peanuts maturity harvest

USING HERBICIDES TO terminate peanut flowering could lead to a more exact way of determining maturity, says Marshall Lamb, research director for the National Peanut Research Laboratory in Dawson, Ga. Lamb is shown here at a field day this past summer.

Research aims to take the guesswork out of determining peanut maturity

Determining peanut maturity has always been an inexact science. Research is looking at terminating flowering to improve maturity distribution.  

It’s one of the most important decisions a peanut producer will make in a year but also one of the least certain — determining crop maturity.

There’s a lot of guessing going on each year around peanut harvest time, and the economic impacts of making a bad decision can come back to bite you, says Marshall Lamb, research director of for the National Peanut Research Laboratory in Dawson, Ga.

That’s reason enough for researchers to try and get a better handle on improving maturity distribution in peanuts, he says.

One such effort focuses on chemically halting flowering late in the growing season, says Lamb.

“We’re asking the question, ‘Can flower termination to prevent immature peanuts lead to improved maturity distribution, flavor, grade, yield, outturn and other factors?’”

The research project began in Dawson in 2012, and was gradually expanded in 2013 based on encouraging results, he says. “We’re looking at actually changing the flowering patterns in peanuts.”

When growers have peanuts that are far black, or approaching far black on the maturity profile board, there is a point to where additional flowers will develop pegs and pods, but those pods won’t help with yield or grade. They’re taking energy away from the plant that could be better utilized by more mature, higher-yielding, higher-grading peanuts, he explains.

“A lot of people don’t realize that the peanut is a perennial plant. It’s not an annual — we simply farm it as an annual because of cold weather coming in and other factors. In research at Tifton, peanuts have actually been kept alive for more than three years,” says Lamb.

“As long as you keep the pesticides on them and keep them watered and fertilized, they’ll live, and they’ll continue to bloom during that time. We simply farm them differently than they grow in nature. The problem is since they’re an indeterminate crop, they’ll continue to fruit without stopping, he adds.

“So it comes down to a judgment call, and all peanut producers have sweated this particular judgment call in the past on when to dig — it’s a very important decision.

“We have the most mature peanuts on the entire vine, yet we have other peanuts that haven’t had time to mature. But you can lose the more mature ones in order to gain the less mature peanuts.”

Make an indeterminate peanut act more determinate

The research, he says, is an attempt to make this indeterminate peanut crop more determinate, and it’s a way to increase the amounts of black, browns and oranges on the profile board because they are the biggest, densest and most mature peanuts. They have the highest oil-to-water ratio so when you dry them they don’t shrink.

“Our concept was to look at two different herbicides. One is glyphosate and the other is diflufenzopyr Na, which is BASF product,” says Lamb.

“We wanted to see if we could come in at different times and terminate flowering. When you’re harvesting peanuts on the black part of the board, you’re blowing lighter ones out of the back of the combine.

“Another problem we have is getting the less mature ones to mature quicker because when a flower turns into a peg and hits the soil, they’re going through the most rapid cell division and cell elongation of any part of the entire plant.

“That is stealing energy from something you will never harvest and never benefit from and not putting the energy where it is most needed.”

This research, says Lamb, is focused on stopping the flowering at a set time to petition the energy away from the peanuts that won’t be harvested.

“We chose our timing based on the black part of the traditional maturity board. We were looking to get about a 15 to 20-day break in the flowering cycle from approximately day 100 to day 110, depending on where the crop is.

“When we started this, we didn’t know which rates to use, so we looked at different rates with these two herbicides.

“We used a 41-percent formulation of glyphosate, which is the case with most generics. For weed control, you’d use 32 ounces per acre. But we used different rates at 2 ounces per acre, 4 ounces per acre, and 6 ounces per acre. We used the lower rates because we don’t want to kill the peanuts. We don’t want a lot of foliage damage — we just want to terminate the flowering.”

There’s a reason for choosing glyphosate, says Lamb.

