Additional Comments on Spots Seen in Peanuts
Comments from a well-respected scientist in South Carolina on the spots we are seeing on peanuts…
We see a lot of all of David’s example photos and I would diagnose them the same from pictures, including “I don’t know” for Barbara’s pic. Here are my observations on the leaf spot that Barbara is looking at:
We see it a lot and it is more prevalent on runners, particularly Ga09B;
It starts as a dead ringer for early leaf spot but lesions become more irregular as they expand;
I can’t make it sporulate but I don’t get beyond the 48 hr moist bag technology.
It can occur in high end fungicide programs – the worst case I have this year got Provost, Headline, as well as regular teb. + cholorothalonil treatment.
Thus far I have not seen it respond to fungicide treatment.
It gives you a lot of different looks. It can occur early in the season and never do much. It can occur late and cause 10-15% defol. but level off and not cause pod loss. This year it appeared mid-season (July) and clearly is going to cause at least some defoliation, but I expect and hope it does not progress.
My assumption at this point is that it is a physiological leafspot (I call it irregular leafspot) and I lump it with the same leafspot symptoms we can get earlier or later in the season. I hope Barbara can find a pathogenic cause to dispel the mystery.
Finally, regarding Maria’s pic, I think it is severe hopperburn which does develop into tip necrosis. There is also sometimes a midline necrotic spot associated with hopperburn that mimics leaf scorch. I lost any confidence that I could identify leaf scorch when we started seeing all the early season irregular leafspot morph into leaf scorch symptoms.
Article first appeared as North Carolina Peanut Note (PNNC-2014-121)