Melonworm

About

A slender green caterpillar with two white stripes down its back, the young of a moth with pearly white wings edged in dark brown. It is a close cousin of the pickleworm but feeds mostly on leaves, especially squash leaves.

Spotting it

Damage

Caterpillars eat the leaf tissue between the veins, leaving lacy leaves. On less favored plants such as melons they also scar the rind or bore into the fruit.

How to find it early

Check the undersides of squash leaves for green caterpillars with two white stripes, and watch for lacy feeding starting in midsummer.

When

Midsummer to fall; much of the year in south Florida.

Life cycle

It survives winter only in south Florida and perhaps south Texas, then spreads north each summer, reaching the Southeast by July and sometimes New England and the Great Lakes. A generation takes about 30 days, and no more than three usually occur in temperate areas before frost kills the plants.

What to do, gentlest first

Start at the top. Sprays are a last step; always read and follow the product label.

1. Plant early and clean up Prevent

   Early plantings often escape serious damage, and destroying vines after harvest removes pupae.

2. Row cover Barrier

   Row covers keep the moths from laying eggs.

   Squash and melons need bees to set fruit, so uncover them when the flowers open.

3. Natural enemies Natural enemies

   Parasitic wasps and flies, predatory beetles and fire ants kill melonworms; parasitism can reach about a quarter of the caterpillars.

4. Bt (Bacillus thuringiensis) Natural enemies

   Bt sprays control melonworm; spray while caterpillars are small.

   Bt carries no bee warning on its label.

5. Pyrethroids Conventional spray

   Mississippi State lists permethrin, bifenthrin and zeta-cypermethrin for melonworm in home gardens.

   Highly toxic to bees, which squash and melons need for pollination. Spray only in the evening, keep sprays off open flowers, and follow the label and pre-harvest interval.

Plants it goes after

Cantaloupe (muskmelon), Chayote, Watermelon, Winter squash and pumpkin, Zucchini and summer squash

Pressure by region

Mainly a southern pest that arrives later in the season farther north (UF/IFAS). South Central is rated moderate because it may overwinter in south Texas. Other low ratings, including Alaska and Hawaii, are estimates.

Ratings come from extension sources where available; some are estimates, as noted above.