Appearing out of nowhere in early summer, the two worst squash pests in North America are squash bugs (Anasa tristis) and squash vine borers (Melittia cucurbitae). Both pests are native, and have probably been sabotaging squash and pumpkins for thousands of years, or as long as these crops have been grown by humans.
Dull gray, hard-backed squash bugs weaken plants by sucking plant juices and hatching dozens of young, and they have been found to transmit the bacteria responsible for cucurbit yellow vine disease, which causes affected plants to turn yellow and die. The damage done by squash vine borers is different but with similar results. These moth larvae feed inside the main stems of summer squash, pumpkins, and thick-vined winter squash classified as Cucurbita maxima. After a couple of weeks of secretive feeding, the base of the plant breaks off and the plant usually dies.
Common Cures for Squash Pests
There are dozens of interventions to try to manage these pests. One of the best involves growing a few ‘Blue Hubbard’ plants as a trap crop, because both squash bugs and squash vine borers have been found to prefer it over other varieties. The trick is to start the trap crop plants early and have them out in the garden when the pests emerge in early summer, and to delay the planting of susceptible squash until the trap plants have time to grow.
You can keep your ‘Hubbard’ or other trap plants in containers to make them easy to handle, or try my low-labor method. In spring I put a few ‘Yellow Crookneck’ seeds in a protected spot near my compost pile, and encourage two plants to grow. ‘Yellow Crookneck’ is not as attractive to squash bugs and borers as is ‘Blue Hubbard’, but it is very well liked and I always have seeds. My trap plants are growing well by the time I plant my summer squash, and serve as indicator plants when squash bugs become active.
Adult squash bugs spend a lot of time hanging out on squash leaves, looking for love, and then the females head to leaf undersides to lay groups of shiny brown eggs. I allow this activity to proceed on the trap plants, and meanwhile do my best to hand pick the few squash bugs that appear in my cultivated squash, located many rows away. When the trap plants have squash bug eggs on many leaves and some of them have started to hatch, I quickly chop up the plant with a spade and stuff it down my stationary composter.
This simple trapping method has kept squash bugs from becoming a serious pest in my garden, though I still patrol my plants daily to rub off eggs with a wet finger, or squash adults I manage to catch (no pun intended!). In years when squash bugs get ahead of me, I place old boards under the plants, and gather squash bugs found hiding beneath them first thing in the morning.
Squash Vine Borer Barriers
Sneaky squash vine borers hatch from tiny brown eggs laid by a large red and black moth on the basal stem of squash plants. If you see borer damage year after year, you should wrap the base of each plant with strips of aluminum foil or cheesecloth, which often give good protection. But if it’s too late for prevention and you see holes near the base of the plant surrounded by sawdust-like frass (borer doo), your options are limited because you can’t poison or hand-pick pests from inside the stem.
You may be able to kill or injure them. The borers are usually feeding about an inch above the frass hole, and I have maimed quite a few by sticking pins through suspicious stem sections, voodoo-style. More aggressive removal by slitting the stem with a knife and fishing out the borers with tweezers can work if you cover the surgical wound with soil. You also can inject Bacillus thuringiensis into the stem using a syringe, which stops borer feeding and buys your plants some time.
With winter squash it’s simple to sidestep squash vine borers by growing butternuts and pumpkins classified as Cucurbita moschata, which are non-preferred by squash bugs and seldom bothered by borers because the stems are so thin that they make poor food plants for borer babies. My current favorite pumpkin is ‘Long Island Cheese,’ because the bugs leave it alone, making it easy to grow carefree bumper crops.