Photo: The Dow Gardens Archive, Dow Gardens, Bugwood.org, showy forsythia, Forsythia x intermedia
At this point, most turf professionals are in the process of making preventative weed treatments to their properties. Soon after, post-emergent weed treatments will also commence. Though hundreds of options exist, are you using the proper formulation for your application?
Have you ever taken a close look at the active ingredients listed on the herbicide label that you use? Most combination products contain 2, 4,-D, dicamba, triclopyr, or MCPA, and are formulated in two ways; amines or esters. Knowing the difference between the two and when to use them can increase your weed control dramatically. Using the right formulation can also prevent damage to non-target plants within the landscape as well.
For the sake of conversation, 2, 4-D will be used as an example. 2, 4-D has been a staple of weed control since the 1940s, and continues to be a primary ingredient in a majority of multiple-ingredient herbicide products. 2, 4-D controls a large number of perennial weeds, but usually has little effect on grasses. However, 2, 4-D can injure non-target species (including grasses) if used incorrectly. Many broadleaf plants including tomatoes, grapes, flowers, and some trees are sensitive to 2, 4-D. While not intended, herbicidal drift occurs on a regular basis. In most cases, drift is a result of 2, 4-D's volatility; when it vaporizes and moves to a non-target area. This can (and does) occur with several other commonly used herbicides.
2, 4-D and other herbicides are commonly formulated as either an amine salt or ester. Esters have higher vapor pressures than amines. Higher vapor pressures result in increased volatilization. Even though there are some "low volatile" esters available, amine salts are generally less volatile than esters. Amine formulations are typically used in landscape settings and scenarios when drift is a primary concern.
The question is then posed "Do esters or amines provide better weed control?" The answer to this question is not cut-and-dry. Ester formulations are typically more active on weeds in comparison to amines. This is due to the fact that esters are more soluble when in contact with the plant's waxy cuticle. Plants are more likely to quickly absorb esters, as amines are more water soluble. Once the chemical is absorbed into the plant (either amine or ester), it is converted to the active acid, which in turn injures or kills plants that are susceptible to the respective herbicide.
As we all know, correct timing is crucial for acceptable weed control. This also comes into play when deciding what formulation to use; ester or amine. During cooler weather (March, April, and early May), ester formulations can be used safely, and typically provide better weed control than amines. As temperatures increase, esters are more prone to volatilization, and a switch should be made to amine formulations if drift is a concern. In warmer temperatures, amines and esters have about the same effect on weed control. Some esters are also "hot", and can injure grasses when temperatures are too warm. Most herbicide labels list a temperature range in which they should be used, so be sure to follow these recommendations.
In conclusion, it is clear that both amines and esters have their place in weed control programs. Depending on the time of year, location, weed pressure, and application technique, you can safely use different formulations of an herbicide to achieve acceptable weed control. Consider using ester formulations in the early spring, for hard-to-control weeds, or for spot spraying small areas. When blanket spraying large areas, think about landscape plantings, trees, and temperatures before making any decisions.
As with any herbicide application, wind speed and direction should also be monitored. No herbicide should be applied when wind can move an herbicide to non-target plants. Always read product labels, and adhere to manufacturer recommendations.