We recently discovered that the hunting billbug is capable of successfully overwintering in the larval stage as far north as West Lafayette Indiana. This insect is mainly a pest of warm-season turfgrasses such as Bermudagrass and zoysiagrass and has become a perennial problem in parts of the state where these grasses are cultured. Although we’ve known for several years that this insect overwinters as an adult and produces two generations per year in this part of the country, its ability to overwinter here in the larval stage was previously unknown. Overwintered adults have been the primary management target, but insecticide applications targeting adults may have little impact on the soil-dwelling larvae. Instead of just 2 generations to think about, managers should be aware that 2 separate cohorts may occur.
|Figure 1. Hunting billbug larvae found in soil during March 2015.|
|Figure 2. Hunting billbug adult (actual size = approximately 1 cm).|
|Figure 3. High- (top) and low- (bottom) cut zoysiagrass damaged by hunting billbug.|
This means is that both larvae and adults may be active and present over much of the growing season. This fact could complicate insecticide timing, narrow the spectrum of useful management options and spread damage over a larger portion of the growing season. The following table contains chemical management recommendations based on my experience and those of our colleagues in North Carolina who have been dealing with this exact issue for some time.
Table 1. Chemical management options for hunting billbug based on target stage of the insect.
|Adults||bifenthrin, deltamethrin, lambda-cyhalothrin, zeta-cypermethrin||As soon as adults become active (late April – early May)|
|Larvae||clothianidin, thiamethoxam, imidacloprid, chlorantraniliprole||When larvae are inside stems or crowns or present in soil|
|clothianidin + bifenthrin (Aloft), imidacloprid + bifenthrin (Allectus)
bifenthrin + zeta cypermethrin + imidacloprid (Triple Crown)
|When adults and larvae are present or after adults have been active for several weeks|
by Doug Richmond and Alexandra Duffy, Department of Entomology, Purdue University