by Thomas Isakeit, Professor and Extension Plant Pathologist

I have prepared two factsheets on bacterial blight of cotton and cotton root rot. They can be accessed at Cotton.tamu.edu. The bacterial blight factsheet has photographs that will be useful in diagnosing this disease. There has been a resurgence in this disease in Texas in recent years, with some yield losses documented in other states such as Mississippi. Since the severity of this disease is driven by rainy weather, I have no prognosis for the 2016 season.

The cotton root rot factsheet is updated from a 1962 publication to reflect the availability of Topguard Terra as a control option. The photographs and descriptions of disease symptoms are a standard component of factsheets, but in my experience, cotton growers in areas of the state where the fungus is present are very familiar with what the disease looks like.

As the fungus is soilborne, the disease is not spreading to new areas. I have noticed that extensively infested fields have been taken out of cotton production. For example, one field in Wharton County used in a deep ploughing control demonstration in the early 1960s is now in pasture (a testament to the ineffectiveness of that control measure). The fungus is certainly still there and the disease will likely show up if the field is cropped to cotton.

This raises the question of how to know if the fungus is present in a field, if there is no previous cropping history, or if that history has been lost. In the 1930s, in one survey, the presence of the fungus in non-cropped areas of west Texas was indicated by the wilting of dicotyledenous plants. As susceptible plants may not be uniformly distributed in a field, this approach would not be effective. Sampling soil for the survival structures of the fungus, the sclerotia, would be like looking for a needle in a haystack. The structures are small, black, and are not uniformly distributed in soil. The best way to know if the fungus is present is to plant a susceptible crop (cotton or alfalfa) uniformly in the field and monitor disease development over several years, since disease development in a particular year can be suppressed by lack of rain.

Thomas Isakeit, Ph.D.
Professor and Extension Plant Pathologist
College Station, TX
t-isakeit@exchange.tamu.edu