News from the Farm: Time to spray wheat?

by | March 31, 2014 4:37 pm

by MARK CROSBY, Emanuel County Extension Coordinator

 Wheat producers here in Emanuel County will have to make some hard decisions very soon concerning their wheat crop. The flag leaf is out in most fields, and head emergence will soon begin. Flag leaf emergence through full head emergence is an important time for wheat because this is the time that farmers must make a decision about a fungicide application. 

   Making a determination of whether or not to apply a fungicide to wheat is based on several factors. The first major factor to consider is how the wheat was managed. How much seed was planted and how much fertilizer was applied to the soil are both important factors to consider. These two factors have a major impact on the number of tillers that the plant is sending up, the closeness of the heads, and the total leaf area. 

   The next area of consideration is moisture. So far this year, rainfall has been very high, with high humidity and leaves staying very wet for long periods of time. The longer the leaves stay wet, they are more susceptible to certain diseases. 

   Another area of consideration is the type of disease (if any) that is present. So far, I have only found powdery mildew in the wheat fields that I have walked. This doesn’t mean that there are not other diseases present. It also does not mean that there will not be late season diseases such as Rust and Septoria to attack the plants. 

   Powdery mildew has been attacking wheat in the lower parts of the plant. Now as the stems are elongating, powdery mildew is moving up the plant. Powdery mildew can be easily seen in many fields by looking at the leaves in the bottom of the plant. Powdery mildew fungus (spores) looks like patches of grey cotton candy on the lower leaves. On the upper leaves, powdery mildew can be seen by holding a leaf up towards the sun and looking for yellow specks on the leaves. 

   Powdery mildew is tough this year on some non-resistant wheat varieties because it thrives when the temperature is between 60 and 72 degrees and the relative humidity is above 85 percent. But keep in mind that as the temperature consistently exceed 75 degrees and the relative humidity falls below 85 percent, powdery mildew will tend to become less and less of a problem.

   Leaf rust has been identified in fields in surrounding counties, but I have yet to find any. Common leaf rust thrives when the temperatures average 50 to 60 degrees. Heavy dews and rainfall during these periods will accelerate the spread. Infections tend to cease when temperatures are consistently over 71 to 73 degrees. 

   Wheat farmers know that the flag leaf must be protected because the flag leaf produces 80 to 90 percent of the energy needed to fill out the grain head. And the time to decide on a fungicide program to protect the flag leaf is almost here. Some products must be applied after flag leaf emergence yet prior to head emergence. Others can be applied after head emergence. The deciding factor is if there is an active disease in the field when the flag leaves are emerging. 

   The final area to consider is yield. A wheat field needs to have a 50 bushel or more yield potential to warrant a fungicide spray. This does not say that diseases are only attacking high yielding wheat, but that a field with 50 bushels or more potential has a better chance of making the farmer money or at least returning the cost of the fungicide and the application. 

   There are several excellent fungicides available to protect the flag leaf from powdery mildew and future diseases. Chemicals and their rates can be obtained by calling the Emanuel County Extension Service at 237-1226. 

   Walking the fields during the next week to judge yield potential and disease pressure will be important. For more information on these and other topics of interest call Mark Crosby at 237-1226 or drop by the Emanuel County Extension Service Office on North Anderson Drive.

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