Thursday, May 31, 2012

Oat and Necrotic Leaf Tips and Margins

When I was out scouting early this week I noticed that many of my oat plots where showing necrosis on the leaf tips and margins (please see below image). I can honestly say I did not give it much thought as I had soybeans to spray. By Wednesday however my email, text, and phone where all buzzing about this consistent and widespread oat issue so I started to do some digging. If you look closely at the below picture you could easily write this crop injury off to our unpredictable spring environment and/or barley yellow dwarf virus (bydv). However after speaking with John Mochon who is the project manager in the oat breeding program and Scott Chapman in entomology they both vividly remember the tremendous influx of aster leaf hoppers (ALH) that arrived in early May. A follow-up conversation with Russ Groves in Entomology confirms that we experienced one the highest ALH influxes in the past decade.  Furthermore, Randy Van Haren, with Pest Pros Inc., has performed qPCR assays on populations in the Central Sands in the past 3-4 weeks with infectivity rates as high as 10-12% which is very high for this pathogen. Since I have never dealt with ALH I found a good article written by Janet J. Knodel at NDSU. She wrote "Aster leaf hoppers feed on plant sap and vector aster yellows, a phytoplasma disease that presents like BYDV. Disease symptoms will appear in 2-3 weeks (which fits with our timeline). Plants infected earlier in crop development are more susceptible to yield loss than mature crops. For example, wheat infected with aster yellows at the seedling stage will not produce kernels due to stunting. A heavy infestation of aster leafhoppers in the field also will increase the incidence of aster yellows." Limited information exists about the susceptibility of grain crops (e.g. oats and wheat) to infection of the aster yellows phytoplasma (AYp).  Work includes oat susceptibility to AYp of Chiykowski and Wolynetz 1981, Can J. Plant Path.  And most recently Hollingworth et al. 2008 ( Over the next few days I will be collecting samples and working with Russ Groves to confirm if this is the potential culprit. Stay tuned... 

Article co-authored with Russ Groves, UW Entomology.

Thursday, May 24, 2012

Fusarium Head Blight Risk Remains Low

The risk window for Fusarium Head Blight infection is rapidly closing as wheat across the state progresses through flowering. Lack of rainfall and low humidity has kept the risk level for infection low statewide (Image 1). A few pockets may still present themselves but for the most part if the model is accurate (which it has shown to be over the last few years) we should have a relatively scab free year. 

Image 1.  Fusarium Head Blight Assessment Tool Risk Map on 5/24/2012.

In scouting our Arlington wheat plots in preparation for this blog article I noted a few varieties showing significant stripe rust incidence and severity (Image 2). This pathogen has been prevalent in the southern U.S.  and was expected at some point.
 Image 2. Stripe rust on wheat in WI.