UNL researchers study damaging wheat curl mite

Winter wheat has been harvested, but the threat of crop destruction has not gone away. The enemy farmers face even after the combines are parked is so tiny that a microscope must be used to see it.

The wheat curl mite itself does not kill a plant. Rather, a virus often carried by the mite, known as wheat streak mosaic virus, can infect a field.

Infected crops can be identified by mottling and light green streaks, which eventually give way to blotches that leave a mosaic pattern.

Justin McMechan from the University of Nebraska Lincoln Agriculture Laboratory is conducting research on the migration and survival of the mite. McMechan has six field projects dedicated to studying both the mite and its survival through the summer. He has learned that a common spring problem—hail—can lead to the spread of the microscopic intruder.

"Basically we get hail pre-harvest, the grain get shattered from the head and falls to the ground,” McMechan explained. “What happens next determines weather mites are going to be a problem or not. If the wheat germinates prior to the wheat being harvested the mites move from that wheat directly to the new germinating wheat."

The new wheat is a green bridge for the mite, which needs a host to survive. If the mite falls from mature wheat to the soil, its survival rate is around 72 hours. Even if only one female lands on pre-harvest wheat, it can restart the infection.

What type of wheat can be a factor in how mites survive, McMechan said.

"Camelot is a variety that will not germinate easily prior to harvest,” he pointed out. “If I take that head and shred it then spread it on the soil and wait for 21 days, very little will germinate. Pronghorn will germinate at a very high rate even prior to harvest.”

McMechan wants producers to understand the risk factor involved in each type of grain. At the same time, he and his team are trying to determine, if the wheat should be damaged by hail, at what stage it will germinate.

"I am trying to develop for them the relative amount of risk, depending on the stage that their crop is in when hailed," he said.

Farmers must control volunteer wheat that shoots up after harvest. A problem, McMechan pointed out, often begins when producers find volunteer wheat with no infestation. This leads to complacency and puts their field at risk.

Cold weather has no effect on the mites.

"They are really temperature tolerant and they create a environment for themselves,” he said. “They call them the wheat curl mite because they go in to the newly emerging leaf and the feed on a cell that is responsible for the leaf to unfold, keeping it folded, like it is curled."

The key to preventing damage is vigilence and control.

"If I could get all the producers to control all of their pre-harvest wheat I would be out of a job tomorrow," McMechan said.