Fall-applied Preemergent Herbicides in a Missouri Vineyard Do Not Control Annual Weeds the following Season

Abstract

Nine preemergent herbicides were applied at maximum label rate in Fall 1986, 1987, and 1988 to a `Catawba' grape (Vitis labrusca L.) vineyard in the Missouri Ozark region. The untreated controls showed 30% total weed cover by 28 Apr. 1987, 21 May 1988, and 18 Apr. 1989. In 1988, less rain fell early in the growing season; thus, weed cover in the untreated controls was delayed until late in the season. The herbicides norflurazon, oryzalin, and oxadiazon gave the longest period of acceptable grass control. Dichlobenil, diuron, oxyfluorfen, and simazine gave the longest period of acceptable broadleaf control. Most of the herbicides lost residual activity by early summer. For this reason, fall preemergent herbicide application cannot be relied on to give season-long control the following year in southern Missouri. Chemical names used: 2,6-dichlorobenzonitrile (dichlobenil); N' -(3,4-dichlorophenyl) - N,N -dimethylurea (diuron); N,N -diethyl-2-(1-napthalenyloxy)-propanamide (napropamide); 4-chloro-5-(methylamino)-2-(3-(trifluoromethyl)phenyl)-3(2H)-pyrdazinone (norflurazon); 4-(dipropylamino)-3,5-dinitrobenzenesulfonamide (oryzalin); 3-[2,4-dichloro-5-(1-methylethoxy)phenyl]-5 -(l,l-dimethylethyl) -l,3,4-oxadiazol-2- (3H)-one (oxadiazon); 2-chloro-l-(3-ethoxy-4-nitrophenoxy) -4-(trifluoromethyl) benzene (oxyfluorfen); 3,5-dichloro-N-(l,l-dimethyl-2-propynyl)benzamide (pronamide); and 6-chloro- N,N' -diethyl-1,3,5-triazine-2,4-diamine (simazine).