Texas AgriLIFE Specialist Dotty Woodson was flooded with questions after last Sunday’s appearance about webworms. Here’s more information that you need to know:
Controlling Webworms By Dotty Woodson
The webworm population is larger this year because female insects lay more eggs when there is plenty of food and the weather is favorable for their young. The rain and cool weather all spring has helped landscapes grow better than usual. This includes the trees webworms like to eat.
Webworms do not kill mature healthy trees but the damage and webbing is unsightly. Young trees that lose all foliage due to webworm damage may survive but are most certainly set back due to lack of photosynthesis.
The webworm moth lays eggs on the more tender leaves near the tips of trees. The female moth only lays eggs on trees their worm-like caterpillars like to eat. When the eggs hatch, the tiny caterpillars start eating leaves and eventually produce webs around new leaves to protect themselves from predators. As these leaves are eaten the webworms extend the webbing, usually at night, over fresh leaves. The tiny caterpillars are only able to skeletonize the leaves by eating the upper and lower epidermis. As the caterpillars grow, they eat entire leaves leaving only the tough major veins. The caterpillars drop to the ground to pupate and morph into mature moths. Several generations occur each summer.
Webworms create webbing for protection from predators. Wasp, assassin bugs, predatory stink bugs, parasitic flies and birds are few of the predators of webworms. Webworms only leave the webbing at night to extend the webbing because the predators are only out during the day. Control webworms by exposing the webworms to predators. Use a pole saw, rake or some other long tool or pole to tear open the webbing in the morning. Wasp, assassin bugs and birds will carry off the webworms to feed their young. If the webbing is small, cut off the branch with the webbing using a pole saw.
To control webworms you cannot reach with a pole saw or tear open, spray an insecticide call Bacillus thuringiensis, Bt., which is a natural organism that only kills caterpillars. Bt will not harm wasp or other beneficial insects. Spray Bt on the leaves outside the webbing so the webworms will die as they expand the webbing and eat the fresh leaves. The spray will not penetrate the webbing. Use a garden hose attachment designed to spray trees. This attachment is available from most garden centers. Spray the trees as soon as you see the webworms hatching for best control. Add a small amount of soap to the spray so the Bt. will stick to the leaves better. Bt. is not a contact poison. The worms have to eat it. Use a ladder or spray from the roof to reach the higher parts of the tree. Several applications are required as new webworms hatch.
Another insecticide, Spinosad, is also recommended. As with all insecticides, thoroughly read the label and carefully follow the instructions.
If you have webworms this year, watch closely for the first signs of webworms next year. Webworms like the same trees every year. Mulberry, pecan, persimmon, black walnuts, sweetgum, ash and about 80 other trees are affected by webworms.
