Alarms should sound in a superintendent’s head when the crocuses start to pop up and daffodils poke their heads above the soil. Those flowers are crying, “It’s time to treat for annual bluegrass weevil!”
Another shout may come from the mowers in the equipment shed because new research shows that lowering your mowing height can help in the fight against ABW.
Some superintendents recall the guideline about checking for ABWs when yellow petals start falling from the Forsythia bushes and the dogwoods start to look pretty, but that might be too late. The insects start to move out of the woods where they have overwintered and head for any area on a golf course that is planted with bluegrass well before dogwood time. In fact, by the time the dogwoods are in bloom, ABWs are probably laying their first round of eggs.
Traditionally, there are two keys to ABW control:
- Early identification of an invasion. That means you need to have a good scouting or trapping program in place.
- Early and consistent control. There are many options, but be sure to have your management strategy in place before ABW starts to manage you.
In 2017, the hot buzz about ABW control comes out of Penn State University and its research into mowing height. Ben McGraw, associate professor of turfgrass science, has been studying ABW since before he moved to Happy Valley in 2014. His most recent work, which should be published soon, is on the impact of mowing height on greens.
After working with Albrecht Koppenhofer at Rutgers University, McGraw wondered, “Why don’t we see as much ABW damage on greens?”
It turns out that mowing height has a major impact on ABW population. McGraw’s research focused on putting green mower heights. Most superintendents mow at 0.110, so McGraw set up greenhouse and field tests to see if mowing at a lower height made a difference – and it did. “Mowing at 0.100, we saw 30 percent removal of the adults,” McGraw says. “That’s a pretty strong effect for a single event.”
Removing roughly a third of adult ABWs reduces the number of eggs laid, which helps lessen pressure on turf. ABW typically place their eggs in the leaf sheaths of the bluegrass.
Surprisingly, ABWs change their behavior under low mowing heights. They no longer put their eggs inside the sheaths but lay them on the surface, making removal easier.
Read more: Mowing Patterns: Aesthetic vs. Function
McGraw cautioned, however, that his research focused on adults, not larvae, and it only looked at greens infestations because it is not practical to mow fairways so low. Superintendents have only two classes of material to use against adult ABWs, and chemical rotation is difficult when trying to kill adults. Larvicides are useful on fairways.
“This research is just starting,” McGraw says. “I’m not saying that you don’t need to treat. Frequent treatment is always a strong strategy.”
2017 ABW Outlook
Cold weather is not necessarily the disaster for ABW that many superintendents might believe or hope it is. “Remember, those insects all made it through the last Ice Age,” says OSU’s Dave Shetlar.
New England temperatures have averaged 8 degrees above normal with little snow cover. “We’ve had a very dry, fairly mild winter,” says Pat Vittum at UMass. “Normally, I’d think that is a good thing, but it’s been so mild they’ve not been set back much. We’ve seen nothing severe enough to reduce populations.”
Shetlar and Vittum agree that typical turf pests like ABW, white grubs and billbugs probably suffer more from a mild winter or a cold winter with early warm-up. If it is mild, the insects get rid of their internal “antifreeze” too early, then get nailed by a late cold front — or their eggs and larvae will.
“Zero temperature effect,” agrees Penn State’s Ben McGraw. “Insects in temperate areas are pretty evolved to handle freezing and frost,” he says, noting that ABWs only burrow down about a half-inch. “Remember, there are insects in Alaska.”
For years, superintendents have tried to incorporate products with different modes of action into their ABW program as a solution. While this is a good strategy with almost any pest, using different chemical families is especially important with ABW. Resistance seems to show up in pockets.
“Switching chemical families is absolutely critical,” says Pat Vittum, an entomologist at the University of Massachusetts. “I’m not seeing any difference in resistance.” However, she is seeing increased distribution of resistant populations, concluding that a number of materials are less effective than they once were.
“It is striking to see how much resistance there is,” Vittum says. “The challenge is that a single spray is not going to do the job.”
A shot of a pyrethroid in the spring can be effective because the weevils that emerge at the end of winter seem to be a bit less resistant than later generations. But after that initial treatment, superintendents need to do something different: Apply a different chemistry, and monitor into the summer to control the summer adults and larvae. On some courses, five or six applications may be needed.
Even before they eat, ABW females lay their eggs for the first generation. Typically starting in mid-to-late April and continuing through most of May, ABWs will lay eggs, and the first swarm of emerging larvae will cause extensive damage to the turf from May through mid-June.
It doesn’t end there. Those first- generation adults will emerge throughout June and July and repeat the cycle their parents started. At this point, a particular bluegrass fairway or green might be home to ABWs in all of the different stages of development, making control even more difficult.
According to Dave Shetlar, Ohio State University extension entomologist, ABW tends to be a localized problem. Although ABW can be found across the Northeast and in Minnesota, Iowa and Indiana, it is not a problem everywhere it is found.
“It is possible that we have an ABW biotype that specializes in high-maintenance, short-cut Poa,” Shetlar says.
Ohio has ABW concerns in an area from Wheeling, West Virginia, up to the Akron-Canton area and over to Lorain by Lake Erie. However, a recent report form the Northwest Ohio Superintendents Association hinted at ABW damage there, too.
The strategy in areas like Ohio, where there is no reported chemical resistance in the ABW population, is plain. “To me,” Shetlar says, “the simplest way is to go is with pyrethroids.”
That is definitely not true in areas of the Northeast where ABW has been a persistent problem.
While it will bring howls from some in the turfgrass industry, Shetlar says he suspects that ABW might be transported in bentgrass and other sods. Keep in mind that even the best bentgrass sod has some Poa annua in it. He suspects that is how ABW turned up on two recently renovated courses in Medina County, and also on some cool-weather courses in the mountains of North Carolina. ABW is not typically found in either area.
“By far the best program for Ohio is Aloft, if superintendents apply it at egg laying,” Shetlar says. “It zeroes them out for the season.” Aloft is a combination of clothianidin and bifenthrin, so it contains a pyrethroid. It provides both fast knockdown and systemic control of pests. He also likes Dursban (chlorpyrifos) granules applied early enough to get the ABW as it moves into the fairways. It also helps to control other pests like crane flies.
Vittum warns that a combination material might not be as effective in New England. “In some cases, using a combination of modes of action is good,” she says. “But once you have resistance in the population, it is no longer reasonable to include a product with a material with resistance. The insects don’t care whether you are using the pyrethroid alone or in combination.”
No matter how rigorous the program, eventually ABW is going to get ahead of the game. Water may be the last resort on golf courses where ABW damage extends into July and August.
“All you can do is manage the damage,” Vittum says. “If it means watering to keep the Poa alive, that’s what you need to do.”
Read more: How to Identify and Control Perennial Pests