Question:

I am checking to see if we have come up with a program to the farmer with pythium and rhizoctonia that is coming in late on his peanuts where tobacco is in the rotation.

Jordan:

I do think excessive potassium after tobacco or any other crop contributes to pod rot (not stem rot.) Excessive K causes issues with calcium nutrition which affects pod and kernel development. Of course, the fertility for 2026 is in place. If soils do not need K, do not apply a remedial rate this coming year.

I have not found a major difference between fungicides that suppress pod rot more than other fungicides that we often use for stem rot. With that said, I know this is not a fulfilling answer. My suggestion is to apply azoxystrobin in the seed furrow when you plant. That is active against Rhizoctonia that affects stand establishment. The same pathogen you are worried about. Applying Propulse in late June may also help. And, I would suggest having a stem rot fungicide with sprays 1-4. The stem rot products likely have activity against pod rot as well.

My recommendation is expensive but stacks things in your favor. I’ve copied several pathologists in case I’m missing something that is a bit more of a “silver bullet.” 

Ultimately, I think high K could be the culprit. But I don’t know that. The high K affects the calcium nutrition in a major way.

Anco:

I don't have much to add to David's comments; I agree with K being an important component in predisposing pods to pod rot based on limiting calcium. We don't see very much pythium pod rot in our area. Last I was aware, phosphite fungicides, which have been very effective against things like pythium, were still incompatible if the harvested crop is to go to the buying point based on international considerations.

Langston:

I’m not particularly comfortable with the primary cause being Rhizoctonia or Pythium.  I will say that tobacco can increase Rhizoctonia inoculum levels. First I’d try to ensure the soil Ca:K ratio favors Ca uptake. If you feel Rhizoctonia is a major player in this, deep turning will help reduce Rhizoctonia's infection potential a lot.  Of course, deep turning is frowned upon these days.  So far as fungicides for Rhizoctonia pod rot I'd recommend using azoxystrobin or a fungicide that has azoxystrobin as a component.  Spraying Rhizoctonia alone would open you up to leaf spot problems which I think has already been mentioned (I have seen glimpses of responses when I first started typing this).  You could "spike" something like Lucento with additional azoxystrobin so that it would be equivalent to the high rate labeled for peanuts.  If you could spray this and irrigate soon after you would increase the amount of azoxystrobin that reaches and penetrates the soil which has been shown to increase it's efficacy against soilborne disease like southern stem rot and Rhizoctonia.  I'd skip using azoxystrobin in-furrow as it has little chance of affecting pod rot caused by Rhizoctonia due to when and where it's applied.

Jordan:

I would have more azoxystrobin in the program. Nothing seems to be needed prior to when you begin your sprays for leaf spot/stem rot from a fungicide standpoint.

I would be very interested in seeing what the K index is. A consensus from the group centers on high K and the impact on calcium nutrition.