Dr. Dan Talks Agronomy

Every year there is a bit of worry about the first killing frost, so it may seem a bit ironic to talk about forcing a frost to bring about harvest efficiency.

In a way, that's what defoliants and desiccants do. These chemical harvest aides dry down weeds and homogenize maturity. Harvest aids are common practice in cotton production, a perennial plant that is managed as an annual. Dry beans also benefit from the practice as they struggle with variable in-field maturity. We see them routinely used in seed corn production. Gramoxone (paraquat) is labeled as a defoliant in some market segments and sodium chlorates such as Helena 6#, Drexel, Defol, and Tide Chlorate and organophosphorus compounds Harvest 5-F, Ginstar, and Quick Pick have long been used in the cotton market but not in Midwestern row-crop agriculture.

Although we haven't traditionally used them in corn and soybeans, the practice could catch on. Pressure to have the crops ready for harvest sooner to catch a market or to combat green stems in soybeans or stay green attributes in corn or just be able to get done combining before the first snows fly may be driving adoption

While there may be a bit of yield loss, the benefits of early harvest, improvements in grain quality and reductions in loss can sometimes more than offset the risk.

"Seed companies often defoliate seed corn fields before black layer to enable earlier harvest," said Emerson Nafziger, University of Illinois agronomist. "They aren't interested in seed weight (yield) only in seed number. And stopping fill early means that there are fewer large kernels and more kernel uniformity, which along with really early harvest is the goal."

Scott Schertz, owner of Schertz Aerial Services in Lexington, Illinois, said products like Defol 5 (sodium chlorate) are a service to corn and soybean management. "It's a tool to manage harvest, reduce losses and maintain quality and it stimulates dry-down, increasing moisture loss from 0.5 to 2 points per day. It's widely adopted on seed corn industry already to maintain quality, storability and produce more consistent seed size."

Dion Ackerman is Midwest Regional Manager with Drexel Chemical, the company that markets Defol 5. "We see large growers who want to plant longer maturities and still harvest early," he said. Defoliants can help in seasons that include a late start, cool summer, cool or wet fall. It helps answer varieties that are slow to dry-down or stay green too long. Fungicide use can also keep foliage and stalks greener for longer, stalks that stay green after black layer. It can also be an answer for those that want to plant cover crops earlier in the fall, he said.

Ackerman said that in field corn, Defol 5 can be applied with little to no loss of yield at R5 or full dent, when milk line starts to move downward. Expect to combine 16 days after application. "At the R5 stage most of starch has been deposited in the kernel," Ackerman explained. "But the closer to black layer the application, the less yield loss, but any loss is still minimal. But don't spray too early or after black layer when the plant is all brown."

Nafziger said sugars move into corn kernels up to the day they mature (black layer.) "In fact, in really good years where there's green canopy up to maturity, there can be kernel fill past black layer. Formation of the black layer simply means that the layer of cells at the tip of the kernel no longer actively transports sugar into the kernel.

He emphasizes though that even after black layer, green plants can still pump sugars into the kernel and those sugars can still contribute to seed size. "The bottom line is that I don't think you can take leaf area off before black layer without lowering yield to some extent."

Schertz explained that desiccants allow growers to plant a fuller season variety and still harvest early. "This reduces drying costs since dry down starts earlier and we can take advantage of warmer and drier weather. Growers can also capture an early harvest premium or run one combine instead of two," he said.

NO BUTTER BEANS

A desiccant such as sodium chlorate can also be used on soybeans. "Desiccants do a nice job of getting rid of plants with green stem and butter beans when other plants in the same field are already brown and at 9% moisture. Desiccants homogenize plant maturity so moisture is more consistent at harvest"Ackerman said. "Defol 5 can be applied after R7 when there are 2 to 5 brown pods on a stem. If you can see 50% brown pod it's a good time to apply."

Schertz said getting a more uniform maturity can also help reduce shatter loss. "This is not a technology for whole farm but for some fields and it can lead to a more efficient harvest," he said.

Nafziger said green stem often occurs when pod numbers/yields aren't as high as they should have been and the plants have no place to push all the sugar so stems stay green longer. He sees defoliation as an emergency measure in these circumstances

However, Nafziger points out the cost of combining beans with green stems is less than we think.

"Once green stem develops, its dollar cost with today's combines is not nearly as high as some people think it is. By the time we see it there won't be enough green leaf area to bother killing anyhow," he said.

He points out defoliating is also a risk. "Green leaves still need to transport their N into the developing seed, and if we kill them even a day before they've lost most of their color, that process will be disrupted and some yield will be lost. And defoliating healthy green soybean plants with good pod numbers before they lose leaf color on their own is a bad idea. If people want to harvest earlier they should use earlier varieties, which will seldom have green stem, but will also seldom yield as well."

Here's a tip on soybeans -- if after opening the pods not all seeds are at physiological maturity then application of harvest aid will result in some yield loss due to lower seed weight.

When considering a defoliant, growers need to decide if the small yield losses can be offset by the convenience of earlier harvest and perhaps a higher quality grain. One thing to remember -- sodium chlorate is not a desiccant like paraquat and won't kill tough weeds like Palmer amaranth, waterhemp or ragweed.

For some thoughts on soybean desiccants from the LSU AgCenter go here: http://mssoy.org/…

Dan Davidson can be reached at AskDrDan@dtn.com

(PS/CZ)

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