One criteria of successful turfgrass managers in the twenty-first century will be their ability to meet their clientele’s expectations for turfgrass quality standards while minimizing chemical inputs. This demand will be a continuation of a 25+-year trend requiring turfgrass managers to maximize turfgrass quality while reducing the chemical load placed on the environment. Specifically, in the area of weed control, much progress has been made in the past 10 years.
Many turfgrass management systems today deliver improved levels of weed control while reducing the quantity of herbicides applied to the turfgrass environment. This progress is due to a number of factors that include the applications by more knowledgeable and better trained personnel, development of more precise application equipment, commercialization of weed control products (i.e. preemergence annual grass control products) capable of providing excellent levels of weed control at lower rates of active ingredients, etc.
Additionally, a number of chemical manufacturers are now examining ways to improve the efficiency of existing products while reducing the necessary rates of active ingredients. One example of such efforts was the development and commercialization of AgrEvo’s Acclaim Extra. This new product contains the same active ingredient (fenoxaprop-ethyl) as the older Acclaim product and delivers an equally efficacious response at a lower rate of active ingredient. The introduction of the new product was possible due to a refinement of the isomers of fenoxaprop-ethyl.
The existence of different compounds with the same molecular formula is called isomerism and the individual compounds are termed isomers. The number of isomers with a given molecular formula increases as the number of diversity of atoms increase for the molecule. In order to distinguish between isomers and elucidate their chemical properties, the molecular structures must be determined. The structural formula is developed based on the molecular formula and the chemical properties of the substance; compounds, which are isomers, have the same molecular formulas but possess different structural relationships. The structures may differ from each other much the same as a right hand differs from the left hand. The hands may both look the same but are not superimposeable. Instead, they are said to be mirror images of each other. Isomers that are mirror images of each other are called enantiomers.
| What The Study Found | ||||||||||||||||||||||||||||||||||||
Data from this Ohio State University study was gathered two and four weeks after treatment. Total control in this study would be indicated with a 100. The product marked “O” is the optical isomer formulation on the product, and the product marked “R” is the racemic mixture formulation. The optical isomer formulation is developed with the new technology that allows manufacturers to deliver the same level of control via products that include half as much active ingredient. |
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The responses of herbicides are dictated by molecular formulas and their three-dimensional structural configuration. Because isomers differ in the three-dimensional structures, one isomer may be highly efficacious and, for example, possess strong herbicidal properties, while the other isomer may produce no weed control response. Mixtures of equal portions of enantiomers are termed racemic mixtures, which are used in some popular herbicides. Refinement of the racemic mixtures to remove one of the two isomers will result in the restoration of optical activity and create an optical isomer.
Let’s assume a commercial herbicide is produced as a racemic mixture of 50 percent herbicidally active isomers and 50 percent herbicidally inactive isomers. Furthermore, let’s assume this hypothetical herbicide is efficacious when applied at a rate of 2.0 quarts product per acre. If this mixture can be refined to remove the inactive isomer, the theoretical application rate could be reduced to 1.0-quart product per acre. This would then reduce the chemical load by 50 percent on the treated area, yet have no impact on the level of weed control.
In May 1998, a broadleaf weed control evaluation was initiated at The Ohio State University, for the purpose of quantifying the efficiency of various experimental herbicides. Special efforts were expended within this trial to compare the performances of racemic mixture formulations vs. formulations of refined active optical isomers of MCPP and 2,4-DP. The two chemical formulations of each herbicide were evaluated on dandelion, buckhorn plantain, white clover and black medic.
Herbicide efficacy data collected on the four broadleaf weeds evaluated in this trial indicate no significant differences in broadleaf weed control performances between the two formulations of either MCPP or 2, 4-DP. In most instances the differences in efficacy are well within the LSD parameters for significance at the 0.05 level. Most, as well, would be statistically the same even at more statistically conservative levels.
“The main thing to note about this development is the environmental effects,” noted Curtis Clark, marketing manager, Riverdale Chemical, Glenwood, Ill. “The end user is now putting down only half as much active ingredient with the optical isomer formulation while getting the same level of control.
“In the old product, half of the product applied would control weeds but the other half wouldn’t do anything,” Clark continued. “Technology is now available to get rid of that half of the molecule that was inactive in both MCPP and 2,4-DP.”
“Basically, if something in the active ingredient isn’t active, then it’s not desirable from a regulatory or environmental standpoint,” agreed Dave Spak, field development manager, AgrEvo, Kansas City, Kan.
Clark noted there will be few noticeable differences for lawn care operators, and application rates will remain the same.
“Contractors will still use the same rate per acre,” he explained. “And there really won’t be any noticeable price increase associated with this technology.”
“We had to adjust some of the application rates to make sure the correct amount of active ingredient was being applied, but contractors shouldn’t worry that they are paying more or even the same price for less product - they’re still getting as much active ingredient per gallon as before,” added Spak.
What contractors should be aware of, however, is the environmental and regulatory benefits of putting less active ingredient in the ground.
“Putting down half as much product means putting half as much product in the risk cup that the EPA will use to measure pesticides,” Clark pointed out. “This is exactly what manufacturers and contractors should be doing as stewards of the environment so that the least amount of product is applied in order to do the job.”
This research will hopefully lead to the commercialization of chemically refined products, which will allow contractors to achieve desirable weed control with lower rates of active ingredients. Ultimately, this will further assist contractors of the twenty-first century in reducing chemical inputs in the culture of ornamental turfgrass.
The author is the State Turfgrass Extension Specialist with the Ohio State University, Columbus, Ohio. Bob West, Editor of Lawn & Landscape magazine, contributed to this article.
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