Fall Herbicide Applications

Getting crops planted in the spring can turn into a tense waiting game when Mother Nature doesn’t cooperate. Cold, wet conditions can push planting dates to the limit, leaving little time for preplant herbicide applications. Even under less extreme circumstances, there’s no time to spare in the spring before planters start rolling.

That’s why more growers are including fall herbicide applications in their weed control programs. Along with greater spring flexibility, growers are enjoying improved weed control with fall treatments that help halt the development of winter annuals and keep fields clean through planting.

Changing Conditions Mean More Winter Annual Weeds
With hard-to-control winter annual weeds such as common chickweed, henbit, marestail, purple deadnettle, mustards, pennycress and others becoming a bigger problem each season, it’s more important than ever to get fields off to a clean start in the spring. When heavy weed cover blankets spring fields, soils remain cool longer, delaying tillage operations and planting. Some winter weeds also provide a haven for insects that attack emerging crops.

A variety of factors are behind this growing problem, including

  • General warming of fall and winter temperatures that improves conditions for weed growth;
  • Increased adoption of no-till and minimum-tillage practices, which allows for more dense weed cover.
  • Movement from effective preplant and preemergence herbicides to glyphosate and other post emergence applications;
  • Glyphosate and other herbicide programs with limited residual activity that don’t affect germination of winter annuals after harvest.

Head Start on Spring Weed Control
An effective way to prevent weeds from producing seeds in the spring is with burndown and residual herbicide applications in the fall. These treatments, which can usually be made any time after harvest until the ground freezes, give growers a head start on spring weed control.

Kyle Rose, who farms 4,000 acres of corn, soybeans and wheat with his father, Joe, in Iuka, Ill., has been using a fall herbicide program to help control marestail, waterhemp, fall panicum and other weeds in corn and soybeans for 10 years.

“Applying herbicide in the fall helps us achieve our goal of having a no- or minimum-tillage program,” Rose notes. “As soon as crops are harvested while fields remain dry, we go out with DuPont™ Basis® herbicide on fields being planted into corn and DuPont™ Canopy® EX herbicide on fields being planted into soybeans. This spring, Basis® weed control held until about May 1. We were still seeing clean fields until the end of May with Canopy® EX. We applied the Canopy® EX about Sept. 20 last fall, so that’s pretty remarkable.

“Fall treatments help make sure our fields are clean in the spring, so weed pressure is not one of our worries whenever we can start planting,” Rose adds. “Plus, having clean fields in the spring means not having to get a sprayer out in front of the planter before a field is in planting condition.”

The economic benefits of a fall weed-control program speak for themselves, Rose notes. “With the high price of diesel fuel, making two or three trips across the field before planting adds up. That’s when a $15- to $18-per-acre application of Canopy® EX makes a lot of sense.”

Since a number of factors affect spring weed growth, the use of fall herbicides does not always eliminate the need for a spring burndown treatment. Other factors, including weed populations and planting schedules, also must be considered when determining an effective weed-control program.

Plant Corn Earlier
For Illinois grower Mark Wankel, early-season weed control gives him the edge he’s looking for each spring. “Making that herbicide treatment in the fall means there’s one less job to do in the spring. Plus, weed coverage shades the ground, keeping it cool and wet longer. By eliminating that problem, you can plant corn a couple of days earlier.”

Wankel, who farms more than 5,000 acres of corn and soybeans, as well as seed wheat for Pioneer Hi-Bred, has used Basis® herbicide for several years, but switched from applying Basis® in the spring to combining a fall treatment with his strip-till program.

“In the fall, we put down strips with anhydrous; in spring, we plant right on top of the strips,” Wankel notes. “Before we made fall Basis® applications, winter annuals were coming up so thick we could barely find the strips in spring. Now, we put Basis® down in the fall and it does a good job of holding back winter annuals through planting. Then we come back with DuPont™ Realm® Q herbicide at the V3 to V4 stage and continue control right where Basis® leaves off. It’s a great program.”

Stopping Weeds Before They Start
Flexibility with his weed-control program is also crucial for Gail Witt, who farms 7,000 acres with his brother and two nephews near Missouri Valley, Iowa. “If you plan for a fall herbicide application and weather doesn’t allow it, you still have a chance to make a spring application,” Witt says. “But if you’re counting on spring preplant application and weather keeps you from getting it done, you have no other choices.”

Gail’s nephew, Johnnie Witt, who handles the operation’s herbicide applications, was able to apply a post harvest treatment with Basis® to about half of the Witts’ harvested soybean fields last fall, which were expected to be planted to corn in 2011. The remaining fields were treated with Basis® this spring. When the corn was about 8 inches tall, he made a postemergence treatment with glyphosate and mesotrione or atrazine.

The fall Basis® treatments provided far better control than the spring applications, he notes, in part because of the unseasonably cool weather this spring. “With the fall spray, none of the weeds had a chance to establish,” Johnnie Witt notes.

“Fall herbicide applications give us a head start on control,” he adds. “With so many acres to treat, preplant applications can become almost overwhelming in the spring.”

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