Melons, cucumbers are under attack

Recently, I wrote about the squash vine borer and the squash bug, some of the insects that attack members of the cucurbit family. These insects do a great deal of damage to the plants they infest, but these are not the only insects that attack cucurbits (members of the gourd family, including cucumbers, melons, pumpkins and squashes).

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There are others that can do just as much damage: cucumber beetles and pickleworms. This spring, I have caught some spotted cucumber beetles feeding on watermelons in my garden.

There are two species of cucumber beetles common in the area: the spotted and striped varieties. They are harmful to cucurbits, particularly young plants. The beetles start feeding on plants as soon as they emerge from the soil, and either kill the plants or greatly slow growth. Cucumber beetles are present throughout the growing season and feed on all parts of the plant, including the flowers and fruit.

Cucumber beetles also transmit bacterial wilt of cucurbits. This disease overwinters in the intestines of the beetles and is scattered from plant to plant as the beetles feed. Infected plants eventually wilt and die. Many new varieties of cucurbits have resistance to bacterial wilt. Also, cucumber beetle larvae feed on the roots of many plants and bore into both roots and stems of cucumber plants.

The spotted cucumber beetle (Diabrotica undecimpunctata howardi) adult is yellowish-green in color and has 11 black spots and a black head with black antennae. The yellow adult striped cucumber beetle (Acalymma vittatum) is about 1/5 inch long with three longitudinal black stripes on the top wings. Some gardeners mistake this beetle for the Mexican bean beetle.

In a home vegetable garden, control measures include the use of fabric row covers, such as spun-bonded polyester. These covers provide an effective barrier between the insect and young plants. Remember to remove the covers during flowering to ensure pollination. Another option is handpicking to remove the beetles. This is time-consuming but effective.

Several predators and parasites are enemies of cucumber beetles. Controlling weeds in and around the garden removes a food source and habitat that the beetles like. The insecticide Sevin gives good control of these beetles, but remember that Sevin will kill bees.

The pickleworm (Diaphania nitidalis) is a late-season pest of cucurbits. This insect severely damage cucumbers, cantaloupes, summer squash and pumpkins. It also feeds on other cucurbits, such as winter squash and watermelons, but usually does little damage.

Pickleworm damage occurs when the caterpillars tunnel in flowers, buds, stems and fruits. They prefer the fruits. Frass (sawdust-like insect waste) often protrudes from small holes in damaged fruits. At times, damaged fruits cannot be recognized until they are cut open. Damaged fruits are not edible. Flowers, buds and sometimes entire plants can be killed.

In our area, pickleworms starve or freeze to death during the winter. They overwinter in Florida and spread northward each spring. Usually, they do not cause severe damage before summer. Heavy populations of these insects generally do not build up before the first flower buds open; however, late crops can be destroyed before blossoming.

Adult pickleworms are brownish-yellow moths that have a rounded brush of hairs at the rear of the body. The brownish-yellow wings have a purplish sheen, translucent yellow-white centers and a spread of about 1 inch.

The moths are active at night. They lay eggs that are yellow, irregularly shaped and resemble grains of sand. They are laid singularly or in small groups on leaves, and hatch in three to four days. The larvae feed first on buds, blossoms and tender terminals, but soon move to the fruits. The larvae is yellowish white at first, but many reddish-brown spots appear on the back after the first molt.

After the last molt, the caterpillar loses its spots and becomes solid green or copper. Finally, the caterpillar stops feeding, becomes pink to pale green and spins a thin silk cocoon around itself, usually within a folded-over portion of a leaf where it pupates.

There are several ways to control this insect. The first is to plant varieties of cucurbits that mature early and plant as soon as the weather permits in the spring. Also, the damaged fruit needs to be destroyed, along with any pupae that are found in rolled-up leaves.

Charles Phillips is a retired Columbia County Extension Service agent and operates Hort Consulting. He can be reached at cphillipshort@comcast.net.