Over 9 yr, bandane (polychlorodicyclopentadiene isomers) at 67 kg/ha, bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide] at 11 and 22 kg/ha, DCPA (dimethyl tetrachloroterephthalate) at 22 kg/ha, and terbutol (2,6-di-tert-butyl-p-tolyl methylcarbamate) at 22 kg/ha applied preemergence controlled 94 to 100% of large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSP] in a lawn of common bermudagrass [Cynodon dactylon (L.) Pers. # CYNDA]. Control from benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) at 5 kg/ha, DCPA at 11 kg/ha, simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] at 5 kg/ha, and terbutol at 11 kg/ha was 90 to 99%. Bandane and bensulide persisted in soil to control large crabgrass a year after treatment.

Laboratory experiments were undertaken to investigate the allelopathic activity of Mexican sunflower in soil as well as to determine the effect of several soil factors on activity. There was a decrease in shoot and root growth of the test plant species when grown in soil previously planted with Mexican sunflower. However, seed germination was not affected. Soil-water separated from the same soil also inhibited shoot and root growth. A water extract from Mexican sunflower leaves applied to soil also reduced shoot and root growth, but the degree of inhibition varied among test plant species. Incorporation of dry Mexican sunflower leaves into soil at the rate of 1 and 2% (w/w) inhibited the growth of rice seedlings. The phytotoxic activity of incorporated leaf residue diminished 4 wk after treatment of soil. The inhibitory effect of a leaf water extract in nonautoclaved soil was less than in autoclaved soil and the phytotoxic effect to rice seedling grown in autoclaved soil was less than in autoclaved sand. It is suggested that the decrease in allelopathic activity of Mexican sunflower extract and its residue in soil is due to the action of soil microorganisms and the soil adsorption of the active components.

Extension workers are sensing pressure to use soils information and chemical characteristics data to guide farmers in selecting pesticides least prone to leach into groundwater. Our objective was to estimate differences in herbicide migration to groundwater under conditions typical for the Southeast Coastal Plain, and to consider how a farmer might be advised to use such knowledge in selecting herbicides. We used a simple computer code for microcomputers to predict persistence and migration of 17 herbicides through a hypothetical, coarse-textured soil typical of the Southeast Coastal Plain. Appropriate herbicides were selected for several common crop-weed problems, such as sicklepod in soybean and Palmer amaranth in corn. Groundwater was assumed to be 3.15 m below the soil surface. Herbicides selected covered a broad range of half-lives and organic carbon partition coefficients. Only after the first-order degradation rate constant was reduced by a factor of five did predicted soil water concentrations of several herbicides at the groundwater interface reach normal detection limits. Still, predicted concentrations were below the level established for health effects advisory purposes. Due to the large number of uncertainties and the inability to estimate practical benefits, we conclude that data relating to soil and herbicide characteristics cannot be used at this time to override cost effectiveness, efficacy, and other factors normally considered by farmers and Extension professionals in herbicides for weed control.

A commercial fertilizer (40-0-0, N-P-K) was screened into seven particle size fractions (23, 58, 165, 465, 1,310, 3,728, or 10,606 particles/g) and coated with dithiopyr (0.345%, wt/wt), prodiamine (0.689%), oryzalin (3.28%), or oxadiazon (2.76%). Dithiopyr and oryzalin provided best southern crabgrass control with a fertilizer size of 465 particles/g or greater, whereas prodiamine controlled southern crabgrass greatest using a size fraction at least 165 particles/g. Southern crabgrass control with oxadiazon was not as dependent on particle size, with all fraction sizes of 58 or 165 particles/g or greater controlling southern crabgrass equally in 1995 or 1996, respectively.

In controlled-environment chambers at 29/33 C day/night and 1000 μE·m-2·s-1 photosynthetic photon flux density (PPFD), increasing the CO2 concentration from 350 to 675 ppm (v/v) did not affect leaf area or total dry weight of well-watered plants of barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG], goosegrass [Eleusine indica (L.) Gaertn. # ELEIN], or southern crabgrass [Digitaria ciliaris (Retz.) Koel. # DIGSP] after 30 days. However, the whole plant transpiration rate per unit leaf area decreased, and the water use efficiency increased, in response to CO2 enrichment. In a subsequent experiment, with water availability limited by an imposed drought, CO2 enrichment reduced the effects of water stress and significantly increased leaf area and total dry weight of the three C4 grasses and soybean [Glycine max (L.) Merr. ‘Ransom’]. Growth enhancement in response to CO2 enrichment was greater in soybean than in the C4 grasses. By improving their water economy, CO2 enrichment can increase the growth of both C3 and C4 plants under water stress. However, growth stimulation can be expected to be greater in C3 plants.

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.

Multiple applications of several preemergence herbicides were evaluated for weed control and for phytotoxicity to gladiolus (Gladiolus X hortulanus L.) grown from cormels in 1984 and 1985. Oryzalin [4-(dipropylamino)-3,5-dinitrobenzenesulfonamide] consistently provided acceptable control of southern crabgrass [Digitaria ciliaris (Retz.) Koel. # DIGSP], goosegrass [Eleusine indica (L.) Gaertn. # ELEIN], and smooth pigweed (Amaranthus hybridus L. # AMACH) and had minimal effect on gladiolus plant growth even after four applications. Pronamide [3,5-dichloro (N-1,1-dimethyl-2-propynyl)benzamide], alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide], and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] provided erratic weed control and reduced yields of gladiolus corms.