Question:

Does high pH cause greater pod rot? How can we get better pod rot control in some fields? Here is some information indicating that pod rot can be a greater problem with higher pH. Should we add AMS to lower pH?

Jordan to Langston:

A distributor reached out to me about getting more effective control of pod rot. There is some information out there about pod rot being a bigger issue with high pH soils. I was not aware of that. I know from historical information that Sclerotinia blight can be more problematic with higher pH. Some of the recent discussion is around applying ammonium sulfate to reduce soil pH and possibly create a less risky case for pod rot. This question seems isolated in that I have not gotten feedback from other growers who have higher pH values in terms of pod rot.

I don't think we need to start adding AMS to our production systems to address pod rot. Is it possible that we are missing something with our stem rot fungicides when it comes to pod rot? In other words, are there sprays for slots 2, 3, and 4 that could be adjusted to make sure we get both pod rot and stem rot (and leaf spot.)

Langston:

Like David, I'm unaware of information supporting the idea that high pH soils leads to an increase in peanut pod rot.  In my mind, lowering pH to decrease peanut pod rot is counter intuitive.  Both high and low pH can reduce Ca availability, which is a driving factor, if not THE driving factor determining the amount of peanut pod rot you see.  Overall though, you will find that in most soils, low pH decreases Ca availability.  I know from experience with tomatoes that ammonium fertilizers lower pH and decrease available Ca, which leads to blossom end rot.  So, from a soil chemistry standpoint, I don't think adding ammonium sulfate is going to help with pod rot.

Calcium can be important from a disease aspect because Ca deficient pods are more prone to attack by pod rot pathogens.  Ca is only a part of that, and you can still have pod rot caused by pathogens and have abundant available soil Ca.   Is this question about pod rot in general?  If you were to ask most peanut plant pathologists what pathogen is most likely associated with peanut pod rot, the answer would be Pythium spp., or more specifically P. myriotylum.   David's comments lead me to believe we may be talking about southern stem rot causing pod rot, which it can do quite well.  I can find no definitive evidence that lowering soil pH reduces pod rot caused by southern stem rot (a.k.a. "white mold").  

*We are still working on the source of the information and possibly fungicide programs.  The key is likely putting in place an “aggressive” stem rot program by the farmer in question.