The ABW has a complete life cycle and can produce one to three generations per year. The insects are small in size during the adult stage, differing in color from black to gray. They average 1/8 of an inch long and have a characteristic weevil snout. During the stage when the adult emerges from the pupal stage they appear reddish in color, but change to a charcoal gray color as their shell hardens. The eggs of the ABW are small and oblong, and can be found in the leaf sheaths of turfgrass plants.
When the larvae emerge from the eggs that have been laid in the leaf sheath, they are legless with a white body and brown head. The pupae stage of the ABW look a lot like an adult, but are smaller in size and have a reddish brown color that darkens over time. The adult and pupae stage of the ABW do not often cause noticeable damage to turfgrasses. Most damage to the turf by the ABW is often noticed in the perimeter of greens and fairways that support a high population of Annual Bluegrass. The majority of the damage is caused by this insect during its larvae stage, and can go unnoticed for sometime. The damage occurs when the female adult chews into the outer sheaths of the grass blade and lays her eggs between the sheaths. This process will weaken the plant and discolor, but not kill it instantly. Therefore the damage cannot be seen as it happens most of the time. The larvae that hatch from the eggs feed on stems and then move into the crown tissue of the plant. When crown feeding occurs the plants can easily be pulled from the soil, and a hollowed grass stem is a sure sign that ABW's are present. The more eggs, the more larvae, the more damage to the turf. The turf will appear purple before it turns brown and dies out. The significant damage that the larvae cause becomes obvious in late May or early June.
During the early fall season the larvae which have became adults at this time, make their way from the close cut turf of greens and fairways to wooded areas. There they over-winter in litter under trees and clippings deposited there or in rough areas. In early April these adults make their way back to the greens and fairways to begin feeding, this however causes little damage. The laying of the eggs during this feeding that will produce the damage when the eggs hatch in a month's time. The larvae will be present feeding on turf from the first part of May until the end of June, with most damage possible during the summer.
The larvae can be detected by cutting a slice of turf two inches deep as seen in the picture above. During the 2010 season we did not detect larvae in many areas, and some areas did not have any at all. However, we must use control methods every year as if we are preparing for year of the worst infestation. For the 2011 season we have adapted transitioning our collars and approaches from Creeping Bentgrass to Perennial Ryegrass. Perennial Ryegrass has been proven to be a resistant variety of turf that ABW's will not feed on, so this measure will keep the greens and surrounding areas protected from damage. As for these areas and the fairways chemical applications will be applied two to three times during the year when needed. This is just one of many things we will be doing to provide the best turf conditions for playability during the 2011 season.
* Biology and Management of ABW in Turfgrass. - Steven McDonald M.S. & Peter Dernoeden Ph.D.