Abstract/Contents: | "Studies were conducted to determine the length of residual control for commonly-used turf preemergence herbicides. In the first study, flats were buried in a field location and filled with native soil. The pH was 5.3 with 1.5% organic matter. Six flats were used per plot. Herbicides applied as sprays and their application rates were: prodiamine, 0.75 lb ai/A; pendimethalin, 3.0 lb/A; dithiopyr, 0.5 lb/A; bensulide, 10.0 lb/A; siduron, 10.0 lb/A; and oryzalin, 3.0 lb/A. The following herbicides were applied in granular form at 3.0 lb/A: benefin, benefin plus trifluralin and oxadiazon. Plots were treated on April 3, 1998. A rain totaling 1.75" fell 1 day after treatment. Flats were removed at 0, 1, 2, 3, 4, and 5 months after treatment (MAT) and seeded with large crabgrass [Digitaria sanguinalis (L.) Scop.] and yellow foxtail [Setaria glauca (L.) Beauv.]. Flats were maintained in the greenhouse. Shoot fresh weight was recorded approximately 1 month after seeding. At 0 MAT, all treatments controlled both weed species greater than 95%. At 1 MAT, all chemicals except benefin plus trifluralin reduced large crabgrass shoot weight by over 95%. All treatments except bensulide, benefin, and benefin plus trifluralin reduced yellow foxtail shoot weight by over 90%. At 2 MAT, only prodiamine, pendimethalin, and oxadiazon reduced shoot weight of both species by over 90%. By 3 MAT, only prodiamine provided over 90% reduction in large crabgrass shoot weight, while oxadiazon reduced shoot weight by 89%. At 3 MAT, numerical reduction in large crabgrass shoot weight was in the order, from greatest to least: prodiamine, oxadiazon, oryzalin, pendimethalin, bensulide, dithiopyr, siduron, benefin, and benefin plus trifluralin. Only prodiamine and oxadiazon reduced yellow foxtail shoot weight over 90% at 3 MAT. By 4 MAT, no treatment reduced large crabgrass shoot weight by 90% or more. Prodiamine reduced large crabgrass shoot weight by approximately 80% while all over treatments gave less than a 50% reduction. Oxadiazon reduced yellow foxtail shoot weight by approximately 85% at 4 MAT. All other treatments provided less than 70% reduction. At 5 MAT, all treated flats had a similar large crabgrass shoot weight as the untreated flats. At 5 MAT, prodiamine and oxadiazon reduced yellow foxtail shoot fresh weight by approximately 55 and 75%, respectively. Shoot weights in the other treatments were similar to that in untreated flats. A second study was conducted in an established turf site. At 3 MAT, prodiamine, pendimethalin, dithiopyr, bensulide, benefin plus triflualin, oxadiazon, and benefin all provided over 80% control of a mixture of large and smooth crabgrass. At 5 MAT, prodiamine, benefin plus triflualin, and oxadiazon controlled large and smooth crabgrass 70% or greater. Pendimethalin, dithiopyr, bensulide, and benefin controlled large and smooth crabgrass less than 60% at 5 MAT. Herbicide longevity is dependent upon the herbicide used and weed species." |