— Written By David Jordanen Español / em Português
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The first two groups of attached pictures are from a field where a patch of stunted or dead peanut plants were in a pocket of otherwise healthy plants. There appeared to be a pattern to the symptoms similar to the width of the planter, and the possibility of running out of product or inoculant during planting was considered. Patterns in a field can tell us a lot about what may or may not have contributed to an issue. The abrupt transition from healthy to dead or stunted plants is characteristic of zinc toxicity. Classic stem splitting was not readily apparent in the field, though after washing some of the intermediately affected plants, the beginnings of stem splitting and purplish lesions associated with zinc toxicity could be found.
After pulling soil samples for analysis, the results were not strikingly dramatic between the good and bad areas of the field near to where the symptoms were located. The zinc levels (6.7 to 8.3 lb/A) were near the low range of when they can start to cause issues, which has more potential to cause toxicity under acidic conditions. The difference in soil pH among the samples was small, corresponding to 5.9 pH in the bad area and 6.0 pH in nearby unaffected areas. For zinc between 6 to 10 lb/A, our standard recommendation is to lime the pH to 6.2. There is the potential that there could have been multiple things contributing to this particular field, but based on the field pattern and trace symptoms of some splitting, I think the zinc and soil pH were involved with contributing to the poor growth and death there in the field. This field was planted to Georgia 16HO. Work remains to determine the extent to which different newer varieties may vary in their sensitivity to zinc under different soil environments.
For comparison, the last attached picture is from a different sandy field where inoculant was left out at planting. Nitrogen deficiency is beginning to be expressed as general chlorotic yellowing, which tends to show up first in the older leaves. Aside from having a yellow canopy, peanut expressing nitrogen deficiency can be smaller and less vigorous than well-inoculated peanut, though a lack of inoculation alone does not approach the extreme stunting and death more typical of spots with zinc toxicity.
