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. 

Stale Seedbed

See Stale Seedbed Technique in the Weed Management section for information on the use of these herbicides.

carfentrazone (Aim EC): REI 12h, Group 14. Apply up to 2 oz/A per application, and do not exceed a total of 6.1 oz/ per season. 

glyphosate (Roundup Power Max): REI 12h, Group 9.

paraquat (Gramoxone SL 2.0*): restricted use. REI 12h, Group 22. Use 2– 4 pts/A. 

pelargonic acid (Scythe): PHI 1d, REI 12h, Group 17. Use a 3 -10% solution (3 to 10 gallons per 100 gallons).

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 can not 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 infomation 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)

Herbicides Used Preemergence to Weeds

bensulide (Prefar 4E): May be used under plastic. REI 12h, Group 8.  Apply 5 to 6 qt/A.  Can be used as a broadcast treatment (no plastic), between rows of plastic, or under plastic.  Preplant incorporate by shallow cultivation (1-2”), or apply preemergence and incorporated thoroughly by irrigation/rainfall within 36 hours of application. Used primarily where grasses are a serious problem. Grass control only; should be supplemented with cultivation or another registered herbicide for broadleaf control. See label for rotation restrictions.

clomazone (Command 3ME): PHI 45d for cucumbers, REI 12h, Group 13.  Can be used as a broadcast treatment (no plastic) or between rows of plastic.  Do not use under plastic. Apply after seeding to the soil surface. For cucumbers, apply 0.4 to 1 pt/A.  For melons, apply 0.4 to 0.67 pt/A.  Use the lower rate on coarse-textured soil and the higher rate on fine-textured soil.  Will control annual grasses and many broadleaf weeds including common lambsquarters, velvetleaf, and jimsonweed.  Combining with Curbit (tank mix or sold as premixed product “Strategy”) will also control pigweed species.  Some temporary crop injury (partial whitening of leaf or stem tissue) may be visible after crop emergence. Complete recovery will occur from minor early injury without affecting yield or earliness. See label for replanting restrictions.

DCPA (Dacthal W75): REI 12h, Group 3.  Not labeled for cucumber.  Preemergence to weeds, but after crop emergence.  Apply 6 to 14 lb/A after crop has 4 to 5 true leaves, is well established, and growing conditions are favorable for good growth.  If weeds have emerged, crop should be cultivated and weeded prior to application. May also be banded to weed-free soil between rows of plastic mulch.

ethalfluralin (Curbit EC): REI 24h, Group 3.  Can be used as a broadcast treatment (no plastic) or between rows of plastic.  Do not use under plastic. Do not soil incorporate prior to planting. Apply to seeded crop at time of seeding or up to two days after seeding, or apply as a banded spray between rows after crop emergence.  A minimum of ½" of irrigation water (within two days after application) or ½” of rainfall (within five days of application) is required for activation. Use 3 to 4.5 pt/A, based on soil texture.  See label for rate selection. Use during cold, wet weather can result in crop injury or stunting.

ethalfluralin + clomazone (Strategy): REI 24h, Group 3 and 13. Use 2 to 6 pt/A, based on soil texture.  See label for rate selection. Can be used as a broadcast treatment (no plastic) or between rows of plastic.  Do not use under plastic. Do not soil incorporate prior to planting. Apply to seeded crop at time of seeding or up to two days after seeding, or apply as a banded spray between rows after crop emergence.  A minimum of ½" of irrigation water (within two days after application) or ½” of rainfall (within five days of application) is required for activation.

pendimethalin (Prowl H2O): REI 24h, PHI 35d, Group 3. Not labeled for cucumber. Row middles only.  Apply up to 2.1 pt/A as a shielded application between rows with 6 inches 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). Make a second shielded application up to 2.1 pt/A per between rows with a minimum of 6 inches on either side of stem or vines or between plastic mulch before melon vine running. Applications must be at least 21 days. Avoid spray contact with melon foliage or running vines because crop injury will occur.  DO NOT apply more than 2.1 pt/A in a single application or more than 4.2 pt/A per acre per season.

s-metolachlor (Dual Magnum): REI 12h, Group 15.  MASSACHUSETTS AND NEW HAMPSHIRE ONLY. This is a restricted label available only to those Massachusetts and New Hampshire growers who register through the website www.farmassist.com 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. Once on the farm assist web site, click products at top left, then indemnified labels.  Create a username and password, select Dual Magnum, and the crop.

Herbicides Used Pre- and/or Postemergence to Weeds

halosulfuron (Sandea): May be used under plastic. PHI 14d cucumber, PHI 57d watermelon and other melon, REI 12h, Group 2.

Can cause temporary stunting. Heavy rains following applications will increase the potential for crop injury. Use of organophosphate insecticides can increase crop injury from halosulfuron.  See the label for other precautions and a list of weeds controlled. Consider using Sandea as a supplement to Strategy (ethafluralin + clomazone) in cases where Strategy has not provided sufficient weed control and when a postemergence application is not practical.

