Application Best Management Practices

Don’t reduce herbicide rates in an attempt to limit costs.While adhering to best practices for herbicide application can seem daunting in terms of the accuracy and discipline required, hand-weeding is becoming a less viable option for most growers.
 
With all of the products available to today’s growers, nurseries can reduce the amount of hand-weeding required in their operations, said Jeffrey Derr, a professor of weed science at Virginia Tech. Derr recommends integrating herbicide application with cultural control methods to reduce weed-management costs. The availability of preemergence herbicides, in particular, is allowing nurseries to control weeds before they germinate. This translates into cost savings for growers, which is especially important in this tight economy.
 
“You want to minimize the need for hand-weeding through use of selective and postemergence herbicides,” Derr said. “A well-developed weed management program is really going to pay off.”
 
Todd Regenscheid, plant health department head for container production at Bailey Nurseries in St. Paul, Minn., applies preemergence herbicide to new plantings within three days of potting. “This ensures the herbicide is present and activated prior to weed seed germination. This is especially important as temperatures rise and weed seeds germinate rapidly.”

Reduce labor
Not all nursery growers rely on herbicides to control weeds. But the burden of high labor costs in a challenging economy is leading more to leave hand-weeding behind in favor of a dedicated application program. Despite what can seem like expensive up-front costs in terms of materials and equipment, effective herbicide programs should end up saving growers money.
 
“Quite simply, hand-weeding costs more,” said Jason Fausey, a field market development manager for Valent Professional Products. “Herbicides are saving nurserymen money and bringing better results. They’re seeing fewer insect and disease problems and they’re controlling weeds better.”
 
To realize maximum benefit from an herbicide program, nurseries should follow best practices as close to the letter as possible. Common missteps include improper technique, mistiming applications or skipping applications and reducing rates in an attempt to limit costs.
 
“What I see being discussed among growers is often a short-sighted view of the issue. They say something like, ‘I want to cut down on applications. I’ll save more money if I put herbicide out three times a year instead of four,’” said Joseph C. Neal, professor of weed science at North Carolina State University. “That line of thinking can be pennywise and pound-foolish in many cases. You have to think of weed management in terms of best practices management. If you do, you’ll reduce labor costs, and labor is the single greatest expense for any grower.”

The importance of accuracy
When mistakes do occur, Auburn University horticulture professor Charles Gilliam said they can usually be attributed to a simple failure to follow directions.
 
“You have to read the label,” Gilliam said. “We try to emphasize that over and over.”
 
One issue above all challenges nurseries when it comes to herbicide application — calibration, Gilliam said.
 
“To me, that’s the No. 1 issue. Growers who don’t use proper calibration get a lot of variability when they’re putting herbicides out.”
 
Straying from labeled instructions on herbicide packaging can compound a weed problem. Gilliam visited a container nursery that was applying herbicides at half the recommended rate.
 
“They figured that if the full rate provided complete control, they could get by with half that,” Gilliam said. “Instead, they got overrun with weeds.”
 
Even when growers use the proper rate, there is a danger of improper distribution. At application time, it’s not enough to know you’re going to put out 100 pounds per acre, Neal said. It has to be uniformly distributed. Neal has recorded 250-percent variation in distribution from one square foot to the next with traditional application methods.
 
Rather than attempt to treat an entire block in one pass, Neal recommends growers make two passes and calibrate their spreaders to put out half the dose in each direction. He also encourages the use of mechanized air-assist spreaders to achieve better uniformity.

Application
With preemergents, which can be applied as early as March and again in late summer or early fall for winter needs, it’s best to go out with a boom sprayer. For existing weeds, a postemergence product will be necessary.
 
For glyphosate application, Derr recommends going out with a backpack sprayer to “control what it hits and what it doesn’t hit.” Glyphosate can injure plant foliage or cause bark-splitting if it makes contact with green stems. Placing a shield around the nozzle can help avoid damaging spray drift, as can low pressure and large droplets.

Making the right choice
Glyphosate should be part of your program, “but not fully relied upon like it has been in the past,” Valent’s Fausey said.
 
Populations of glyphosate-resistant weeds in field crops continue to increase, and glyphosate-resistant horseweed and pigweed are starting to show up in field nurseries, Neal said. Derr suggests using preemergents to control most annual weeds and spot treat with glyphosate or other postemergence herbicides for control of weeds that escape the preemergence application.
 
“Moving to a preemergence program may be the way for field growers to reduce the amount of injury they’re seeing from glyphosate,” Neal said.
 
Another way to reduce costs, Neal said, is by shifting to liquid herbicide applications for containers. “Granules are more expensive and difficult to apply,” Neal said. “You can apply a liquid more accurately and efficiently.”
 
Once new plants are potted, Derr suggests treating with a preemergence herbicide as soon as possible. When treating with granules, make sure the foliage is dry, Derr said. “You need to get the granules down on the growing medium where the weeds are germinating,” Derr said.
 
Container nurseries that apply herbicides three to six times per year must increase product rotation. That requires growers to be well versed on the primary weeds in their nurseries.
 
While mastering best practices might seem to require a major investment in both time and capital, growers will likely be rewarded for their efforts.
 
“Attention to detail up front can yield returns down the road. You’ll end up with better results, better environmental protection and better products,” Neal said.