The following update was prepared by Clemson Peanut Specialist Dan Anco.
Most of the state’s peanut crop is continuing to look good into this latter half of July. We have been fortunate in many places to have received a healthy amount of rain at pretty decent intervals, and this has provided needed moisture to flush out canopies and encourage healthy pod development. We all know it ain’t over till it’s over, but this is a good place to be in at this time of year. Late leaf spot has started popping up in some fields (bottom of the canopy), with this being more common in fields that either followed peanuts last year or had peanut volunteers this year.
Many fields are at the 75 days after planting mark and are typically receiving their third fungicide spray. As a reminder to prevent late leaf spot resistance development, our recommended practices avoid using products with the same mode of action back-to-back, unless chlorothalonil is tank mixed with the application. We can double check fungicide modes of action by looking at the label, or pages 50 and 51 of the Money-Maker. Also keep an eye out for manganese deficiency showing up as yellowing between the veins on the leaf.
I Zinc, Therefore I am…in Trouble? Peanuts can have a tendency to show some interesting stress symptoms from time to time. This can show up across an entire field after making an application (like with surfactant or various herbicide injuries), or it can occur in scattered pockets that at first-look don’t seem to have a rhyme or reason why we would see it in one place and not another. The pictures below are from one of these fields. Some spots were completely dead, some parts looked great, and others had leaves with yellow splotches.
Closer inspection revealed that the problem areas were largely accompanied by different degrees of stem splitting. This is a characteristic symptom of zinc toxicity.
Soil tests came back with clearly elevated zinc levels, being about 95 lb/A in the dead zones (pH under 6.0). Depending on the pH of our fields, we want to start being careful with zinc levels much over 10 lb/A. We can lime fields that have moderate amounts of zinc before we plant to decrease its availability, but as with most things there is a practical limit. Looking at the numbers from this field and the symptoms, there isn’t much we can do this year but take this as an opportunity to reinforce the value of pre-plant soil tests, particularly when going into a field we don’t know the history of. Other than this the peanuts looked great.
Also as a friendly reminder, think twice if considering inexpensive fertilizer options such as steel mill filings – what we put into the soil may not be so easy to take out later.