HPAL sawfly research

Justin McMechan, UNL graduate student, discusses research on over-summering hosts at the UNL High Plains Ag Lab field day. The plot in the background contains potential alternative hosts for the wheat curl mite, including pre-harvest wheat, post-harvest wheat, corn, foxtail millet, barnyardgrass, and green foxtail. Mite movement is monitored using trap cones.

Wheat producers hear update on UNL research

SIDNEY – Damage from the wheat streak mosaic virus costs wheat growers a lot of money in western Nebraska and other wheat-growing regions of the High Plains.

How do environmental conditions affect the spread of the virus and the risk of disease? Answering that question is one of the objectives of a U.S. Department of Agriculture grant project that is funding research at the University of Nebraska-Lincoln High Plains Ag Lab (HPAL) near Sidney and other wheat-producing areas.
One of the goals of the USDA grant is improving risk assessment and forecasting for the mite-virus complex in wheat in the Great Plains. Wheat curl mites are a vector for spreading wheat streak mosaic virus and several crop-damaging viruses. Area producers heard updates on some of the field research at the HPAL field day in late June. They also heard updates on how soil conditions might affect next year's crop, which will be planted in a little more than two months.

UNL graduate student Justin McMechan is at HPAL to evaluate the risk of alternative over-summering hosts. McMechan is working on the project with Dr. Gary Hein, UNL entomology professor and director of the Doctor of Plant Health program at UNL's Institute of Agriculture and Natural Resources (IANR). The objective is to determine the risk of alternative hosts as a source for wheat curl mites and viruses, and the impact that hosts have on fall-planted winter wheat. McMechan tracked mite movement on several other alternative host plants, including barnyard grass, foxtail millet, green foxtail and corn.

He told the producers at the field day that volunteer wheat in fields struck by pre-harvest hail has a very high risk of hosting wheat curl mites. The early volunteer wheat provides a "green bridge" for wheat curl mites to survive in the field over the summer. But post-harvest volunteer wheat has a minimal risk.
If a wheat field is struck by hail before harvest, McMechan told the producers at the field day, it's important to kill the volunteer wheat that's left in the field. "It's important to control pre-harvest volunteer wheat," he said.

Hein, who was formerly the entomologist at the UNL Panhandle Research and Extension Center, conducted much research on wheat curl mites at High Plains Ag Lab while he was stationed in the Panhandle.

Post-doctoral research associate Dr. Everlyn Wosula reported on field work she is conducting at HPAL on the effect of planting dates and wheat variety on wheat streak mosaic virus severity. Five wheat varieties, three of them resistant and two susceptible, are being compared across three planting dates – early September, mid-September, and early October. She said virus presence and impacts have been limited by rainy and cool weather in the fall and spring, and infestation techniques need to be improved to provide significant presence of the virus.
Wheat, the major dryland crop in western Nebraska, is always one of the main topics at the HPAL field day.

Dr. Stephen Baenziger, UNL wheat breeding specialist, led a tour of 2014 winter wheat varieties being tested in HPAL plots. The HPAL variety tour was one of several wheat variety tours in the Panhandle.

Dr. Gary Hergert, UNL soil and nutrient management specialist, stressed the importance of soil sampling to determine how much nitrogen fertilizer to apply to next year's crop. At present, there is a good amount of stored moisture in the soil, according to Hergert. Because rain has pushed the moisture down in the soil profile, Hergert said, it will be important to collect samples to a depth of 3 to 4 feet. The soil moisture creates ideal conditions for mineralization, a process in which nitrogen converts from organic forms into ammonium, a form that can be used by growing plants.
Hergert said an Extension Circular, "Fertilizing Winter Wheat" (EC143), has nitrogen recommendations for wheat that take into account factors such as wheat price and nitrogen fertilizer price. "It now looks like 50 to 60 pounds of nitrogen (per acre) will be profitable, based on wheat price, nitrogen price and soil samples," Hergert said.

Elsewhere on the front in the battle between wheat and pests, the wheat stem sawfly continues to impact wheat, with an average infestation rate per field of 30 percent across 27 locations sampled in the Panhandle, according to UNL Entomologist Dr. Jeff Bradshaw. In infested fields, the percentage of plants that lodged (bent over at the stem, close to ground level) varied widely, from 20 percent to 80 percent. Sawfly larvae grow inside wheat plant stems, cutting notches in the stem near the soil level when they are mature. The stems often break at the weakened notch just before harvest. So far this year, sampling of adult wheat stem sawflies has found as many as 260 adult stem sawflies per acre in fields in the Panhandle, according to Bradshaw. He is seeking a USDA grant to do more research this fall.

Some winter wheat varieties appear to have more resistance to sawfly, according to Bradshaw, and they will be examined to see what makes them resistant and whether that gene can be introduced into other lines. The research also will compare hollow stem varieties to solid stem varieties, Bradshaw said.
In response to audience questions, Bradshaw addressed other factors that might affect wheat stem sawfly infestations. Tillage systems might have an effect, the effects of field size are unknown; and regarding crop rotation, some crops grown in the region are known not be sawfly hosts, he said.

Wheat stem sawfly will be one of the production challenges addressed at the Wheat Production Workshop scheduled for Aug. 4 at the Panhandle Research and Extension Center at Scottsbluff. The workshop also will focus on kochia, virus and moisture. Speakers from UNL, U.S. Department of Agriculture and Kansas State University will provide the latest research-based information on challenges facing wheat producers. The Panhandle Center's website at panhandle.unl.edu has more information and contacts. Registration closes July 21.