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March 2, 2001

Trap Crops
Can reduce pesticide use in vegetable crops...

By Lana Robinson
Field Editor

If given a choice, cucurbit pests like squash bugs and striped and spotted cucumber beetles prefer squash and pumpkins to watermelons, cantaloupes, cucumbers, and gourds—in that order.

With that in mind, Sam Pair, research entomologist for USDA's Agricultural Research Service in Lane, Okla., has been experimenting with the use of squash and pumpkins as "trap crops" to reduce the use of pesticides.

Speaking to a room full of vegetable and melon producers at the recent Central Texas Vegetable Growers Conference in Comanche County, Pair explained the concept of using the host preference as a management tool for attracting and concentrating the insects.

Trap crops offer early season control, which is advantageous in that: (1) pests are at their lowest population levels; (2) pests are actively seeking food plants and mates; and (3) producers can exercise an offensive rather than a defensive strategy.

"Early season suppression helps prevent late season build up. The idea is to plant border rows of trap crops on the edges of the field of your primary crop and trap the insects there early, where you don't have to spray the entire field. The trap crop needs to be in the field one week before the primary crop is planted," he said.

According to Pair, both the striped cucumber beetle (Mexican corn rootworm) and the spotted cucumber beetle (corn rootworm), known to transmit bacterial wilt, generally aggregate at field margins, mostly the southern edge. They typically migrate to the first cucurbit they see. Thus, the larger, visual plant is their cue.

"It worked very well in trials," Pair reported. "We were able to attract nearly 40 percent of the cucumber beetles to a trap plant out of the field. Even in squash, using squash in squash, we were able to lure 32 percent—using the larger trap plants is the trick—and in watermelon, it was even better, 65 percent.

"We use up to three squash plants in seedlings—the beetles prefer the squash themselves and larger plants," the USDA-ARS entomologist continued. "We applied Furadan to the squash plant and recently, Admire. Furadan offers about two weeks' protection. Admire lasts a lot longer. The more trap density the better. Four rows is better than two rows. These are good techniques on cucumber beetles. The opportunity is there to do something early. "

Pair said the percentages of squash bugs attracted to the trap plants were even more impressive—95.9 percent for cantaloupe; 32 percent for squash; and 91 percent for watermelon.

"The squash bug is a serious pest of watermelon in the Cross Timbers region. Adults are fairly hard to control. They destroy the plant's vascular system, causing a general decline of the vine and blemishes, delayed fruit set, higher water requirements, and a shorter leaf life span—especially the crown—making it easier for aphids to invade," he said. "We believe it also has some role in the presence of yellow vine decline, but we're not sure. It may be as a stress factor."

Pair said a lot of squash varieties will work. He had good luck with Peto 391, a summer bush-type squash, with "staying power" and 35-40 days of fruit, if you keep it picked.

"The cucumber beetle and particularly the squash bug likes the big bush. The squash bug stays and doesn't disperse like the cucumber beetle. The key is to monitor the squash crop. If you have large wide fields, it is a benefit to have squash across the end. Again, get the trap crop in early, use systemic approved insecticides, and keep it picked. You might even be able to find a market for the squash," he suggested.

Pair said there is some evidence that squash bug management may reduce incidence of yellow vine in melons.

"When we have encountered it, yellow vine decline appeared in the trap crop first. The vector sees it first, so the squash is more susceptible. In fact, the entire squash crop succumbed while only 1- 5 percent of the primary crop is affected," said Pair.

In this instance, Pair said he allowed a 12-foot row between the trap crop and the melon crop. He also followed the same protocol of fertility and water for the trap crop as if it were the primary crop.

"We found that yellow vine decline is worse in black plastic than any other plastic. You tend to get the earliest influx of cucumber beetles on yellow plastic, so you might want to consider using the yellow with the trap crop to enhance attractiveness," he suggested. "Also, there may be some reduction using red plastic mulch."