Weed Control : New England Vegetable Management Guide : UMass Amherst

NOTE: This is a list of herbicides registered for use in rhubarb in the Northeast, but that there is no specific crop safety data or efficacy data available for these products on rhubarb in our region. Always use caution when using new products until you have a sense on how they will perform in your field conditions on your crop.

Preemergent Herbicides (before weeds germinate)

clomazone (Command 3ME): REI 12h, Group 13. Apply 64 fl oz/A per application, only 1 application per year. Apply when rhubarb is dormant, before leaf emergence. Apply in a minimum of 10 gal/A of spray.
dichlobenil (Casoron 4G): REI 24h, Group 29. Apply 50 lbs/A per application, only 1 application per year. Apply when rhubarb is dormant and incorporate into the soil with water through irrigation or rainfall.
prometryn (Caparol 4L): PHI 40d, REI 12h or 48h, Group 5. Apply 2-4 pt/A per application, only 1 application per year. Apply when established rhubarb is dormant, before leaf emergence. Apply in a minimum of 20 gal/A of spray. Use the lower rate on sandy soils and the higher rate on silt and clay soils.
s-metolachlor (Dual Magnum): PHI 62d, REI 24h, Group 15. Apply 0.67-1.33 pts/A per application, only 1 application per year. Apply when rhubarb is dormant, before leaf emergence, as a broadcast spray to soil surface in early spring.
sulfentrazone (Aquesta 4F): REI 12h, Group 14. Apply 8 oz/A per application, only 1 application per year. Apply just before rhubarb plants break dormancy at least 80 days before harvest in a minimum of 10 gal/A of spray.

Pre- and Postemergent Herbicides

halosulfuron (Sandea): PHI 60d, REI 12h, Group 2. Apply 0.5-1 oz/A per application, only 1 application per year. Apply when rhubarb is dormant, as late as possible, prior to the breaking of rhubarb dormancy. Sandea may cause significant crop stunting, so begin with the lower rate to determine potential sensitivity to its use along with speed and degree of recovery. For best results use a NIS if labeled weeds are emerged. Apply in a minimum of 15 gal/A of spray.
linuron (Lorox DF): REI 24h or 8d, Group 5. Apply up to 3 lbs/A per application, only 1 application per year. Apply when rhubarb is dormant, before leaf emergence. Make application as a broadcast or banded over-the-row treatment. Do not use on soils with less than 1% organic matter. Preemergence can control annual weeds as they germinate. Postemergence can control up to 2” tall annual grasses and up to 6” tall broadleaf weeds.
mesotrione (Callisto): PHI 21d, REI 12h, Group 27. Apply up to 6 oz/A per application. Only 1 application per year. Apply when established rhubarb is dormant, before leaf emergence. Rainfall or irrigation after application may increase the risk of injury to emerging rhubarb. If weeds are emerged at the time of application it is recommended to add an adjuvant (crop oil at 1% v/v or NIS at 0.25% v/v).
quinclorac (QuinStar 4L): REI 12h, Group 4. Apply up to 12.6 oz/A, up to 2 applications allowed per year, a minimum of 30 days apart. Do not exceed 25.2 oz/A per year. Apply as a foliar application in a minimum of 10 gal/A of spray. A crop oil concentrate at a rate of 2 pints per acre may be included in the spray mixture, but can cause injury if used under hot and humid conditions. Do not apply to stressed crop or injury may occur.

Postemergence Herbicides (after weeds germinate)

carfentrazone (Aim EC): PHI 0d, REI 12h, Group 14. Apply 0.5-2 oz/A per application. Do not exceed 6.1 oz/A per season. Can be applied as a preplant burndown no later than 7 days before seeding or immediately before transplanting crops. Can also be applied to row middles of emerged crops with hooded sprayers to control emerged weeds, including crops grown on mulch or plastic. 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 30d, REI 24h, Group 1. Apply 9-16 oz/A per application, up to 4 applications allowed per year, 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.
fluazifop (Fusilade DX): PHI 14d, REI 12h, Group 1. Apply up to 16 oz/A per application, up to 2 applications allowed per year, a minimum of 14 days apart. Do not exceed 32 oz/A per year. Apply to actively growing grasses. Add either crop oil concentrate (0.5-1%, 0.5-1 gallon per 100 gallons of spray) or nonionic surfactant (0.25-0.5%, 1-2 qt per 100 gal of spray).
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.
paraquat (Gramoxone SL 2.0*): REI 12h or 24h, Group 22. Apply 1.7-2.7 pts/A per application, up to 2 applications allowed per year, a minimum of 7 days apart. Do not exceed 5.4 pts/A per year. Apply during the dormant season before buds begin to grow. Apply in a minimum of 10 gal/A of spray. May be fatal if swallowed or inhaled. *Restricted use: Applicators must complete an EPA-approved paraquat training every 3 years: https://www.epa.gov/pesticide-worker-safety/paraquat-dichloride-training-certified-applicators.
pelargonic acid (Scythe): PHI 1d, REI 12h, Group 0. Apply a 3-10% solution (3-10 gal/100 gal of spray). Apply in 75-200 gal/A of spray. Can use preplant, or as a directed and shielded spray during crop growth. Avoid contact with foliage or crop damage may occur. Spray to wet, but do not allow runoff of spray solution.
quinclorac (Quinstar 4L): REI 12h, Group 4. Apply up to 12.6 oz/A per application, up to 2 application allowed per year, a minimum of 30 days apart. Do not exceed 25.2 oz/A per year. Apply as a foliar application. Can add a crop oil concentrate. Apply in a minimum of 10 gal/A of spray. Do not apply when crops are stressed.
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). 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.