Weed Control

NOTE:  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. 

Growing on Plastic Mulch

Many growers choose to grow cucumber, muskmelon, and/or watermelon on plastic mulch. Herbicides can be applied before laying down plastic to help control weeds that may grow underneath the plastic or in planting holes.  Herbicides can also be used between rows of plastic.  Some herbicides cannot be used under plastic, even if they are registered for use in the crop. Read labels carefully! See notes on specific herbicides in the following section for more information on use and timing.

Labeled for preemergence weed control under plastic:

  • bensulide (Prefar)
  • halosulfuron (Sandea) (not labeled on muskmelons)

Labeled for preemergence weed control between plastic rows (directed and shielded band app)

  • bensulide (Prefar)
  • clomazone (Command)
  • ethalfluralin (Curbit)
  • halosulfuron (Sandea) (not labeled on muskmelons)
  • pendamthalin (Prowl) (not labeled for cucumbers)

Labeled for postemergence application between plastic rows

  • halosulfuron (Sandea) (not labeled on muskmelons)
  • paraquat (Gramoxone SL 2.0)
  • clethodim (Select Max)
  • sethoxydim (Poast)

Stale Seedbed

See Stale Seedbed Technique for information on the use of these herbicides or flaming.

  • carfentrazone (Aim EC): PHI 0d, REI 12h, Group 14.
  • glyphosate (Roundup Power Max): PHI 14d, REI 4h, Group 9.
  • paraquat (Gramoxone SL 2.0*): restricted use. REI 12h or 24h, Group 22.
  • pelargonic acid (Scythe): PHI 1d, REI 12h, Group 0.

Preemergent Herbicides (before weeds germinate)

bensulide (Prefar 4E): REI 12h, Group 0. May be used under plastic. Apply 5-6 qts/A per application. Can be applied to flat planted or bedded crops. Incorporate 1-2” into the soil within 36 hours by shallow cultivation or with water through irrigation or rainfall. Grass control only; should be supplemented with cultivation or another registered herbicide for broadleaf control.

clomazone (Command 3ME): PHI 30d for cucumbers, REI 12h, Group 13. For melons, apply 6.4-10.7 oz/A per application, only 1 application per year. For cucumbers, apply 6.4-16.2 oz/A per application, only 1 application per year. For summer squash, apply 6.4-21.3 oz/A per application, only 1 application per year. For all cucurbits can be applied after seeding but before emergence or before transplanting. Be sure to place the roots of transplants below the treated soil. Summer squash should be direct-seeded just after treatment but be sure to place the seed below the treated soil. Apply in a minimum of 10 gal/A of spray. Use the lower rate on sandy soils and the higher rate on silt and clay soils.

DCPA (Dacthal): REI 12h, Group 3. For seeded melons only, apply 6-14 lb/A per application, only 1 application per year. Apply after crop has 4-5 true leaves, is well established, and growing conditions are favorable. Apply in a minimum of 20 gal/A of spray. Activate with 0.33-0.5” of water through irrigation or rainfall. Rate based on soil texture. If weeds have emerged, cultivate or use herbicides to control emerged weeds.

ethalfluralin (Curbit EC): REI 24h, Group 3. Apply 3-4.5 pt/A per application, only 1 application per year. Has not been tested on all varieties, crop tolerance should be verified before treating the entire field. Can be applied up to 2 days after seeding but before the crop emerges, or as a banded spray between rows after crop emergence. Activate with a minimum of 0.5" of water through irrigation (within 2 days after application) or rainfall (within 5 days of application) or a shallow cultivation. Rate based on soil texture. Do not use during cold, wet weather or crop injury or stunting may occur.

pendimethalin (Prowl H2O): PHI 35d, REI 24h, Group 3. For melons only. Apply up to 2.1 pt/A per application, up to 2 applications allowed per year, a minimum of 21 days apart. Do not exceed 4.2 pts/A per year. Can be applied as a shielded application between rows with 6” on either side of row middles (before melon transplanting or before a seeded crop has emerged), or between rows covered with plastic mulch (before holes are punched in plastic for melon planting). Avoid spray contact with melon foliage or running vines because crop injury will occur. If applying a 2nd time, maintain a minimum of 6” on either side of stem or vines or apply before melon vine running.

