Take Control of Cucumber Beetles
Striped cucumber beetle is known to cause major losses in cucurbit crops including cantaloupe, cucumbers, squash, and pumpkins. Because the beetle transmits the bacteria Erwinia tracheiphila, also known as bacterial wilt, managing damage caused by the pest requires a multipronged approach.
According to Shelby Fleischer from the Department of Entomology at Pennsylvania State University, adult beetles overwinter and feed on both the above- and below-ground portions of cucurbits including plant tissue, leaves, and roots. If you are growing large-flowered crops such as pumpkins or winter squash, beetles also will aggregate inside the flowers.
Adult beetles are yellow-green in color with three black stripes down their backs, and are ¼ of an inch in size.
Adults lay eggs near the base of the plant, which hatch into slender worms that graze on root hairs. If populations are high enough, Fleischer says root damage may occur, causing a significant reduction in water absorption.
The maturation process from egg to adulthood takes roughly 50 days when the soil is at 70°F and 25 days when soil temperatures are at 86°F, resulting in an average of about four to six weeks from start to finish.
Beetle And Plant Behavior
Beetles are attracted to volatiles emitted through plant tissue as well as the yellow color of the flowers, Fleischer says. Furthermore, after a plant has been infected and starts expressing symptoms of wilting, more volatiles are released, attracting the pest to damaged portions of the crop.
“As the leaf starts to wilt, the blend of volatiles that come off the plant change and beetles are actually attracted to that wilting tissue,” Fleisher says.
“However, the next morning, that wilting plant will not have as attractive of a flower, so they’ll move over to the flowers of the healthy plant. That’s how the bacteria spreads.”
The bacteria enters the plant through feeding wounds and reproduces inside the xylem of the plant, clogging it up and migrating down to the plant roots. In smaller plants, symptoms may appear in seven to 10 days, but might take as long as three weeks, depending on plant size and maturity.
The first symptoms of bacterial wilt manifest as pale, wilted sections of leaves, which spread from localized sections leading to the collapse of individual vines and eventually plant death.
When To Scout
Scouting for the pest should begin immediately at seed germination or right at transplanting.
“You have to scout at the beginning and be prepared with your control measures, whether it’s an insecticide or row cover. If there are volatiles or molecules that emanate from the cuttings, the plants will be very attractive to beetles at this stage,” Fleischer explains.
He notes that if you begin scouting and see there is a minimum of one beetle per 50 plants, you can assume beetles are laying eggs at this time.
Furthermore, early on in the immigration process, beetles tend to aggregate among fields or in-field, and controlling the first generation of beetles will help reduce pressure from second generations.
One of the first control options is crop rotation so the disease doesn’t build up over plant generations. Fleischer says a three-year rotation is ideal.
Using trap crops is another cultural control option, which consists of planting crops attractive to cucumber beetle around the perimeter of the field to deter them from feeding on marketable crops.
“You can transplant a big gourd-like species, for example. Different species have been evaluated, and ‘Blue Hubbard’ squash seems to be a popular one. A week or two later you put your crop out there in the center. If you control them on the ‘Blue Hubbard’ squash, you can protect the rest of your crop,” Fleischer explains.
He also mentions the use of yellow mulch around the field perimeter, which the beetles are attracted to for its color. The use of yellow sticky cards also may be used to monitor pest presence.
Chemical And Biocontrol Options
Using neonicotinoid seed treatments can be an effective chemical control, but Fleischer cautions growers not to apply the chemical anywhere other than the seed to keep residue levels low.
“Don’t run it into the drip line and don’t run it into the soil trench. Just use it as a seed treatment, and that should be effective for a few weeks and keep the residue below detectable levels,” he explains. “This works well when you’re direct seeding. However, it does not work well when you’re using transplants because by the time you’re putting the transplant into the field, you stop some of the efficacy of the neonicotinoid.”
Organic insecticides including spinosyns such as SpinTor (Bayer), Entrust (Dow AgroSciences), Blackhawk (Dow Agrosciences), and Radiant (Dow Agrosciences) also have proven to be effective.
Fleischer also mentions research being done to increase ingestion of these chemicals through the addition of a botanical compound from the buffalo gourd — another cucurbit species — which induces excessive feeding in cucumber beetles.
Regarding biocontrols, much research is still being done to evaluate their effectiveness on the pest, but research has shown these products can be successful on both eggs and adult populations.
“We have run entomopathogenic nematodes through the drip line targeting the larvae,” Fleischer says. “We were only able to do it once, and we saw 50% control. That may be an option for some growers, but it will not help with adult populations.”
Lastly, arthropods have been known to eat beetle eggs in the soil, and the presence of these beneficial insects can be supported through cover cropping and other soil-enhancing practices.