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Publication #HS190

Weed Management in Cucurbit Crops (Muskmelon, Cucumber, Squash, and Watermelon)1

Peter J. Dittmar and William M. Stall2

Crop Competition

Establishing a good crop stand in which plants emerge and rapidly shade the ground is an often overlooked tool for reducing weed competition. The plant that emerges first and grows the most rapidly has the competitive advantage. Good production management practices, such as fertility, well-adapted varieties, proper water control (irrigation, drainage), and establishment of adequate plant populations, are very helpful in reducing weed competition. Everything possible should be done to ensure that the crop—not the weeds—has the competitive advantage. Tests with watermelons and muskmelons have shown that if weeds such as smooth pigweed emerge 4–5 weeks after the crops, they will not reduce crop yield. If the weed emerges and competes with the crop in the first 4 weeks, however, yield will be reduced by competition. Two nightshade plants growing in-row between watermelon plants have been shown to reduce yield 80%–100% in open culture and 60%–75% in mulch culture production.

Mechanical Control

Mechanical control includes field preparation by plowing or disking, cultivation, mowing, hoeing, and pulling weeds by hand. Mechanical control practices are among the oldest weed management techniques. Seedbed preparation by plowing or disking exposes many weed seeds to variations in light, temperature, and moisture. For some weeds, this process breaks weed-seed dormancy, leading to early season control with herbicides or additional cultivation.

Cultivate only deeply enough in the row to achieve weed control; deep cultivation may prune roots, bring weed seeds to the surface, and disturb soil previously treated with an herbicide. Follow the same precautions between rows. Watermelon roots may extend as far as the tips of the vines, even when grown on mulch. Turning the vines and deep cultivation in the vine area may destroy a large number of roots, reducing water and nutrient uptake. Timely cultivation is extremely important.

Mulching

Polyethylene mulch has been shown many times to increase cucurbit yield and earliness. Properly injecting fumigants under the mulch controls nematodes, soil insects, soilborne diseases, and weed seeds. Mulches act as a barrier to the growth of many weeds. Nutsedges, however, are weeds that can and will grow through the mulch.

Herbicides

Properly selected herbicides are effective tools for weed control in cucurbits. Most of the labeled herbicides are for preplant or preemergence applications to the crop and weeds. At the present time, only two herbicides are labeled for postemergent crop applications. Care must be exercised to use these materials at the proper rate and correct time to avoid crop damage. Cucurbits as a group have very limited tolerances to most herbicides.

Two herbicides were removed for use on cucurbit crops by their respective companies in 1985 because of crop injuries resulting from "inadvertent misuse." This severely limits the number of herbicides available for use in Florida.

Before applying an herbicide, carefully calibrate the sprayer. Make sure the proper speed, pressure, and nozzles are being used in the field. Worn nozzles can increase the number of gallons sprayed significantly. Always use the same size nozzles.

Most of the new herbicides being tested for labeling on cucurbits have a narrow range of tolerance. A mistake in calibration or application will cause damage to the crop. They must also be applied in the proper manner.

There are two categories of soil-applied herbicides: surface-applied and incorporated herbicides. Surface-applied herbicides require rainfall or irrigation shortly after application for best results. Lack of moisture often results in poor weed control; however, they are relatively easy to apply. Incorporated herbicides are not dependent on rainfall or irrigation and have generally given more consistent and wider-spectrum control. They do, however, require more time and equipment for incorporation. Herbicides labeled for surface application may cause phytotoxicity to melons if incorporated.

Do not use herbicides that are not labeled for use in Florida. Use of unregistered materials can result in destruction of the crop, a fine, or both. Use of herbicides with pending labels can also delay or jeopardize subsequent registrations.

For tolerance purposes, the EPA has recently defined which crops may be included under certain general commodity names. The general term "melon" on a label includes muskmelons as well as hybrids and/or varieties of Cucumis melo (including true cantaloupe, cantaloupe, casaba, Santa Claus melon, crenshaw melon, honeydew melon, honey balls, Persian melon, golden pershaw melon, mango melon, pineapple melon, and snake melon) and watermelons, including hybrids and/or varieties of Citrullus spp.

The term "summer squash" includes fruits of the gourd (Cucurbitaceae) family. Fruits in this category are consumed when immature, are 100% edible either cooked or raw, cannot be stored once picked, have a soft rind that is easily penetrated, and have seeds that, if they were harvested, would not germinate (e.g., Cucurbita pepo [i.e., crookneck squash, straightneck squash, scallop squash, and vegetable marrow], Laginaria spp. [i.e., spaghetti squash, hyotan, and cucuzza], Luffa spp. [i.e., hechima and Chinese okra], Memordica spp. [i.e., bitter melon, balsam pear, balsam apple, and Chinese cucumber], and other varieties and/or hybrids of these).