For cucumber, cantaloupe, honeydew, and crenshaw melon:  Apply 0.5 to 1 oz/A uniformly with ground equipment in a minimum of 15 gal of water per acre. Use the lower rate on lighter textured soils with low organic matter

  • Preemergence
    • Grown on plastic mulch: Apply following final bed shaping and just prior to the installation of the plastic mulch. Crop may be seeded into this treated area no sooner than 7 days after application and the installation of the plastic mulch unless local conditions demonstrate safety at an earlier interval.
    • Grown on bare ground: Preemergence - apply after planting, but prior to soil cracking for direct seeded crops. Can be used as a pre-transplant application. Crop may be transplanted into this treated area no sooner than 7 days after application unless local conditions demonstrate safety at an earlier interval.
  • Postemergence (grown on bare ground only) - Apply Sandea after the crop has reached at least 3 to 5 true leaves but before first female flowers appear. If transplanted crop, apply to transplants that are established and actively growing and in the 3 to 5 true leaf stage or no sooner than 14 days after transplanting unless local conditions demonstrate safety at an earlier interval.  May be applied as an over-the-top application, a directed spray application, or with crop shields to minimize contact of the herbicide with the crop.
  • Postemergence (row middles) - Apply between rows of direct-seeded or transplanted crop. Avoid contact of the herbicide with the planted crop. If plastic is used on the planted row, adjust equipment to keep the application off the plastic.

For nutsedge control in cucumber: A preemergence application can be followed by a postemergence application.  Use a spot treatment method, treating only areas of emerged nutsedge. Application rate should not exceed 1.0 oz/A.  Avoid contact of the herbicide with the planted crop. It may be necessary to use a second postemergence spot application to areas where the nutsedge has emerged or regrown. For these situations, use a spot treatment method treating only those areas of emerged nutsedge. Do not apply more than 2 applications not to exceed a total of 2 oz/A per 12 month period (including pre- and postemergence), including applications to the crop and to row middle/furrows.  Allow a minimum of 21 days between applications.

For watermelon: apply 0.5 to 0.75 oz/A in a minimum of 20 gallons of water per acre.  Use the lower rate on lighter textured soils with low organic matter. Where soil is fumigated prior to planting, allow at least five days after soil fumigation before an application of Sandea.

  • Grown on plastic mulch: Pre-seeding/pre-transplant – Apply following final bed shaping and just prior to the installation of the plastic mulch. Watermelons should be seeded or transplanted into this treated area no sooner than 7 days after the application and the installation of the plastic mulch unless local conditions demonstrate safety at an earlier interval. Use the lower rate on lighter textured soils with low organic matter. Care should be taken to limit movement of herbicide treated surface soil during the transplant process to avoid injury.
  • Grown on bare ground: For direct seeded crop, apply after planting, but prior to soil cracking.  For transplanted crop, watermelons should be transplanted into this treated area no sooner than 7 days after application unless local conditions demonstrate safety at an earlier interval. Care should be taken to limit movement of herbicide treated surface soil during the transplant process to avoid injury.
  • Row Middle Applications: Apply between rows of direct-seeded or transplanted crop, while avoiding contact of the herbicide with the planted crop. If plastic is used on the planted row, adjust equipment to keep the application off the plastic. Reduce rate and spray volume in proportion to area actually sprayed. Runners that come in contact with the plastic can pick up residual Sandea and may exhibit a visual crop response. Do not apply more than 2 applications or 1 oz/A of product per 12 month period. (includes applications to the crop and to row middle).

Herbicides Used Postemergence to Weeds

carfentrazone (Aim EC): REI 12h, Group 14.  Aim is a burndown herbicide and will injure any foliage it comes into contact with. Apply Aim 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 inches tall and rosettes less than 3 inches across. Good coverage is essential for good control.  Apply up to 2 oz/A per application, and do not exceed a total of 6.1 oz/ per season. 

clethodim (Select Max): PHI 14d, 24hr REI, Group 1.  Will control grass weeds only. Apply to actively growing grasses.  See label for rate selection.  Multiple applications permitted of 9 to 16 oz/A per application, minimum 14-days between applications, not to exceed 64 oz/A per year.  Add 0.25% v:v nonionic surfactant (1 qt per 100 gal of spray).  Can also be used as a spot-spray by mixing 1/3-2/3% (0.44 to 0.85 oz per gallon) Select Max and 0.25% v:v nonionic surfactant (0.33 oz per gallon).  Spray to wet, but do not allow runoff of spray solution.

pelargonic acid (Scythe):  PHI 1d, REI 12h, Group 17. Use a 3 -10% solution (3 to 10 gallons per 100 gallons). Use a 3 to 5% solution for annual weeds, a 5 to 7% solution for biennial and perennial weeds, and 7 to 10% solution for maximum burndown. Delivery rate for boom applications should be 75 to 200 gals of spray solution per acre; complete coverage of weed foliage is essential. Use a DIRECTED/ SHIELDED SPRAY; contact with crop will cause injury. For hand-held equipment, spray to completely wet all weed foliage but not to the point of runoff. Repeat applications as necessary. Tank mixes are allowed with this product. See label for complete details.

sethoxydim (Poast): PHI 14d (3 day PHI for cucumber and muskmelon), REI 12h, Group 1.  Controls grass weeds only.  Apply to actively growing grasses (see product label for susceptible stage).  Maximum 1.5 pt/A per application, minimum 14-days between applications.  Do not exceed 3 pt/A per year. Use with crop oil concentrate (2.0 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 used as a spot-spray by mixing 1-1.5% (1.3 to 1.9 oz per gallon) Poast and 1% v:v crop oil concentrate (1.3 oz per gallon).  Spray to wet, but do not allow runoff of spray solution.