Landscape and Turf - Yellowjackets are Dangerous This Time of Year

Yellowjacket stings are a common problem for lawn care workers and landscapers, especially this time of year. The following is some information.

Yellowjackets are dangerous wasps encountered around homes and buildings. Nests are often located underground in an old rodent burrow, beneath a landscape timber, or in a rock wall or wall of a building. If the nest can be located, it can usually be eliminated by carefully applying a wasp spray insecticide into the nest opening.

Late summer is the time of year when populations of yellowjackets and other social wasps become large and noticeable. Because colonies start as a single queen in May, populations are very small through the early part of the summer. Yellowjacket wasp populations reach a peak at late summer when each nest may have up to approximately 5,000 wasps.

Yellowjackets are commonly observed hovering back and forth at the small nest opening or around garbage cans and other areas where they forage for food. The workers from the colony travel up to a few hundred yards from the nest while looking for food. In the early summer the wasps forage for caterpillars and other "meat" items, but in the fall prefer sweets such as pop and candy residue in garbage cans.

The eastern yellowjacket is our most abundant yellowjacket. However, up to 40% of the eastern yellowjacket nests are parasitized by other species of yellowjackets each year. Most of the eastern yellowjacket colonies that are not parasitized reach a population of about 3,000 workers and a few colonies may have almost 5,000 workers. Queens are produced in late summer and early fall. A healthy colony may produce 2500 queens each of which has the potential to found a new nest the following spring! Yellowjackets do not reuse their old nests. Apparently they do not even reuse the individual cells in which the new workers and queens develop.

Sevin (tm), or Ficam (tm), dust is very effective provided a handduster or similar type applicator is used to dispense several puffs of the insecticide dust in to the nest opening (an empty, dry liquid detergent bottle, filled no more than halfway with dust and shaken before dispensing works well).

Treatment should be performed late at night after all yellowjackets are in the nest and less active. It's best to pinpoint the nest opening during the daytime so you will remember where to direct your treatment after dark. Approach the nest slowly and do not shine the beam of the flashlight directly into the nest entrance as this may startle the wasps; instead, cast the beam to the side to illuminate the nest indirectly and place the light on the ground rather than in your hand. Similar to hornets, yellowjackets are extremely aggressive when the nest is disturbed. It may be prudent to call a professional pest control company, particularly when access to the nest is difficult.

Information from the University of Kentucky, North Carolina State University and Iowa State University fact sheets and newsletters.