Fusarium Head Blight Risk
The risk for Fusarium head blight remains moderate to high for highly susceptible varieties for most of Minnesota through the coming weekend (Figure 1). The marked difference in the risk of infection between highly susceptible and moderately resistant varieties remains the same (Figure 2).
Figure 1. Fusarium head blight risk for very susceptible varieties for July 9 through 12. Darker orange indicates moderate risk and red indicates high risk.
Figure 2. Fusarium head blight risk for moderately resistant varieties for July 9 through 12. Darker orange indicates moderate risk and red indicates high risk.
Harvest Management
It isn't hard to find scab in the University of Minnesota spring wheat and barley variety trials across the Red River Valley that were seeded in the second half of April. It's a bit too early yet to see symptoms of infection in the yield trials trials that were seeded in May.
None of these trials are sprayed with a fungicide to suppress Fusarium head blight and are therefore a worst-case scenario. However, at this point in time, the incidence and severity are high enough already that I have to dust off some old blog posts on how to best approach harvest and improve the odds that you have grain to sell that will be accepted by your local elevator.
First - Scout your fields about 3 weeks after your last fungicide to get an idea of how high the incidence of the disease is. To get an accurate estimate of the level of disease I ask that you grab 10 heads at random in 5 to 10 spots in the field and count the number of spikelets that have a bleached appearance as a percentage of the total number of spikelets. That percentage correlates reasonably well with the yield loss caused by the disease. The correlation with the amount of deoxynivalenol (DON) in the grain is less robust but for simplicity's sake assume that 1% incidence in the field is equal to 1 ppm of DON in the harvested grain if nothing is done to reduce the number of visually scabby kernels in the grain.
Second - Develop a harvest and grain storage plan in which your goal is to limit the amount of comingling of fields/varieties with a high incidence of scab and fields/varieties with lower or no incidence of scab.
Third - Early infections cause the highest yield losses and produce proportionally the highest amount of DON. Fortunately, these early infections produce the shriveled, chalky-white tombstone kernels. These kernels can readily be removed from the sound grain during combining by adjusting the fan speed and the amount of grain on the return auger. Your goal should be to avoid any of the tombstone kernels ending up in the grain tank on the combine. Your harvest losses will be higher but you disproportionally reduce the amount of DON in the harvested grain (henceforth the less robust correlation between the incidence of the disease and DON concentrations in the harvested grain).
Fourth - Use a Kwik Kleen or similar grain cleaner to remove any whitecaps and other non-grain wheat material (pieces of rachis) from the harvested grain either before putting the grain in the bin or before delivering the grain to your local elevator. These non-grain plant parts can all contain DON and so will the grain dust that is generated from these plant parts. Removing some or all will further help lower the DON content when testing the grain.
Late infections are much more cumbersome to deal with. The yield losses are much smaller as late infections do not result in the shriveled, chalky-white tombstone kernels. Instead, a relatively sound-looking kernel will contain enough DON to bring the grain above the 2 ppm FDA limit for whole grain when delivering the grain to the elevator.
Let's collectively keep our fingers crossed that, on the 30th anniversary of the 1994 FHB epidemic which made us realize that the previous year's epidemic wasn't just a fluke, this isn't that.
In Other News
A couple of instances of damaging numbers of armyworms have been found along the eastern beach ridge of the Red River Valley. Scout for feeding damage, especially in lodged grain, first to determine if you have army worm problem.
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