Field studies were conducted from 1995 to 1997 near Tifton, GA, to determine the benefits of stale seedbed weed control in cucumber. Three stale seedbed management systems—(1) power till stale seedbeds twice (2 ×), (2) glyphosate application immediately after planting, and (3) combination system of stale seedbeds power tilled once 2 wk prior to planting followed by glyphosate application immediately after planting cucumber—were evaluated as main plots. Subplots were weed management systems after planting cucumber: intensive, basic, and cultivation alone. Weed densities were generally greater in 1996 and 1997 than in 1995. Yellow nutsedge was the overall predominant species in 1995 (46 plants m−2), with Florida pusley being the predominant species in 1996 and 1997, at 80 and 124 plants m−2, respectively. Generally, stale seedbeds shallow tilled 2 × had fewer weeds and greater cucumber yields than stale seedbeds treated with glyphosate. Glyphosate did not adequately control emerged Florida pusley on stale seedbeds, resulting in reduced cucumber yield. Clomazone preemergence and bentazon/halosulfuron postemergence were used for broadleaf weed control in the intensive weed management system. These herbicides injured cucumber plants, delayed maturity, and reduced yield. Based on our results, stale seedbeds shallow tilled 2 × can be integrated into cucumber production and provide effective cultural weed control. Furthermore, these systems will replace the need for potentially injurious herbicides.

Studies were conducted from 1990 through 1994 near Tifton, GA, on the population dynamics of yellow nutsedge and certain annual weeds in peanut—corn and peanut—cotton rotations. Converse rotation sequences were included to eliminate year effects. Continuous fallow plots (noncrop) were included for comparison. Within each crop, including fallow, were 3 levels of weed management: low, moderate, and intensive. Weed densities and numbers of yellow nutsedge tubers were not affected by crop rotations, but they were affected by individual crops and weed management systems in each crop. Fallow plots, including those with intensive fallow weed management using tillage and nonselective herbicides, consistently contained more yellow nutsedge plants and tubers than other plots. Moderate and intensive weed control systems in peanut and cotton reduced yellow nutsedge densities and tubers, but only peanut yields were increased by intensive weed management. Weed management systems did not affect yellow nutsedge densities in corn, although yields were increased by moderate and intensive systems due to improved control of other weeds. Our results suggest that uninterrupted plantings of peanut, corn, or cotton with moderate levels of weed management are generally sufficient to suppress yellow nutsedge and allow for optimum crop yield. If fields are fallow, yellow nutsedge population densities and tubers will increase exponentially, even with intensive fallow weed management.

Greenhouse and laboratory studies were conducted to evaluate responses of ivyleaf morningglory, pitted morningglory, palmleaf morningglory, and smallflower morningglory to several herbicides in relation to leaf structure, epicuticular wax, and spray droplet behavior. Two- to four-leaf stage plants of each species were highly susceptible to acifluorfen, bentazon, bromoxynil, glufosinate, and glyphosate. However, at the five- to eight-leaf stage, these species were less susceptible, and control was herbicide specific. Spray droplets of these five herbicides had a higher contact angle on ivyleaf morningglory than the other three species with a few exceptions. Stomata and glands were present on both adaxial and abaxial leaf surfaces of all species, and palmleaf morningglory and smallflower morningglory had more of these than did the other two species. Trichomes were present on all species except palmleaf morningglory. Epicuticular wax mass was highest in ivyleaf morningglory (57 μg cm−2) and lowest in smallflower morningglory (14 μg cm−2). Wax consisted of homologous short-chain (< C18) or long-chain (> C20) hydrocarbons, alcohols, acids, and triterpenes. Smallflower morningglory waxes lacked short-chain length components. Triterpenes were absent in palmleaf morningglory and smallflower morningglory epicuticular waxes. Untriacontane (C31 hydrocarbon) and tridecanol (C30 alcohol) were common major long-chain components in waxes of all four species. Heptadecane (C17 hydrocarbon) and octanoic acid (C18) were common major short-chain length wax components in pitted, ivyleaf, and palmleaf morningglory. In spite of some differences in leaf surface structures, wax mass, and wax components among the four species, there was no clear relationship between these parameters and herbicide efficacy.

