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Why are my cucurbits wilting?

Author: Natalie Hoidal

This week I've visited multiple farms with patches of wilting cucurbits, mostly summer squash and zucchini. If you notice this happening on your farm, there are a few potential causes:

1. Squash vine borer

Squash vine borer (Melitta curcurbitae) lays its eggs at the base of plants in the cucurbit family, and larvae bore into the stem, which blocks water flow to the rest of the plant. Check wilting plants for small holes near the base of the stem; you'll often see frass as well, which has the consistency of w
et sawdust and is typically green or orange. To check for certain, you can take a knife and slice along the stem. If larvae are present they should be easily detectable.

Tips for managing squash vine borer - this is from the yard and garden site, but it includes helpful information for commercial growers as well.

Image: Natalie Hoidal, squash vine borer adult

Photo: Rupinder Singh, Bugwood, squash vine borer larvae

2. Bacterial wilt

Bacterial wilt (Erwinia tracheiphila) is a bacteria that lives through the winter in the guts of striped and spotted cucumber beetles. When cucumber beetles feed on cucurbit leaves, the bacteria is transferred from their mouths and enters the plant through wounds, which can be caused by feeding, hail, or other damage. Cucumber and musk melon are particularly susceptible to bacterial wilt.

Wilt symptoms caused by E. tracheiphila are distinct; plants will wilt during the day, but recover overnight. As the disease progresses, overnight recovery slows and eventually the plants wither and die. If you see high populations of cucumber beetles on or near your wilting plants, consider sending a sample to the plant disease clinic to confirm the presence of bacterial wilt. Cucumber beetles that feed upon infected plants can spread the disease to nearby plants; if the disease is only present in a small area, consider removing diseased plants to prevent the spread to non-infected plants. 

More info on bacterial wilt.

Photo: Gerald Holmes, Bugwood striped cucumber beetle

3. Flooded soils

With all of the heavy rains we've been having, most farms are seeing a bit of flooding in low spots. If you're seeing wilt in low, wet parts of your field, the wilt is likely a symptom of water-logging. Plants in water-logged soil cannot take up oxygen, which in turn prevents water uptake. Plants in wet soil are also more prone to root rots.

Other potential causes: Phytopthera blight and squash bugs can also cause wilting in cucurbits. We have not seen damage from either this season.

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