Field and greenhouse studies were conducted to evaluate selected PRE-applied herbicides for sprangletop control. In greenhouse studies, oxadiazon and dithiopyr provided excellent (> 89%) red sprangletop (L. filiformis) control. Pendimethalin and metolachlor + atrazine provided good (80–89%) to excellent control for 6 mo and 2 mo during studies 1 and 2, respectively. Isoxaben and atrazine provided poor (< 70%) control during both greenhouse studies. In field studies, good to excellent bearded sprangletop (L. fascicularis) control followed dithiopyr, pendimethalin, metolachlor, and metolachlor + atrazine treatments. Dithiopyr at 0.8 kg ai/ha provided best (> 95%) sprangletop control throughout the 6-mo testing period. Under field conditions, control was inconsistent following oxadiazon with good to excellent control during one study and poor control in another study. Better or equal control than metolachlor + atrazine followed dithiopyr, pendimethalin, and metolachlor alone treatments. Oxadiazon also provided similar or better control than metolachlor+atrazine in three of four studies. Over all studies, dithiopyr provided best sprangletop control, followed by metolachlor, metolachlor + atrazine, pendimethalin, and oxadiazon. Isoxaben and atrazine treatments provided poorest or inconsistent sprangletop control.

Variation in interference relationships have been shown for a number of crop-weed associations and may have an important effect on the implementation of decision support systems for weed management. Multiyear field experiments were conducted at eight locations to determine the stability of corn-foxtail interference relationships across years and locations. Two coefficients (I and A) of a rectangular hyperbola equation were estimated for each data set using nonlinear regression procedures. The I and A coefficients represent percent corn yield loss as foxtail density approaches zero and maximum percent corn yield loss, respectively. The coefficient I was stable across years at two locations and varied across years at four locations. Maximum yield loss (A) varied between years at one location. Both coefficients varied among locations. Although 3 to 4 foxtail plants m−-1 row was a conservative estimate of the single-year economic threshold (Tc ) of foxtail density, variation in I and A resulted in a large variation in Tc . Therefore, the utility of using common coefficient estimates to predict future crop yield loss from foxtail interference between years or among locations within a region is limited.

Bahiagrass is used for roadsides, pastures, and lawns in the southeastern United States mainly because of drought and nematode tolerance. Metsulfuron is a sulfonylurea herbicide, which selectively controls bahiagrass in bermudagrass. Certain cultivars of bahiagrass were observed to be tolerant to recommended rates of metsulfuron. Therefore, research was conducted to investigate the susceptibility of five major bahiagrass cultivars to metsulfuron applied at increasing rates to 42 g ai/ha. Five bahiagrass cultivars were evaluated: ‘Pensacola’, ‘Tifton-9’, ‘Argentine’, ‘Common’, and ‘Paraguayan’. Argentine, Common, and Paraguayan cultivars showed a four- to fivefold increased tolerance to metsulfuron compared with Pensacola. Because of yearly inconsistencies, results for Tifton-9 were inconclusive.