Cotton Seedling Disease

Seedling disease has been making an appearance in isolated pockets over the past week to ten days.  Primarily we have been observing Rhizoctonia, also known as soreshin, on cotton in the north Delta.  Seedling disease, caused by Rhizoctonia solani, is more common on sandy, well drained soils and symptoms can be exacerbated by sandblasting injury.  Soreshin is typically characterized by reddish brown, sunken lesions at or below the soil line.  Symptoms on cotton that we observed last week were below the soil line and discolored, sunken lesions were present.  In the picture below, note the discoloration on the stem as well as the sunken lesions and the overall difference in height between the healthy plants and those diagnosed as having seedling disease caused by R. solani.

In addition, seedling disease was observed in multiple varieties regardless of seed company or seed treatment fungicide active ingredients.  Generally, seedling disease is more frequent during cool, wet conditions similar to what we experienced during early May 2011.  Also, no-till or flat planted cotton may be more susceptible to seedling disease compared to cotton planted on beds.

Sandblasting injury can result in an increase the occurrence of seedling disease.  Damage to seedling cotton from sandblasting can provide an avenue for fungi to enter the plant and cause damage.  Injury as a result of sandblasting is often observed on the side of the stem from the direction the wind was blowing.  Cotton that is hill dropped may have one or more plants in a given hill that do not have sandblasting injury as they were protected by the other plants within that hill.

Control of seedling disease requires a proactive approach rather than a reactive approach.  Generally, this is accomplished through the use of seed treatments, and in years past, through in-furrow fungicides.  All (or nearly so) cotton seed planted today is treated with a fungicide which brings up the question of why is seedling disease showing up?  Environmental conditions have been favorable (although dry soil conditions have been problematic for some) for cotton growth and development.  However, anything that slows early season growth and development such as PRE herbicides, thrips, cool weather, lack of moisture, etc. can increase the incidence of seedling disease.  Once cotton has emerged, the best cure for seedling disease is warm weather, good soil moisture, and/or a reduction in the overall presence of stress.