The key to understanding spring broadleaf weed control is that herbicides used for this purpose are postemergence and primarily foliar absorbed, pointed out John Street, extension agronomist, Ohio Cooperative Extension Service, The Ohio State University, Columbus, Ohio, in the Ohio Turfgrass Foundation’s TurfNews.
Street said key environmental factors influencing the absorption and translocation of foliar absorbed broadleaf weed herbicides in the spring include:
- Air and soil temperatures
- Soil moisture
- Light intensity
- Relative humidity
- Dew formation
- Wind
- Rainfall after application
Herbicide formulation also plays a major role in determining the success or failure of broadleaf weed control in the spring, Street pointed out. “Weeds tend to absorb and translocate ester formulations more readily than amines under the cooler, more erratic conditions of early spring,” he said. “Amines are more effective later in the spring when air and soil temperatures are warmer.
“In addition, broadleaf herbicide applications are usually more effective in late spring/early summer than in late winter/early spring because more sugar/photosynthate is translocated downward,” Street continued. “Therefore, fall applications normally provide a broader range of broadleaf weed control than spring applications.”
Data from a three-year study of broadleaf weed control conducted at Purdue University shows that early spring broadleaf weed control is difficult to achieve with any formulation, Street remarked. “In general, both amine and ester formulations provided good-to-excellent weed control before late March,” he said. “Ester formulations provided go-to-excellent weed control the first three weeks in April and were superior to amine formulations. However the effectiveness of amine formulations began to equal that of esters typically from late April and beyond.”
As a final note, Street said that the effectiveness of broadleaf weed control depends on a combination of herbicide selection, environmental factors and cultural practices.