University of Maryland Extension

Early Season Scouting For Wheat Diseases

Author: 
Andrew Kness
wheat field at green up
By Andrew Kness, Agriculture Extension Agent
University of Maryland Extension, Harford County
 

Spring is a busy time on the farm that demands a lot of different tasks; one of the tasks that can be overlooked is scouting your small grains now for the presence of diseases. For a few select diseases, scouting now could pay off later in the season.

Most of the wheat in Maryland is somewhere between Feekes 5 (green up) and Feekes 6 (jointing), and most has received its first shot of nitrogen. This is the perfect time to scout your fields for foliar diseases like powdery mildew and the leaf blotch complex diseases.

Powdery mildew growth on a wheat plant
Figure 1Powdery mildew growth on lower leaves/stems of a wheat plant (red arrow). Image: Mary Burrows, Montana State University, Bugwood.org.
 

Powdery mildew (Figure 1) is one of the more common diseases of wheat in our region and it’s important to keep tabs on it early in the growing season. The fungus that causes powdery typically colonizes wheat in the fall when the plants are small, then goes dormant inside the plant over the winter. Green up is the perfect time to scout for powdery mildew because you will be able to see the powdery white tufts of fungus growing on your wheat plants (Figure 1). These signs are typically observed close to the crown deeper in the canopy and/or on plants that are in double-planted pinch rows or headlands. The disease is often more severe on over-fertilized fields, too. It is good to scout for the presence of powdery mildew now, but do not treat until the wheat begins to joint. Powdery mildew will not begin actively growing until the wheat plant comes out of its winter slumber and begins rapid growth (jointing, Feekes 6), and fungicides have little to no activity on dormant fungi, especially the DMIs. Instead, hold off on a fungicide application until your second nitrogen application at jointing. If you only notice a few sporadic instances of powdery mildew now, you may not even need to treat at jointing, especially if weather conditions are dry and hot (powdery mildew requires moist, humid, and mild temperature conditions to grow). If you decide to hold of on a Feekes 6 application, you’ll still want to keep an eye on it, especially as the flag leaf emerges. The top three leaves, especially the flag leaf, contributes to nearly all of your yield.

Also, know your wheat variety because there are significant differences in resistance and tolerance. Data from University of MarylandUniversity of Delaware, and Virginia Tech can help you determine your wheat’s susceptibility. In addition, varieties containing the pm6 resistance gene have broken down and are no longer providing adequate resistance here in the mid-Atlantic region, so consider those varieties susceptible.

Similar management should be taken against the leaf blotch complex diseases. If you find them now, hold off on a fungicide application (if at all) until at least Feekes 6. And again, protecting the flag leaf is your main priority, so if the disease is slow to progress due to inadequate weather conditions or host tolerance and the disease is present at low levels, then a fungicide application at Feekes 6 may not be warranted at all. Also, the fungicides we commonly use to manage Fusarium head blight/head scab (DMI, group 3) will also work on powdery mildew and the leaf blotch complex; so our fungicide applications at early flowering typically do a good job at keeping these diseases from progressing to the flag leaf. However, if you see these foliar diseases creeping up closer to the flag leaf prior to head emergence and flowering, then you may want to consider an additional early fungicide application other than your flowering application to manage head scab.

Another factor to consider when using additional fungicide applications is cost. Recent research in Delaware found that a two pass program at Feekes 6 and 10.5.1 did not yield a return on investment until wheat prices exceeded $5.00/bu.

For help with identifying diseases on wheat, you can send samples to the University of Maryland Plant Diagnostic Lab, or call your local Extension Agent.

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