Environmental influence on postemergence chemical control of crabgrass (Digitaria spp.) in turf

The influence of environment on efficacy of postemergence herbicides was quantified. A three-fold approach included: first, use of field test sites to select an herbicide sensitive to environmental conditions; second, quantify herbicide responses to temperature, moisture, and morphological conditions; and third, conduct laboratory research to determine if differential uptake, translocation, or metabolism would account for these responses to the environment.

Section one of the research was designed to determine if field research can be used to detect herbicides sensitive to environmental influences. Herbicides compared were: imazaquin, BAS 514 and tridiphane to fenoxaprop-ethyl (the cool-season herbicide standard) for postemergence control of large crabgrass (Digitaria sanguinalis) in Kentucky bluegrass (Poa pratensis) and bermudagrass (Cynodon dactylon) turf. BAS 514 was significantly influenced by variable environment.

Section two of the research studied control of southern crabgrass (Digitaria ciliaris) by BAS 514 as influenced by morphological and physiological factors. BAS 514 efficacy was influenced by crabgrass growth stage, air temperature, and irrigation level. Flowering crabgrass plants were the most tolerant, while preemergence and true-leaf stages were the most sensitive. Plants held at soil moisture levels near saturation and 25° C were the most sensitive to BAS 514. BAS 514 was not effective against plants grown at low moisture levels and 15° or 35° C.

Section three of the research compared the uptake, distribution, and metabolism of ¹⁴C BAS 514 in southern crabgrass and Kentucky bluegrass plants, a sensitive and non-sensitive species. Foliar applied BAS 514 was rapidly absorbed by both species. Uptake and partitioning was similar in both species from 0.5 to 32 h, but different at 128 h, with bluegrass more uniformly distributing the herbicide. Metabolism of BAS 514 was low with only 3% metabolism in both species. Uptake, distribution, and metabolism apparently are not involved in differential sensitivity to BAS 514.

Field research can be used to select an herbicide sensitive to environmental influences. Temperature and soil moisture influenced the herbicidal activity of BAS 514. Uptake, translocation and metabolism did not appear to influence selectivity of this herbicide.