I know some of you out there are having squash and zucchini problems this year and you aren’t alone. A week ago, I noticed my first and most prolific zucchini plant starting to yellow and wilt. I checked the stem to see if there were any squash borers and sure enough there were a couple a cracks in the stem and some saw dust like stem bits hanging out beside the cracks. Hoping to save the plant I stuck a sharp wire into the holes hoping to kill the borers and covered it with soil (like the U.K. entomologists say). Saturday the plant was just about gone, so I pulled it up, dissected the stem and found 7 one-inch long borers about as big around as a pencil munching away! I have to admit I took great pleasure avenging my beloved zucchini plants death.
Squash bugs obviously kill their host by eating the inside of the stem and they can be darn near impossible to control after they are inside (unless you don’t mind killing the plant). To control borers you need to apply an insecticide to the stems before the borers are present. As they try to burrow into the stem they eat the insecticide and die. Squash borer moths are active for about a month and a half, so you will need to spray weekly from June through July. Sprays should be directed to the stems especially at the base. Insecticides such as sevin, methoxychlor, rotenone, pyrethrum, and malathion are labeled for squash borers. Be sure to spray the stems early in the morning or late in the evening when the blooms aren’t open. You don’t want to get insecticides into the blooms and kill the hard working pollinating bees. Physical barriers of aluminum foil or old panty hose around squash stems can also help control the borers keeping them from having access to the stems.
At the end of the season be sure to clean all squash, zucchini, pumpkin, etc. vines out of the garden and discard them far away or burn them. These provide overwinter cover for the moths and if you can kill them before the season starts you are going to have much better luck.
Another squash insect was also present Saturday along with dozens of bronze eggs stuck on the leaves. The squash bug starts out a light gray color and changes to dark grayish charcoal as it matures. Several baby squash bugs fell off the plant while I dissected the stem; they received the same fate as the borers.
Squash bugs suck plant sap and can kill plants as their population increases. I try to squash the squash bug eggs as I see them but they are really hard and are connected to the leaves tightly. The easiest way to get them is to tear that piece of leaf off and destroy it. The disease squash bugs vector causes the most damage to cucurbits, actually much more than their feeding. As squash bugs feed on plants they inject a substance that causes it to wilt much like bacterial wilt would do.
Squash bugs take up to six weeks to reach adulthood and only lay eggs once during a season but they lay eggs over a long period of time meaning control is difficult. Also, squash bugs hide when disturbed so hand picking isn’t really an option. As with squash borers insecticide applications work best. Sevin is labeled for squash bugs as is rotenone but they both work better against the young ones.
One very effective way to reduce the number of squash bugs is to keep the plants covered with tobacco canvas (remay) until they start to bloom. This will give you several weeks of production before the squash bugs even find your plants! If you have several praying mantises in your garden give them a ride over to the squash, I have witnessed them feeding on squash bugs which makes a pretty big meal for them. Also, you will take great pleasure in watching them eat your pests!
Again, like with squash borers sanitation this year will help you next year. At the end of the season destroy all plant debris or at the very least get it far away from your garden.
Submitted by Dennis Morgeson, Agent for Horticulture, Washington Co. Cooperative Extension