Weed Control in Melons

Commercial growers can follow basic guidelines to control problem weeds

There’s nothing better than stepping into a melon patch and pulling a fresh watermelon or cantaloupe from a vine. Of course, watch where you step, if weed clusters are present. Those slippery and forked-tongued varmints might be lurking, and the outcome likely won’t be good.

To reduce weed growth, much of the commercial melons raised are grown under plastic mulch, and growers also apply herbicides, which help control weeds around the hole where the plant is planted as well as any weeds that may grow under the plastic.

First, it’s important to identify what weeds are usually present in your respective fields and choose the herbicides that control them. The Virginia Tech scientists in the Commercial Vegetable Production Recommendations guide suggests matching selected preplant incorporated and pre-emergence herbicide rates to the soil type that growers have and the percentage of organic matter in the soil. They strongly advise growers to follow good management practices so the weeds won’t build up resistance to the herbicide used.

Herbicides with the following active ingredients are available to growers to use under the plastic:
• bensulide (for annual grasses and certain annual broadleaf weeds including common lambsquarters, smooth pigweed and common purslane)
• halosulfuron (yellow nutsedge and common cocklebur, redroot, pigweed, smooth pigweed, ragweed species and galinsoga)
• terbacil (annual broadleaf weeds)

Directed or shielded band applications

According to Virginia Tech’s Commercial Vegetable Production Recommendations guide, to control soil strips between rows using a directed or shielded band application, pre-emergence options may include herbicides with these active ingredients:
• bensulide or bensulide plus naptalam (annual grasses and annual broadleaf weeds including common lambsquarters, smooth pigweed and common purslane)
• clomazone (annual grasses and broadleaf weeds such as common lambsquarters, velvetleaf, spurred anoda and jimsonweed)
• ethalfluralin or ethalfluralin plus clomazone (annual grasses and certain annual broadleaf weeds including carpetweed and pigweed)
• halosulfuron (broadleaf weeds such as common cocklebur, redroot, pigweed, smooth pigweed, ragweed species and galinsoga)
• terbacil (annual broadleaf weeds)

If trickle irrigation is used, the tubing left behind may encourage weed growth because the water can leach away some of the herbicide, according to scientists in the guide. Growers can minimize this by burying tubing several inches in the plant bed.

To prepare the land, Virginia Tech scientists advise to apply fumigant and spread the plastic mulch on raised beds 30 days before planting. They warn against applying herbicides before forming any beds because the herbicide rate and depth that the herbicide is incorporated may be increased and may cause injury to the vegetables grown. They recommend spreading the plastic three- to four-feet wide and lay it out on six- to eight-foot centers over the fumigated soil.

When applying the plastic, growers must make sure the soil is moist so the fumigant will work as labeled. Also while preparing the bed, Virginia Tech’s weed scientists remind growers to fertilize and keep in mind that at least 50 percent of the nitrogen must be in nitrate form.

To control soil strips between rows using a directed or shielded band application, postemergence options are available for weed control under the following active ingredients:
• halosulfuron (yellow nutsedge and broadleaf weeds such as common cocklebur, redroot, pigweed, smooth pigweed, ragweed species and galinsoga)
• clethodim (annual grasses and certain perennial grasses such as annual bluegrass)
• sethoxydim (annual grasses and certain perennial grasses)

Broadcast applications

For seeding into soil without plastic mulch using a broadcast application, the preplant incorporated or pre-emergence herbicide options with the following active ingredients are bensulide and bensulide plus naptalam (annual grasses and broadleaf weeds such as common lambsquarters, smooth pigweed and common purslane).

At pre-emergence, they can use:
• clomazone (annual grasses and broadleaf weeds including common lambsquarters, velvetleaf, spurred anoda and jimsonweed)
• ethalfluralin and ethalfluralin plus clomazone (annual grasses and certain broadleaf weeds such as carpetweed and pigweed)
• halosulfuron (yellow nutsedge and broadleaf weeds including common cocklebur, redroot, pigweed, smooth pigweed, ragweed species and galinsoga)
• terbacil (annual broadleaf weeds)

During postemergence, active ingredient choices include clethodim (annual grasses and certain perennial grasses) and sethoxydim (annual grasses and certain perennial grasses)

Postharvest

Weed management doesn’t stop once the melons are all picked. Growers need to practice postharvest weed control whether they have used plastic mulch or not. Virginia Tech scientists advise growers to keep any populations of weed seeds to a minimum. To do this, prevent weeds from producing seeds. They recommend destroying all weeds right after harvest but before the first frost and applying herbicide if needed.

Inquire first

Make sure you check with your local Cooperative Extension agent to see what brand-name herbicides are available and whether the herbicides listed here are used in your area, because others may be available under Special Use Permits. You can also check with them on specific rates.