Field studies were conducted in 1996, 1997, and 1998 to determine the effectiveness of several grasses as filter strips for reducing sediment and herbicide losses in runoff. Big bluestem, eastern gamagrass, switchgrass, and tall fescue reduced total runoff volume by at least 55, 76, 49, and 46%, respectively. Within the 127-d sampling period, each perennial grass filter strip investigated reduced total sediment loss in surface runoff by at least 66%. All four species reduced total fluometuron loss in runoff at least 59%. Big bluestem and eastern gamagrass reduced norflurazon loss in runoff 63 and 86%, respectively. When a filter strip was present, fluometuron and norflurazon losses did not exceed 5 and 3% of the total applied, respectively, compared to 12 and 5%, respectively, when a filter strip was not present.

A survey was conducted in 2000 across 38 counties in Mississippi on 192 randomly selected soybean fields to assess the most common occurring weeds. Statewide, prickly sida, which was present in 40% of the fields sampled, was the most common. Pitted and entireleaf morningglory were present in 34 and 29% of the soybean fields, respectively. Broadleaf signalgrass and barnyardgrass were the most common annual grasses, and yellow nutsedge was the most common sedge observed. Trumpetcreeper and redvine were the most common perennial vines. In the Mississippi Delta region of Mississippi, prickly sida was present in 45% of the fields sampled. The trend of occurrence of other species in the Delta mirrored statewide results. In eastern Mississippi, prickly sida and broadleaf signalgrass were found in 43% of soybean fields. Sicklepod, common cocklebur, and balloonvine were more prevalent in eastern Mississippi, when compared with the Mississippi Delta. Since 1982, there has been a sevenfold decline in the occurrence of common cocklebur and a fourfold decline in the occurrence of johnsongrass in Mississippi soybean. Also, the occurrences of redroot pigweed, common ragweed, and fall panicum have declined. Conversely, the occurrences of yellow nutsedge and broadleaf signalgrass have increased. The occurrences of barnyardgrass, prickly sida, redvine and trumpetcreeper have been relatively static over the past two decades.

In 1994, herbicide efficacy and competitive index databases were adjusted in the soybean herbicide recommendation program HERB to best reflect data for Mississippi. Field experiments were conducted to compare efficacy and economics of postemergence herbicides recommended by HERB and MSU-HERB. The study was conducted utilizing four locations over 2 yr, which provided different soil types, weed spectra, and environmental conditions with which to evaluate weed control from herbicides recommended by these programs. HERB and MSU-HERB agreed on an herbicide recommendation in 62% of the modeling runs. Herbicides recommended by both software versions were generally effective for controlling the predominant weed species at each location. In instances where there was a significant difference in herbicide efficacy between herbicides recommended by HERB and MSU-HERB, improved weed control resulted from herbicides recommended by MSU-HERB. In 1994, excellent moisture conditions enabled soybean to gain a significant competitive advantage over weeds and, as a result, yield loss predictions after treatment were overestimated in most instances. Conversely, 1995 environmental conditions better represented average Mississippi growing conditions, and yield loss predictions after treatment were more accurate. Yield loss prediction accuracy of HERB versions was related to the length of interference between soybean and weeds. Thus, prediction accuracy of HERB and MSU-HERB was similar. Soybean yield increase and net economic gain following MSU-HERB recommendations was as high or higher than following HERB recommendations.

A laboratory experiment was conducted to compare the adsorption and desorption of fluometuron between two soils, one collected from an eastern gamagrass filter strip and the other from a cropped field. Fluometuron adsorption to soil collected from the filter strip was higher than to soil collected from the cropped field. K d values for fluometuron ranged from 1.9 to 3.6 for soil from a cropped area, compared with 2.9 to 5.3 for soil from the filter strip, indicating a weak to moderate binding affinity for fluometuron. The total fluometuron desorbed ranged from 48 to 79% of that adsorbed, most of which (50 to 59% of the total amount desorbed) occurred during the first desorption cycle with both soils. Approximately 11% less fluometuron desorbed when a filter strip was present. Results indicate that eastern gamagrass filter strips can influence adsorption–desorption processes between fluometuron and a Brooksville silty clay soil by altering the soil properties, specifically soil organic matter.

Field validation studies were conducted in seven Mississippi environments at three application timings to confirm postemergence (POST) recommendations generated by the computer herbicide decision aids HERB and SWC. HERB and SWC agreed on herbicide treatments in only 14% of the location–application timing combinations. Weed scientists involved in the study agreed on treatment recommendations approximately 33% of the time. The HERB model agreed with a faculty member on only one herbicide treatment, while the SWC model was slightly more agreeable in this regard. Subsequent weed flushes, varied production practices, and delayed weed emergence accounted for a majority of the underestimated predictions given by HERB. Only 55% of the predicted values presented for estimated weed control ratings were similar to actual weed control ratings. Over 75% of the predictions that differed from actual weed control values were underpredictions. Recommendations from both computer models were effective in reducing yield loss below that of the untreated check, and recommendations from the HERB model generally improved yield more than those from the SWC model in most instances. HERB and SWC predictions of yield losses with no weed control were not significantly different from the actual yield loss from the untreated check in nine of the 12 instances at Starkville, seven of the 12 instances at Brooksville, six of the 12 instances at Newton, and three of the six instances at Hollandale. The HERB model estimated yield loss similar to that of the actual yield loss 83% of the time, while predictions from the SWC model were accurate 76% of the time. HERB overestimated yield loss in six of 21 application timing–experiment combinations and underestimated yield loss only once. Yield loss was overpredicted as high as 78%. SWC overpredicted yield loss in five of 21 instances and also underestimated in five instances. SWC did not overpredict yield loss to the same magnitude as HERB in many instances.