There Come the Annual Bluegrass Weevils

By David Oatis, Director, and Jim Skorulski and Jim Baird, Agronomists
April 22, 2005

Winter Injury Update

Winter damage is spotty from the reports received thus far, and most is reported in northern parts of the region where there were early winter rain events followed by very cold temperatures and snow. The condition of annual bluegrass in damaged areas is difficult to determine. Some days it looks like it is recovering and improving only to take a step back with cooler or dry, windy weather. Permeable covers can help maintain some moisture and provide a lift in temperatures that may be just enough to push the ailing annual bluegrass in the right direction. The extent of damage will become more clear with the moderate temperatures.

Annual Bluegrass Weevil

Spring is finally upon us and for many golf courses in the Northeast that means preparing yourselves for the annual attack of the annual bluegrass (AB) weevil (formerly Hyperodes) insect. Adult AB weevils usually begin their migration from over-wintering sites in pine litter and adjacent woodlands onto turf around the time between Forsythia petal drop and dogwood full bloom. Application of an insecticide like a pyrethroid during this period will be most effective on adults and young larvae before they enter the leaf sheath.

Greatest turf damage usually occurs on annual bluegrass from the larval stage of the insect as it bores into the leaf sheath near the crown of the plant. First generation larvae are usually active in June or earlier in warmer parts of the region, and between 2-4 or more generations of the insect can be expected during the season. Keep in mind that populations tend to escalate from one generation to the next. Larvae appear much healthier and happier when annual bluegrass is plentiful and, even though they can be found everywhere and will feed on bentgrass, they seem to prefer lower cut annual bluegrass turf on the edges of fairways, tees, and greens.

Weevils are small insects so scouting and sampling are recommended prior to employing a control measure. A recommended sampling technique is to submerge about a cup cutter-sized area of turf with a quart of lukewarm water containing a 2/3 cup of table salt. All stages of the insect except the eggs will float to the surface. What is the threshold level for control? A general rule of thumb is 30-80 larvae/ sq. ft. in the spring and 10-40 larvae/sq. ft. during the summer months when turf is under greater stress, however lower populations may cause intolerable damage that warrants control. If sampling indicates mostly young adults, then use a pyrethroid insecticide. If mostly larvae are present, then use a more soluble insecticide with the ability to penetrate thatch. If mostly pupae are present, then wait to control the adult stage as chemicals are not effective against the pupal stage.

Chemicals are not the only means of controlling the AB weevil, but usually they are the most effective. One cultural strategy that may or may not be effective is to minimize litter under trees, especially white pine needles since they are a preferred over-wintering site for this insect. Overall, try to minimize stress to annual bluegrass by raising the height of cut and/or switching to solid front rollers on reel mowers to reduce turf wear. Of course, it would be best to minimize annual bluegrass populations on your golf course, which is much easier said than done. Lastly, several biological control organisms have shown promise against the AB weevil including entomopathogenic nematodes and bacteria, however further field testing is warranted.