Small Grains Disease and Pest Update for 06/11/21

Two larger weather systems have brought some measurable precipitation across much of Northwest Minnesota in the past 48 hours, providing at least temporary relief from the drought and heat stress to crop had to endure in recent days.  

The scouts continue to find little to no leaf diseases across Minnesota.  Aphids continue their march north and have now been found up to the Canadian border. Overall a third of the fields have some aphids but  most fields in the survey were below the treatment threshold yet. Aphid numbers about doubled west-central Minnesota and in the southern Red River Valley from a week ago and have or will soon reach the economic threshold. Likewise, grasshoppers numbers are creeping higher across the whole state.

The disease risk model Fusarium head blight remained low over the past few days and is almost certain to remain low until at least the middle of next week (see in the paragraph below why).  The risk for tan spot, leaf rust, and Septoria is likely to increase as the combination of rain and higher dew point will mean that we will start getting some early morning dews, and thus leaf wetness periods that are long enough for initial infections to take occur.

The earliest spring wheat fields across the state and the winter wheat in northwest Minnesota are starting to head.  The decision to apply a fungicide to suppress FHB and control the leaf disease will be difficult for the fields that are heading over the weekend. Leaf diseases are absent in most fields, especially if they received a fungicide at Feekes 5. The risk of initial infections will increase but it takes 2 to 3 disease cycles for these diseases to reach damaging levels. The very dry conditions and lack of any moisture in the topsoil until just yesterday or this morning across much of Northwest Minnesota have meant that Fusarium graminearum has not had an opportunity to produce perithecia which in turn produce the ascospores that can infect the crop. This means that there will likely be no initial infections of FHB when the crop is most vulnerable to yield and quality losses, whilst the crop itself fought through a week of record-breaking heat and substantive drought stress.