Act Now to Control Squash Bug Populations
June 27, 2020
Squash bugs decimated my plants and my crop last summer. What should I be doing now to prevent this from happening again?
- Sarah H., Las Cruces
You are not alone, and I’m glad you’re already gearing up. Last year I addressed multiple questions about controlling squash bugs in September and October columns. However, by then, most squash bug problems were beyond help, and I promised to address this issue earlier this year. This week, I’ve collected recommendation snippets from archived columns going all the way back to 2008. Thanks to Drs. Amanda Skidmore, Curtis Smith, Carol Sutherland for their contributions. For links to the original columns, including advice on using kaolin clay and diatomaceous earth, visit my Desert Blooms blog this week.
I’ll also link to a very helpful YouTube video from the Southwest Yard & Garden show where John White, retired garden curator at the UTEP Centennial Museum and Chihuahuan Desert Gardens in El Paso and Doña Ana County Extension Agent, demonstrates how to monitor your plants for squash bug eggs.
Squash bugs are difficult to control, and even more so as the bugs mature because their populations get out of control and insecticides are a much less effective tool. Squash bugs have distinct lifecycle stages, so be sure to keep an eye out for eggs, nymphs, and adults.
Some people delay planting squash until July to avoid the squash bug, but this tactic is not foolproof. As many gardeners have reported again and again, delayed planting seems to work some years, but not reliably.
Dr. Carol Sutherland, NMSU Extension Entomology Specialist and NMDA Entomologist, has suggested that you take a hint from their name and “squash” the mature squash bugs. Look for clusters of shiny orange-brown eggs on the underside of the lower leaves and smash them too. Sutherland also suggests that you handpick or scrape the bugs and their eggs from the plant into a can of soapy water. (I might use a large can or even a five-gallon bucket to save on repeated trips to dump and refill.) Manual removal is the most effective way for homeowners to manage this common garden pest at this stage. Manual removal is also the preferred control method earlier in the season, in addition to scouting for eggs and destroying them.
I know some readers are getting stressed thinking about collecting—and squashing—all of the bugs that are smothering their poor pumpkins right now. NMSU Extension Integrated Pest Management (IPM) Specialist, Dr. Amanda Skidmore, shared a trick: “One way to get them to congregate is to put some newspaper, cardboard, or old boards near the base of the plant overnight. Squash bugs like to be in protected areas, especially when it starts to get cold at night. Check underneath in the morning and remove any squash bugs.”
If they are in the area and they detect your squash, they will appear in your garden. This can happen at any time during the summer. Sutherland explained that squash is not their only food supply. They feed on any cucurbit (squash, cucumber, ornamental gourds, and even native gourds). They do have favorite plants, and if they are feeding on native gourds and detect your squash, they will leave the gourds and infest your squash. If you choose not to plant squash for several years, this will not ensure a year without squash bugs if these alternate hosts exist nearby, or if neighbors' gardens have been supporting squash bugs.
Skidmore added, “Insects have many different forms of communication, and pheromones are one of the main ways they pass messages to one another. True bugs (including squash bugs) are known to have both "aggregation" and "alarm" pheromones. An aggregation pheromone basically says, "I found a great resource, come join me," while an alarm pheromone says, "Danger, avoid!" From researching your question, I haven't come across anything saying that crushing squash bugs would attract more to your plants. Crushing a squash bug would release an alarm pheromone, which would then send a signal to other bugs to avoid that area. These pheromones won’t last long in the environment (especially if the insect is dead and not actively releasing it), so I would say remove them by hand if you have a small number of plants. You can try swiping them into a bucket of soapy water or corral them under cardboard, as discussed in last week’s column. One reason you might see an increase in the number of squash bugs on a plant is that the plant may also be sending a chemical signal into the environment, telling the insects that it is in distress and attracting more pests to it.”
Check out the NMSU Extension publications, Pocket Guide to the Beneficial Insects of New Mexico, for pictures of two natural enemies that eat squash bugs and tips on how to draw beneficial insects into your garden.
Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: firstname.lastname@example.org, office: 505-865-7340, ext. 113.
Please copy your County Extension Agent and indicate your county of residence when you submit your question!