In some of the early flowering wheat fields we are seeing VERY LOW levels of Fusarium head blight (FHB). The worst field I have seen I estimated to about 1% incidence, meaning that 1 out of 100 heads have symptoms of FHB. However, most fields are well below this level and fall under 0.25% incidence, meaning that 2-3 heads per 1000 have symptoms.
It is important that measures are taken to remove the bleached out kernels or “tombstones” even at these low levels. This is because tombstones often have very high levels of DON that can throw off a DON test at the elevator come harvest time. For example, an asymptomatic kernel that is infected with the FHB pathogen after flower may have 1-2 ppm DON. Tombstones may have more than 100ppm DON.
You can imagine that it may take only a couple tombstones to throw off a test, particularly if vacuum probes are used. The best thing you can do for removing tombstones is to increase the fan speed of the combine, thereby removing these kernels from the bin.
Harvesting is also a component of the integrated management approach. In a 2014 paper researchers at THE Ohio State University examined the effects of integrated management practices including cultivar resistance, fungicide use, and harvesting strategy on FHB control.
The study was conducted from 2011 to 2013, and examined the impacts of integrating moderately resistant varieties, fungicides recommended for FHB suppression, and harvesting strategy on disease suppression and economic returns. In terms of harvesting strategy, treatment 1 consisted of fan speed set at 1,375 rpm and a shutter opening of 70mm, whereas treatment 2 consisted of the same fan speed but an opening of 90mm.
Overall, plots harvested with the second harvester configuration (90mm shutter opening) had higher test weights than those for treatment 1. The greatest benefit of the second harvester configuration was realized when a moderately resistant cultivar was combined with a recommended fungicide around the onset of flowering.
Integration of all three practices resulted in a 30-51% reduction in estimated price discount, $51.40-$126.31 dollars per acre increase in gross cash income, and an economic benefit ranging from $12.55- $110.12 dollars per acre depending on the severity of FHB, grain price, and cost of fungicide application. The article, published online in the journal Plant Disease in April, 2014, can be found here: Paper on Economics of harvesting for FHB.