Sunday, September 19, 2021

Follow these tips to finish the 2021 season strong

• By Travis Faske •

southern blight pathogen
Figure 1. White hyphae of the southern blight pathogen, Sclerotium rolfsii, colonizing a peanut limb.

Based on U.S. Department of Agriculture Farm Service Agency reports, there were approximately 34,000 acres of peanut planted in Arkansas. This is 8% fewer acres than planted in 2020 (37,000).

Some of this had to do with less-than-ideal plant stand and planting conditions in April and May. June was also a cooler than normal month, which was less than ideal for peanut production. Currently, the Arkansas peanut crop is slightly behind that in 2020, so here are a few considerations for a strong finish to the 2021 production season.

Watch for southern blight

First, southern blight (caused by Sclerotium rolfsii) has picked up recently. A late start for the disease was observed in 2020 when it started showing up in late August (Fig. 1).

Typically, fungicides are applied to protect peanut plants against this disease starting in July. But for the past two seasons, it has been first detected in August. This could be due to a good fungicide program, but fungicides do not control 100% of southern blight.

It could also be due to canopy coverage occurring later in the cropping season, thus the environment for disease development starts later. Both are likely contributing factors. With that said, fungicides to target for southern blight are as important in July and August. So continue to protect against southern blight.

Look out for late leaf spot

Second, be on the lookout for late leaf spot. Some farmers or consultants are on a scheduled program of three fungicides only. This could be risky if late leaf spot (caused by Nothopassalora personata — previously known as Cercosporidium personatum) develops in September and harvest is delayed (Fig. 2).

late leaf spot
Figure 2. Peanut field with significant defoliation from late leaf spot (November 2018). The cultivar on the left is Georgia 09B and on the right, TUFRunner 511. The fall conditions were extremely wet in 2018.

Late leaf spot can cause some significant defoliation on susceptible peanut cultivars. Though cultivars vary in susceptibility, most of the peanut cultivars grown in Arkansas are susceptible. So continue to scout for leaf spot disease. If harvest is 30 days away, consider protecting plants with a fungicide.

Significant defoliation by late leaf spot causes the plant to “shut down,” which can contribute to weak peg strength (i.e., digger loss). Most peanut fungicide programs end with chlorothalonil (Bravo, Equus, Echo), but a rain shower will wash that off the plant. So  consider a systemic fungicide like tebuconazole to provide some systemic protection.

Use peanut maturity board to gauge harvest date

Finally, use the hull scrape method to determine the time of harvest rather than days after planting. In 2021, some farmers decided to start based on planting date but stopped due to low grades and pod yield.

peanut maturity board
Figure 3. Peanut sample where most pods are immature (yellow) and thus more than 30 days from digging.

Digging too early can result in several hundred pounds of yield loss per acre. So use the peanut maturity boards to determine maturity (Fig. 3).

Many of the county Extension agents with peanut in their county have had the opportunity to experience this simple process. Several samples of peanut plants are pulled in the field (avoid the edges and near ploy pipe), pods are removed, and a power washer is used to expose the mesocarp.

Dark peanut pods are ready to harvest, but the number of dark pods should be 75% or better.

Dr. Travis Faske is a University of Arkansas Extension plant pathologist. He may be reached at tfaske@uark.edu.

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