In a 3-year field study in corn (Zea mays L.), several herbicides and combinations were studied for the control of yellow nutsedge (Cyperus esculentus L.), giant green foxtail [Setaria viridis var. major (Gaud.) Posp.], and fall panicum (Panicum dichotomiflorum Michx.). Best yellow nutsedge control (87 to 88%) resulted from applications of 4.48 kg/ha of either alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] preplant incorporated or atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] preplant incorporated plus atrazine postemergence with a phytobland oil. Between 72 to 83% control of yellow nutsedge resulted from applications of 2.24 kg/ha of alachlor, 4.48 kg/ha of butylate (S-ethyl diisobutylthiocarbamate), and combinations of atrazine plus butylate. Greater than 90% control of giant green foxtail and fall panicum resulted from butylate plus atrazine or alachlor; postemergence applications of atrazine resulted in significantly less control of fall panicum or giant green foxtail.

Experiments were conducted to examine the effects of low soil moisture on yellow nutsedge emergence in relation to thermal and chronological time and test the ability of thermal models generated previously to predict emergence under water stress. Unsprouted tubers from California and Arizona were planted in pots, buried at field sites in California and Arizona, and subjected to wet or dry treatments. Pots were monitored weekly to determine date of emergence and number of emerged shoots. The California genotype emerged 47 to 61 days after planting (DAP) in the dry treatment and 33 to 49 DAP in the wet treatment, depending on planting site. The range for the Arizona genotype was 51 to 76 DAP in the dry treatment and 43 to 61 DAP in the wet treatment. Days and degree-day intervals to first emergence differed between irrigation treatments and planting sites but interactions were not significant. All models were accurate in predicting emergence dates for genotypes in the wet treatment at the California site, while emergence in Arizona was underestimated by 9 d. Tubers subjected to the dry treatment needed a higher number of accumulated degree-day units before emergence occurred and had fewer emerged shoots as compared to the wet treatment. Degree-day models generated for yellow nutsedge under optimal conditions lack sufficient robustness to be predictive under water stress conditions.

Laboratory studies were conducted to determine the effect of rainfall timing and antecedent moisture on atrazine leaching through intact soil cores taken from no-till and conventional-till corn fields. Simulated rainfall was applied to no-till and conventional-till cores 1 to 14 d after atrazine application and, in a second study, one d after atrazine was applied to no-till and conventional-till cores at 1 to 800 kPa soil moisture. Increasing the lag time between atrazine application and rainfall from one to 14 d reduced the amount of atrazine leached by about 50% for both no-till and conventional-till soil cores. During the same time period, the amount of atrazine adsorbed to soil increased by about 30% for both tillages. Soil dryness (antecedent moisture) at the time of atrazine application had no effect on the amount of atrazine leached through conventional-till cores. However, leaching decreased in no-till cores as antecedent moisture decreased from 1 to 33 kPa; drying to 800 kPa had no further effect. The leaching rate of atrazine was much higher for the initial 0.5 pore volume than for the next 1.5 pore volume at all rainfall timing and antecedent moisture levels. This behavior is indicative of preferential transport.

A system, including a specialized treatment vessel for pesticide uptake studies, was developed and experiments were carried out to determine the ability of Glomus intraradices (Schenck & Smith), G. vesiculiferium (Thaxter), and indigenous vesicular-arbuscular mycorrhizae (VAM) fungi to influence 14C-atrazine uptake and transfer to corn. Uptake by root systems with and without VAM infection was compared to uptake by VAM hyphal systems by controlling access to 14C-atrazine-treated soil. Hyphal systems of Glomus species were able to remove 14C-residue from soil and transfer these to corn. Amount of 14C-residue transferred to corn through hyphal systems was highly correlated to the level of VAM root infection which varied among VAM species. In root systems, variations in 14C-residue uptake resulting from mycorrhization were largely explained in terms of the negative correlation between level of infection and root mass located in 14C-atrazine-treated soil. Allocation of 14C-residue to shoot tissues of corn was greater when 14C-residues were taken up through root systems rather than through hyphal systems. There were significant effects of VAM species on 14C-residue compartmentalization between methanol extractable and nonextractable portions of corn tissues. Data from these experiments in a confined soil system were related to VAM cost-benefit relationships and indicate a significant role for VAM in determining atrazine fate in agricultural systems.

