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Sunday, August 29, 2010

Invasion of Spotted Cucumber Beetles

Ozarks Gardening
Jim Long

An Invasion of Cucumber  Beetles

Hordes of the twelve-spotted cucumber beetles arrived in my garden last week. As if the eight weeks of no rain in our area wasn’t bad enough, here come the bugs!

The first wave of cucumber beetles hatch out of the soil in early spring, just when most of us are planting curcurbits (the plant family which includes cucumbers, melons, squashes and pumpkins). As the beetles emerge from the soil they eat the seedling curcurbits, both the leaves and the young stems. Then things settle down for awhile, with another wave of the pests in late summer.

Cucumber beetles are present throughout the United States and cause serious damage to most curcurbit crops. Over wintering adult insects cause feeding damage on young plants, larvae in the soil feed on plant roots and second-generation adults cause feeding damage on plant leaves, blossoms and fruits.

The adult insects transmit bacterial wilt and squash mosaic virus. Organic management measures include delayed planting in spring, trap crops, floating row covers, parasitic organisms and botanical pesticides.

However, there is no one single solution for these pests. Some people spray with conventional insecticides, but that has little effect simply because of the large numbers of the insects. The additional problem with the spraying broad-spectrum insecticides is the chemicals kill the beneficial insects along with the beetles, and only the cucumber beetles that come in contact with the insecticide are effected. In my garden, the numbers of spotted cucumber beetles are so vast, there is no way of spraying, even if I was willing to kill everything alive in the garden.

Control measures consist of preventing the larvae in the spring from hatching and destroying plants by the use of a combination of parasitic nematodes and biopesticides. Parasitic nematodes produce ineffective spores that attach to the larval host, multiply inside the host and killing the larvae. Parasitic nematodes find and penetrate soil-dwelling larvae of cucumber beetles. (Mycotrol-O is a commercially available mycoinsecticide formulation containing spores of the fungus).

The next step in controlling spotted and striped cucumber beetle is the use of trap plants around the edge of the garden, if you have the space. There are several curcurbits the beetles like most, and the idea is to plant these crops a week or two earlier than your other curcurbits, hoping the beetles go after the tender, tasty ones first, giving you a couple of additional weeks longer to harvest your crop.

My late planted cucumbers were wiped out in just two days. The cucumber beetle population has exploded and just walking through my garden means dozens of beetles lighting on my arms and face. They’ve devastated the tomatoes, killed the leaves of the okra and defoliated several basil plants. They’re eating into the not quite ripe peaches on the peach trees, ruining those, just as they are eating into the remaining tomatoes. They're eating the blossoms of my loofah sponge vines and are defoliating my sweet potato vines.

Predators and parasites that prey on cucumber beetles include hunting spiders, web-weaving spiders, soldier beetles, carabid ground beetles, tachinid flies, braconid wasps, bats and entomopathogenic fungi and nematodes. Bats eat large numbers of cucumber beetles and several web sites suggest putting up bat houses, too.

To see photos of both the twelve-spotted and the striped cucumber beetle, as well as links for more information, including sources of the controls I’ve mentioned, go to the Ozarks Gardening blog: Meanwhile, I hope your garden is doing better than mine this week. Questions and comments can be posted on the comments page of the blog.  (You can also sign up to follow Ozarks Garden blog, to be notified when a new column is posted and it's possible to search the columns by subject). Happy gardening!

For more information about controlling cucumber beetles: National Sustainable Agriculture Information Service.

Companies that sell beneficial insects, parasitic insects and biopesticides, scroll to the bottom of this page:

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