Are those brown spots on the turf caused by billbugs or another pest?

April 28, 2023 -  By
Hunting billbugs, found in warm-season turf, can overwinter as both larvae and adults which makes controlling them that much harder. (Photo: Syngenta)

Hunting billbugs, found in warm-season turf, can overwinter as both larvae and adults which makes controlling them that much harder. (Photo: Syngenta)

It’s a routine service call. The client has islands of dead turf littering the yard. It’s a no-brainer for an experienced lawn care operator (LCO). A hot early spring coupled with recent precipitation makes these unsightly spots the likely symptoms of early onset summer or brown patch. From the truck, you determine that a fungicide treatment should set this right.

But not so fast. Those ugly spots on the Kentucky bluegrass lawn could point to turfgrass pathogens, overfertilization or improper chemical applications. Or they could be signs of billbugs.

An incorrect diagnosis is a waste of time, money and resources. Here’s how to better determine whether billbugs are at the heart of your turf problem.

Get down and dirty

First and foremost, turf experts recommend LCOs avoid diagnosing from the curb. 

“No. 1, get out of your truck,” says Richard Fletcher, a turf and ornamentals technical services manager for Nufarm. “No. 2, get down on your hands and knees because you have to figure out why (the turf) died.”

The best way to determine the problem is to take a sample of damaged turf between your thumb and index finger and pull upward. 

“If it comes up fairly easily, then there’s a good chance (damage) could be related to billbug feeding,” says Matt Giese, a Midwest turfgrass technical field manager for Syngenta.

Examine the stems of that sample closely to see if they’re hollowed out and appear ragged or chewed on the bottom. While hollow stems are a telltale sign of billbug larvae feeding, the clincher is the presence of frass, a fine, sawdust-like material. Further investigation into the soil profile will reveal white larvae. 

“You have to dig around a little bit in the turf to be sure you can rule (billbugs) out,” Giese says.

Know your bugs

In cool-season turf, the bluegrass billbug overwinters as an adult, emerges in the spring as soil temperatures increase and then lays an egg in a slit it cuts into a turf stem. The larvae emerge and gorge on stem tissue until they’re big enough to pupate into adult billbugs. Then, with the season’s first intense bout of heat, the damaged plant can’t get enough water, so it browns and dies.

By comparison, the warm-season and transition-zone billbugs — predominantly hunting billbugs, but also lesser and unequal billbugs — can overwinter as both adults and larvae, depending on the soil temperature and proximity to the transition zone. Overwintered hunting billbug larvae emerge early in the spring to do damage, and adult billbugs spawn a new generation of larvae later into the summer. This generational overlap is responsible for confusion and misdiagnosis among LCOs managing warm-season turf, such as zoysiagrass.

“When you get a certain soil temperature — 55 to 60 degrees F — the billbug larvae start to get active and feed on the crowns … which means you now have crown damage opportunities before the turf has even broke dormancy,” says Fletcher. 

Scouting for billbugs

Both bluegrass and hunting billbug life cycles follow a seasonal calendar of sorts. Therefore, historical data on emergence and treatment help LCOs make accurate diagnoses. 

“While you can base (diagnosis and treatment) on a calendar, it probably needs to be a loose association knowing there are additional factors — growing-degree day units and thresholds — that can help guide LCOs for when they need to go out and start scouting,” Giese says.

As part of this scouting strategy, Giese recommends a pitfall trap — a disposable cup buried flush in the turf. After a few days, adult billbugs will fall into the cup and can’t get out. 

If you have a history of billbugs in your turf, you can monitor how many adults you find,” he adds. “If you’re not finding very many, then maybe there are not that many there, or they’re just not active yet.” 

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