Issue 3, May 20, 2019
What’s in a Rate?
If a little is great, and a lot is better, then way too much is just about right!- Mae West It might hold with some things, but when it comes to pesticides, rates are critical for control. Some labels have a range of pesticide application rates. These rates are based on timing and conditions. Applying the wrong amount of herbicide can result in problems that include, nonperformance in the control of weeds, and injury to off-target vegetation, turf, and non-target species. Most serious problems encountered with herbicide use often stem from improper application. Errors in application often occur with inaccurate calibration, mixing, improperly operating equipment, and failure to read the product label. A study conducted at the University of Nebraska looking at agriculture pesticide use found-"that the primary problem with ag chemicals is not the chemicals themselves but the people who apply them.” Misapplication wastes an estimated $1 billion annually. With these things in mind, applicators should take time to ensure the application is done accurately, with the correct amount applied at the right time.
So what is the need for the full labeled rate?
The definition of a labeled rate is a rate or range of rates set by herbicide manufacturers to consistently provide effective control of weed species across growth stages and site conditions.
The definition of a low rate is a rate applied below the labeled rate that may provide control at a single location, but will not be consistent over a wide range of conditions.
Weeds that are routinely exposed to low rates can allow a portion of the population to survive, leading to the evolution of herbicide-resistant populations.
When speaking with pesticide distributors, a concern was expressed that many applicators start off using too much of a product and often at the wrong time of the year. For example, a pesticide dealer mentioned selling a lot of, Quinclorac, a herbicide for crabgrass control, for use in late July.
If we dive into this issue, we will see that the problem isn't with the product, it is with the timing of use. The label recommends for use on crabgrass but it is not recommended for use over 90 degrees Fahrenheit as it will result in turf injury. We, unfortunately, aren't given more information on the amount other than it is “too much”. The label has one rate only for use, and so I am left with an unanswered question.
With an unanswered question of amount, we could dive into what would cause an applicator to apply more product than the recommended rate? Could it be an issue that they don't trust the label and that they think more is better? Or maybe they didn't get a good kill previously and want to ensure a better kill this time? Is the issue that the product was ineffective, or is there possibly a resistance issue at hand? The reverse can be asked as to why a person might be tempted to use a lower rate. Do they not trust the label? Do they believe that they can save money by using a lower rate and still gain control?
As we run the questions in our head about why someone would use too much or not enough of a product, we go back to the core lesson of reading and following the label directions. Many hours and thousands of dollars are invested in product research studies to determine the amount and time that they are most effective for control of pests. It is the law to follow the label directions. As an applicator, it is your responsibility to read and follow the label. Scouting and correctly identifying the pest will allow you to determine the pesticide for treatment. Following these steps can provide better weed control and can save time as well as money in retreatment. Herbicides may not be necessary in a healthy well maintained lawn. When they are needed, use them as part of an integrated pest management program.
Sources-
Applied Weed Science- Ross, Merrill, Lembi, Carole.
http://wssa.net/wssa/weed/resistance/
Authors:
Maria Turner
Michelle Wiesbrook