Rideout: What's killing your cucumbers and squash vines?

Experienced vegetable gardeners know that when cucumber and squash vines start to wilt there may be more than lack of water at fault.

Plants in the cucurbit family include cucumbers, squash, muskmelons, gourds and pumpkins. On occasion, gardeners may find vines or whole plants of these cucurbits wilted and dying.

There are three possible reasons why you may have a wilted cucurbit: bacteria, fungus or insects.

Each of these pests exhibit different symptoms. Learning the symptoms can help you decide which problem you have and what you can do about it.

Is it a bacterial problem?

Bacterial Wilt is caused by a bacterium transferred to cucurbits during the feeding of cucumber beetles throughout late May to August. Bacterial Wilt produces a gum that interferes with water transport inside the plant. Symptoms begin as dull green patches on insect-damaged leaves.

The disease spreads from leaves into the stem and then individual vines or the entire plant wilts and dies. This process may be completed in less than two weeks.

To verify this disease, cut the stem near the ground. Squeeze the stem so that sap oozes out of the end. Touch a clean knife to the sap and pull the surfaces apart. If there are fine threads that string between the surfaces, the plant has Bacterial Wilt.

Although this test is effective, a negative response does not mean you do not have Bacterial Wilt. There is no treatment for this pest and infected plants should be pulled and destroyed. However, because cucumber beetles transfer the disease you can prevent this problem by controlling the insect.

Protect young plants by using row covers, cheesecloth or other mechanical barriers. As the plants grow, barriers should be removed to allow for pollination. Insecticide sprays of Sevin or Thiodan should be used where insect pressure is high.

Apply insecticides in late evening to avoid contact with bees and use the lowest mixed rate to avoid damaging your plants, since insecticides easily injure cucurbits. Watermelons are naturally resistant to this disease. Many types of winter squash (for example, butternut, ebony, acorn and buttercup) are also resistant.

Is it a fungal problem?

Fusarium Wilt is a fungus that attacks most cucurbits.

Fusarium Wilt survives by overwintering in plant debris or in the soil. The fungus will enter the plant through root tips, natural openings or wounds. The fungus interferes with the plant’s water transport and will lead to wilt symptoms.

In older plants, a wilt of the entire plant occurs repeatedly during the heat of the day. Eventually, leaves show some tip-browning and the plant will die. Young plants will rot at the soil line and then die.

Cutting an infected plant near the base lengthwise may reveal a light brown discoloration of stem tissue.

Fusarium Wilt is severe during warm, dry weather and commonly found in watermelon, squash and cantaloupes.

During wet weather, a pinkish-white fungal growth may appear on vines. Planting Fusarium-resistant varieties is your best option of avoiding this problem. Once Fusarium is introduced into a garden, the fungus may persist in the soil for many years.

Limit planting resistant varieties in infected fields to once every five to seven years; non-resistant varieties should be planted no more than once every 15 years.

It could also be an insect problem

Squash vine borers are the third, and maybe the best bet, wilt-causing pest of squash, pumpkins, zucchini, and gourds. This pest overwinters in the soil and emerges as an adult in June.

The adult is a moth that resembles a wasp. Its dark body is marked with orange-red and the hind legs are feathery with some orange hairs. It is active during the day and can often be seen flying in a zigzag pattern around plants.  The moth lays an egg on the stem of the plant usually near the base.

The egg hatches into a larva that enters the stem to feed. While feeding, the borer girdles the stem tissue preventing water movement and causing wilting of vines or the entire plant and eventual death. Squash vine borer can be controlled culturally by destroying vines that contain the larvae. Disking gardens in fall or spring may also destroy overwintering larvae.

Borers can be removed physically by slitting the stem with a knife, removing the borer and then covering the wounded stem with moist soil to promote new roots.

Stems can be covered with strips of nylon stockings before attack to prevent larvae from tunneling into the plant. Chemical control is effective only if applied before larvae enter the stem.

Treatments of Sevin or Thiodan are most effective. Read and follow the label for directions of use.

P. Andrew Rideout is the UK Extension Agent for Horticulture and can be reached at [email protected].

This article originally appeared on Evansville Courier & Press: Rideout: What's killing your cucumbers and squash vines?