Extremely high daytime temperatures, coupled with extended periods of drought during the critical pod-set stage of peanuts, may result in a significant loss in yield across the Carolina-Virginia peanut belt.

The biggest threat is from the heat. Temperatures in excess of 95 degrees significantly reduce pollination and peanut plant growth.

Peanuts are an indeterminate crop, and peanut plants will keep on blooming, which can be a good thing or a bad thing. For certain, it will make for some difficult management decisions at harvest time.

Suffolk, Va., grower John Crumpler says his peanuts look okay and mid-August rain no doubt helped the appearance. His concern is the impact record heat in June and July had on pod set and development.

“We lost our corn crop to the heat and drought, but August rains and cooler weather has helped our peanuts and cotton. I think we have a chance to have a decent peanut crop,” he says.

If the maximum daily temperature gets all the way up to 104 pollen viability can drop to around 70 percent and seed set to around 50 percent. Southeastern Virginia had several days in July and early August with temperatures above 100 degrees On one July day, the temperature topped out at 106 degrees, beating the all-time record by five degrees. 

Crumpler, who farms near the Tidewater Agricultural Research and Extension Center, carefully monitors their weather station. “I’m only a couple of miles away from the station, and several times they would get a trace of rain and I wouldn’t, and vice-versa. From April to August, neither of us got much rain,” he adds.

The Virginia grower says he doesn’t expect nearly the peanut yield Virginia peanut growers have produced the past couple of years, but contends peanuts have time to recover to produce a decent crop. The big concern, he stresses, is how much pod set was reduced by the heat.

In South Carolina, Clemson peanut specialist Jay Chapin says, “Peanuts planted mid-May were 86 DAP as of Aug. 9. Nearly all our crop in South Carolina is in the R-6 growth stage which means the oldest pods have seeds filling the hull, but no darkening was apparent by mid-August on the inside surface of the hull.”

Peanuts planted the last week of April are in the R-7 stage which means the oldest pods are starting to mature and show some darkening on the inside of the pod wall.

South Carolina fared better

South Carolina has been the least affected by the combination of heat and drought among the upper Southeastern peanut-producing states.

Timely rainfall throughout the South Carolina peanut production belt has provided ample moisture in most cases and has helped reduce the damage done by extremely hot day and nighttime temperatures.

Chapin says, “For the most part we have been extremely lucky in South Carolina to avoid the most obvious and severe effect of high temperatures — drought stress. Drought stress not only directly reduces yield, but also causes some problems that we don’t even want to think about: Calcium deficiency, reduced weed control, lesser cornstalk borer, burrower bugs, aflatoxin contamination, and on and on.” 

While peanuts can sometimes sit in the ground and produce a big crop, the risk is high for leaving them there in most years. Two years ago Clarke and Cliff Fox had a nine-month crop that produced over 5,500 pounds per acre in Capron, Va. The Fox brothers are veteran peanut farmers and neither recommends that kind of waiting.

The big question for peanut growers in 2010 is likely to be whether the crop will be early or late. Reduced pollination points toward a late harvest season, while rapid plant growth and development in hot weather points toward an earlier than usual harvest.

The truth probably falls somewhere in between. Even though peanut development is driven by heat unit accumulation, there is an upper limit.  Eighty-six degrees is about ideal for peanut, and temperatures above 95 actually start to slow plant growth.  So hotter weather only accelerates peanut development up to a point.

“Despite the prolonged high temperatures, most of the fields I have looked at have about what we would expect in a taproot crop at this point in the season.  Overall, I think the crop looks good and “on schedule”.  Even in fields where pod development might be lagging, we still have time to make a very good crop if we protect it from leaf spot,” Chapin says.

Veteran North Carolina State University peanut specialist David Jordan says peanuts in the Tar Heel State have been negatively affected by the heat and dry weather.

“Dry conditions and high temperatures most likely will contribute to lower yields compared to both 2008 and 2009. However, we learned that peanuts can yield well even with limited water (2008 peanut crop) and this may hold true for the 2010 crop. 

Crop delayed

“High temperatures may have affected flowering and pollen survival, and in a number of instances crop development may have been delayed.  While this certainly seems to be a less than optimistic view of the crop, rainfall in the coming weeks, combined with good fall weather, could go a long way in bringing in good yields and quality,” Jordan says.

As to whether the 2010 peanut crop will be early or late in North Carolina, Jordan says, “We all know that delaying digging until optimum maturity, especially if the crop has developed slowly over the season, can move digging operations into October. Although October is often one of the driest months of the year, cooler temperatures also make drying conditions less favorable if we happen to have excessive or frequent rainfall. 

Early digging is completely understandable because so much investment has already been poured into the crop. And, weather conditions, especially wet weather, can prevent timely digging and can result in substantial pod shed and subsequent yield loss.

However, in some cases, like with the Gregory variety of peanuts planted in early to mid-May, digging one week earlier than optimum reduced yield by 12 percent.

“In the fall, we generally tell growers when we think the peanuts will be at optimum maturity and we don’t tell them when to dig peanuts. If pressed, I’ll end up saying, if they were my peanuts I’d probably dig them by a certain date.

We can estimate pod maturity, but we can’t estimate stress and anxiety when the crop is still in the field and so much has been invested in that crop.  One thing we can do is keep the vines protected from disease well into the fall. When the vines are healthy we have a lot more flexibility in deciding when to dig.” Jordan says. 

Manage late leaf spot

Keeping peanuts healthy late in the season means managing late leaf spot. Chapin says even a low level infection (less than 1 percent of leaflets with late leaf spot) is cause for concern and should be treated aggressively. The recommended rescue program for late leaf spot is immediate treatment with either Headline 9-12 ounces, Tilt / Bravo 1.5 pints plus 5 ounces Topsin, or Bravo 24 ounces plus Topsin 5-10 ounces. Any of these treatments should be followed in 10 days by an application of Bravo 24 ounces plus Topsin 5-10 ounces or Tilt/Bravo 1.5 pints plus 5 ounces Topsin.

If there is a silver lining to the heat and drought damage to the 2010 peanut crop, it may come in the marketing end. Despite reducing acreage last year, high yields kept peanut supplies high and contract prices low. This year’s crop is likely to make a bigger dent in carryovers, even if acreage remains about the same as 2009.

Across the region corn was devastated, which will likely encourage some growers to plant wheat — if they can find seed — to take advantage of residual nitrogen. Typically more wheat means more double-crop beans, which means less peanut acreage. So, an indirect advantage may be of further reducing peanut acreage in some areas of the V-C Belt.

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