Gardeners know that as the weather improves and temperatures rise, they’re getting closer to fresh produce such as squash, melons and cucumbers.
Unfortunately, that excitement can be “squashed” when the squash bugs arrive, said David Hillock, Oklahoma State University Extension consumer horticulturist.
“You certainly didn’t invite them into your garden, but they’ve moved in and are wreaking havoc, which can be extremely disappointing,” Hillock said. “The squash bug is the most serious pest of squash and pumpkins in the United States and seems to be particularly troublesome in southern regions where it produces multiple generations per year.”
The insect’s feeding behavior causes plants to wilt, yellow and often die back as squash bugs transmit viral infections from plant to plant. Horticulturists typically receive more inquiries about squash bugs than anything else. It is one of the most difficult pests to control.
Eric Rebek, OSU Extension entomologist, said squash bugs begin appearing in cucurbit crops in late April and can continue throughout the growing season.
“The adults are emerging from their overwintering sites from the garden and surrounding area,” Rebek said. “The adults begin to mate and lay eggs, typically on the underside of the leaves of their host plants. Crops can tolerate a moderate amount of squash bugs, but we see damage in heavy infestations when the bugs begin feeding on the leaves and fruit.”
A heavy infestation will reduce produce quality and quantity, he said.
Squash bugs feed on cucurbit varieties such as summer squash, winter squash, pumpkins, melons and cucumber. However, some cultivars are more susceptible than others to squash bug damage. So, what is a gardener’s first line of defense?
“When selecting plants and seeds, choose varieties that are pest-resistant,” he said. “Yellow straightneck and yellow crookneck summer squash are highly susceptible to squash bug damage. Try substituting zucchini for the yellow squash, as it has demonstrated higher tolerance to squash bugs in numerous studies. Experiment with different cultivars of squash listed as resistant to determine which works best in your garden.”
While cucumbers also are a favorite of squash bugs, cucumber beetles tend to be an even greater problem. Again, many cultivars are resistant or tolerant of cucumber beetle damage. Cucumber beetles are stimulated to feed by the chemical cucurbitacin, which gives some cultivars a bitter taste and causes intestinal discomfort in some people. Varieties listed as burpless or non-bitter contain little to none of the chemical compound, making them less attractive to cucumber beetles.
Hillock said selecting resistant cultivars is just one line of defense against squash bugs and cucumber beetles. The garden pests often require gardeners to implement multiple management strategies. Covering planted rows with floating row covers excludes both squash bugs and cucumber beetles from the plants, which in turn prevents these pests from laying eggs. The row covers must be tightly secured to the ground to exclude pests.
Cucumbers and squash are insect-pollinated crops, so gardeners who use row covers must remove them once plants begin flowering. At that time, hand-picking insects and smashing egg masses provides additional control. Another option is to place wooden boards near the plants. This provides a place where the squash bugs will congregate overnight. In the morning, you can lift the boards and easily remove the insects.
If using chemical control, Rebek suggests doing so when the squash bugs are in their nymph stage and most susceptible to the chemical.
“Research has shown that a product with the active ingredient spinosad is the most effective against the nymphal stages,” he said. “When the squash bug pest reaches an older stage, consider using a product with the active ingredient pyrethrin or cypermethrin.”
Rebek also said vigilance is key to successful gardening and suggests checking the garden at least twice a week for signs of pest development. More information about squash bug control is available in the TV show Oklahoma Gardening. OSU Extension also offers more vegetable garden pest control information.
“Taking an extra precautionary step or two to thwart pests can help ensure a fruitful gardening season,” Hillock said.