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Squash vine borer invades the garden

Last week the zucchini plants in my garden began to flower. I knew that it would not be long before I would enjoy all the culinary pleasures of this versatile cucurbit. My concern was that all the bees, needed for pollination, seemed to be enjoying the flowers of a nearby bottlebrush plant and not visiting my vegetable garden. I even hand pollinated a few female flowers just to ensure that my dreams of zucchini bread would be fulfilled.

So when I spotted a small flying insect hovering around the zucchini plants, my heart leapt with joy. Then in a split second, the thrill was gone and a rush of adrenalin flowed through my veins. That was no pollinating honey bee; it was a squash vine borer moth. To make matters worse, this orange moth curled her abdomen under a stem and laid an egg. This is war!

The squash vine borer adult is a clearwing moth, common in Florida home gardens. It is a serious pest of vine crops, commonly attacking summer squash, winter squash, and pumpkins.

The adult is a moth about 1/2 inch long with an orange abdomen and black dots. Squash vine borer adults are relatively good fliers and resemble wasps in flight. These moths are unusual because they fly during the day while nearly all other moths fly at night.

Adult squash vine borer adults are called clearwing moths because a large portion of their hind wings lack scales. They are colorful moths approximately ¾-to 1-inch long with 1-to 1½-inch wingspan.

They lay eggs singly on the plant concentrating their efforts at the plant’s base. Eggs are flat, a rusty-brown color, and about 1/25 inch long. Approximately one week after they are laid, the eggs hatch and the resulting larvae, or caterpillar, bore into stems to feed. The caterpillars are cream-colored with brown heads, growing to almost an inch in length. They feed through the center of the stems, blocking the flow of water to the rest of the plant.

Adult females lay rusty-brown eggs on leaves and stems.

Often the first symptom of a borer attack is wilting of infested plants. Closer observation often reveals holes near the plant’s base filled with moist greenish or orange sawdust-like material called frass. Over time, the base may become mushy or rots away altogether.

Squash vine borers are challenging to prevent or manage. Most management options are focused on controlling the hatching caterpillar before they enter the plant. Once they invade the stem, it is difficult to treat squash vine borers.

Home gardeners should be proactive by monitoring your plants for the presence of adult borers. Monitoring tells you if and when squash vine borers are present. There are two methods for detecting squash vine borer adults. The first is actual observation of adult activity in the garden. These moths are conspicuous insects when flying and easy to detect. You can also use yellow trap pans to detect squash vine borer adults. This can be any container (e.g. pan, pail, bowl) colored yellow and filled with water. Because squash vine borer adults are attracted to yellow, they will fly to the container and be trapped when they fall into the water. When you notice squash vine borer adults in your traps you know they are active and it is time to take further action.

If insecticides are needed, spray the stems at their base when the first adult moths are detected. Repeat in 7 to10 days. Look for insecticides that contain Bacillus thuringiensis (Bt), permethrin or bifenthrin. As always, read and follow label directions.

If, despite you efforts, your crop is successfully attacked by borers, you can try to kill the borer inside the vine. Although the chance of saving the plant is not good, you do not have much to lose. As soon as wilting is noticed, use a sharp knife to cut a slit in the affected stem. Slice carefully up the vine until you locate the borer (or borers). Once you have killed any borers with the tip of the knife, mound moist soil over the cut area and keep this spot well watered. New roots may grow along the cut stem, allowing the plant to survive.

Permanent link to this article: http://santarosa.ifas.ufl.edu/blog/2012/04/10/squash-vine-borer-invades-the-garden/