By Nathan Kleczewski
El nino is really making it an interesting winter. On one hand, the excessively warm temperatures have helped produce some really nice wheat and barley stands. On the other hand, the extended warm weather may potentially increase the risk of some diseases. The key to reducing your risk of suffering losses due to these diseases is to stay on top of your fields. Nobody wants to be out scouting in December, but you should continue to do so as long as we are hovering in the 50-60 F range. Weather forecasts are calling for temperatures approaching 70 F next week!
What should you be looking for?
We are seeing powdery mildew popping up in some fields. This disease likes it cool, so unfortunately our recent weather has been ideal for disease development. I normally would not advise an early fungicide application (Feekes 5) but if you notice powdery in your fields now, you could be at risk for severe disease development in the Spring. A cheap triazole (tebuconazole or propiconazole) will do the job. Quilt Xcel has a small grain label allowing a cut rate application at FGS 5. The strobilurin component may provide you with some additional residual control. Avoid pushing nitrogen levels in fields with powdery mildew as this can exacerbate the disease.
Keep an eye on aphid populations. Bird Cherry Oat Aphid, English Grain Aphid, and Greenbugs can vector Barley Yellow Dwarf Virus. Predicting when and where a BYDV outbreak will occur is difficult. However, in 2012 we had a similar warm winter and spring and growers did see some virus in some fields. In general, impacts are greater when the virus is transmitted in the Fall when plants are very young. Typically we do not see the severe strains in our area, which is important to keep in mind. Historically BYDV has not been considered to be a significant disease in Delaware and Maryland, but it is important when you move South to Virginia and Kentucky.
The bottom line is that the more aphids you have now, the more potential there is to see BYDV next season. Although there is no commercially available resistant wheat, varieties do differ significantly in viral tolerance, meaning that symptom expression is less severe or yields are less affected by viral infection. The Virginia Tech Small Grain Program rates their varieties for BYDV tolerance because they have more consistent infestations than we do in DE and MD. Use this information to help you with your variety selections in future years. It is important to have symptomatic plants tested to confirm the virus (Agdia Inc. is one option) because issues such as nutrient deficiencies and other soilborne viruses (Wheat Spindle Streak and Wheat Soilborne Mosaic Virus) can cause similar symptoms. Contact your IPM or Entomology Extension Specialist for aphid control recommendations.
Lastly, other viruses such as Wheat Soilborne Mosaic and Wheat Spindle Streak Virus could be out there. These viruses are derived from the soil and persist in the absence of wheat for many years. If you have fields that tested positive for these viruses you may start to see symptoms expressed under current environmental conditions. Plants typically grow out of symptoms once temperatures start to increase, which makes it hard to determine yield losses. Now or early in the spring are good times to identify symptomatic fields. Always plant varieties with good soilborne virus resistance if you are going to plant wheat into a field with a history of either virus.
Lastly several growers are playing around with Fall applications of fungicides. Keep in mind that we do have powdery mildew out there, so if you see differences next season it may not be do to purported “plant health” benefits but rather to suppression of powdery mildew at this point in time. The best way to determine if disease suppression is involved is to assess your untreated checks for powdery mildew now and compare this to the treated areas (I know you all include those right?).