Arkansas Peanuts: Late Season Irrigation Scheduling and Pod Rots

Pod rot caused by Rhizoctonia. Photo: Travis Faske, University of Arkansas

Based on the USDA-FSA there are 26,000 acres of peanut in Arkansas, a 10% reduction from 2017 in which there were 29,000 acres planted in the state.  Some of the reason for this reduction was higher cotton pricing and low peanut pricing.  This reduction was not exclusive to the Mid-South. There was a 20% reduction in acreage in Georgia and 30% reduction in acreage in Texas. 

Although Arkansas does not boast the greatest number of acres in the South, in the past we have had among the greatest yield per acre and excellent quality.  As we get close to the 110 day mark of the 2018 peanut crop, here are a few final reminders about production and disease management.

First, peanuts are not terminated by shutting off the irrigation but rather by digging, and the digging date is based on optimum peanut maturity.  This maturity can be estimated by a process called “pod blasting.”

Basically a pressure washer is used to remove the outer shell of the peanut and the color of the inner hull is used to determine maturity.  Ideally, the majority of the “pod blasted” pod colors should be a dark brown to chocolate color before harvesting.

Second, as we reach the 110 day mark, the amount of irrigation needed by peanut decreases by about 0.5” per week.  So, peanut at 16, 18, and 20 weeks after planting need about 1.75″, 1.25″, and 0.75”/week, respectively.

Irrigated fields should taper off the amount of irrigation per week for optimum peanut production.  It is easy to over water furrow-irrigated peanut fields as vines reduce the speed at which water moves to the bottom of the field.

Enlarged white fluffy structures called lenticels can be seen on peanut pods and pegs when soil is saturated with water.  These lenticels can be an indication of overwatering and too much water can contribute to pod rots.

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Peanut pod rots are commonly caused by fungi, both Pythium and Rhizoctonia.  Pythium causes a “wet rot”, which can be problematic in waterlogged or overwatered fields.  Rhizoctonia is the most common pod rot in the state, and though referred to as a “dry rot,” can appear wet in fields that are saturated with water.

Optimizing watering can minimize but not eliminate pod rotting as these fungi will remain in the field from one copping season to the next.  Rotating with grass crops like grain sorghum or corn can be beneficial. Fungicides like Abound (azoxystrobin) can reduce some pod rot, but the best results are often when these fungicides are applied at early pod development (mid-July).

Finally, although leaf spots have not been a major issue yet, for those growing Florida cultivars like TUFRunner 297 and 511, that are more susceptible to late leaf spot than the Georgia cultivars, continue to scout for leaf spots until they are dug.

Last year, Florida cultivars harvested later in the fall, late October, had more leaf spot than some of the Georgia cultivars. So, they may need protection with a fungicide to finish the season.  The disease severity was still low compared to that in the southeast peanut production region, but something that will likely increase with continued peanut production.

 


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