Small Grains Disease and Pest Update 07/01/24

Fusarium Head Blight Risk

Fusarium head blight risk for spring wheat varieties with a rating of 6 or worse will be moderate to high across all of Minnesota through the end of the week  (Figure 1). A marked difference in the risk of infection exists between highly susceptible and moderately resistant varieties (Figure 2).

Figure 1. Fusarium head blight risk for very susceptible varieties for July 1 through 4. Darker orange indicates moderate risk and red indicates high risk.

Figure 2. Fusarium head blight risk for moderately resistant varieties for July 1 through 4. Darker orange indicates moderate risk and red indicates high risk.

One or Two Fungicide Applications to Suppress FHB?

The continued wet weather has some of you wondering whether a second application of a fungicide to suppress FHB is warranted.  Dr. Andrew Friskop,  as part of one of the US Wheat & Barley Scab Initiative Coordinated Projects, evaluated the two-application strategy against the standard single application at the optimum timing of Feekes 10.51 in spring wheat and Feekes 10.5 in barley.  You can find a summary of the results in the June 27th edition of the NDSU Crop & Pest Report here.  The bottom line is that two timings didn't improve control of the disease when overall disease pressure was relatively low.  The same study was also conducted in other states where disease pressure was generally higher than in North Dakota these past two years. In the combined analysis across years and locations, the sequential applications of Miravis Ace at anthesis followed by Prosaro Pro or Sphaerex 4 to 6 days later showed significantly lower mean FHB incidence and DON contamination of grain than all single-treatment fungicide application programs. 

Photo 1. A stripe infection in spring wheat with the tell-tale parallel rows of orange pustules along the leaf blade's veins that are actively sporulating (Photo courtesy of Ryan Casacan).

Insect Pest 

The scouts also continue to find grasshoppers on field edges in nearly every field and aphids in about a quarter of the fields.  The numbers in all cases were below the respective economic thresholds. Cereal leaf beetle (CLB) was found in fields in Red Lake, Norman, and Pennington counties. CLB feeding generally is restricted to the flag leaf once it has emerged. The number of larvae in each field where they were found, exceeded the threshold of one or more eggs and/or larvae per plant. Insecticide applications should be delayed until 25 percent of the eggs have hatched and larvae have emerged because the insecticide is targeted toward the larvae.

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