The two weather systems that brought some measurable precipitation across much of Northwest Minnesota at the end of the week allowed the risk for tan spot and leaf rust to increase to 'likely' for two consecutive mornings. And as soon as the soil surface dried up, so evaporated the risks of any initial infections of tan spot and leaf rust.
The immediate forecast does not look promising for any measurable and widespread precipitation. 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 end of this week. Likewise, the risk for tan spot, leaf rust, and Septoria to develop will also remain low.
Fungicides do not alleviate drought stress nor can they increase yield, fungicide can only preserve the yield potential that was there. As the yield potential dwindles because of drought stress so will be the portion that can be saved with a fungicide should diseases have a chance to reach economically damaging levels yet. After all, 5% of 80 bushels is not the same as 5% of 30 bushels.
This will mean that the decision to apply a fungicide to suppress FHB and control the leaf disease will become even more difficult as the drought stress in individuals fields intensifies. The decision to consider a fungicide is now in part guided by whether the crop has still yield potential left.
This week's weather and the extended forecast are - other than the lack of precipitation - actually almost ideal for small grains. The decision to consider a fungicide at all, therefore, will be truly on a field-by-field basis and based on the yield potential that is left. That in turn is at this moment driven by how much moisture reserves are left in the soil profile to give the crop a fighting chance. The color of the crop, rather than the height, during the heat of the day, is very telling in this case: As long as you do not see that blue hue, the crop still has its toes in the water.
Meanwhile, I do ask you to continue scout for aphids as their numbers are likely to increase with the current conditions. Apply an insecticide as soon you find one or more aphids on 80% of the individual stems across the field. Do not apply an insecticide after the crop reaches anthesis.
--Jochum Wiersma, Small Grains Specialist, University of Minnesota