Striped cucumber beetles' poop contains a bacteria that can cause plants to wilt. The insects gather in large number on plants, attracted by a chemical produced by the plant. Credit: Courtesy of Griffin Gill

It’s bad enough when insects chew on growing vegetables.

But one beetle takes it one step further by killing plants simply by pooping on them.

Maine gardeners who are seeing their cucumbers, melons or gourds wilt this summer may have the striped cucumber beetle to blame. The insect carries a disease that it defecates on plants and causes its vines or leaves to wilt and turn yellow. If it gets bad enough, it will kill the growing vegetable.

Cucumbers are among the plants that produce chemicals that attract the striped cucumber beetle in the first place. Once or two show up on a plant, those numbers can quickly become a large mass as pheromones produced by those first beetles attract more beetles who then engage in what is best described as an eating, mating and pooping frenzy.

As if eating the plant’s leaves were not damaging enough, the striped cucumber beetle harbors a bacterium in its digestive tract, according to Frank Wertheim, agriculture and horticulture educator with the University of Maine Cooperative Extension. When the beetle defecates on the plant, it passes along the bacteria to the plant causing bacteria wilt.

This can be a serious disease for the plants. Once the bacteria gets inside, they clog up the plant’s vascular system making it incapable of transporting water from its roots to its stems or leaves.

It usually starts with just one heavily chewed-on leaf wilting, and then this wilting progresses to the stem of the leaf and then to major vines of the plant. The process for vines and the entire plant to wilt down can take two to six weeks after initial infection.

Striped cucumber beetles’ poop contains a bacteria that can cause plants to wilt. The insects gather in large number on plants, attracted by a chemical produced by the plant. Credit: Courtesy of Griffin Dill

“There are a lot of different diseases that cause wilting,” Wertheim said. “But the one we see a lot is bacteria wilt from the striped cucumber beetle.”

There’s not much you can do once it’s there. There is no cure.

Prevention, Wertheim said, is the best strategy when it comes to striped cucumber beetles. He suggests keeping young plants or seedlings covered with row covers for as long as possible to keep the beetles from getting into the plants.

Striped cucumber beetles are around a quarter-inch long, have black heads and three black stripes running down yellow-orange wing covers. If you see them on your plants, you can pick them off, vacuum them up or even knock them onto a piece of cardboard placed below the plants and dispose of them.

If there are no beetles, any wilt is likely the result of the ongoing drought in the state, Wertheim said. Effective watering can help.

“People like to come home at the end of the day, get out the hose and start watering,” he said. “They keep watering until the soil is nice and dark and they think they did a good job.”

Unfortunately, in many cases the water will only penetrate to just below the surface which does not do the plant any good.

“Watering less often but more deeply is a better strategy,” Wertheim said.

If gardeners have any question on what is causing plants to wilt, Wertheim said they can bring specimens into their county extension office or email high-quality photos of the damage.

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Julia Bayly

Julia Bayly is a reporter at the Bangor Daily News with a regular bi-weekly column. Julia has been a freelance travel writer/photographer since 2000.