Question: My zucchini plants are healthy and producing many blossoms and fruit now. Last year many squash plants in my garden were infested with the squash borer but I can’t remember when I first noticed them. When does the squash borer typically show up in our Tucson gardens and what can be done to keep their damage to our plants to a minimum?
Answer: The squash vine borer (Melittia cucurbitae) is something you should be looking out for as soon as your plants are in the ground. The temperatures are warm enough in Southern Arizona to accumulate their required 100-degree days early in the year, and this allows the adults to start flying as early as late February. You can calculate degree days for your specific microclimate to be more precise or you can use one of the calculators on the internet. I like the visualization tool from the National Phenology Network that allows you to choose specific dates and locations to track the temperature accumulation (www.usanpn.org/data/visualizations). The adult moth looks a bit like a wasp, has an orange body with black wings, and will lay eggs near the base of the plant. The eggs can be removed by hand if you find them. They are very small, these reddish-brown circular eggs, and you must get close to the ground and lift some leaves to see them. Once they hatch and the larvae enter the stem, they are mostly protected by the plant. Where the young larvae bore into the plant there will be a small hole with frass (insect poop+debris) near the port of entry. Some people will turn into plant doctors and do minor surgery on the stem to remove the larvae once the signs are apparent. This is a test of your dedication to the zucchini.
Peter L. Warren is the Forest Health Program Coordinator for the Arizona Department of Forestry and Fire Management. Questions, photos and videos may be emailed to email@example.com