Herbicide Phytotoxicity, Movement, and Persistence in Asphalt

Abstract

Emulsifiable cationic (CM-4,CRS-1H,CSS-1,CSS-1H) and anionic (SS-1H) asphalts mixed with bromacil (5-bromo-3 sec-butyl-6-methyluracil) varied in their toxicity to green foxtail [Setaria viridis (L.) Beauv.] and velvetleaf (Abutilon theophrasti Medic). Bromacil, picloram (4-amino-3,5,6-trichloropicolinic acid), prometone [2,4-bis(isopropylamino)-6-methoxy-s-triazine], and tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N-dimethylurea} mixed with CRS-1H or CSS-1H gave excellent control of green foxtail and velvetleaf. In greenhouse experiments prometone leached readily from SS-1H while bromacil, picloram, and tebuthiuron leached the least. Leachate from picloram and tebuthiuron at 10,000 ppmw gave excellent control of green foxtail and velvetleaf. After leaching combinations of bromacil or tebuthiuron in SS-1H asphalt with 554 cm of water, enough herbicide still remained in the asphalt to control green foxtail and velvetleaf. Results indicate control would persist for 7 yr if annual rainfall was 76 cm or less and the herbicides were applied at 10,000 ppmw. Bromacil, picloram, prometone, and tebuthiuron moved laterally and resulted in more vegetation kill along a highway shoulder than on a level smooth brome (Bromus inermis Leyss.) area. Herbicide rates of 1,000 and 10,000 ppmw often resulted in excessive lateral movement and vegetation kill 2 yr after treatment. Combining herbicides with asphalt appears to be a feasible method of controlling weed growth, reducing lateral herbicide movement, and lengthening herbicide persistence.