University of Illinois Extension
What could be killing my squash plants?
 

[August 02, 2021]    There’s nothing more devastating than walking out to your garden to discover your squash plants are wilted or dead. An insect known as the squash vine borer is one that will cause damage to your cucurbit plants by tunneling into the stems. Once you have had an encounter with squash vine borer, it is one you will never forget.

Damage done by the squash vine borer appears around mid-summer and is typically unnoticed until after the borer has done its damage. The insect overwinters as a full-grown larva or a pupa below the soil surface and pupates in the spring. Adult moths begin to emerge in early summer and lay eggs on the stems of cucurbit plants. After hatching, the larvae bore into the vines and feed for 14 to 30 days before returning to pupate in the soil.

The key to controlling squash vine borer is to control the borers before they enter the stem; once inside the vine, insecticides are ineffective. Home gardeners may have success with deworming vines by slicing the vine lengthwise near damage; these areas should be immediately covered with soil and kept well-watered. In early summer, monitor plants weekly for adults. Adult moths are dark gray with 'hairy' red hind legs, opaque front wings, and clear hind wings with dark veins.

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Unlike most moths, SVB moths fly during the daytime appearing more like a wasp than a moth. Insecticides can be used to control moths or newly hatched larvae; however, application timing is extremely important for effective control which can be difficult to achieve.  Other measures of control include removing and destroying infested vines to break the life cycle. Tillage can also help to expose overwintering insects. By rotating the squash to another location within the garden, you can also reduce insect pressure.

Good Growing Fact: Of course, there are other common insects or diseases including squash bugs, cucumber beetles, spider mites, and powdery mildew that can cause issues with growing plants in the cucurbit family. It is important to scout frequently for disease and insects. When scouting, be sure to thoroughly check plants including under leaves. If you are unsure of what insect or disease you have, contact your local Extension office.

[SOURCE/WRITER: Katie Parker, Local Foods & Small Farms Educator]