Recognize Both The Issues & The Opportunities
Carroll G. Smith
In the South, corn and soybeans have been the two primary rotational crops for cotton. Alabama cotton specialist Charlie Burmester says, historically, corn is probably the No. 1 rotational crop because of the spread of reniform nematodes across Alabama. Corn is not a host for reniform nematodes but can increase root-knot nematode numbers. In areas of Alabama where root-knot nematodes are damaging, peanuts is the best rotational crop.
Today, after wheat and soybean prices began rising significantly, more and more farmers are turning to wheat and double-cropped soybeans, which may be followed by cotton next season.
“With this system, the producer gets the advantage of moisture conservation from the wheat straw and soybean residue, plus a small amount of nitrogen from the soybeans,” Burmester says. “This is a great rotation for cotton as long as reniform nematodes are not a problem. Most of the soybean varieties are not resistant to reniform nematodes. That’s why corn is hard to beat in north Alabama right now.”
Burmester also urges producers to get familiar with any plant-back restrictions associated with the herbicides used on different crops.
Managing Weed Resistance
As for weed control, herbicides like atrazine, dicamba and the bleaching herbicides such as Calisto can be used on weeds in corn. These same weeds have never been exposed to them in a continuous cotton system.
“This scenario is a good way to break up herbicide resistance that may be building up in a field,” says Tennessee weed scientist Larry Steckel.
He adds that farmers also need to be more aggressive with glyphosate-resistant horseweed in corn.
“In cotton, we can use dicamba 2,4-D as a burndown 15 to 30 days before planting,” he says. “With corn, we can use that product in-season and at higher rates. Later in the season, the bleaching herbicides like Calisto have good activity on herbicide-resistant horseweed as well.”
Steckel says soybeans are not as good a rotational partner as a herbicide resistance tool because there are fewer in-season herbicide choices for controlling these weeds. He notes that one choice is Reflex, which is pretty good on herbicide-resistant pigweeds.
Another challenge of implementing a diverse crop mix is managing the Roundup Ready crops.
“For volunteer Roundup Ready corn, Select (gramicides) would be at the top of the list,” Steckel says. “For volunteer Roundup Ready soybeans, there is basically one choice – Envoke – which can be used after the fifth leaf. It does a pretty good job.”
Insect Control In Rotation Systems
Although corn, soybeans and cotton are a popular rotational mix, wheat acres have increased significantly in the last couple of years.
Mississippi entomologist Angus Catchot cautions producers to be on the lookout for increased thrips populations in cotton as the pest begins to move out of wheat when the crop starts to dry down. He also says the potential exists for increased plant bug pressure, particularly around the edges of the field, where cotton and corn are planted next to each other.
Catchot stresses that nozzle selection also can affect insect control.
“When farmers are piggybacking a herbicide and insecticide in a tankmix, they generally choose a low-drift tip, which produces large droplet sizes,” he says. “A better choice for insecticides would be a hollow cone or flat fan with high pressure to break up the droplet size for better canopy penetration and better coverage.”
Contact Carroll Smith
at (901) 767-4020 or firstname.lastname@example.org.