Droplet Size Determines Product Efficacy
Kruger admitted it is a daunting task to think that every product on the market could be tested under different scenarios.
“I think the key is to try and find a trend in the data. We are starting to get there. The reality is that we will never be able to address every individual applicator situation because there are so many variables. But we think there are things we can do to understand how flat fan nozzles behave compared to turbo chamber nozzles versus air-induction nozzles. I think there are trends we can pick out in terms of adjuvants, too. Every company has their own adjuvant, but if you break it down all those adjuvants fall into a few similar classes—non-ionic surfactants, crop oils, methylated seed oils, polymers, micro-emulsions and others.” Kruger said.
The latest work spurred ahead when the EPA became frustrated with the number of drift complaints they were hounded with from chemical trespass complaints.
COARSE DROPLET PROBLEMS
Kirk Howatt, weed scientist, teaching researcher at North Dakota State University, Fargo, noted how the EPA was headed toward demanding pesticides, and especially herbicides, be applied with coarse to very coarse droplets to mitigate drift potential. But Howatt has determined that those large droplets don’t make sense in some situations.
“We started looking at systems and tried to identify if we increase the droplet size what will happen to the performance of a herbicide. We realized with some herbicides as you increase the droplet size the weed control decreases,” Howatt said. “For some herbicides small droplets are the best, and as they get bigger, the worse the control.”
He continued, “We have had some research plots where the weed control was about 50 percent of the maximum possible. Instead of getting 95 percent control, we were only getting 45 percent to 50 percent, and that is a big concern.”
He has primarily worked with growth regulator products such as 2,4-D and dicamba. The research of the last couple years has shown for some herbicides that small droplets are not optimal and large droplets are not optimal either. With herbicides, when droplets are categorized into five different sizes—very fine, small, medium, coarse and very coarse—very fine droplets aren’t often effective in weed control, although small droplets are quite often effective.
The research has shown that some herbicides alone or mixes containing adjuvants do not show much variance in weed control as the droplet size changes, and in those cases, use of the very coarse droplet makes the most sense to limit drift risk.