Research Triangle Park, North Carolina, USA
February 26, 2013
Moisture is on the minds of growers as they plan for 2013. And it isn’t just the possible subsoil moisture shortage. It’s also how moisture received during the season affects dissipation of residual herbicides and any impact there might be on crops planted in 2013.
Residual products like Corvus® and Capreno® herbicides provide corn growers with excellent weed control and the moisture received most seasons contributes to their timely dissipation. While the late-season moisture received after those herbicides were applied in 2012 often didn’t benefit the corn, it does aid the dissipation of residual herbicides.
“For growers to gain comfort about the dissipation of residual herbicides, they need to look at their herbicide application records and then review the product labels,” says Brent Philbrook, Bayer CropScience regional manager for field development. He’s responsible for much of the Midwest and Northeast, areas hard hit by the drought.
“When total moisture limits are developed for product labels, we have taken some extremes into consideration. And, think about your area.” He asks corn growers, “How often don’t you really make the minimum moisture requirement? Remember, fall rains help meet the moisture minimums.”
Labels for residual products are just the starting point for a discussion, Philbrook notes. “You have to consider everything in the tank because another product could have greater restrictions for follow crops. Atrazine in the tank mix, for example, can have greater restrictions for certain following crops.” A product used sequentially also needs to be reviewed for any restrictions.
Moisture limitations also need to be considered for corn following soybeans. In recent years, soybean growers have faced some weed resistance. To take on those tough challenges, many growers are using products like ALS, and particularly PPO-inhibitors that they may not have used in the past, Philbrook says. ”They need them now.”
“For instance, if they are treating resistant amaranth, they may find as they read the product label that there may be some carryover that will affect their next corn crop,” he points out. Minimum moisture requirements will be noted on those labels also.
While moisture has been top of mind for most growers, don’t forget about the timing of herbicide applications. “Sun and heat have contributed to degradation since the products were applied, especially for pre-emergence applications made near planting. Although the herbicides have residual characteristics there has been a lot of elapsed time toward the dissipation of the active ingredient,” Philbrook says.
Jim Bloomberg, Bayer CropScience product development manager for corn and soybeans, fungicides and herbicides, points out, “PPO chemistries take longer to break down in the soil than Corvus herbicide.” He encourages corn growers to discuss any concerns with their crop consultants and agricultural retailers as they plan for 2013.
Soil pH can also be a factor in herbicide dissipation, Philbrook notes. “Soils in much of the Midwest are near neutral to slightly acidic and we would expect a herbicide to degrade at a predictable pace on these soils. However, in areas where the soil pH is above 7.5 the dissipation time for certain herbicides can be extended, these extended periods due to higher pH limits are noted on the product labels for specific crops.”
Finally, the sensitivity of follow crops to specific herbicides needs to be considered. The interval for planting typical follow crops is also stated on every product label.
Bloomberg summarizes steps to take in proactive planning for 2013 crops:
- Consider all herbicide products used during 2012, whether in a tankmix or applied sequentially.
- Look for hybrids or varieties that are a little more tolerant to a specific chemistry.
- Wait to plant until the seedbed is in the best possible condition; definitely not in cold and wet soil.
Testing for Herbicide Residues
Bioassays may be another planning aid for 2013. There are two methods growers can use to gain additional information.
Growers can submit soil samples to soil laboratories for chemical or bioassays to see if an active ingredient is still present to affect a sensitive rotation crop.
Growers can also set up a simple soil assay using soils collected from areas such as end rows or boom overlap areas, as well as weedy and less weedy areas. Plant the rotation crop seed, place the soil in a warm and sunny spot to grow and then evaluate the plants.
Species
