Head Scab Beginning to Show Up in WI Wheat
Fusarium head blight (scab) was detected this morning (6/17/08) during a routine survey of our winter wheat variety trial located at Lancaster WI. Given the rainfall and temperatures during flowering this was not unexpected. Since the winter wheat head and foliage are still green now would be a good (easier) time to look for head scab in your area. The easiest way to inspect a field is to stand with your back to the sun and look for bleached heads or white spikelets. Once you identify a suspect head look at the base of each spikelet for a salmon color (image 1). Be careful not to confuse head scab with with hail injury or spikelet abortion as seen in Image 2.
Image 1. Head scab in wheat.
Image 2. Hail injury to wheat.
To follow up on Shawn’s posting, two useful references that can help guide assessing the incidence and severity of head scab are:
“A Visual Scale to Estimate Severity of Fusarium Head Blight in Wheat” by Stack and McMullen (http://www.ag.ndsu.edu/pubs/plantsci/smgrains/pp1095w.htm). This includes photos of different levels of head scab severity with varieties that have awns. For a visual example for varieties without awns, the following fact sheet is useful, “Fusarium Head Blight Severity Scale for Winter Wheat”, by Engle et al. (http://ohioline.osu.edu/ac-fact/0049.html).
Some definitions for terms used in those publications:
Average plot (or site) severity = the average severity for all heads that were individually assessed for a severity value, including the 0 values.
Average infected head severity = a conditional value for severity that is based on the average severity for only those heads that were found to be infected.
Incidence of infected heads = the number of heads found to be infected divided by the total number of head assessed.
As noted in the NDSU bulletin, these three measures are interrelated as:
Plot severity = Incidence X Head severity
and this value is often presented as an “index” if you scan various publications on wheat head scab.