Head scab risk low, but stripe rust showing up
click image to zoom Most of the wheat in the state is now at the early grain fill stage of development. The last three weeks, during the time most of the wheat reached anthesis (flowering), conditions were cool and dry. This has kept the risk for head scab low across the state. However, cool conditions are favorable for other diseases such as rust, and there have been reports of strip rust in some fields.
Three different types of rust, stem, stripe, and leaf rust, affect wheat. Of there, leaf rust is the most common in Ohio. However, so far this season, the level of leaf rust has been very low, but stripe rust is developing in some fields. There is a very clear difference in variety reaction to this disease. Only field planted with highly susceptible varieties are being affected. Unlike leaf rust, which prefers warmer conditions, optimum of 68 to 77F, stripe rust develops best under cool conditions (optimum between 46 and 59F), similar to those we have experienced over the last few weeks.
Symptoms of stripe rust are very characteristic and can be easily distinguished from leaf rust, especially when they occur side-by-side on the same leaf. Pustules of leaf rust are round or slightly elongated and are commonly scattered on the leaf. Pustules of stripe rust, on the other hand, are small and round and usually occur in groups, forming stripes on the leaf surface, hence the name, stripe rust. In addition, leaf rust pustules are brown, whereas those of stripe rust are yellowish-orange.
Occurring this early during grain fill, stripe rust may still affect yield if high levels develop on the flag leaf. However, the warm, dry weather forecasted for the next few weeks will likely slow this disease down considerably. Scout fields for stripe rust; there still may be time to apply a fungicide to fields planted with susceptible varieties. Read fungicide labels carefully and pay attention to pre-harvest intervals before making a decision to apply a fungicide.