Sawfly infestation threatens some panhandle wheat fields

Nebraska farmers who've been dealing with drought for the past few years now have a new pest new pest to worry about.

Wheat stem sawfly is a small wasp that lays eggs in the growing plant. The sawfly's feeding reduces crop yield, but the real damage is done when the larva scores a line in the stem. When this happens, wind can easily knock flatten damaged crop, an event called lodging. Once the wheat is knocked over, combines generally skim over the grain, without picking it up.

"It's been a growing problem in the last three years," said Jeff Bradshaw entomologist at Panhandle Research and Extension Center.

Quite a few farmers in the panhandle area remain unaware of the sawfly's presence, blaming the rate of lodging on weak stems.

"It's becoming more and more of a problem," said Karen DeBoer extension educator at the University of Nebraska Lincoln extension in Cheyenne County.

Sawfly was an issue in this area during the 1980s in spring wheat, but then it shifted to winter wheat in Montana and has steadily been moving south and east ever since. It's now a problem all through the panhandle and in northeastern Colorado.

In the panhandle, sawfly is most problematic in Scotts Bluff, Banner and Morrill Counties, but is present throughout the region.

"You can find it in any county in the panhandle," Bradshaw pointed out.

Scientists aren't entirely certain what causes the spread of sawfly. Reduced tillage because of new farming practices is probably a contributing factor as well as fallow wheat systems.

"I wouldn't recommend tillage as a solution," Bradshaw said.

Any practice that conserves the sawfly habitat could contribute to its survival and potential to thrive.

However, Bradshaw warned, “There certainly are conventional tillage systems that have sawfly," Bradshaw said.

Although the sawfly isn't a strong flier, its prominence in this area is becoming an issue.

"I think we've reached a threshold," Bradshaw said. "It's becoming a much bigger problem."

At this point there are no effective insecticides to kill sawfly.

"Unfortunately, this is a very difficult insect to deal with," Bradshaw said.

The adults don't feed, so ingestible insecticide isn't an effective option. Because the insect emerges over a three to four week period, no ready timetable exists to spread chemicals. The larvae are also difficult to kill, as they emerge inside the stem of wheat.

The most popular strains of wheat are hollow stemmed, but hard stemmed versions could be an option to attempt to quell the spread of this insect. These strains are more difficult for the sawfly to cut through, but also produce a lower yield than most common grains. One option might be to plant hard stemmed wheat just around the periphery of fields.

Bradshaw also suggests crop rotation as a possible solution. Crops that don't host sawfly include barley or dry peas—although he admits that there's not a large market for barley in Nebraska.

Another option is to use a floating head combine which is able to pick up wheat lower to the ground. But this system can't be used in rocky areas and can also be very pricey.

"Those options are not ideal," Bradshaw said.

Currently, Bradshaw is working on a research project which will last at least two years and is funded by the Nebraska Wheat Board and the Agriculture Research Division of the University of Nebraska.

During his study, Bradshaw will strive to understand the contributing factors to the sawfly problem. The study will look at current production practices and overlay them with a map of infestations. This will help Bradshaw determine which farming practices are most sawfly-friendly.

"There isn't a perfect solution at this point," Bradshaw said.

It would be ideal to find genes in the wheat which hold some sort of resistance to sawfly. Scientists think that they're dealing with one species of sawfly in the great plains, but there are different species, and they can't be sure.

"It's a tricky beast to work around," Bradshaw said.

Sawfly apparently hasn't spread to Kansas. Bradshaw believes that the problem would get more attention if it was affecting the huge amount of wheat growing in that state.

Although this insect has only been a problem in this area since around 2010, Sawfly has been in the United States for a long time. Some of Bradshaw's colleagues have been working to understand the sawfly for their entire careers.

"It does intimidate me a little bit," Bradshaw said.

He's still hopeful that his research will yield some positive results.

"We'll know more in two more years," he continued.

His organization has been doing a survey for the past three years using 30 wheat producers with 30 separate fields. Participants in the study collect wheat stems and send them into the lab where workers document the rates of cutting and infestation from sawfly.

"The majority of fields we sampled have a greater than 20 percent infestation," Bradshaw said.

DeBoer thinks that there could be a significant number of Sidney area farmers who don't know much about sawfly.

"It's somewhat of a new pest in our area," she said.

She's learned out about infestations in Cheyenne County through conversations with nearby farmers. Sometimes they don't realize that there's a problem until this time of year, closer to harvest when the wheat looks like it's been sheared off with a razor blade.

"I'm trying to make a bigger effort to educate people," Bradshaw said.