Above Photo: Larvae and adults of annual bluegrass weevil.
All Photos: Sam Camuso, Syngenta
As winter releases its icy grip on the Northeastern United States, golf courses across the region are coming to life. Along with warmer weather, however, comes the Annual Bluegrass Weevil (Listronotus maculicollis), which feeds mainly on low-mown Poa annua.
While the epicenter of ABW is the Northeastern U.S., it extends from there into eastern Canada, south to North Carolina and as far west as eastern Ohio, according to Rob Golembiewski, Ph.D. of the Bayer Green Solutions Team. ABW generally has between one and three generations a year, though it depends on the region. “The first generation larval feeding tends to result in the most significant damage – usually during late spring to early summer,” he says.
The areas ABW has hit hardest include the New York metro, Long Island, Connecticut, New Jersey and Philadelphia, says Benjamin A. McGraw, associate professor of turfgrass ccience in Penn State University’s Department of Plant Science. He’s most leary of the time from Memorial Day to mid June, which is when damage appears in many areas.
Mike Agnew, Technical Services Manager for Syngenta, doesn’t take any of the generations lightly, as they can all cause damage to turf. “The first generation is over-wintering adults that lay eggs in the spring, and if left untreated, this generation typically has the highest number of feeding larvae,” he says. “However, the summer generations do not require very high numbers to cause damage, as high temperatures and lower soil moisture will exacerbate damage.”
As for areas of the course affected the most, look no further than the pest’s moniker. “As the name indicates, you’ll tend to see more ABW in the intensely managed annual bluegrass playing surfaces, like fairways, tees, approaches, collars, and – to a lesser extent – greens,” Golembiewski says.
Unfortunately, there is no such thing as complete prevention. “It’s important to realize that 100 percent control of any ABW population isn’t possible,” Golembiewski says. “Success should be defined by managing ABW populations at levels that are below those that can cause visible damage, while also using the fewest possible insecticide applications.
“ABW overwintering adults are usually most abundant near tree lines and around trees, so removing tree litter and leaves will help suppress populations,” he added. “Creeping bentgrass can also be injured by ABW, but damage usually isn’t as common or as severe when compared to annual bluegrass. The best preventative control option is to keep annual bluegrass populations as low as possible. You can do that by using cultural practices and herbicides to help promote creeping bentgrass.”
Agnew concurs, adding while it is impossible to eradicate the insect, the best approach is to control the first larval generation with insecticides that move systemically into the plant so they are present when the insect begins to feed.. “Products like Ference insecticide offer this benefit, providing systemic control of ABW at all larval stages (first through fifth instar) and stopping turf-feeding damage within minutes after ingestion,” he says.
There are different opinions on battling ABW, McGraw says, but one view is universal - the earlier, the better. “Each approach has pros and cons,” he says. “In hard-hit areas, sequential applications against overwintering adults and larvae are necessary to keep populations from reaching damaging levels.”
If you suspect ABW present in your turf, Golembiewski says to start looking within the low-mow perimeter. Superintendents will often see damage from the first generation ABW larvae in the perimeter of short-mowed turf areas,” he says. “Injury to plants starts when adult females lay their eggs between leaf sheaths – it results in yellowing. Then, as the instars feed on the crown tissue, damaged turf will often get small, yellowish-brown spots, and you can easily pull it from the soil. A hollowed out grass stem is a key indicator when it comes to diagnosis. As the damage progresses, scattered spots will grow together, and the turf might even look like it’s under severe drought stress and eventually die.”
WeevilTrak, an online tool that provides assistance with both timing and possible products to use, is helpful when attempting to spot ABW trouble spots, Agnew says.
“Superintendents should take advantage of WeevilTrak, an ABW monitoring program offered by Syngenta,” he says. “This free subscription-based resource includes a blog updated by industry-leading ABW researchers, observations from fellow superintendents, an Optimum Control Strategy outlining a proven ABW treatment protocol and more. This year, WeevilTrak subscribers can also sign up for text message alerts that will deliver timely updates about their local ABW activity.”
But don’t be fooled by what you see, alone.
“WeevilTrak managing consultant Steve McDonald put it best when he said, ‘ABW damage to Poa annua putting greens can mimic anthracnose, and identification is best completed by cutting into the soil and looking for larvae. Small yellow pits of Poa annua greens height turf is classic ABW larvae damage.’
“Additionally, small yellow pits on collars and fairways and the subsequent dying are reflective of drought injury, since the insect has interrupted the water uptake process by feeding on the plant,” Agnew continued. “Scouting is the best tool to determine if the insect is present. Use soap flushes to find the adults, and salt flushes to look for the larvae. Videos for how to scout using these methods can be found on the GreenCast website (www.GreenCastOnline.com/WeevilTrak).
Staying in front of the potential problem is paramount for superintendents, Agnew says.
While last year’s activity won’t necessarily dictate what a superintendent can expect this year, McGraw says there are certainly indicators. “Each year is a new year. If you had late season damage last year, you can probably expect that quite a few adults can be invading in the spring,” he says. “Other than that, we don’t suspect that winter mortality rates are very high.”
One year to the next can be different because responses from ABW populations can vary greatly, Golembiewski says.
“ABW is the most difficult to control insect pest when it comes to short-mown golf course turf in the northeastern U.S. And damage can be influenced by a lot of factors – like larval density, turfgrass species, the intensity of your management practices, and just overall plant stress,” he said. “And no two ABW populations are identical. Because of the stresses imposed on the turf and the history of product use, different ABW populations also respond differently – even to similar control measures. In 2018, superintendents should try to improve on what they did successfully in 2017 and focus on mitigating plant stress and developing a comprehensive control strategy for ABW.”
Want to make an educated guess on what to expect this year? Agnew said to look at the weather.
“Every year is truly different. When the spring is cool and wet, insect development will be slower,” he said. “Hot, dry spring seasons will accelerate the insect development and greater damage may occur.”
When battling ABW, McGraw suggests it’s best not to attack it alone. Do your due diligence, but don’t be afraid to lean on others.
“Scout your turf. The more techniques the better,” he says. “Call your university turf specialists and ask them what they are seeing for your area.”
As for Golembiewski, he recommends taking your standard practices one important step further.
“Many adults survive mowing, even at very low heights of cut, so make sure to discard clippings with significant adult numbers far away from playing surfaces,” he says. “The ‘half green/half gold’ stage of Forsythia (when the plant has lost half of its yellow flowers) has been associated with high densities of overwintered adult on short-mowed turf – so it’s usually the most effective time to apply an adulticide. A good time to start larvacide applications is from when dogwoods are in full bloom through the late bloom of rhododendrons.
“Because there are pyrethroid resistant populations and ABW can cause a lot of damage, superintendents should plan on making several insecticide applications targeted against emerging adults, their offspring and summer generations,” Golembiewski adds. “In areas where pyrethroid resistance hasn’t occurred, continue to rotate insecticides with different modes of action. Dylox, for example, is an effective rotational product for larval control with no documented cases of resistance.”
Rob Thomas is a Cleveland-based writer and frequent GCI contributor.