Maximizing Residual Length

When it comes to herbicide management, the mantra is “start clean, stay clean.” The foundation set at the beginning of the season will often decide the fate of crops come harvest. Bob Kavinsky, Syngenta agronomy service representative based in Nebraska, says growers should maximize the residual length of their herbicide applications to keep fields clean of weeds from planting through harvest. One such way is through split shot applications…

“One of the things that we run into with overlapping residuals of herbicide is we’re trying to add value and length to residual to a product. By putting on a two-third rate up front, what we’re doing is getting good weed control. But we’re also timing that application so we take care of those early weeds. And many of our problem weeds like waterhemp and Palmer tend to germinate more in the middle of the season or later on in the spring. By putting on a second application and filling in the rest of that rate, in other words using the other third of the rate or in combination with other chemistries, what we’re doing is we’re adding back into refreshing that top inch or 2 of soil with the herbicide. And that just adds to the overall residual.”

Kavinsky says there are several factors that growers should keep in mind to get the most out of their residual herbicides…

“Rainfall could make a big difference. This spring, we’ve had a lot of rain, and that rain tends to move chemistries around. Where that chemical is in the soil profile can make a difference, and where it’s activated can make a difference. Regardless of the chemistry, using a full use rate is absolutely essential. Of course, canopy can really help us a lot. So any time we can hold back the weeds until the time that the canopy form for the corn or soybeans, weeds don’t compete well in shade. And then the type of herbicide, again, two sites are better than one.”

Maximizing residual length also helps in the fight against herbicide resistance…

“Weeds adapt, and they’re not a one and done situation. In many cases, they germinate over a wide window of timing. Our preemergence herbicides have to have extended control, or we typically use a two-pass system, putting down an Acuron® and then following up with a Halex® GT, or putting down a Bicep® II Magnum followed by a Halex GT or something like that. Many times it’s that multiple modes of action, multiple timings, that can help offset some of that herbicide resistance from the residual control aspects. A general rule of thumb is always choose a residual. Never spray a chemical by itself that does not have a residual.”

Kavinsky offers other stewardship tips when it comes to residual herbicides…

“Most importantly is always use multiple sites of action. Typically, you want a minimum of three. Many of Syngenta programs are four effective mode of actions. Tillage can be helpful, so reasonable to help break up the soil bank. Always use the full label rates. So, full use rates, multiple modes of action. Where possible, use a two-pass system. Today, if we can manage our weeds effectively, and we can, we do so by using those two-pass systems, multiple modes and full use rate.”

Syngenta works with growers through the Resistance Fighter® program to teach weed identification, coach in resistance management and provide localized solutions. They can visit www.ResistanceFighter.com to learn more. Always read and follow label instructions. Acuron and Bicep II Magnum are Restricted Use Pesticides.