“If you remember when Roundup Ready cotton first became available, we were spraying it with Roundup almost season-long. But we discovered that the late-season application of glyphosate was affecting the pollination of the flowers in cotton and reducing yield. When we discovered that, we knew best how to use it.”

Diflufenzopyr is being used as a herbicide, but it also has been shown that it will interrupt the flowering as well, he says.

“We’ve got three different rates of each of these, and we’ve got irrigated and non-irrigated, three different timings — one time at day 100, one time at day 110, and then we have a repeated application at 100 and 110, so it’s a double application. We’re trying to determine timings and rates.”

The research includes an untreated check and hand-removal of the flowers every day for 20 days, he says.

Eliminate immature peanuts and improve the flavor profile

“When this project began, it was funded by one of the major peanut manufacturers because if we can eliminate immature peanuts, we will improve the flavor profile of peanuts.

“Also, if we can eliminate the immature peanuts, it makes them easier to dry because the immature peanuts are higher in water than mature ones.

“In addition, you’d eliminate off-flavors. So we’ve been looking at this mainly from a quality standpoint. But we’ve found other advantages as well.”

The research has included the painstaking task of counting the flowers in a 3-foot section across the treatments on a daily basis, says Lamb.

“Within these 3-foot sections, we had about 15 flowers every day — some of the old ones would drop off, and some of the new ones would come on. We counted the new additions. Where we had herbicide treatments, we basically took flowing to zero over about 18 days.  Even the flowers that were on the plants were not viable flowers. The pollen in them was not viable.

Where they are treated, the flowers are about one-fourth the size of a normal flower, and they’re very opaque or white as compared to the usual bright yellow flowers. The process totally destroyed how they were flowering.”

This past year’s counts followed exactly the same trend, he says, but there were not as many flowers on peanuts in 2013 as in 2012. That’s an environmental factor due to more rainfall this past year.

“We determine when to dig with the hull-scrape profile and the black column. In the control or untreated plots, we had only five pods in the black column, and that’s an indicator to begin digging.

“As a grower, you’re ready to go whenever you fill the black column. Where we had the treatments, we had a three to four-fold increase in the amount of pods that were in the black column on the profile board.”

That indicates, he says, that the treatments were successful in petitioning energy away from the immature pods and into the mature pods.

“We were mainly looking for quality attributes, and we tested all of these for residues, fatty acids, protein, fat, sugar and moisture. Maturity is directly related to some of these factors. We also tested for roasted peanut flavor. One of the biggest complaints received by manufacturers is off-flavor, and this is typically associated with immaturity. The peanut contains too much water, and it doesn’t roast the same.”

Lamb says he also wanted to look at the effect on yield and grade, though he didn’t expect the yield benefit.  

“We saw a yield benefit, which was very surprising. The non-treated and the dryland averaged 3,250 pounds per acre. With some of the diflufenzopyr treatments, we were making about 3,600 pounds per acre, about a 400-pound yield increase. I started looking into this — out of every plot, we took 100 kernels of jumbos, mediums and number ones, separately — and we actually measured the density of the kernels.

“The kernels that were treated were denser, and that makes them heavier, so we had an increase in yields of about 400 pounds, and, on the non-irrigated an increase of 1 ½ percent in sound mature kernels and sound splits, which all goes back to the kernels being denser.”

It’s important, he says, to get the rates right because some of the heavier glyphosate rates damaged yields.

“We saw an even bigger effect on the irrigated, which we weren’t expecting. The non-treated peanuts averaged 4,700 pounds per acre. Where we treated — mainly with diflufenzopyr Na — we were up to 5,300 and 5,500 pounds per acre, or an increase in yield of roughly 600 pounds with these treatments, and a 2.5 percent increase in grade, which is also significant.”

Lamb cautions that the research is in its early stages. “But it could be a way to petition the energy in the plant towards what we’re going to harvest by eliminating the part of the fruit-load that we don’t want to harvest but is taking the most energy.

“It’s just research, and we’re not making any recommendations. Give us a couple more years on this study, and I think we’ll have these rates and the timings bracketed down to where we’ll have a recommendation for producers.”

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