A field experiment was conducted during three cropping seasons to compare weed control and cotton yield provided by conventional (CV), glufosinate-resistant (LL), and glyphosate-resistant (RR) weed management systems under standard (102 cm) and narrow (38 cm) row spacing grown in conventional and conservation tillage systems. The conventional tillage and/or CV cotton received a PRE application of pendimethalin. The CV, LL, and RR cotton varieties received two POST applications of pyrithiobac, glufosinate, and glyphosate, respectively, at two- and four-leaf cotton growth stages. A final (LAYBY) application of trifloxysulfuron was applied to 38-cm row cotton while a LAYBY POST-directed spray of prometryn plus MSMA was used in 102-cm row cotton. The LL and RR weed management systems controlled at least 97% of large crabgrass, Palmer amaranth, sicklepod, and smallflower morningglory, while the CV system controlled 89, 73, and 87 to 98% of large crabgrass, smallflower morningglory, and Palmer amaranth, respectively. Sicklepod control increased from 85% in 102-cm rows to 95% in 38-cm rows in the CV herbicide system. Yellow nutsedge and pitted morningglory control exceeded 98% and was not affected by tillage, row spacing, or weed management system. Cotton yield was not affected by row spacing any year, by tillage in 2005, or by weed management system in 2004 and 2005. In 2006, yield in the RR weed management system was 27 and 24% higher than LL and CV weed management systems, respectively. In 2004, yield of conventional tillage cotton was 18% higher than conservation tillage cotton, but in 2006 the yield in conservation tillage was 12% higher than conventional tillage.

Research was conducted to determine the effect of planting pattern, plant density, and levels of weed management intensity on intercepted photosynthetically active radiation (IPAR), weed control, and cotton lint yield in glyphosate-resistant cotton. Twin-row planting pattern canopy IPAR was 55% 7 wk after emergence (WAE) and 76% 9 WAE compared to 48% for single-row planting pattern 7 WAE and 59% 9 WAE. Regardless of cotton density, row spacing, or weed management intensity, control of browntop millet and Florida beggarweed was at least 88% 18 WAE. Benghal dayflower, sicklepod, and smallflower morningglory control was greater in twin-rows compared to single-rows at a cotton density of 7 plants m−2. Control of Benghal dayflower and sicklepod increased when cotton density increased at low weed management intensities; however, cotton density had no effect on weed control at higher levels of weed management input. At a cotton plant density of 7 plants m−2, twin-row cotton yielded 220 kg ha−1 more than the single-row planting pattern. Data indicates twin-row cotton production is feasible and that control of various weeds was better in twin-row than single-row pattern at lower cotton density and weed management intensity.

An experiment was conducted to determine the utility of multispectral imagery for identifying soybean, bare soil, and six weed species commonly found in Mississippi. Weed species evaluated were hemp sesbania, palmleaf morningglory, pitted morningglory, prickly sida, sicklepod, and smallflower morningglory. Multispectral imagery was analyzed using supervised classification techniques based upon 2-class, 3-class, and 8-class systems. The 2-class system was designed to differentiate bare soil and vegetation. The 3-class system was used to differentiate bare soil, soybean, and weed species. Finally, the 8-class system was designed to differentiate bare soil, soybean, and all weed species independently. Soybean classification accuracies classified as vegetation for the 2-class system were greater than 95%, and bare soil classification accuracies were greater than 90%. In the 3-class system, soybean classification accuracies were 70% or greater. Classification of soybean decreased slightly in the 3-class system when compared to the 2-class system because of the 3-class system separating soybean plots from the weed plots, which was not done in the 2-class system. Weed classification accuracies increased as weed density or weeks after emergence (WAE) increased. The greatest weed classification accuracies were obtained once weed species were allowed to grow for 10 wk. Palmleaf morningglory and pitted morningglory classification accuracies were greater than 90% for 10 WAE using the 3-class system. Palmleaf morningglory and pitted morningglory at the highest densities of 6 plants/m2 produced the highest classification accuracies for the 8-class system once allowed to grow for 10 wk. All other weed species generally produced classification accuracies less than 50%, regardless of planting density. Thus, multispectral imagery has the potential for weed detection, especially when being used in a management system when individual weed species differentiation is not essential, as in the 2-class or 3-class system. However, weed detection was not obtained until 8 to 10 WAE, which is unacceptable in production agriculture. Therefore, more refined imagery acquisition with higher spatial and/or spectral resolution and more sophisticated analyses need to be further explored for this technology to be used early-season when it would be most valuable.