Wheat flag leaves infected with stripe rust in a field located near Gobles on May 27, 2016. There are limited numbers of plants with this level of severity in fields, but the number of infected plants is growing.
Wheat flag leaves infected with stripe rust in a field located near Gobles on May 27, 2016. There are limited numbers of plants with this level of severity in fields, but the number of infected plants is growing.

Wheat fields continue to look good across southwest Michigan. However, with the return to wet conditions, high humidity and a threat of rainfall in the forecast, wheat diseases continue to pose an important threat to this rapidly developing crop. Many folks applied fungicides to their wheat to protect the plants from head scab this season. That is good because it looks like we will have almost perfect conditions for fusarium head blight during this flowering period. This is particularly true if you planted wheat in a field that was planted to corn last season. While fusarium head blight is a challenge we face in moist years during flowering and early head development, we have also seen an increase in the incidence of a relatively new pathogen to wheat in our area, stripe rust.

Stripe rust has been reported in many states west of us this spring at higher than normal incidence. Until recently, we have not seen much sign of the pathogen in the southwest Michigan region, although it was reported in several fields in other parts of the state. Now we can find evidence of the disease in many wheat fields in our area as well. The incidence is still quite low, but warrants closer watching because of the high humidity and anticipated extended periods of leaf wetness. While the daytime high temperatures are a little warmer than ideal for the rust pathogen (75-77 degrees Fahrenheit), the evening temperatures are well within the range for rapid development. With cooler temperatures expected with the passing of a cold front through the area by early this week, we could be looking at weather conditions that would be conducive for further development of this disease.

Monitor your fields for incidence of stripe rust. The goal is to keep the upper two to three leaves free from the disease. It is important to monitor fields where you already applied a fungicide to make sure the application is working and the disease is not progressing up the plant canopy. A second application of a fungicide may be warranted if the disease continues to move up the plant. Remember, the fungicides most commonly used on wheat tend to be more protective than curative, so new lesions on previously uninfected leaves or plants are the best indicators of how successful the fungicide was.

Michigan State University Extension wheat educator Martin Nagelkirk provided an excellent overview of the fungicide options available for growers in his May 12 article, “Scout for stripe rust and other wheat diseases now.” Advanced fields of wheat are flowering right now (Feekes Stage 10.5 and beyond), so some materials can no longer be applied to wheat. Also, there are restrictions on the amount of each component fungicide that can be applied to the crop each growing season. Consult the Fungicide Efficacy for Control of Wheat Diseases table or the fungicide labels for more information on fungicide options, growth stages and pre-harvest intervals that need to be observed.