Jimmy Brackman nearly always keeps a hoe in his pickup. So does his 89-year-old father, Tom. Tom does it by habit, having faced cantankerous weeds long before glyphosate and other herbicides came on the market. Jimmy does it in today’s never-ending battle against herbicide-resistant pigweed,
“In some soybean fields, there’s no way to control pigweed,” said Brackman, who farms near Bradley, Ark. “Roundup is just not doing what it used to do.”
The younger Brackman has farmed in the southwest Arkansas region most of his life. Cotton, once king in the area, now takes a backseat to soybeans, corn and wheat. About 80 percent of his crops are irrigated from either center pivots or poly tubing in furrow watering systems.
Irrigated corn makes 150 bushels to 200 bushels per acre or more. Full-season soybeans average 50 bushels to 60 bushels. Beans double-cropped after wheat usually cut 35 bushels. Wheat averaged about 70 bushels per acre this year.
In nearly every field, weed resistance is the biggest problem he faces.
“Atrazine normally does a good job on holding down pigweed early in corn,” Brackman says. “That helps when we see escapes from soybeans fields rotated into corn the next year.”
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He works with his crop consultant, Steve Schutz of Shreveport, La., to scout fields and determine which weed control program will work best. On full-season beans, Schutz recommends 2 ounces of Valor applied in the fall and 1 ounce in early spring. “Right after planting, a combination of Dual and a glyphosate is applied,” Shutz says. “That usually provides good control. We may also apply some Reflex within two weeks of planting.
“Our biggest pigweed control problem is with wheat-beans. It’s harder to get preemergence control. By depending totally on irrigation in June, it’s more difficult to get the herbicide activated. Rainfall does a better job for us.”
Bob Scott, University of Arkansas Extension weed specialist, says most farmers “are learning to live with resistant pigweed, but we haven’t gained a lot of ground.
“Glyphosate resistant pigweed is the most troublesome and costly weed in Arkansas soybean and cotton production. Even with best management practices and near perfect herbicide programs, the soil seed-bank can increase to near unmanageable levels. A single female pigweed plant is capable of producing over 1.5 million seed.”
Scott says soil residual herbicides are needed for effective pigweed management in all systems. “These herbicides require moisture for activation and without rainfall or irrigation after application, they are less effective and may allow weeds to become established. Early applications are more likely to receive rainfall in a timely manner than later season applications.”
A good burndown program is the first step to good weed management in early spring. “If pigweeds are present at planting time, Gramoxone Inteon or other paraquat herbicides are very effective to remove existing vegetation,” Scott says. “Preemergence herbicides, such as Dual, Valor, Authority MTZ or one of the Valor containing premixes, such as Envive, may also be used.”
Scott says cover crop mulch can be used in combination with soil residual herbicides to reduce pigweed germination on flat-planted fields. In addition, Prowl or Treflan applied pre-plant incorporated will also provide control or suppression of Palmer amaranth.
“Flexstar at 1.25 pints per acre applied in-crop will provide good control of Palmer amaranth less than 2 inches tall,” Scott says. “This may be as early as 10 days to 14 days after soybean emergence. Flexstar can be tank-mixed with glyphosate for effective control of other weeds present.”
Additional residual herbicides have shown good pigweed control. And the LibertyLink over-the-top herbicide system is another alternative. “Rotation to LibertyLink soybean and proper use of Liberty herbicide is a good resistance management option,” Scott says. “Liberty should be applied to 2-3 inch pigweed, following an effective residual preemergence treatment, such as Prefix.”
Schutz says some growers south of Shreveport are seeing good pigweed control in LibertyLink soybeans. “However, a lot of farmers don’t want to switch varieties because of good 70-bushel yields they’re seeing. But if you don’t get pigweed before they’re 4 inches tall, you’re not going to get them.”
Scott says an Arkansas Extension “zero tolerance program” is helping hold pigweed down in some areas. “We’ve had success with this program.Growers make a commitment to not let any pigweed seed out of their fields.
“But that can be difficult. If you harvest one field that has pigweed then move the combine to a zero tolerance field without cleaning the combine, the pigweed problem starts all over again. Pigweed can find its way around the system.”
Brackman says he hasn’t seen any ryegrass resistance to glyphosate. “A good rotation is the best way to handle resistance,” Brackman says.