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Squash Vine Borer

Closer Look Of The Squash Vine BorerThe presence of these pesty insects, in their worm (larva) phase, are wilted runners or vines, and clumps of yellow, moist sawdust-like frass near the bases of joints and stems. If you cut the stems lengthwise with a knife you will notice one or more fat white worms, up to 1” long with brown heads, eating the stem insides. This is the squash vine borer, and by the time you notice the damage plants it is many times too late to save it. These are very destructive worms! In the north, there is normally only one generation of the vine borer, but in the south, two generations are possible.


Adult

Squash Vine Borer AdultThe adult is a wasp-like moth that is orange/red and black, very quick and elusive, a wing span about 1 1/2” long, with clear orange/red wings. It looks to home gardeners as an oversized hornet and will normally appear in late spring, laying eggs just as the squash are about to flower. The female adults locate the exact area by feel and will settle for any place within a few inches of where the stem touches, or is very near, the ground. Adult moths live for about five weeks, depositing as many eggs as they can. Most are daytime fliers, are noisy and colorful, and should be somewhat easy to spot. Remember: look for them when the squash are just about to flower.


Eggs

The eggs of the vine borer are flat brown circles, about 1/10” across, normally deposited to the stems at the base of the host plant. They hatch in one to two weeks where they enter the larval phase of their lives. Egg laying happens in April and May in the south and June and July in the north.


Larvae

Squash Vine Borer NymphThe larvae of the vine borer are 1” long ugly white worms, with brown heads and small brown legs. They produce a sawdust-like frass inside of the stems and hollows of plants. They feed for four to six weeks inside of the soft plant stems, causing to plant wilt and look anemic. If you cut the stem open, you’ll see the worm and a lot of sawdust-like material. This is the give-away that you have the squash vine borer larvae in your squash plants!

Squash Vine Borers On Zucchini Stem If your plants are growing properly and appear to be healthy and then suddenly begin to wilt, suspect the squash vine borer. Take a knife and cut into one of the lower stems near the ground and look for a white worm. Also, look for a sawdust-like residue at the base of stems or near holes in the vines. There may be three or four worms in a single plant stem.

Later in the season, when fully mature, the worms can leave the insides of the stems and begin feeding on the fruit of the plant. Later, they leave the plant and descend into the soil to spin a cocoon where they hibernate over the winter.


Pupa

Squash Vine Borer PupaAfter the borer larvae has matured it burrows into the soil and spins a silk cocoon in which it remains until the following spring. Cocoons normally reside within one to five inches of the top of the soil, are mahogany brown in color and about 5/8” long.


Vegetables That Squash Vine Borer Like To Eat

Cucumbers Melons Winter sqaushes* Summer squash
Gourds Pumpkins

* Blue and Butternut squash are somewhat resisitant
Hubbard squash is most severely injured

Control

Plant an early crop of summer squash, as the plants can withstand an attack better when they are more mature. A later planting may miss the feeding larvae altogether, so try timing your plantings of susceptible vegetables to avoid damage if possible.

We have had some luck by placing shinny foil around the base of target plants, which confuses the adult moth from laying her eggs at the base of the plant. (See "Care Mulches")

Insecticides are not normally effective once the borer is inside of the stem. Slitting the stem open and removing the worm is one option for the home gardener.

Carbaryl is said to be effective against the borer as is Methoxychlor. Be sure to apply these chemicals in the early evening when bees are not present. Esfenvalerate and Malathion are also said to be effective if applied when the eggs are just beginning to hatch. Timing is most critical here as you have to catch the borer just as the eggs are hatching.

Floating Row CoverRotenone or pyrethrin power will control borers if applied regularly, especially if you see any borer eggs. Finally, floating row covers always seems to work well for the small home gardener.


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