I wanted send out a brief update on corn disease progress as of the end of June. We are scouting fields regularly now and with storms blowing into the state from south and west, a number of corn leaves where Southern rust was suspected have been brought to the lab here in Jackson.To date we have not confirmed any Southern rust in the state, however Gray Leaf Spot and common rust are becoming easier to find. Common rust does not require treatment, and usually produces darker pustules ‘common to both sides of the leaf’. Dr. Kelly posted an excellent article recently on this Blog on identifying common versus Southern rust.
What do do? Monitor Southern rust progress by checking the national IPM Pipe website found at https://www.ipmpipe.org/ which is updated regularly. As you can see from the latest map, there are positive finds in southeast Arkansas and upper northwest Mississippi as of today’s date. If grower fields are in the pathway of storm systems that are traveling from Southern rust ‘hot spots’, scout fields for the next few weeks and treat only if needed.
We typically don’t treat the majority of our dryland corn acres for Southern rust. However, a fungicide application may be needed where Southern rust has been confirmed in the field, conditions are optimal for widespread disease development and corn is pre-tassel or within a few weeks after silking. Corn that has reached the early dent stage usually does not require treatment for late season foliar diseases. If you are finding something that looks like rust, but are not sure whether you have common or Southern rust, bring leaf samples to Jackson for a diagnosis.