Peanut pod rots are influenced by many factors. Such things as rotation, water quality, drainage, variety, and chemical control, as well as cultural practices and the type of pod rotting organism present all play a part in the pod rot question.
Rotation is the first and most important part of the picture. Rotation allows the background population of microorganisms to change continuously. All microorganisms have a preferred carbon source or organic matter on which they prefer to feed. Without rotation we quickly select out the strains that prefer to feed on peanut and they become dominant and more difficult to control.
Water quality also can play an important role. Water with excessive dissolved salts or pH tends to cause a weaker peanut plant more susceptible to fungal invasion. Some fields and water sources are simply not suitable for peanut growth.
Soil drainage, both surface and internal, also play a role in pod rot. A “wet spot” in a field caused by either temporary surface ponding or subsoil that “holds” water often allows the pythium pod rots to develop rapidly. In many cases this lack of drainage can be corrected. Deep plowing to break up a hard pan may correct internal drainage. Improvement of surface drainage to prevent temporary ponding may help. Planting these fields on a higher bed may also be helpful.
Peanut variety or cultivar may be another important factor. For example, Flavor-runner 458 appears to be excessively susceptible to all pod rots and thus should be avoided in problem fields. The Tamrun-96 variety lacks some of the desirable qualities of 458 but displays superior pod rot resistance. It is one of the most resistant varieties to Sclerotinia blight.
Chemical control is the crutch most often used to allow peanut production in spite of pod rotting difficulties. Growers should take care to rotate chemicals in some way. Some prefer to rotate chemicals from application to application while others prefer a year-to- year rotation.
We must not simply rotate chemicals, we must rotate classes of chemicals. For example, Folicur and Tilt are both in the “sterol inhibitor” class and for the purpose of rotation should be considered similar. In the “Stroby” group we have such chemicals as Flint, Headline and Abound. Although these chemicals are different they must be considered in the same class for rotation. If one chemical in a class develops fungal tolerance problems it is a good bet that others in the same class will develop the same problems.
Cultural practices, in particular crop residue management, play important roles in pod rot. Most pod rotting organisms do not actively feed on living tissue. Most produce some exudates, which kill tissue in advance. Consequently, they can start the cycle much faster if old crop residue is in close proximity to the peanut plant. Consequently, anything that moves soil and organic matter to the base of the peanut plant will enhance pod rots. The moving agent may be a plow or it may simply be wind.
Types of fungi
There are several types of pod rotting fungi. For the most part we group them as follows: rhizoctonia, Sclerotium, Sclerotinia or pythium. Most grow on the above-ground parts of the plant also. Pythium is the exception as it only grows below ground. Other lesser organisms such as fusarium, verticillium and botrytis sometimes cause problems too. Across Texas, rhizoctonia is the No. 1 problem in terms of total acreage. On a field-by- field basis, Sclerotinia is the most devastating. Thankfully, it is not so wide spread.
Regardless of what the organism is, it is going to require thoughtful management. We should always remember that pod rots are much easier to prevent than control.