Feb 25, 2016

Control measures can negate squash bug woes

Helene Doughty, a research specialist senior at Virginia Tech’s Hampton Roads Agricultural Research and Extension Center, said a number of control measures can be put in place by growers to curb squash bug infestation.

“Before the advent of synthetic insecticides, a number of cultural practices were recommended to reduce squash bug populations, including proper field sanitation to reduce debris and old squash plants serving as shelters for squash bug, crop rotation to eliminate host plants on the farm and early planting to reduce infestation levels,” Doughty said. “Each of these strategies has merit and can contribute to the integrated pest management of this pest.”

Because there is considerable variation among species and cultivar susceptibility to damage, Doughty said varietal selection can impact squash bug infestation levels.

“In Virginia, we consistently observed the highest densities of squash bug on zucchini. Winter squash such as green striped cushaws and Waltham butternut are not as attractive to squash bug, and the bug does not survive well on them compared to summer squash.”

Other varieties of C. moschata (sweet cheese), C. pepo (royal acorn) and C. maxima (pink banana) also demonstrated resistance or less susceptibility to damage by the squash bug, Doughty said.

“However, during field observations in a commercial organic farm in Virginia in 2009 and 2010, squash bug infestations and damage were quite extensive on Waltham butternut squash,” she said. “Thus, there may be local adaptations and preferences among squash bug populations for certain cucurbit plants, or the availability of more preferred host plants may impact pest densities on a specific crop.”

Eliminating weeds and straw or organic mulch, which provide hiding places for the insect, may reduce infestation levels and damage.

“As squash bugs also have been observed quite frequently hiding in the planting holes, minimizing the use of plastic mulch also may reduce infestations,” Doughty said. “However, because there are many benefits of using both organic and plastic mulches (i.e., soil moisture retention, weed control, cleaner fruit at harvest, etc.), it is often not a compatible pest management tactic to eliminate them from cucurbit production systems.”

Alternatively, because squash bugs have an affinity to seek shelter, the practice of placing wooden boards between the rows of crops can be used to trap bugs below, where they may be crushed by stepping on the board.

Polyester floating row covers offered some respite from early infestations by the squash bug in summer squash, but populations quickly rebounded following removal of the covers.

In coastal Virginia, the use of row covers from the time of transplanting to first flowering (11 days) led to a reduction in squash bug adults and egg masses on plants, she said. However, cucurbits need to be pollinated and row covers are only practical for a short time.

“Moreover, we observed that the use of row covers actually had a negative impact on squash yield despite removal at flowering. Row covers appeared to affect the overall health of the squash plants (wilted, shrunken appearances) under hot and humid conditions.”

Biological control

Squash bug eggs, nymphs and adults are attacked by various generalist predators such as spiders, carabids, staphilinids, geocorids and coccinellids, all of which contribute to lowering population levels, Doughty said.

Predation of squash bugs may be increased by employing farmscaping strategies that conserve predators. However, the most important natural enemies of squash bug are parasitoids.

“In coastal Virginia in 2009, we recorded an average parasitism rate of 12 percent (20 percent in organic fields, 8 percent in conventional fields).”

Egg parasitism also plays a major role in the biological control of squash bug.

Chemical control

Chemical control is the most widely used strategy to prevent crop damage from squash bug. Insecticides are often applied to target the nymphal stage, which is easier to kill than adults. Effective control of squash bug nymphs can be achieved with foliar applications of pyrethroids such as bifenthrin, cypermethrin, fenpropathrin, lambda-cyhalothrin and others, as well as neonicotinoids such as thiamethoxam, imidacloprid, clothianidin and acetamiprid, and organophosphates such as disulfoton and metasystox-R.

“However, foliar applications of pyrethroids, which are the most commonly used foliar insecticides by growers because of their low cost, have deleterious effects on natural enemy populations and can cause outbreaks of secondary pests such as melon aphids,” Doughty said. “All of the aforementioned foliar insecticides, with the exception of acetamiprid, are also highly toxic to pollinators.”

One option is changing the application method, she said.

“Because of their ability to be taken up by the roots from the soil as systemic insecticides and transported to the foliage, neonicotinoids can be applied to cucurbits quite effectively, efficiently and economically via drip chemigation. However, the efficacy of soil-applied neonicotinoids will decrease over time and may not provide control over the growing season, particularly when needed for squash bug later in the crop cycle.”

Other, more IPM-friendly insecticides have been evaluated for squash bug control. Novaluron, a benzoylphenyl urea insecticide, has demonstrated efficacy against squash bug nymphs, Doughty said.

“As an insect growth regulator, it offers an alternative to broad-spectrum insecticides with a better fit in an IPM program.”

The spinosyn spinosad has also been evaluated, but shown to be not very effective against squash bug.

“Other reduced-risk insecticides that may show promise for control of this pest in the future include sulfoxaflor, flonicamid and cyclaniliprole,” she said. “Additional field efficacy tests are needed to confirm results from laboratory bioassays.”

Doughty said organic producers have fewer chemical control options.

“Applications of pyrethrins and azadirachtins can suppress squash bug nymphal densities,” she said. “However, under heavy pest pressure, these insecticides have not provided effective or consistent control in the field.”

For more on the squash bugs impact on cucurbit crop production, see “Squash bugs put dent in cucurbit crop production.“

— Gary Pullano, associate editor