.
	(Buctril)	1–1.5 pt	24	Garlic: 112
	WSSA MODE OF ACTION GROUP NUMBER1: 6
	COMMENTS: Apply by ground when onions have 2 to 4 true leaves. Use at least 50 gal water in spray mix. Various conditions will lead to crop injury; consult label before application. Can be used in sequence with oxyfluorfen. Very good for control of mustard species.
G.	OXYFLUORFEN	0.12–0.25 lb a.i.
	(Goal) 2XL	See label	48	Onions: 45; Garlic: 60
	(GoalTender) 4F	See label	48	Onions: 45; Garlic: 60
	WSSA MODE OF ACTION GROUP NUMBER1: 14
	COMMENTS: In onion, apply Goal 2XL by ground when onions have 2 to 4 true leaves; GoalTender can be applied at the first true leaf stage. GoalTender is less active as a burndown material and is most effective on young weeds; it causes less damage to crop foliage than the 2XL formulation. Will control small annual grasses postemergence. Goal has some residual soil activity after application. Very good for control of little mallow (cheeseweed). In garlic, apply it as a directed spray before the last irrigation. Controls nightshade. Will damage foliage if it gets on crop. Garlic must be at least 12 inches in height and weeds should be in the seedling stage and actively growing.
H.	SETHOXYDIM	0.09–0.28 lb a.i.
	(Poast)	0.5–1.5 pt	12	30
	WSSA MODE OF ACTION GROUP NUMBER1: 1
	COMMENTS: A selective, foliar herbicide for control of grasses. A surfactant (crop oil concentrate or nonionic surfactant) is recommended. Safe to the crop. Not effective on drought-stressed grasses or on certain species (e.g., annual bluegrass, sprangletop).
I.	FLUAZIFOP-P-BUTYL	0.185–0.75 lb a.i.
	(Fusilade DX)	0.74–3 pt	12	45
	WSSA MODE OF ACTION GROUP NUMBER1: 1
	COMMENTS: For use on dry bulb onions and garlic. A selective, foliar herbicide for control of grasses. A surfactant (crop oil concentrate or nonionic surfactant) is recommended. Safe to the crop. Not effective on drought-stressed grasses or on certain species (e.g., annual bluegrass, foxtail, sprangletop).
J.	CLETHODIM	0.095-0.2496 lb a.i.
	(Select Max)	13–34 fl oz	24	45
	WSSA MODE OF ACTION GROUP NUMBER1: 1
	COMMENTS: Labeled for use on onion (dry bulb only), garlic, and shallots. Controls annual bluegrass in the 2- to 3-leaf stage as well as other annual and some perennial grasses. Do not apply through any type of irrigation system. Always apply with a crop oil concentrate. Use higher rate on perennial grasses.
K.	ETHOFUMESATE	0.5 lb a.i.
	(Norton) 4 SC	16 fl oz	12	30 (+/-2)
	MODE OF ACTION GROUP NUMBER1: 8
	COMMENTS: Up to four foliar applications after crop emergence at evenly spaced intervals can be made; do not apply more than 0.75 gal/season.
Layby
A.	DCPA	4.5–10.5 lb a.i.
	(Dacthal) 75W	6–14 lb	12	0
	WSSA MODE OF ACTION GROUP NUMBER1: 3
	COMMENTS: Labeled for layby applications in onion. Cultivate before application to remove emerged weeds. Apply as a directed spray when the crop has 4 to 5 leaves. Do not apply over the top of crop. Good control of annual grasses and some annual broadleaf weeds. Do not incorporate mechanically.
+	Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) 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. For more information, see http://www.plantprotection.org/HRAC/.
—	Not applicable.

PUBLICATION

UC IPM Pest Management Guidelines: Onion and Garlic
UC ANR Publication 3453
Weeds
R. Smith, UC Cooperative Extension, Monterey County
S. A. Fennimore, Vegetable Crops/Weed Science, UC Davis/Salinas
S. Orloff, UC Cooperative Extension, Siskiyou County
G. J. Poole, UC Cooperative Extension, Los Angeles County
Acknowledgment for contributions to Weeds:
C. E. Bell, UC Cooperative Extension, San Diego County
D. W. Cudney, Botany and Plant Sciences, UC Riverside

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