The conversion of 5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone (pyrazon) to N-chloro-4-phenyl-3(2H)-pyridazinone glucosamine (hereinafter referred to as N-glucosyl pyrazon) in intact seedlings and in leaf discs of red beets (Beta vulgaris L., var. Detroit Dark Red) was significantly greater in the light than in the dark. Pyrazon conjugation with glucose was dependent on the carbohydrate status of the leaf tissue, since the formation of the N-glucoside in the dark was further reduced with dark pretreatment but could be restored to the level observed in the light by infiltrating the leaf discs with supplemental sucrose.

Field experiments were established in 1998 and 1999 to evaluate the effect of giant smutgrass competition and hexazinone application on bahiagrass forage yield. The experimental design was a split-plot, with low (< 20% groundcover), medium (20 to 70% groundcover), and high (> 70% groundcover) giant smutgrass density as the main plot factors and hexazinone application or no hexazinone application as the subplot factors. In 1998, without hexazinone, bahiagrass biomass accumulation was 1,164 kg ha−1 mo−1 under low giant smutgrass infestation but 590 and 154 kg ha−1 mo−1 under medium and high giant smutgrass densities, respectively. From harvests occurring 1 yr after hexazinone application, bahiagrass yield in the weed-free area was similar to that growing under low giant smutgrass density. However, as giant smutgrass density increased to moderate or high levels, bahiagrass yield was reduced relative to the weed free. Giant smutgrass biomass accumulation was also measured over time. Giant smutgrass biomass, in both years, increased dramatically in the late summer months at the medium and high densities but not at the low density. It was concluded that bahiagrass was competing with the giant smutgrass at low density and depressed late season growth but was not capable of doing so at higher infestation levels. A rapid increase in late-season giant smutgrass growth was partially explained by the fact that bahiagrass is a short day plant that begins to flower in mid- to late summer, and aboveground biomass production decreases in late summer. This shift in carbon allocation in bahiagrass would exert less competition on giant smutgrass and thus partially be responsible for the late season increase in giant smutgrass growth. Economic analysis performed on these data illustrated that a net loss of $15.20 per stocking unit (cow–calf pairs) would be realized if hexazinone were used to control low densities of giant smutgrass. However, a net gain of $29.28 and $55.75 per stocking unit was observed if hexazinone was used to control giant smutgrass that had reached medium or high levels of infestation, respectively. It was concluded from these data that giant smutgrass should not be controlled until densities reach approximately 35% infestation.

Movement and persistence of the herbicide metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] was assessed following two annual applications to a loamy sand soil under irrigated potato production in east-central Minnesota. Russet Burbank potato (Solanum tuberosum) was grown in plots in 1989 and 1990. Metribuzin was applied prior to potato emergence at rates of 0.56 and 1.1 kg ha-1. Water samples were collected weekly from suction samplers 90 and 150 cm deep. Bromide tracer and water balance data confirmed the movement of water to a depth of 150 cm. Metribuzin was not detected in soil samples below 45 cm during either year. Metribuzin was detected (mean concentration, 0.6 μg L-1) during 1990 in 17 of 473 (3.6%) water samples collected at the 90- and 150-cm depths in 8 of 16 plots. Averaged across rates and years, time for 50% dissipation of metribuzin was 30 d. At the end of the cropping seasons, an average of 17% of initial soil metribuzin remained in the 0- to 45-cm soil layer. Surface soil (0 to 15 cm) metribuzin adsorption coefficients, Kd and Koc, were 1.7 and 120, respectively. Metribuzin appeared to remain in the surface 15 cm of soil where it then degrades.

