Finding The Right Residual
With planting just a few weeks away, many growers and dealers will begin reviewing last year’s herbicide programs to determine which products worked best on their farms.
This year, however, more growers and dealers — with the 2009 replants and late-winter harvests still fresh in their minds — will be looking at residual herbicides to help manage some of the early-season headaches they dealt with last year.
“Last year was one for the record books,” says Tommy Thompson, manager at Crop Production Services in Fancy Farm, KY. “We had growers who either couldn’t get into the fields or who were forced to replant their crops multiple times. Those who weren’t using a residual herbicide as part of their burndown program often had a tougher time keeping their fields clean early and getting an overall good start on the season.”
Though residual preemergence herbicides are becoming an increasingly popular component of many successful spring practices, it is important for growers and dealers to know which residual herbicide will work best for their needs.
Researchers suggest that residual herbicides should be evaluated on several factors, such as weed control, length of residual, and rotational flexibility. Preemergence residual herbicides such as Envoke, Valor, or Authority can vary in performance in the different factors.
As with any herbicide program, it is important to determine what types of weeds the product can be expected to effectively control. Tough weeds can differ by geographical area, type of soil or even overall history of chemical use in a field.
“Growers need to be sure that the residual product they are choosing to use will thoroughly control the specific weed problems in their fields,” says Kevin Bradley, University of Missouri weed scientist. Bradley suggests that understanding the weed profile of the specific geographic area is the first step in effective weed management.
Weed scientists are also reinforcing the role of preemergence residual herbicides in the fight against glyphosate-resistant or glyphosate-tolerant tough weeds.
“It is so much easier to control or reduce the population of glyphosate-resistant waterhemp with a preemerge compared to using a postemerge. It’s one of our top recommendations and top lines of defense against glyphosate-resistant waterhemp,” Bradley says. “Our research trials frequently show that you can control glyphosate-resistant waterhemp most effectively with a preemerge herbicide. No question, the research shows preemerges work better on tough weeds.”
In Thompson’s area, glyphosate-resistant marestail is extremely prevalent, and he believes other resistance issues may be just around the corner. He often recommends a 2-ounce rate of Valor in burndown programs to his customers who struggle with glyphosate-resistant marestail.
“The best way to kill tough weeds such as marestail is to hit them when they are small or not even out of the ground,” Thompson says. “This is why I recommend using a preemerge residual herbicide.”
Experts agree — one of the most important factors in choosing a residual herbicide is the length of control the herbicide provides. Many products today offer a range of a few days to several months of residual control, making it important for growers and dealers to know what to expect from various residual herbicides.
Length Of Residual
Dealers may ask: How long is enough control? Many university researchers suggest that a residual should give control for at least four weeks.
Bradley says in the case of residual herbicides, the longer the control the better.
“A lot of research has shown that if it is a particularly unpredictable year like 2009 and you use a product that only gets two weeks or less of control, you may have to come back with not only one but two post applications — which is usually too many trips across the field,” he says. Thompson has similar recommendations for his customers.
“A residual should have control for three to four weeks to be effective and a good investment,” he says. “This timeframe can usually hold you over until you can get in the field with a post application if needed.”
The unpredictable nature of farming makes the ability to use one product on a variety of different crops extremely important. For example, the erratic spring weather many experienced in 2009 pushed some growers to plant a different crop than planned. Fluctuating market prices can also move growers to shift to a more profitable crop. The ever-changing future that growers experience makes choosing a residual with rotational flexibility a wise decision.
“Using Valor is like a shotgun effect; you do one application and it can take care of several crops, should plans have to change,” Thompson says. “My customers appreciate that flexibility.”