By Mark Gleason

Plant Pathologist

Iowa State University Extension

Muskmelons (aka cantaloupes) are among the finest products of Iowa summers. Whether you grow your own or just harvest them from a supermarket shelf, muskmelons rank right up there with tomatoes as indispensable summer treats.

If you do grow your own muskmelons, you already know that they face many perils between May and August. Probably the greatest threat to Iowa muskmelons is a disease called bacterial wilt. Bacterial wilt causes the vines to collapse, wither and die. Many home gardeners have given up on muskmelons because of the trauma inflicted by this fearsome disease.

Bacterial wilt is caused by an oddball bacterium by the name of Erwinia tracheiphila. One of the odd things about E. tracheiphila is its penchant for living inside certain cucurbit plants (muskmelons, cucumbers and sometimes squashes) and insects. The two insect species that harbor the bacterial wilt bad boy are striped and spotted cucumber beetles. When the bacterium isn’t inside cucumber beetles, it’s usually wreaking havoc inside a cucurbit plant.

Like other wilt bacteria, E. tracheiphila multiplies in the water-conducting parts of a muskmelon vine, to the point where it blocks water movement. Once that happens, the thirsty vines overheat and die.

The bacterial wilt story also is the story of cucumber beetles. When the adult beetles go to sleep for the winter, E. tracheiphila shelters in their digestive tracts. In the springtime when hopeful gardeners are laying out their tender transplants, hungry cucumber beetles rise from their beds in the soil and buzz into the air with two urgent missions: find a cucurbit plant and eat it. 

Then comes the ugly part: transmission. Cucumber beetles feeding on cucurbits release E. tracheiphila from, well, both ends of themselves. The bacteria manage to move into the leaves and stems through the feeding wounds created by their beetle taxis. Within a week to 10 days, bacteria have multiplied prodigiously inside the vines, and the heartbreak of wilting commences. 

As if this disaster scenario weren’t bad enough, cucumber beetles feeding on the sick plants can pick up the bacteria, and a new generation of beetle taxis is created.  In fact, several generations of cucumber beetles can hatch and do their voracious thing in a single growing season.

So what’s a gardener to do? One strategy – the one adopted by commercial growers – is to spray insecticides every week or two, all season long, to deter cucumber beetles. Many gardeners (and even some commercial growers) are unwilling to wage such intense chemical warfare, so they have sought other solutions.

At ISU over the last three years, our research group tested some no-pesticide and reduced-pesticide tactics at several ISU farms around the state. The most successful approach against bacterial wilt was row covers.

Row covers are long, thin sheets of translucent polyester or cotton fabric that are installed on metal hoops over young cucurbit transplants in May. A row cover forms a tunnel about 18 inches high over the row, with the edges and ends tucked into the soil. 

An obvious purpose of row covers is to keep cucumber beetles away from the plants. But they also keep the soil warmer, providing the heat-loving cucurbits with a head start. The result is larger plants and an earlier melon harvest.

Like all good things, row covers must end. They need to be removed when the cucurbit plants start to bloom, since they exclude not only cucumber beetles but also bees and other pollinators. At that point (mid-June or so), the plants are once again exposed to the depredations of cucumber beetles.

Despite this loss of protection, muskmelon plants that were covered for the first month of the season tend to suffer less damage from bacterial wilt than plants that were never covered – and have higher yields, too. So the early protection pays off.  Field experiments in three Iowa locations over two years confirmed the advantages of row covers in suppressing bacterial wilt and raising yields.

Can plants that are exposed to cucumber beetles after the row covers are removed succumb to bacterial wilt?  Yes – but the chances are less than if the plants had never been covered. Even if you use insecticides after uncovering, at least you didn’t need to spray during the covered period. But even if you don’t use any insecticides, or just those that are organically approved, row covers give you an edge in the cucumber beetle-bacterial wilt wars.

Commercially available row covers are fairly durable, so they can be reused in later years if handled carefully. One word of caution: avoid planting a cucurbit crop where you grew any cucurbits the previous year, since you don’t want cucumber beetles emerging from the ground right under your row covers.

The cucumber beetles won’t thank you, but using row covers can make it easier to beat bacterial wilt and have sweet, juicy muskmelons to harvest in August.

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