Clods of three sizes (1.5-, 3.3-, and 5.3-cm diameter) and two hardnesses [soft (0.3 MPa) and hard (2.2 MPa)] were made by incorporating seed from one of the five following weed species: corn poppy (Papaver rhoeas L. # PAPRH), shepherdspurse [Capsella bursa-pastoris (L.) Medic. # CAPBP], smooth crabgrass Digitaria ischaemum (Schreb.) Muehlenb. # DIGIS], common lambsquarters (Chenopodium album L. # CHEAL), and Canada thistle [Cirsium arvense (L.) Scop. # CIRAR], listed by increasing seed size. Under conditions of this experiment, higher germination occurred with larger seed. The higher germination was connected with fewer dormant seed remaining in the clods. Germination significantly decreased (13%) in the larger soft and hard clods with the smaller seed sizes (less germination associated with more dormant seed remaining in the clod). Germination of the two larger seed decreased (23%) only in the larger soft clods but was less significant with both small seed. Non-emerged seedlings increased with larger clods and was most significant with the three large seed in the hard clods and absent with the three large seed in the soft ones. On the average, 70% of the germinated seed emerged. Differences in germination as well as in nonemerged seedlings caused decreased emergence on larger clods. Clod influence in germination and emergence was explained by the volumes of the clod layers involved, and in some comparable aspects corresponded with volumes (depths) of soil layers.

In a 3-year study propanil (3′,4′-dichloropropionanilide) at 6.7 or 9.0 kg/ha was applied postemergence as single or split applications to rice (Oryza sativa L. ‘Starbonnet’ and ‘Nova 66′) 15 to 75 days after crop emergence. The effect on crop injury, maturity, grain yield, and seed and milling quality was measured on rice grown in weed-free plots. Residues of DCA (3,4-dichloroaniline) in grain and straw from treated rice plants and of propanil and TCAB (3,3′,4,4′-tetrachloroazobenzene) in treated soil were determined. Propanil applied at all times and rates in 1968 and 1970 or applied at all rates at 15 to 55 days after crop emergence in 1969 did not reduce grain yields, but 6.7 kg/ha applied 65 and 75 days after crop emergence in 1969 injured rice plants vegetatively and reduced grain yields. Plant maturity, seed viability and milling quality of grain were not affected. Residues of DCA in grain and straw were highest from treatments applied 65 and 75 days after crop emergence; rice straw contained more DCA than did grain.

False broomweed (Ericameria austrotexana M.C. Johnst.) had lower near-infrared (0.75- to 0.90-μm waveband) reflectance than did six other associated rangeland species and mixed herbaceous vegetation. False broomweed's low near-infrared reflectance was attributed to its erectophile (erect-leaf) canopy structure. Other species had planophile (horizontal-leaf) or intermediate-leaf orientation. False broomweed's low near-infrared reflectance caused its image to be dark reddish-brown on color-infrared (0.50- to 0.90-μm waveband) film, compared with red or magenta images of other rangeland species. Microdensitometric measurements made on the film showed that false broomweed had significantly higher optical counts than those of associated species and mixtures of species.

Several weed-free and bermudagrass competition periods were established and maintained in cotton to evaluate their influence on cotton yields and reproduction of bermudagrass. Cotton sprayed with fluazifop for bermudagrass control 4 or 8 weeks after emergence yielded 93 and 90% as much as weed-free cotton. This compared to losses of 16 and 26% when bermudagrass was permitted to compete with cotton for 12 and 25 weeks, respectively. Cotton handweeded for 8 to 12 weeks yielded the same as weed-free cotton and 9% more than cotton weed free for only 4 weeks. Bermudagrass seed production was prevented and rhizome production was negligible when weed competition did not exceed 8 weeks and weed-free periods exceeded 4 weeks. Bermudagrass produced significant amounts of seeds (45 to 88% of weedy checks) and rhizomes (9 to 31% of weedy checks) in plots weed free for 4 weeks and in plots where control was delayed for 12 weeks. Cotton grades were reduced because the cotton lint was contaminated with grass in plots weed free for only 4 weeks, and in plots where bermudagrass competed for 25 weeks.

