Diminished shell strength from rainfall when peanuts are in windrows at harvest

Authors: McIntyre, Joseph; Cook, Hunter; Read, Quentin; Sorensen, Ronald; Bucior, Erika; Lamb, Marshall

Submitted to: Peanut Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/24/2026
Publication Date: 4/9/2026
Citation: Mcintyre, J.S., Cook, H., Read, Q.D., Sorensen, R.B., Bucior, E.R., Lamb, M.C. 2026. Diminished shell strength from rainfall when peanuts are in windrows at harvest. Peanut Science. Volume 53:1. https://doi.org/10.3146/0095-3679-53-PS1665.
DOI: https://doi.org/10.3146/0095-3679-53-PS1665

Interpretive Summary: Peanut pods after digging can be exposed to rain while awaiting harvest in the field. Peanut exposure to rain after digging can reduce peanut price for the farmer. Effects of rain exposure on pods was investigated for harvest years 2021 to 2024 from irrigated experimental plots of runner peanuts Georgia 06G cultivar. Experimental peanut plots were managed at four irrigation levels 0% (dry land), 33%, 66%, and 100% of recommended irrigation. Peanuts were left in windrows and exposed to simulated rainfall in steps of 25 mm(1 in) to a total of 100 mm(4 in) by irrigation and then harvested one week after each rainfall using an experimental peanut combine and dried to below 10% moisture. Pod hull integrity was measured by compressing 3,599 sample pods in a universal mechanical testing machine to record the force and displacement required to reach rupture stress on the pod suture/seam. Dryland (0% irrigated) peanut pods showed no significant difference in the stress on the pod suture at rupture between the unexposed pods and those receiving any amount of rain. Irrigated peanut pod seam stress at rupture significantly decreased after 25 mm (1 in) rainfall exposure at all irrigation amounts. Pod integrity was not significantly reduced with added rainfall exposures after the first. Peanut farmers should schedule peanut digging when rainfall is not expected before harvest to maintain hull integrity.

Technical Abstract: Peanut pods after digging are placed in windrows, which can be exposed to rainfall while awaiting harvest. Peanut pod exposure to rainfall after digging can reduce peanut grade quality. Effects of rainfall exposure on pod hull strength were investigated for harvest years 2021 to 2024 from irrigated experimental plots of runner peanuts, Georgia 06G cultivar. Experimental peanut plots were managed at four irrigation levels 0% (dry land), 33%, 66%, and 100% of the recommended irrigation. Peanuts were left in windrows and exposed to simulated rainfall in amounts relative to the irrigation level and then harvested one week after each rainfall using an experimental peanut combine and dried to below 10% moisture. Pod hull strength was measured by compressing 3,599 sample pods in a universal mechanical testing machine to record the force and displacement required to reach rupture stress on the pod suture or seam. Dryland (0% irrigated) peanut pods showed no statistically significant difference in the stress on the pod suture at rupture between the unexposed pods and those exposed to any amount of simulated rainfall. Irrigated peanut pod suture stress at rupture significantly decreased after a single rainfall exposure at all irrigation levels. Pod integrity was not significantly further reduced with subsequent rainfall exposure. When the force needed to rupture pod sutures is reduced, the number of loose shelled kernels at grading may be increased which reduces the value of the peanuts. Peanut farmers should schedule digging peanuts when rainfall is not expected to maintain pod hull strength. If peanuts are exposed to rainfall while inverted in windrows, handling peanuts before shelling should be minimized to reduce the likelihood of generating loose-shelled kernels.