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• Some peanuts put on 30 percent of their growth in the last two to three weeks of the season — that’s huge. When it comes to economics, we’ve got to make the best decision possible when it comes to digging peanuts.
• Since peanuts are underground, growers can’t just ride by a field, take a quick look, and tell if they’re ready to dig. And you can’t put them back once you dig them, so you have to be spot on.
Some don’t fit board
“Some peanuts just don’t fit the board. AP-3 never turned black. The profile board was developed over 30 years ago, and it’s still very relevant, but we need to come up with some updates.”
Researchers are working on a growing degree day method for determining maturity, says Faircloth. This is a method commonly used in cotton and known as DD-60s. It’s the amount of heat units received by a plant.
“There’s quite a good correlation with DD-60s on peanuts — you just have to make a few modifications,” says Faircloth. “It’s very accurate and a very good correction factor for the profile board. It’s not a stand-alone method to predict maturity, but maybe with some other features built in, it very well could be.”
With peanuts, the cotton DD-60 becomes a DD-56, he says. The DD-56 is a threshold, assuming that below 56 degrees F., a peanut plant is not engaged in high growth such as putting on flowers and pods
A DD-56 would be calculated by adding the maximum and minimum temperature, divided by two, minus 56. You add up DD-56s to determine the heat unit for a given period of time.
“The important part of this is that you have to add in the water. It doesn’t take just heat to mature a peanut — it also takes water, and you must have both together. It’s a pretty good tool for determining peanut maturity.”
This method was evaluated last year, and every variety tested peaked at 2,500 growing degree days, plus or minus eight to 10 growing degree days, depending on growing degree days, says Faircloth.
In July or August, when daytime temperatures are in excess of 95 degrees F. and low temperatures at night are in the 70s, a peanut plant can accumulate about 15 growing degree days per day, he says.
“We’ve got a lot more research to do with this, but it’s a great correction factor when you’re using the hull-scrape method. You can look at the distribution on your board, and then look at the heat accumulation and make a good determination.”