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Ask a Master Gardener: Squash bugs — and how to squash them

by Peter Sutter | June 12, 2022 at 3:55 a.m.


I just came in from the garden checking out my zucchini plants and found a couple of squash bugs. I think I have quoted the old saying "know thy enemy," and although it is an old wartime quote, it is very true in the garden as well. Now that summer is here, one must be intelligent and vigilant against the pests and diseases that attack the garden. Squash plants especially fall into this category.

One case in point is the squash bug, the nemesis of anyone attempting to grow squash. This somewhat hard shell pest has piercing/sucking mouthparts so it bores into the plant passing up the protective spray/insecticide you applied to the plant. This causes damage by sucking nutrients from leaves and disrupting the flow of water and nutrients, which can cause wilting and, if not controlled, will kill the plant.

For small patches of squash, hand picking the adult bugs and egg patches is a good option. Clusters of eggs are usually laid on the underside of the leaf in a characteristic "V" shape pattern following the leaf veins. Some have had success in placing a board next to the plant. At night, the squash bugs will congregate under the board and can then be destroyed each morning.

It can be hard to kill the adult bugs. If using an insecticide, it is most effective to spray just as the eggs are hatching as the small nymphs are more easily controlled. During bloom, sprays should be made early in the morning or later in the evening to reduce the effect of insecticides on honeybees or other pollinators. It is always a good idea to keep the good bugs in mind when using insecticide.

There is another insect that can cause considerable damage to the vine plants and that is the Cucumber beetle, a small yellow bug with either black stripes or spots. Although these bugs cause damage by eating the leaves and stems, the most damage comes from bacterial wilt. The bacteria is secreted in the beetle's system, and when they bite the plant, they spread it to the plant. The bacteria spreads to the plant's system and causes the leaves to wilt. Pruning off infected stems will help slow it from spreading (maybe even long enough for the fruit to ripen), but there is not much that can be done once it sets in.

As I stated in a article a couple of weeks ago, floating row covers are one of the best preventive protections against these two pests. But the covers must be removed for pollination.

The squash vine borer is another insect pest of cucurbits. Summer squash, pumpkins and gourds are preferred by this insect while cucumbers and melons typically remain unaffected. As the name implies, the larvae of the squash vine borer literally bore into the stem near the crown. Stems can be girdled and cut off from water and nutrients. Affected vines usually wilt and die, depending on the size of the vine and number of bore holes.

The adult squash vine borer is a stout dark gray moth with "hairy" red hind legs. Unlike most moths, they fly about the plants during the daytime, appearing more like a paper wasp than a moth.

To prevent borer damage, insecticides must be applied at the base of the plant before the larva enter the stem. Once inside, insecticides are of little control value. Some gardeners have reported successful control by wrapping the base of the plant with aluminum foil. This either confuses the adult or prevents larva from entering the stem after the eggs hatch.

Preventative measures can be taken to reduce the harmful insect population by removing debris located in and around the garden. Destroying or removing debris should be done throughout the season and is especially important during the fall to limit overwintering sites.

Some success has been achieved using "trap crops." These are plants that are planted next to a higher value crop so as to attract pests. This prevents or makes it less likely the pest will attack the main crop. Insects congregated in trap crops can be more easily attacked by natural enemies and/or killed by insecticides or by other physical means. The blue hubbard squash has proved effective for this.

These are just a few of the insect problems affecting the squash/cucumber/melon crops. Diseases like powdery mildew and gummy stem blight seem to make it almost impossible to grow these crops, but in spite of these problems, I have a bountiful harvest most years. I'll admit some years are a little lean, but I am determined to win this war. Know thy enemy!

Peter Sutter is a lifelong gardening enthusiast and a participant in the MU Extension's Callaway County Master Gardener Program. Gardening questions can be sent to [email protected]


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