Laboratory and greenhouse studies were conducted to determine the response of four plant species to 4-amino-3,5,6-trichloropicolinic acid (picloram). Germination of soybean (Glycine max (L.) Merr., var. Lee) seeds was inhibited, step-wise, by 10−8 to 10−3 M concentrations of picloram. Safflower (Carthamus tinctorius L.) germination was inhibited at 10−3 M; however, radish (Raphanus sativus L.) and barley (Hordeum vulgare L.) were not affected by any concentration studied (10−6 to 10−3 M). Measurement of several parameters of growth such as fresh and dry weight, shoot height, number and dimensions of leaves, percent necrosis, hypocotyl or epicotyl length, and hypocotyl diameter revealed that picloram was both growth promotive and inhibitory to safflower, radish, and barley. Levels of picloram required for growth promotion or inhibition varied with the species, stage of plant growth, herbicide concentration, the specific tissue, and the parameter being measured. Typical malformations such as twisting of stems, death of growing points, and occurrence of callus growth (depending on the species and herbicide dosage) were observed in picloram-treated seedlings. Studies on water loss by evapotranspiration suggested that picloram caused a possible alteration of stomatal behavior and/or a disturbance of water metabolism in plants under appropriate conditions.

Tomatoes (Lycopersicon esculentum ‘Roma VF’) and weeds were seeded at two locations in 1973 and 1974. In separate plots, jimsonweed (Datura stramonium L.), tall morningglory [Ipomoea purpurea (L.) Roth.], and common cocklebur (Xanthium pensylvanicum Wallr.) seedlings were thinned to densities ranging from 2.7 to 86 plants/m2. Densities of large crabgrass [Digitaria sanguinalis (L.) Scop.] ranged from 11 to 430 plants/m2. There were a few instances of difference in nutrient concentrations in tomato and weed leaf tissue, but no clear relationship was evident between concentration of N, P, K, Ca, Mg, and S and weed density. Considerably more fruit weight was produced per kilogram of total assimilated N, P, and K in the weed-free than in the weed-infested tomato plots.

Field research was conducted in Tennessee at Jackson in 1991 and at Milan in 1992 to compare the effect of MSMA and pyrithiobac on cotton development, yield, and quality. In separate treatments to different plots, pyrithiobac at 0.14 kg ai ha–1 did not affect development, yield, and quality of cotton. MSMA at 2.24 kg ai ha–1 decreased cotton plant internode length 10 to 15% and height by 15% 5 wk after late treatment both years. MSMA applied to 50 cm cotton reduced subsequent plant height in 1992, but other plant characteristics were not affected. In 1991, MSMA increased squares and decreased blooms and bolls for monopodia and sympodia position one and two, which suggested a delay in plant development. In 1991, mechanical harvest lint yields were decreased by MSMA at first harvest while increasing second harvest lint yields. However, in 1991 only MSMA applied late decreased total harvest lint yield 20%. Plant mapping data determined that the yield decrease was a result of decreased yields at sympodia positions one and two. Cotton seed arsenic analysis indicated that MSMA-late increased arsenic levels by ≈ 1 ppmw in 1991 for sympodia at position one and two compared to the untreated check, while position two contained the highest level of 1.8 ppmw.

Phytotoxicity of chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} in cell cultures of Canada thistle [Cirsium arvense (L.) Scop. # CIRAR] was approximately 30-fold greater than in leafy spurge (Euphorbia esula L. # EPHES) cultures. Differences in chlorsulfuron phytotoxicity in these two species were attributed to large differences in cellular metabolism of the herbicide. Leafy spurge cells metabolized all of the applied 14C-chlorsulfuron within 72 h of treatment, while Canada thistle metabolized less than 2%. Acid hydrolysis of the metabolic products isolated from leaf disks and cell cultures of leafy spurge yielded a radioactive product that cochromatographed with a 2-chlorobenzenesulfonamide standard. Therefore, metabolic transformation occurred on the heterocyclic portion of the molecule. A major metabolite was further characterized as 2-chloro-N-[[4-(hydroxymethyl)-6-methoxy-1,3,5-triazin-2-yl]aminocarbonyl]-benzenesulfonamide by cochromatography with the authentic standard.