Herbicides must be applied at exactly the correct rate and time to selectively control weed growth in a vegetable crop. Obtain consistent results by reading the herbicide label and other information about the proper application and timing of each herbicide. To avoid confusion between commercial formulations, suggested rates listed in Tables 1 and 2 are stated as pounds of active ingredient per acre (lb. a.i./A). Read and follow all label directions.

Tables

Table 1. 

Pretransplant or preemergence chemical weed control in cucurbit crops (muskmelon, cucumber, squash, watermelon)

Active ingredient

lb. a.i./A

(Trade name)

amount of product/A

Crops

Weeds controlled / remarks

Bensulide

5–6

(Prefar®) 4E

5–6 qt.

All cucurbits

Annual broadleaf and grass control. Incorporate or irrigate 1–2 in. within 36 hours of application. Nonlabeled crops should not be planted within 120 days of application.

Carfentrazone

Up to 0.031

(Aim®) 2 EC

Up to 2 fl. oz.

All cucurbits

Emerged broadleaf control. Postdirect hooded application to row middles for burndown of emerged broadleaf weeds. Use crop oil concentrate (COC) or nonionic surfactant (NIS) at recommended rates.

Clomazone

0.15–0.38

(Command®) 4ME

0.4–1 pt.

Cucumber

Annual broadleaf and grass control. Use lower rates in coarse soils.

Clomazone

0.15–0.25

(Command®) 4ME

0.4–0.67 pt.

Melon (muskmelon, watermelon)

Annual broadleaf and grass control. Use lower rates in coarse soils.

Clomazone

0.25–0.5

(Command®) 4ME

0.67–1.33 pt.

Summer and winter squash

Annual broadleaf and grass control. Use lower rates in coarse soils. Consult label for cultivars where application is prohibited. Do not apply under plastic; apply only between plastic-covered beds.

Ethalfluralin + Clomazone

0.4–0.6 +

0.13–0.19

(StrategyTM)

2–3 pt.

Cucumber, melon, summer and winter squash, pumpkin, watermelon

Annual broadleaf and grass control. Must be applied no later than 2 days after seeding. Overhead irrigation or rainfall of 0.5 in. within 5 days. Do not apply under row mulch or over the top of plants.

Flumioxazin

Up to 0.125

(Chateau®) 51 WDG

Up to 4 oz.

Cucumber,

muskmelon, watermelon, pumpkin, summer and winter squash

Broadleaf control. Row middles only. Do not apply after crops are transplanted / seeded. Raised plastic beds must be at least 4 in. higher than treated row middle and 24 in. wide bed. All applications must be made with shielded or hooded equipment. Label is a Third-Party Registration (TPR, Inc). Use without a signed authorization and waiver of liability is a misuse of the product.

Glyphosate

0.3–1.0

(Various formulations)

Consult labels

All cucurbits

Controls emerged broadleaf and grass weeds. Consult individual labels for restrictions.

Halosulfuron

0.024

(ProfineTM, Sandea®) 75 DG

0.5 oz.

Cantaloupe, cucumber, crenshaw, honeydew

Yellow and purple nutsedge and broadleaf control. Apply uniformly with ground equipment in a minimum of 15 gal. of water/A.

Halosulfuron

0.024–0.036

(ProfineTM, Sandea®) 75 DG

0.5–0.75 oz.

Watermelon

Yellow and purple nutsedge and broadleaf control. May be applied preemergence to seeded watermelon on bare ground or preseeding to mulch-cultured watermelon. Transplanting should be no sooner than 7 days after application. Use lighter rates on sandy soils with low organic matter.

Halosulfuron

0.024–0.036

(ProfineTM, Sandea®) 75 DG

0.5–0.75 oz.

Pumpkin, winter squash

Yellow and purple nutsedge and broadleaf control. Apply before soil cracking or pretransplant. Transplanting should not be made sooner than 7 days after application. May be applied after crop emergence over the top of the crop when plants reach the four to five true leaf stage but before first female flowers appear.

Paraquat

0.5–1.0

(Gramoxone®) 2 SL

2.0–4.0

(Firestorm®) 3 SL

1.3–2.7

Cucumber, muskmelon, cantaloupe, pumpkin, squash, watermelon

Controls emerged weeds. Apply prior, during, or after planting, but before crop emerges. Use an NIS.

