WEED MANAGEMENT AND TALL FESCUE QUALITY AS INFLUENCED BY MOWING, NITROGEN, AND HERBICIDES

A 3-yr field study was conducted to determine the influence of N level (98 and 196 kg ha-1 yr-1), mowing height (3.2, 5.5, and 8.8 cm), and three herbicides on weed encroachment and overall quality of tall fescue Festuca arundinacea Schreb. cv. Rebel 11. The major objective of this study was to identify cultural methods of excluding weed development in tall fescue. Dithiopyr [3,5-pyridinedicarbothioic acid, 2-(difluoromethyl)-4-(2-methylpropyl)-6-(trifluoromethyl)-S,S-dimethylester] and pendimethalin [N-(1-ethylpropyl)-3, 4-dimethyl-2,6-dinitrobenzenamine] were applied preemergence for smooth crabgrass [Digitaria ischaemum (Schreber) Schreber ex Muhlenb.] control, and fenoxaprop [(+/-)-2-[4-[(6-chloro-2-benzoxazolyl)oxy]- phenoxy]propanoic acid] was applied postemergence for crabgrass control. Rates of dithiopyr and pendimethalin were reduced or eliminated on selected plots in the last 2 yr of the study to determine if reduced herbicide inputs would continue to provide effective crabgrass control. Tall fescue mowed at 8.8 cm resisted smooth crabgrass invasion, exhibited best visual summer turf quality in 1990 and 1991, had poorest winter turf quality, and had highest white clover (Trifolium repens L.) populations. Other environmental factors and lower mowing height (3.2 or 5.5 cm) reduced summer turf quality in 1990 and 1991. High N improved fall and winter turf quality, but not summer quality. Nonherbicide-treated plots receiving high N had less smooth crabgrass than low N plots, but high N provided no additional crabgrass reduction in herbicide-treated plots. High mowing (8.8 cm) was the best cultural management strategy for reducing smooth crabgrass encroachment and maintaining tall fescue cover. Results indicated that smooth crabgrass control with label use rates of herbicides was warranted when mowing tall fescue at 3.2 or 5.5 cm.