As cotton producers enter the home stretch with their 2006 crop, weed scientists are advising growers they have some new and potentially new layby options for keeping weeds under control into harvest.

The first step in any layby program, says Roy Vidrine, the new Extension weed specialist for the LSU AgCenter, is to make sure you have a height difference between cotton and weeds before you reach this point in the season.

“If Roundup Ready or Flex cotton is planted and early season Roundup applications are timely, then a reasonable difference in cotton/weed height should exist, which would allow effective post-directed herbicide applications,” he said. “If conventional cotton is planted, several overtop and early post-directed herbicides are available.

“Thus, when layby herbicide applications are due, a suitable situation should exist for optimum spray contact of small weeds and enough soil surface area exposed for effective residual herbicide applications, which should last throughout the remainder of the growing season.”

Vidrine, who now holds a joint research/Extension appointment, has been conducting weed control research at the LSU AgCenter's Dean Lee Research Station near Alexandria, La., for a number of years.

Speaking at the recent Northeast Research Station Field Day, he listed the following layby herbicide options:

Caparol or prometryn (80 WP) can be applied to cotton that is at least 15 inches tall to control most small-seeded annual grasses and broadleaf weeds. “Pre-emergence weed control can be expected with this herbicide,” he said.

Cotoran/Meturon or Fluometuron (80 DF) at 1.25 pound or Cotoran/Meturon (4L) at 1 quart on all soil types and applied to cotton at least 15 inches tall for controlling most annual grasses with fair control of broadleaf weeds. Vidrine says residual control can also be expected.

Karmex or Diuron (80 DF) can be used to control most small-seeded annual grasses and broadleaf weeds. “Less activity can be expected on broadleaf signalgrass and browntop millet,” he said. “The herbicide provides less residual weed control than other herbicides.”

Linex or linuron (4L) can be expected to control most small-seeded annual grasses and broadleaf weeds. Limited pre-emergence weed control may be noticed with this product, says Vidrine.

Layby Pro is a premix of the active ingredients diuron and linuron. “Layby Pro activity is similar to Karmex and Linex although it may be slightly more effective on emerged weeds and will provide residual control of smellmellons and gourds.”

Metolachlor (Dual Magnum and others) can be used as a tankmix partner for any of the layby products. “It will not control emerged grasses or broadleaf weeds pre-emergence,” Vidrine notes. “However, metolachlor can provide effective pre-emergence control of small-seeded annual grasses and pigweed.”

Valor SX or flumioxazin (51 DG) at 2 ounces per acre can be applied to cotton, but the cotton must be at least 18 inches tall and have at least 4 inches of bark. “This treatment is effective on pigweeds, prickly sida, copperleaf, most morningglory species, sicklepod and cocklebur,” says Vidrine.

He says growers should not apply more than 2 ounces of Valor per application or more than 4 ounces per season. Use instructions require the addition of a non-ionic surfactant, but not of a crop oil concentrate, organo-silicone surfactant or methylated seed oil.

“Valor will control emerged weeds given sufficient spray coverage and will also provide adequate pre-emergence activity throughout the remainder of the growing season,” he notes. “However, Valor is not an effective grass herbicide.”

Vidrine said Karmex or Direx may be used alternatively at layby by splitting the application rate into two equal portions. The second half should not be applied if the weed problem is not justifiable. Either or both of the split portions may be applied with 1 pint of surfactant per 25 gallons of water in the spray mixture.

“This is necessary if small weeds are present when applied,” he said. “A surfactant will probably be essential any time the second portion of layby is applied. Do not exceed the single application rate in the two split applications.”

He said Syngenta Crop Protection Inc. has requested a new Section 3 label for Reflex post-directed or layby in cotton. Reflex or fomesafen is currently labeled in soybeans but not cotton.

“Reflex would provide an alternative to available herbicides in controlling existing weeds and providing pre-emergence activity,” said Vidrine. “The herbicide is most effective and consistent applied postemergence when controlling morningglories, pigweed, sesbania and several other broadleaf weeds with some residual soil activity expected.

“If the new label is approved, it would provide another tool for farmers,” he said.

With winter wheat selling for higher prices in recent months, more growers may be considering planting wheat after cotton or soybean harvest this fall.

Vidrine said growers should be aware of the rotational crop restrictions following cotton post-directed or layby herbicides.

The recrop intervals for wheat planting: For Sequence, 4.5 months; Suprend, 3 months; Valor, at the 2-ounce rate at least 30 days with 1 inch of rainfall; Caparol, following year; Cotoran/Meturon, Fluometuron, 6 months; Linex, 4 months; Karmex/Direx, following year.