Small Grains Disease and Pest Update 06/14/24

This week's drier weather has been great for small grains and many, including us, have had an opportunity to catch up on their weed control programs. Winter wheat and winter rye are well into grain fill in southern Minnesota and are either approaching or have reached anthesis in the Red River Valley. The earliest seeded spring wheat in south and west central Minnesota has or will be heading soon while it is reaching the flag leaf stage in the Red River Valley.

Symptoms of BYDV have become more pronounced in those same winter wheat trials now that the crop is fully headed and approaching anthesis (Photo 1). Incidence is low and predictably patchy throughout the trial with here and there one or two symptomatic plants. 

 The low dew points have resulted in a low risk for FHB,  the Septoria complex, and leaf rust for much of the state since last weekend.  Next week's forecast suggests that frequent rains will return across much of the state while temperatures are predicted to be about the same. 

This will likely mean that the tan spot model will indicate a risk of infection most days.  The risk for initial infections of stripe rust will closely mirror that of tan spot.  Continue to scout for both these diseases to determine whether a fungicide application is warranted if you have not completed your weed control program yet or whether that decision can be delayed to either an application Feekes 9 (Flag fully extended ) or the application at Feekes 10.51 (Beginning of anthesis). Spraying a fungicide in the absence of either disease will provide no future control as younger leaves will not be protected.

I expect the risk of initial infections for the Septoria complex, leaf rust, and even FHB to remain relatively low, largely because the daytime highs and nighttime lows are a bit cooler than these diseases like it, even if leaf wetness periods will be longer. If your winter wheat or spring wheat reaches anthesis this weekend, consider a fungicide to suppress FHB only when you meet the following criteria; 1) you also found tan spot, stripe rust, leaf rust, or one of the three Septoria diseases in the middle or higher parts the canopy and 2) are growing a variety that has a rating worse than a 4 for any of those diseases.

The scouts completed their second week and found more of the same on their routes this week; low numbers of grasshoppers in field margins of half the fields that they scouted and very low numbers of aphids in a third of the fields across the state. Cereal leaf beetle was confirmed for a second year in two fields in Norman County.  The scouts reported tan spot in just two fields and no incidence of stripe rust or leaf rust.  To date, stripe rust has only been confirmed on the St. Paul campus and leaf rust was detected in one plot in one of the winter wheat trials at the Northwest Research & Outreach Center.