Pelargonic acid

(Scythe®) 4.2 EC

3%–10% v/v

All cucurbits

Controls emerged weeds. Apply before crop emergence. Product is a contact, nonselective, foliar-applied herbicide. There is no residual activity. May be tank mixed with soil residual compounds.

S-metolachlor

0.95–1.26

(BrawlTM, Dual Magnum®)

1.0–1.33 pt.

Pumpkin

Annual broadleaf and grass weeds and nutsedge control. Apply as interrow or interhill application. Leave a 1 ft. untreated area over the seeded row (6 in. on either side of the row). Use lower rates on lighter soils. Apply before weeds emerge.

Terbacil

0.1–0.2

(Sinbar®) 80 WP

2–4 oz.

Watermelon

Annual broadleaf weed. Direct seeded: broadcast application after seeding and before crop emergence. Transplanted: Sinbar® can be applied under plastic mulch and to row middles before transplanting. PHI 70 days.

Table 2. 

Posttransplant or postemergence chemical weed control in cucurbit crops (muskmelon, cucumber, squash, and watermelon)

Active ingredient

lb. a.i./A

(Trade name)

amount of product/A

Crops

Weeds controlled / remarks

Carfentrazone

Up to 0.031

(Aim®) 2 EC

Up to 2 fl. oz.

All cucurbits

Emerged broadleaf control. Postdirect hooded application to row middles for burndown of emerged broadleaf weeds. Use crop oil concentrate (COC) or nonionic surfactant (NIS) at recommended rates. PHI 0 days.

Clethodim

0.94–0.125

0.07–0.125

(Arrow®, Select®) 2 EC

6–8 fl. oz.

(Select Max®) 1 EC

9–16 fl. oz.

Cucumber, squash, melon, and all commodities in crop group

Annual and perennial grass control. Use a COC at 1% v/v of the spray volume for Arrow® and Select®. Use an NIS in Select Max®. PHI 14 days.

DCPA

4.5–10.5

(Dacthal®) W75

6–14 lb.

(Dacthal®) 6F

6–14 pt.

Muskmelon, cantaloupe, honeydew, watermelon

Annual grasses and certain broadleaf control. Apply only when plants have four to five true leaves, are well-established, and growing conditions are favorable for good plant growth. Cultivate prior to application to control emerged weeds.

Ethalfluralin + Clomazone

0.4–0.6 +

0.13–0.19

(StrategyTM)

2–3 pt.

Cucumber, melon, summer and winter squash, pumpkin, watermelon

Annual broadleaf and grass control. After transplanting, apply to row middles only. Does not control emerged weeds.

Glyphosate

0.3–1.0

(Various formulations)

Consult labels

All cucurbits

Controls emerged broadleaf and grass weeds. Apply to row middles only. Consult individual labels for restrictions.

S-metolachlor

0.95–1.26

(BrawlTM, Dual Magnum®) 7.62 EC

1.0–1.33 pt.

Pumpkin

Annual broadleaf and grass weeds and nutsedge control. Apply as interrow or interhill application. Leave a 1 ft. untreated area over the plant (6 in. on either side of the row). Use lower rates on lighter soils. Apply before weeds emerge. PHI 30 days.

Paraquat

0.47–0.93

(Gramoxone®) 2 SL

1.88–3.72 pt.

(Firestorm®) 3 SL

1.25–2.48 pt.

Cucumber, muskmelon, cantaloupe, pumpkin, squash, watermelon

Controls emerged weeds. Row middles only. Limit of three applications per year.

Pelargonic acid

(Scythe®) 4.2 EC

3%–10% v/v

Cucumber, gourd, muskmelon, cantaloupe, pumpkin, squash, watermelon

Controls emerged weeds. Row middles only. Use a shielded sprayer directed to the row middles to reduce drift to the crop.

Sethoxydim

0.19–0.28

(Poast®) 1.5 EC

1.0–1.5 pt.

All cucurbits

Growing grass weeds. Include a COC. Efficacy is decreased if weeds are under stress. Use 1 pt. for seedling grasses and 1.5 pt. on perennial grasses. PHI 14 days.

Footnotes

1.

This document is HS190, one of a series of the Horticultural Sciences Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date March 1999. Revised December 2012. Visit the EDIS website at http://edis.ifas.ufl.edu.

2.

Peter J. Dittmar, assistant professor, and William M. Stall, emeritus professor, Horticultural Sciences Department, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611.

The use of trade names in this publication is solely for the purpose of providing specific information. It is not a guarantee or warranty of the products named, and does not signify that they are approved to the exclusion of others of suitable composition. All chemicals should be used in accordance with directions on the manufacturer's label. Use pesticides safely. Read and follow directions on the manufacturer's label.


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U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.