It’s May, and that means gardeners in our area are planting melons, squashes, and cucumbers.
These warm-season vegetables grow great in our climate. I’m convinced a single zucchini plant could feed a whole family, that is if it doesn’t get obliterated by squash bugs first. (Anasa tristis)
Squash bugs are native to North America and are the worst pest we encounter in the Eastern Sierra on cucurbit species like squash. Insecticides are commonly used to control these pests, but even when applied to adults, they may not be very effective.
The best approach to these pests is to try many approaches.
They overwinter as adults in debris near the garden or in last season’s crop residues. In mild winters, like we’ve had the past few years, more adults survive. Crop rotation, destroying infested plants from the previous season, and eliminating overwintering sites are all good places to start.
It's possible to use some sort of cover early in the season to exclude these from your plants, but in the real world, it's not very practical. Assuming you can achieve a good seal that keeps the critters out, row covers still have to be removed for pollination, and it doesn't take too long before temperatures get too hot under the cover anyway.
When the weather warms in late spring, adult squash bugs emerge from hiding and begin laying eggs. They especially like pumpkins and summer squashes. At this early phase, manually removing adults and egg masses is very helpful in delaying the inevitable Squash Bug Apocalypse.
Gardeners have tried many tactics for this individual, hand-to-hand combat. The most practical are removing bugs by hand or knocking them into a pail of soapy water. I’ve also seen more creative options using vacuums or gas torches. Lawyers and insurance carriers will remind you to be careful with more “exciting” control methods.
There are a number of sprays that can help manage squash bugs, but be aware that most will also kill beneficial insects. (See UC IPM’s recommendations for control.) Insecticides tend to work better on the softer-bodied nymph stages. Many arthropods, and even lizards, feed on squash bugs, so heavy spraying may reduce help from these natural enemies.
An interesting, though hit-or-miss, control method is the parasitic fly Trichopoda pennipes. It lays an egg on a squash bug’s back that hatches and consumes the bug from the inside out, like the monster in Alien, if you’ve seen that. It’s unclear whether this parasitoid will stick around if squash bug numbers are low, but for many of us, that’s not a problem!
A method not often used but potentially effective is planting a “trap crop” that squash bugs prefer more than your main crop. This works especially well if you're growing melons or cucumbers. By planting some summer squash nearby, you can attract the pests there and then control them on that sacrificial crop. (Still monitor your entire garden!) Control options on the trap crop include removing the entire plant (bugs and all), spraying, or covering the crop tightly with plastic and cooking them. Essentially, you use the same control methods, but now you have the option to sacrifice a few plants for the greater good.
Some research suggests that the mating pheromone for the striped cucumber beetle may also attract squash bugs, opening up interesting control possibilities, although more research is needed.
Squash bug control in the garden is really a numbers game. Vigilance is key. When your defenses are down, even for a few days, they can get the upper hand.
A fairly common outcome when growing squash bugs — I mean, cucurbits — is that your plants become so infested that continuing the battle no longer makes sense. If you're the type who goes on vacation in the summer, this a common problem. Two weeks away can lead to an awful mess! In this case, don't feel too bad if you decide to surrender. If the plants are wilted, damaged all over, and the fruits are covered with adults and nymphs, that's a good sign you've lost the fight. Don't worry: you're in good company. Join the club!
My personal control method? I don’t plant either summer squash or pumpkins! If I grow zucchinis, my plants would be ready at the same time as everyone else’s. Those gardeners who did plant them are usually eager to give away extra produce. And that’s how I get zucchini, without worrying about squash bugs.
Three Excellent Resources:
- UC IPM Pest Note on Squash Bugs (Recently updated and much improved!)
- Squash Bugs – Colorado State University
- Farmscaping to Enhance Biological Control by Rex Dufour (ATTRA)