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12
Sep
2013
Considerations for late season peanut diseases and determining when to dig
Author: Travis Faske, Extension Plant Pathologist

Though planting was delayed due to cool, wet weather in the spring and wet, cloudy conditions during pegging and pod formation were less than ideal for peanut production, overall, the crop is looking good to excellent.  This year half of the total acres (~11,000) were planted in high oleic runners (GA09B, FloRun 107 and FL 07) with the remaining acres in a conventional runner (GA06G).  All of these cultivars were planted in 2012 with the exception of FloRun 107.   Additionally, two high oleic Spanish peanut cultivars (cv. Tamnut OL06 and Olin) were planted this year on a few hundred acres.  Given the condition of this year’s crop, the estimated average yield for runners will be similar to 2012 at ~4500 lb/A, though several producers will likely exceed 5500 lb/A in a few fields.  Most producers will begin to dig at the beginning of October though some will wait as long as possible (mid-October) for maximum yield.

Figure 1.  Runner peanut cv. GA09B late July, 2013 near Augusta, Arkansas.

Figure 1. Runner peanut cv. GA09B late July, 2013 near Augusta, Arkansas.

Southern blight, caused by the soilborne fungus Sclerotium rolfsii, was the most common disease issue this year for producers.  Disease incidence ranged from <1% to 3 in several fields, which is relatively low compared to other peanut producing regions (i.e. SE U.S.).  Many fields with no previous history of the disease remained free of southern blight.  If southern blight has not been observed in the field this late in the season it is unlikely to be an issue this year.  For future reference, note areas of the field with southern blight as this would be the best location in the future to scout for the disease in peanut.  In other peanut growing regions, leaf spot diseases are often a serious issue late in the season when temperatures begin to cool; however, leaf spot diseases have not been confirmed in Arkansas.  There are many leaf spots on peanut plants during the growing season, some resulting from herbicide injury.  These spots do not contain any fungal-producing structures (i.e. fuzzy structures) in the center of the necrotic spots when examined with a hand lens.  Given the wet weather during pod development, pod rots may be an issue on older pods that were saturated for several weeks during the season.  It is recommended to evaluate inverted plants for dark black pods with water-soaked hulls.  These are classic symptoms of Pythium pod rot.  Though there is little that can be done for pod rot this late in the season, it is a good opportunity to identify pod rot issues for future management considerations.

Figure 2. Numerous reddish-brown sclerotia and white mycelium of Sclerotium rolfsii near the peanut crown.

Figure 2. Numerous reddish-brown sclerotia and white mycelium of Sclerotium rolfsii near the peanut crown.

Since peanuts are indeterminate and will continue to flower until harvest, determining when to dig is key to maximizing profit.  For runner peanut, a hull-scrape method is commonly used to predict a harvest date.  Harvest based on planting date alone is risky and may result in significant yield losses.  Generally, runner peanut matures in 150 to 165 days after planting; however, a peanut crop harvested one week early can result in a yield loss of 200lb/A.   A hull-scrape method is based on the hull changing from white to yellow to orange to brown to black as the peanut matures.  Wet pod blasters (power washers) are often used to rapidly remove the peanut hull and expose the mesocarp.  Pods are grouped by color on a peanut profile board to predict a harvest date when 65 to 70% of pods are mature.   A representative sample should be taken from several plants in the field for a total of ~100 pods.  The first sample should be taken at 120 to 130 days after planting and then a second at 10 days before the predicted harvest date.

Figure 3.  Leaf spots caused by herbicides on peanut leaves.

Figure 3. Leaf spots caused by herbicides on peanut leaves.

Inverted plants should remain dry in windrows for 3 to 5 days with favorable weather conditions.  Rainfall during windrow drying shortly after digging (i.e. pods with 20% moisture) may promote mold and lower the grade value.  Remember pods are cleaned and cured with heated air (~11% final moisture) for long term storage, thus; final yield weights will be lighter than total tons unloaded at the buying point.

Figure 4.  Digging mature peanut plants in 2012 with a six-row digger-inverter.

Figure 4. Digging mature peanut plants in 2012 with a six-row digger-inverter.

 

 


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