Soybean South


Scout, Spray Early

Although this year may bring a spring full of tough weeds,
scientists seem positive that with a little early planning and vigilance
throughout the season, weeds can be kept under control.

Across the South, many soybean farmers experienced vast amounts of rainfall last year – leaving them unable to effectively control spring weeds and pushing harvest well into the fall. For this reason, some weeds may be lurking in soybean fields this year, and researchers predict that many tough or resistant weeds such as volunteer corn and Palmer pigweed could be extremely prevalent.

According to Dr. Jason Bond, weed scientist at Mississippi State University, “Like many places across the South, it started raining in Stoneville, Miss., last year in early September and didn’t stop for six weeks. Corn fields not harvested prior to early September were left in vulnerable conditions that could lead to volunteer corn and other overwintered weeds this year.”

Bond said the amount of end-of-season corn on the ground varied from field to field last year. Many Southern corn fields had weeks of standing water in low areas or were filled with certain corn hybrids that may be less tolerant to late-season, heavy or long-term moisture. These factors, combined with the late harvest, mean that more Roundup Ready corn likely hit the ground later in the year and now may be overwintering for a spring appearance.

Dr. Larry Steckel, weed scientist at the University of Tennessee, agreed that conditions are ripe for a stronger showing of both volunteer corn and Palmer pigweed this year.

“I anticipate 2010 to be one of the worst years we’ve had for Palmer pigweed. I expect a lot of growers will get hit, and if not caught early enough, there will be significant yield losses,” Steckel says.

No. 1 priority: Field inspection
Researchers agree that scouting regularly and applying a residual herbicide will be the best defense against tough weeds this spring.

“You need to go into spring with a game plan – farmers really need to start scouting fields early to determine weed issues before they become an unmanageable problem,” Steckel says. “If you don’t start controlling Palmer pigweed until it is 10 inches, you’re not going to kill it at all.”

Other weeds, such as volunteer corn, may not be as high on the priority list as Palmer, but still need to be detected early for easier control.

“When the soil and air temperature get just right in the spring, you’ll start seeing volunteer corn emerge,” Bond says. “You’ll see tall soybeans and cotton and taller corn in between, but you want to start controlling volunteer corn before it gets to this point.”

Bond said farmers can start scouting for volunteer corn long before it is seen from across a field. Close inspection of soybean fields may be the best approach for combating this resistant weed.

“When you are scouting for other summer annual weeds, make note of areas infested with volunteer corn,” Bond says. “Get it early. The best control we’ve seen for volunteer corn is Select Max – this herbicide knocks it out quickly before it becomes established and is competing with the developing crop.”

Steckel agrees that spraying volunteer corn in the early stages is the best solution in fighting it. “In soybeans, we recommend getting an application down early, prior to the stalks getting up to six to seven inches,” Steckel says.

Apply a residual herbicide
To fight tough weeds before they become an unmanageable problem, researchers suggest applying a residual herbicide prior to planting.

“If you wait until a postemergence application to control weeds, many of them are going to be too large to kill,” Steckel says. “Farmers should go in with a residual, such as Valor or Valor XLT, to start killing weeds early.”

Spraying a residual also gives farmers more flexibility if poor weather conditions occur. For example, if farmers were to spray a pre-emergence with four weeks or more of residual control, they would have a larger window of time to get in the field with a post application after planting.

Archer Malmo, who represents Valent, contributed information for this article.