s-metolachlor (Dual Magnum): REI 24h, Group 15. MASSACHUSETTS and NEW HAMPSHIRE only. Make sure the label for your state is available for download before using this product. This is a restricted label available only to growers who apply through the website www.syngenta-us.com/labels/indemnified-label-login(link is external) and agree to a waiver of liability. Main target weeds for this registration are galinsoga and yellow nutsedge. All label instructions will be supplied after the application for use is completed.

sulfentrazone (Aquesta 4F): REI 12h, Group 14. Apply 3-8 oz/A per application, only 1 application per year. Rate based on soil texture, organic matter and soil pH. For citron melon, muskmelon, and watermelon only. Apply from 48 hours before planting up to just before seedling emergence. If seedlings are close to soil surface or have emerged, do not apply solution directly to melons. Do not use on soils that contain less than 1% organic matter.

Pre- and Postemergent Herbicides 

halosulfuron (Sandea): PHI 14d cucumber, 30d squash, 57d watermelon REI 12h, Group 2. Apply 0.5-1 oz/A per application, up to 2 application allowed per  year, a minimum of 21 days apart. Do not exceed 2 oz/A per year. Apply in a minimum of 15 gal/A of spray or 20 gal/A of spray for watermelon. Use the lower rate on sandy soils and the higher rate on silt and clay soils.

Can be applied after planting seeds but prior to soil cracking, or before transplanting. Transplant into treated area no sooner than 7 days after application and take care to limit movement of treated soil. If using with plastic mulch, apply after the final bed shaping but before plastic installation. Crop may be seeded or planted no sooner than 7 days after application. Can also apply to row middles.

Can also be applied after the crop has reached at least 3-5 true leaves but before 1st female flowers appear and at least 14 days after transplanting if applicable. May be applied as an over-the-top application, or a directed spray application with shields to minimize contact of the herbicide with the crop. Can be applied to row middles of direct-seeded or transplanted. If plastic is used on the planted row, adjust equipment to keep the application off the plastic (over-the-top applications not allowed on plastic mulch).

Split applications will help with control of nutsedge (although not allowed in watermelon). Either apply before the crop emerges and gain after the crop emerges, or twice after the crop emerges. Use a spot treatment to target emerged nutsedge and do not exceed 1.0 oz per treated acre.

Can cause temporary stunting. Heavy rains following application or organophosphate use will increase the potential for crop injury.

Postemergent Herbicides (after weeds germinate)

carfentrazone (Aim EC): PHI 0d, 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 year. Apply 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. Can also be applied as a preplant burndown no later than 7 days before seeding with 15-30 gal/A of spray with a methylated seed oil. 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 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.

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. Allow a minimum of 3 days between application and seeding and do not apply after seeding for many varieties. 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*): restricted use. REI 12h or 24h, Group 22. Apply 2-4 pts/A per application, up to 3 applications allowed per year, a minimum of 7 days apart. Do not exceed 8 pts/A per year. May be fatal if swallowed or inhaled. Applicators must complete an EPA-approved paraquat training listed on the following website https://www.epa.gov/pesticide-worker-safety/paraquat-dichloride-training...(link is external). The training must be completed a minimum of every three years.

pelargonic acid (Scythe): PHI 1d, REI 12h, Group 0. Apply a 3-10% solution (3-10 gallons per 100 gallons 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.

sethoxydim (Poast): PHI 3d for cucumber and muskmelon, 14d for all other cucurbits, 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. Apply 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.

trifluralin (Treflan HFP): PHI 60d for watermelon, 30d for all other cucurbits, REI 12h, Group 3. Apply up 1-2 pt/A per application, only 1 application per year. Rate based on soil texture and rainfall. Apply after crop has emerged when plants have 3-4 true leaves as a directed spray between the rows avoiding contact with foliage or crop injury may occur.