As wheat flowers across the state, and rain in the forecast this weekend, concern for fusarium head blight or scab rises. This fungal disease of small grains poses a significant threat to grain quality, causing reduced grain test weight and contamination with vomitoxin or DON. Spikelets of infected plants will prematurely die and become bleached or straw-colored after flower initiation. Residue from corn and small grain crops is the main source of fungal spores (inoculum). These spores are wind and rain-dispersed to open flowers and will then germinate and grow in developing wheat kernels. In a susceptible variety, the fungus will continue to grow and infect the remaining head and produce vomitoxin if weather conditions favor disease development. Infection risk is highest when warm, wet, and humid weather occurs during flowering. 

So, how do we manage scab and avoid quality loss? 

The first step is to select a resistant variety. Though no variety is 100% resistant to fusarium head blight, many moderately resistant varieties are available. Visit the Ohio Wheat Performance Trials website at go.osu.edu/wheattrials to view head scab resistance rankings for tested varieties. 

Infection potential is further lowered by crop rotation and residue management. The fungus that causes scab also causes Gibberella stalk and/or ear rot in corn. That is why the risk of fusarium head blight is higher when planting wheat following corn. Though the fungus can also infect soybean and cause seed rot and damping off, it is still preferred to plant wheat after soybean than corn or another small grain crop. Both crop rotation and residue management will lower inoculum levels. 

When infection risk is high, a fungicide application at early flowering can reduce vomitoxin and manage scab. Not all fungicides are effective, and strobilurins are associated with higher vomitoxin levels. Select a demethylation inhibitor (DMI) that belongs to the Fungicide Resistance Action Committee (FRAC) Group 3. Keep in mind efficacy varies between products in this group. You can find multi-state field trial results evaluating fungicide efficacy at go.osu.edu/wheatfungicideeval. Always read and follow the label when applying a fungicide. Unlike foliar diseases, a fungicide should be applied to manage scab before symptoms appear. Aim to apply a fungicide at early flowering stage or when the yellow anthers (flowers) are visible. Recent work from State Specialist Dr. Pierce Paul has shown that a late fungicide application (4 to 6 days after recommended timing) can still offer good control if rain delays occur. When making a fungicide decision, use the Fusarium Risk Tool developed by Dr. Pierce Paul in partnership with the U.S. Wheat & Barley Scab Initiative at wheatscab.psu.edu. This tool will factor location, weather conditions, and variety resistance level to estimate the risk of scab occurring. Fungicide use alone though, cannot provide adequate disease and vomitoxin control and needs to be part of an integrated management plan.