Randy Drinkard County Extension Agent
September 20, 2013
Earlier this month the Troup County Extension office was inundated with calls concerning armyworms, brown patch disease in lawns and yellow jackets. Now we are receiving just as many calls from homeowners who are being bothered by two pests, both insects: fungus gnats and orange-striped oakworms.
Black, fly-like fungus gnats are appearing on the sides of buildings and homes by the hundreds, whereas orange-striped oakworms are being seen chewing leaves of various types of oak trees.
Adult fungus gnats are about 1/10- to 1/8-inch long, slender, delicate, somewhat mosquito-like, with dark-colored antennae and long legs. Some species are gray to black in color, while others are orange-to-yellowish in color.
Larvae or maggots are legless, thread-like, white with black heads and 1/4-inch long. They are somewhat transparent, so food in their guts can be seen through the body wall. The larvae spin silk-like cocoons to form pupae.
Fungus gnats develop in moist, shaded areas in decaying organic matter such as leaf litter. They complete their life cycle in about four weeks depending on temperature and other environmental conditions. Adults fungus gnats live about 7 to 10 days.
The female deposits 100 to 300 eggs in batches of two to 30 each in decaying organic matter. Eggs hatch in four to six days; larvae feed for 12 to 14 days. The pupal stage lasts about five to six days.
The key to solving fungus gnat problems is to find and eliminate the source, i.e., find the area(s) of excess moisture. The most likely problem spots are landscaped and/or heavily mulched areas or low-lying areas in the yard that remain extremely wet following heavy rainfall, overwatering or a leaking outdoor water spigot. Correcting the problem may simply be a matter of modifying drainage problems in that area (grading and/or contouring the area, using gravel to allow water to drain properly, etc).
Adult fungus gnats are killed easily with pyrethrin sprays or aerosols labeled for use against “gnats” or “flying insects.” However, these chemicals are a very short-term and very temporary solution. Unless you can access and treat the source, then once the chemical dissipates more flies are likely to appear.
Treating outdoor areas may produce mixed results particularly if you cannot identify the key areas that are infested with fungus gnats. Outdoor landscaped areas can also be treated with beneficial nematodes. Regardless of how “safe” you consider any pesticide or insect control product, always read the label and follow directions and safety precautions.
Orange-striped oakworms (Anisota senatoria) are often found on oak trees and other hardwoods in late August and September. They are usually recognized in the caterpillar stage because of their defoliation of oak trees.
The full grown caterpillars are 1.5 to 2 inches long, black in color with several narrow, yellow-orange longitudinal lines. Behind the head are a pair of stiff, blunt spines, about the thickness of the body. The remaining segments of the body have pairs of smaller spines.
The orange-striped oakworm caterpillar generally appears in Georgia in August, September and sometimes as late as October. They defoliate sections of various oak species and sometimes completely defoliate smaller trees. This insect is extremely troublesome when present in oaks over patios, driveways, sidewalks, etc. because of the large amount of excrement from the insect’s body.
The winter is passed in the pupa stage in the ground. Adult moths emerge from June to August, mate and deposit eggs on the undersides of foliage on host plants.
Usually, there is only one generation per year and control measures are not necessary. If, however, control measures are necessary, such as to protect a small seedling oak, treat with Dipel or Thuricide (both are Bacillus thuringiensis or Bt, a biological control) or use an insecticide such as cyfluthrin or Sevin.