Squash Bugs, Vol. 7, No. 9

Anasa tristis

“We planted three hills of yellow squash and two of zucchini.  That should make enough squash to feed the neighborhood.  Now three of them have suddenly wilted and died—just before they were about to start blooming! Same thing happened last year.  We’ve had trouble growing squash lately.  Even when they make, they only last a couple of weeks or so.” 

 

Squash bugs are one of the most important pests of squash and pumpkins; they sometimes damage melons as well.  Adults are brown or dark grey, while the nymphs are ash grey.  Heavy infestations cause whole plants to suddenly wilt and die.  The plant looked fine yesterday, but not today.  This damage is often not recognized as insect damage and is attributed to disease or lack of water instead.  Look carefully around the bases of wilted plants, or around the bases of live plants growing near dead plants, to find the real culprits.
 
Squash bug adults and nymphs concentrate at the base of plants where they suck sap from the stems, injecting saliva into the plant as they feed.  This saliva is toxic to the plants and heavy squash bug feeding can cause plants to suddenly wilt and die, a condition known as “squash bug wilt.”  Infestations that are not heavy enough to kill plants can still result in poor growth and reduced yields.  Squash bugs also vector an important bacterial disease known as cucurbit yellow vine decline.  This a damaging garden pest that needs to be controlled if you want to make a good crop of squash or pumpkins, especially if you hope to keep picking squash throughout the summer.
 
Squash bugs aren’t the only pests that cause squash and pumpkin vines to wilt suddenly.  Squash vine borers are day-flying moths that produce caterpillars that bore inside the vines.  In general, squash bug wilt tends to occur earlier, on younger plants, than vine borer damage, but both are major pests.  Fortunately, the treatments used to control squash bugs also work on vine borers.  See Bug's Eye View No. 10 of 2020 for more information on vine borers.
 
Control:  Control squash bugs in home vegetable gardens with sprays containing zeta-cypermethrin or permethrin.  Both products have one day preharvest intervals, which doesn’t much matter with pumpkins, but is important with zucchini and yellow squash.  Products with 3-day PHIs just don’t work well for these crops.  Direct sprays to the base of the plant where adults and older nymphs are concentrated, as well as to the leaves, where egg masses and newly hatched nymphs occur.  Start spraying weekly as soon as plants are well-established and growing well, especially if you see squash bugs or their eggs on the plants.  There are no good organic treatments for squash bugs, but regular hand-picking of adults, nymphs, and egg masses can be helpful if one only has a few plants and is diligent.  
 
See Extension Publication 2347, Insect Pests in the Home Vegetable Garden for more information on garden insect pests, including squash bugs and vine borers.