The 2010 wheat harvest has finished and, as we plan for the 2010-2011 season, let us take a quick look back and learn from this past crop. We had everything this year — head scab and vomitoxin, Stagonospora leaf and glume blotch, powdery mildew, leaf rust, head smut, cereal leaf beetle, plus a very hot late-spring-early-summer. The big problem this year was head scab and vomitoxin, with incidence ranging from 3% to 60% and vomitoxin from less than 1 to 18 parts per million (ppm). Both Stagonospora and powdery mildew were also very severe, with a severity score of 7 out of 10 this year. Diseases combined with a short grain fill period resulted in low to moderate yield and grain quality, with average yield ranging from 40 to 90 bushels per acre and test weight from 45 to 60 pounds per bushel.
The good news is rarely did we see all of the disease problems in the same fields. As is usually the case, some fields still escaped most of these problems. This is largely because those fields were either planted with resistant varieties, were planted after soybean, treated with a fungicide at the right time, flowered before or after the rains, or various combinations of the above.
Even in areas where the scab levels were high, some of the fields with the lowest levels of vomitoxin, highest yields and test weights were those that received a fungicide application at flowering. However, vomitoxin levels were still higher than 3 ppm in some of the treated fields. Similarly, fields treated for Stagonospora also had better grain yield and quality than fields left untreated. Combining variety resistance with fungicides added a few more bushels to yield and pounds to test weight. Another positive from this season was the fact that the scab forecasting system did a good job of alerting us about the risk of scab. We did have more scab in 2010 than we had in 2009 and the risk tool clearly indicated that was going to be the case.
As we plan for the 2010-2011 crop, here are a few things to consider from a disease standpoint. We will almost always get some powdery mildew. If it is wet and humid during the early and middle portions of the season, we will certainly see Stagonospora and Septoria leaf blotch. If it is wet and humid during flowering we will more than likely see head scab.
The scab forecasting system will help us to detect this risk early, and generally when there is a high risk for scab, Stagonosora glume blotch tends to be high also. Foliar diseases can be managed effectively with resistance or with a well-timed fungicide application if the variety is susceptible, with as high as 90% control.
Resistance must be combined with a fungicide application at flowering to achieve the best results in terms of scab and vomitoxin control. Since it is almost impossible to find a variety that is resistant to scab, Stagonospora, powdery mildew, and rust, and still yield well, we would suggest that priority be given to scab resistance if you cannot find a variety that is resistant to multiple diseases. Be prepared to use a fungicide to manage other diseases if the weather conditions become favorable. In fact, planting resistant varieties with different flowering dates (maturity) will almost certainly reduce the chance of your entire field being affected by a disease, even if the weather becomes favorable.
What did we learn from 2010? Disease management needs to be one of the top things on our list if we are going to have a great wheat crop. In any given season, if the weather conditions are favorable, diseases can take a bite out of both yield and quality of even our highest-yielding varieties. In 2010, the more aggressive managers had the better wheat. Some folks were just lucky, but in general, those who had resistant varieties planted and applied a fungicide at the right time, saw better yields, test weights, and had lower levels of vomitoxin. We need to start right this fall by choosing resistant varieties, especially to head scab, as we plan for our next wheat crop.