Two Key Squash Pests, Vol. 9, No. 10
Two Key Squash Pests
“Something is causing our squash plants to suddenly wilt and die. This happens every year. My neighbor says it is some kind of worm that crawls in from the dirt. Is there anything we can do to stop it?”
Two important insect pests can cause squash and pumpkins to suddenly wilt and die.
Squash Bugs: Adult squash bugs are dark grey to brown insects about ½ inch long that deposit loose clusters of brown football-shaped eggs on the leaves. Adults and the ash-grey nymphs both have piercing-sucking mouthparts and concentrate their feeding at the base of the plant. Because the saliva they inject while feeding can be toxic and interfere with nutrient transport, heavy infestations can cause plants to suddenly wilt and die. This condition, known as “squash bug wilt,” is often mistaken for a plant disease, but a careful search around the base of affected plants will often reveal the real culprits.
Squash Vine Borers: Squash vine borers are the caterpillars of colorful, day-flying moths that mimic paper wasps. The moths deposit eggs on leaves and stems of squash and pumpkins. Newly hatched caterpillars borer into the stems and begin feeding toward the base of the plant. Initial damage is minor, but once they reach the base of the plant the caterpillars grow rapidly and feed heavily. Their feeding cuts the stem from the inside, causing infested vines, and even whole plants, to suddenly wilt and die.
At this point there may be frass exuding from infested stems. If you use a pocketknife to perform an autopsy you may find a fat, creamy-white caterpillar inside, but maybe not, because once they are fully grown, the caterpillars will exit the plant to pupate in the soil. Note that the caterpillars crawl from the plant into the soil and not the other way around.
Control: Although these are two very different types of insects, control is similar. Both pests are relatively easy to control with timely, repeated sprays. Pyrethroid insecticides such as zeta-cypermethrin (GardenTech Sevin Insect Killer is one example) or permethrin (Bonide Eight and Hi-Yield Garden, Pet and Livestock Spray are two examples) work well on both pests. Begin spraying as soon as plants begin to run or set bloom buds and repeat at 7-to-10-day intervals.
Take care to get good spray coverage of all areas of the plant. Focus sprays on the base of plants to control adult squash bugs and older nymphs but be sure to spray the rest of the plant to control young squash bug nymphs and newly hatched vine borers. Vine borers are safe from insecticides once they have bored into the plant. The key to controlling vine bores is to have the insecticide residue on the plant when eggs are hatching so young larvae are controlled before they bore in.
“But squash need to be picked every two to four days. How do I avoid excessive insecticide residue?” Plan your spray schedule carefully and choose labeled insecticides with short preharvest intervals (PHIs). Pick first, then spray the same day, and pick extra “close” on days you plan to spray. Use an insecticide like zeta-cypermethrin or permethrin, which both have one-day PHIs, rather than a product with a longer PHI, and wash squash well before cooking. For added margin, wait an extra day or two beyond the preharvest interval before picking if you can. To protect pollinators, spray as late in the day as possible.
See archived issues of Bug’s Eye View for more information on squash bugs and squash vine borers.
Which pest caused this butternut squash plant to wilt? Squash bugs, but plants wilting because of vine bore damage look similar—until you check out the base of the plant.
Blake Layton, Extension Entomology Specialist, Mississippi State University Extension Service.
The information given here is for educational purposes only. Always read and follow current label directions. Specific commercial products are mentioned as examples only and reference to specific products or trade names is made with the understanding that no discrimination is intended to other products that may also be suitable and appropriately labeled.
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