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

Peter J. Dittmar and Nathan S. Boyd 2

Crop Competition

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 covers the ground most rapidly has the competitive advantage. Good management practices, such as correct fertility rates, well-adapted varieties, effective water management (irrigation, drainage), and establishment of adequate plant populations all help reduce 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 weeds emerge and compete with the crop in the first 4 weeks, however, yield will be reduced. Two nightshade plants growing within the row and between watermelon plants have been shown to reduce yield by as much as 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 as deep as needed to adequately control the weeds. Excessively deep cultivation may prune crop roots, bring weed seeds to the surface, and disturb soil previously treated with an herbicide. 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 and reduce water and nutrient uptake. Timely cultivation is also extremely important. In general, small weeds are more easily killed by many cultivators than large weeds, and weeds should be cultivated before or during early flowering to prevent seed production.

Mulching

Polyethylene mulch has been shown many times to increase cucurbit yield and earliness. Properly injecting fumigants under the mulch can help control nematodes, soil insects, soilborne diseases, and weeds. Mulches inhibit the germination and growth of most broadleaf and grassy weeds. Nutsedges, however, are able to penetrate the plastic mulch.

Herbicides

Properly selected herbicides are effective tools for weed management in cucurbits. Most of the registered herbicides are for preemergence or pre-transplant applications to the crop and weeds. 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.

Accurately calibrate all equipment before herbicide application. Make sure the proper speed, pressure, and nozzles are being used in the field. Worn nozzles can significantly increase the application volume. Always use the same size nozzles across the boom. 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. 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.

Preemergence herbicides can be categorized as surface-applied or 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 which, 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).

Tables

Table 1. 

Pre-transplant or preemergence herbicides for weed control in cucurbit crops (muskmelon, cucumber, squash, watermelon)

Table 2. 

Post-transplant or post-emergence herbicides for weed control in cucurbit crops (muskmelon, cucumber, squash, and watermelon)

Table 3. 

Footnotes

1. This document is HS190, one of a series of the Horticultural Sciences Department, UF/IFAS Extension. Original publication date January 1996. Revised December 2012, December 2015, and January 2019. Visit the EDIS website at https://edis.ifas.ufl.edu for the currently supported version of this publication.
2. Peter J. Dittmar, associate professor, Horticultural Sciences Department; and Nathan S. Boyd, associate professor, UF/IFAS Gulf Coast Research and Education Center; UF/IFAS Extension, 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.

Publication #HS190

Date: 1/17/2019

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    • Peter Dittmar