How to stop spring turf stressors

Spring is here, which means it’s time for lawn care operators (LCOs) to prepare to battle the season’s most common weeds and pests. Poa annua, billbugs and dollar spot are three issues that can affect lawns this time of year, but knowing when and how to treat these problems can minimize the damage.

Timing is vital to minimize billbug damage. If turf thinning is visible it’s probably already too late. (Photo: PBI-Gordon)

The 411 on Poa annua

Poa annua, or annual bluegrass, is one of the most common grassy weeds. David Hillger, Ph.D., Midwest and Northeast turf and ornamental research field scientist for Corteva Agriscience, says LCOs in northern areas should begin thinking about Poa annua in the early fall as temperatures begin to cool. In southern regions, Poa annua control should start in the winter. The first thing LCOs will notice is seed heads, which Hillger says can generate at all heights of cut and in any condition.

“A small tuft of grass that is light green with seed heads at half-inch height is very likely Poa annua,” Hillger says.

Poa annua thrives in soil with poor drainage and over-fertilized turf. It can even germinate and grow on sidewalks, rocks and drain tiles.

“The more mismanaged the soil and turf, the better Poa annua can compete,” Hillger says.

When treating Poa annua, Hillger says many LCOs often underestimate how much of the weed they are dealing with. He recommends doubling the estimate to ensure treatment is effective. Two sequential preemergent herbicide applications — or a split application in the South — is the best option for treatment, Hillger says. Postemergent products can be used for cleanup.

David Hillger (Photo: Corteva)

“It’s best to start with a preemergent as a strong foundation and then use post emergence herbicide products to clean up any misses,” Hillger says. “Control is a long-term process due to the high level of seeds. Early prevention is key.”

The 411 on billbugs

A billbug is a type of weevil or snout-beetle that feeds on grass stems and roots. There are nearly 70 different types of billbugs in North America. Different species are found in different regions. Billbugs overwinter as adults and become active at temperatures above 50 degrees Fahrenheit. Females lay eggs in the stems of turfgrass in the spring. After the eggs hatch, the larvae begin feeding on the turf. Billbugs are most prevalent in well-maintained turfgrass, but occasionally can be found in less healthy turf.

Chris Williamson (Photo: PBI-Gordon)

“Billbug damage first appears as thinning or dead areas of turf, and these damaged areas often coalesce into large, damaged areas,” says Chris Williamson, Ph.D., Midwest and pacific coast research scientist for PBI-Gordon Corp. “Billbug damage is often mistaken for other problems, including drought stress, turfgrass diseases or injury from other insects.”

Billbugs are among the most misdiagnosed turfgrass pests, Williamson says. He notes the “tug test” can help LCOs confirm their presence.

“This is accomplished by grabbing tufts of dead or dying turfgrass and pulling on them,” he says. “Should they pull out easily, severing near the crown, look for the presence of billbug larvae and/or sawdust and shredded plant parts.”

If you identify billbugs, the timing of treatment is crucial to minimize damage, Williamson says. Effective strategies include a curative treatment with an application of insecticides when adults are first observed and preventive treatment with an insecticide application when larvae are identified.

“Once billbug damage has occurred, it is too late to make a treatment application to resolve the issue,” Williamson says. “This mistake can be avoided by monitoring for billbug adults when temperatures are above 50 degrees Farenheit. This is an opportune time to begin making preventative insecticide applications.”

The 411 on dollar spot

Dollar spot is one of the easier turf issues to identify, Hillger says. LCOs should look for cream-colored patches in the turf measuring 3 to 6 inches in diameter. Individual blades of grass will have tan-colored, hourglass-shaped lesions and a cotton-like mycelium in the morning, especially when there is dew on the ground.

“Low-nitrogen lawns are weakened and tend to favor dollar spot, which can take over easily,” Hillger says. “Dollar spot can infect most turf species, but it needs higher humidity and a few days with the right temperature and moisture to really get going.”

Brian Aynardi

Brian Aynardi, Ph.D., Northeast research scientist for PBI-Gordon, says dollar spot is typically seen when daytime temperatures exceed 75 degrees Fahrenheit, nighttime temperatures are above 55 degrees Fahrenheit, and there is significant wetness or extended periods of high humidity.

“LCOs should have dollar spot on their radar a month before they traditionally see disease symptoms develop, but should remember that the disease won’t occur if the right environmental conditions do not exist,” Aynardi says.
While cultural practices can help manage dollar spot, Hillger says fungicides are the best solution when used in rotation.

Preventive treatment of dollar spot is most effective, and applications should be made several days before the right environmental conditions occur.

“Fungicide rotation is key, as dollar spot is notorious for being resistant,” Hillger says. “Another key mistake is waiting too long to spray. Once dollar spot starts for the season, it’s too late and LCOs will have to play catchup for the rest of the year trying to control it. Prevention is their best bet.”