There is no disease I enjoy battling more than I do white mold.  White mold attacks with stealth.  White mold feeds silently deep in the peanut canopy and just below the soil line.  White mold may go unnoticed until it erupts in a blaze that leaves scorched plants behind in its path and significant pod loss at harvest.  White mold is rarely eliminated. At best, it is corralled.

White mold, known also as southern blight and stem rot, is one of the most important diseases that peanut growers in the Southeast face each year.  Threat from this disease is greatest when peanuts are planted in short rotations and during periods of hot humid days and warm humid nights. 

The disease is best managed with effective crop rotation, such as peanuts planted to a field once every three years, and use of Georgia 12-Y, which has partial resistance to white mold.  An effective fungicide program is at the core of white mold management for most peanut farmers.  If nothing else, it is critically important to stop this disease before it becomes well-established in a field.

Included in here are pictures sent to me by University of Georgia Extension agent Macie Wheeler-Mosteller from Turner County, Ga.  In the first, located at the top of this page, a single wilted plant in each of two rows of peanut is visible. Conditions had been quite hot and dry when the picture was taken.  To find a few wilted and dying plants scattered across a young field of peanuts is common under such conditions and this is very often the result of Aspergillus crown rot. 

In fact, both Macie and I expected that the culprit here was Aspergillus crown rot. However, when she sent the second picture of the lower stem and roots from an affected plant, the true villain became obvious.  While there is a dark lesion visible on the lower stem, I cannot be sure from the image that crown rot is present.  However, I can clearly see that thin white threads of fungal growth are associated with lesions and wilt of the young limbs. This is Agroathelia rolfsii, the fungus that causes white mold.

This is Agroathelia rolfsii, the fungus that causes white mold. By Macie Wheeler-Mosteller/UGA Extension.

For the wilted plants in the first picture, it really doesn’t matter if it is crown rot or white mold.  They are not going to make it.  But to the grower it is essential to know which disease is present.  The reason to know the difference is simple. 

Aspergillus crown rot is a disease of seedlings and young plants.  It does not spread from plant to plant and there is really nothing to do to protect the crop once the furrow is closed, except irrigate as one can to cool the soils.  This is not the case for white mold.  These single infected plants are like a lit match burning brightly.  As the flame of white mold consumes one plant, it spreads to neighboring plants along the bridge of overlapping limbs and foliage.  White mold burns from plant to plant most easily up and down a row.  The disease is less likely to spread across rows. Planting in a twin-row pattern may also help to slow the spread of white mold as plants are spaced further apart than they would be in single rows.

The teachable moments from Macie’s pictures are important.  First, her pictures capture initial hits of white mold in a field.  The plants may, or may not, also be affected by Aspergillus crown rot. As crown rot does not spread from plant to plant and is best managed with in-furrow fungicides and seed treatments, there is little to be done, or needs to be done, now. 

This is NOT true for white mold.  It is nearly impossible for any fungicide program to stop initial infections that may ignite a field in white mold.  However, it is critical NOW that the grower quenches the developing epidemic with the right fungicide program.  

The equation for the right fungicide program for management of white mold in peanut = an effective fungicide + an effective rate + appropriate timing + sufficient spray volume to penetrate the canopy + rainfall or irrigation within 24 hours to redistribute the fungicide from the leaves to the crown of the plant where the diseases is active.  

The final lesson to learn is that unless your field is carefully scouted, it is best not to wait until white mold is observed to begin an effective fungicide program.  Most growers should begin a fungicide program sometime between 45 and 60 days after planting.  It is much easier to corral white mold early. It is much more difficult to stop it after it is established in the field.  Truly, it is not just for white mold. It is for every disease in your peanuts, cotton, corn and soybeans. You must protect the crop before the diseases are established. 

I love the hunt.

Kemerait is a University of Georgia Extension plant pathologist and regular contributor to Southeast Farm Press.