Two diseases are particularly impacted by winter temperatures – stripe rust and eyespot (strawbreaker foot rot). Low temperatures are less favorable to both diseases, but for different reasons. For stripe rust, fall infection of winter wheat allows the stripe rust fungus to survive the winter; very low temperatures reduce survival of the rust fungus in infected plants, but the temperatures needed for this are in the single digits and negative numbers with no snow cover.
For eyespot, the most important time for infection is also during the fall – October to December – when it’s raining. Low temperatures during winter prevents new infections from occurring and slows disease spread in already infected plants; any temperatures below freezing with no snow cover will suffice.
Last month I discussed Dr. Chen’s first stripe rust prediction of the season (published January 3) and although it was good news because there wasn’t much rust around, I also mentioned that we would know more in March since his rust survival models are based on temperatures from December through February. Consequently, the very mild temperatures during January and February have not only allowed the rust to survive, but to begin growing again in areas with very mild temperatures.