Small Grains Disease & Insect Update 07/08/2019
The risk assessment models for FHB continues to show a near continuous high risk for FHB in all of Minnesota but the northern half of Polk County and the counties of Marshall and Kittson and the eastern beach ridge of the Red River Valley between Thief River Falls and Fergus Falls. Like last week’s update – much of the difference in risk can be explained by overall drier conditions in those areas.
Aphids, meanwhile, have reached the Canadian border. Scout later seeded spring wheat for aphids and treat fields if the threshold of 80% of the stems having one or more aphids is exceeded prior to heading.
Because of the aforementioned drier conditions in Polk, Marshall, and Kittson counties, grasshopper counts are also on the rise. The threshold to treat field margins is 30 nymphs or 20 adults per square yard. Check not just the field perimeter if the wheat was no-till seeded into standing soybean stubble. A threshold of 8 to 14 adults per square yard is used inside the field to start control.
I also found some armyworm larvae in my yard that were quite happy and growing. Check headlands and lodged areas in the field for feeding damage first and treat when 5 or more larvae are present per square foot. If the migrations were smaller and localized, you, again, may only need to treat field margins rather than whole fields.
Finally, this hot, humid weather is pushing the development of the wheat. Having some cooler night not only would lower the risk of FHB but also greatly help preserve the yield potential of this year’s crop.
Source: University of Minnesota Extension: Minnesota Crop News