As the harvest season ends for some crops and begins for others, the agriculture markets begin to see new produce.

But while in the store looking at all the options, one probably doesn’t think of the problems farmers had to deal with just to produce their crops that year.

Farmers who grow cucumbers, muskmelon or pumpkins often come across bacterial wilt of cucurbits.

Cucurbits is the scientific name for a family of plants that consists of cucumbers, muskmelon, pumpkins, squash and watermelon. Cucurbits are grown commercially in Iowa, on hundreds of farms. The acreage of these crops is tiny compared to corn or soybeans, but they are very valuable on a per-acre basis.

Bacterial wilt is an important disease of cucurbits that is caused by a bacterium, Erwinia tracheiphila, a cousin to the bacteria that causes Goss’s wilt. This bacteria thrives in the bodies of striped and spotted cucumber beetles. 

A cucumber beetle first gets in the bacteria by eating an already infected plant. When that beetle travels to another plant, it begins to eat the new plant — wounding it.

As all creatures must do eventually, the beetle answers the call of nature and leaves fecal matter (frass) on the plant’s leaves. The bacteria in the beetle frass eventually gets into the wounded leaf and begins to spread.

The bacteria gets into the plumbing system of the plant, multiplies and ends up creating a sort of slime. This slime eventually ends up blocking the flow of water causing the plant wilt — eventually killing it.

“The disease can be very damaging and may cause up to 80 percent yield loss on muskmelon and cucumber,” said Erika Saalau Rojas, a diagnostician at ISU Plant and Insect Diagnostic Clinic and graduate student in plant pathology and microbiology.

There are, however, ways to prevent the beetles from killing the cucurbit plants.

One method being researched at Iowa State is to cover the plants with non-woven fabric made of 100 percent polypropelene called row covers.

“The point is to cover up the plants early in the season so the cucumber beetles can’t reach them,” said Mark Gleason, professor of plant pathology and microbiology.

“The real risk period for muskmelon and cucumbers is when the plants are very young. So we only want to protect them for maybe the first month of the growing season, when they’re most vulnerable. In addition, cucumber beetles are really attracted to the young plants.”

A second and more widely used method for protecting these plants is spraying insecticides.

“You can spray insecticides and kill the beetles, but you have to spray a lot, and not everyone is excited about spraying insecticides because they have some environmental hazards associated with them,” Gleason said. “The environmental hazards are not only to people, they’re also to the bees that pollinate the crops. If you spray trying to kill cucumber beetles, you may kill bees as well.”

The third and experimental method to protect the plants is by using perimeter trap cropping (PTC).

In this method, one plants the chosen cucurbit plant, like muskmelon, in a field, but the two outside rows around the field are planted with a different cucurbit plant that’s more attractive to the beetles. This outer row of plants draws the attention of the cucumber beetles as they fly into the field, and they leave the muskmelon plants alone.

One possible drawback of the PTC method is that the farmer has to grow and sell two types of cucurbit crops.

The highly attractive outer rows needs protection, so the farmer must spray or find another way to protect those outer row plants.

Despite the damage done to cucurbit plants by this bacterium, it doesn’t hurt humans.

“No, we don’t have any information suggesting that E. tracheiphila is harmful to humans,” Rojas said.

Bacterial wilt of cucurbits has been reported in other places, but is mainly impacting the U.S.

“Although it has been reported in other countries, this disease has economic importance only in the U.S., where it affects cucurbit growers mainly in the midwest and northeast,” Rojas said.

While the number of farms growing cucurbit plants is small, cucurbit plants are high value crops. All of the 300 to 500 Iowa farmers who grow these crops can be threatened by bacterial wilt. But bacterial wilt of cucurbits is not just a farmer’s problem.

“If you care about eating, you should care about pathogens,” Gleason said.