We are seeing a good bit of yellowing areas in peanut fields. It’s worse where we have high pHs. We suspect most of this is the micronutrient Manganese (not Magnesium) deficiency. This is due to the fact that Manganese is not as available to the plant at a high pH. We may want to spot spray manganese in these areas if we are 3 weeks or longer to digging. In the fields where I took these photos this week, the pH in some areas was 6.5 to 7.1. The narrowing band on the chart below from my old soil science book indicates the lessened availability when the pH gets higher.
Here are some comments from Dr. John Beasley, UGA Extension Scientist, concerning this situation.
“ It looks as if the primary issue is manganese deficiency. If you look closely, the yellowing only
goes down 3-4 nodes from the terminal. Most of the leaflets are showing the
typical Mn deficiency symptom of interveinal chlorosis. You could soil
sample to confirm pH levels in those areas. Manganese
deficiency is associated with a high pH (6.5 or greater). The symptoms are
also associated with a flush of new growth due to more frequent rainfall events
and “slightly” cooler temperatures. If the fields showing the
conditions are within 3 weeks of harvest there is no economic advantage to
treating them. If the fields are greater than 3 weeks from harvest, spot
spraying the affected areas with manganese sulfate is recommended.”
Here’s some information from the UGA Plant Analysis Handbook concerning correcting Mn deficiencies in Peanut.
Manganese deficiencies may occur on sandy soils with a pH greater than 6.3. If
Mn deficiency occurs, apply a broadcast spray of Mn using 1/2 pound Mn per acre
as manganese sulfate or 0.15 to 0.25 pound Mn per acre as chelated Mn in 20
gallons of water per acre. If symptoms persist, the spray should be repeated at
2 week intervals. In most cases, multiple applications will be required. High Mn
levels are generally due to low soil pH.