Bioassay techniques were evaluated for the determination of chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} residues in soil and water. A linear response of corn (Zea mays L.) primary root length to chlorsulfuron concentrations (InX+1) of 0.0 to 16.0 μg/L was observed in the water bioassay. Several soil extraction bioassay methods were attempted and found to be highly variable. A Ca(OH)2 soil extraction bioassay technique produced a linear response of primary corn root length to chlorsulfuron concentrations ranging from 0.0 to 64.0 μg/kg. The efficiency of the Ca(OH)2 extraction bioassay was determined by the use of 14C-chlorsulfuron. Recovery efficiency at 1.0 μg/kg was 74% and averaged 62% at all higher chlorsulfuron concentrations.

Field experiments were conducted in 1997 and in 1998 to determine the effects of density and time of emergence on Eriochloa villosa growth and seed production in Zea mays. E. villosa was transplanted at four densities (3, 9, 27, and 81 plants m−2) to simulate emergence at four Z. mays growth stages (VE, V2, V5, and V10). Compared to E. villosa plants that emerged with Z. mays plants, total above-ground E. villosa biomass at maturity of plants grown at 3 plants m−2 was reduced by 54, 97, and 99% when emergence was delayed until the V2, V5, and V10 stages of Z. mays, respectively, in 1997. In 1998, total aboveground E. villosa biomass at maturity was reduced by 70, 87, and 99% when emergence was delayed until the V2, V5, and V10 stages of Z. mays, respectively. E. villosa aboveground vegetative biomass per plant at maturity was linearly related to seed production per plant in each year. E. villosa seed production m−2 decreased nonlinearly as density decreased and time of emergence was delayed. Based on estimated model parameters, maximum seed production was 57,100 and 12,700 seeds m−2 in 1997 and 1998, respectively. Within time of emergence, E. villosa density did not affect seed mass per seed, however, seed mass of late-emerging cohorts was less than that of early-emerging cohorts. Time of weed emergence relative to the crop was a very important factor in determining biomass and seed production. Results suggest that late-emerging plants may not be very important to long-term management of E. villosa.

We have isolated both a genomic and near full length cDNA clone for a D-class cyclin gene from the perennial weed leafy spurge. Sequence analysis indicates that this gene has the highest similarity to CYCLIN D3-2 of Arabidopsis. This gene is preferentially expressed in growing shoot apices and is up-regulated in adventitious buds on resumption of growth following loss of correlative inhibition (apical dominance). CYCLIN D3-2 is also induced in nongrowing adventitious buds of plants treated with gibberellic acid or after removal of leaves—treatments known to up-regulate expression of G1 to S phase transition–specific genes such as HISTONE H3 in adventitious buds. CYCLIN D3-2 was not induced on removal of the apical and axillary buds. Expression of CYCLIN D3-2 is down-regulated in adventitious crown buds during initiation of ecodormancy in early winter. Sequence comparisons of CYCLIN D3-2 with its putative orthologue from Arabidopsis identified several conserved motifs in the promoter region and a conserved region capable of forming a stable hairpin loop in the 5′ untranslated region. Conservation of these noncoding sequences across species strongly suggests they have a regulatory function.

In the range of 4.4 to 49 C, there is an exponential relationship between temperature and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) diffusion coefficients. Diffusion is low in air-dry soil for all temperatures. It increases to a maximum value when the soil has between 8 and 15% w/w soil moisture content and then decreases steadily as moisture content increases. When the air-filled fraction of soil void space is reduced below approximately 40% v/v by either compression or addition of moisture, diffusion begins to decrease. An equation was developed to predict trifluralin diffusion coefficients from a factorial experiment with seven soil moisture contents, five soil temperatures, and two bulk densities. Diffusion coefficients range from 3.8 X 10-11 cm2/sec to 2.8 X 10-6 cm2/sec. Fifteen terms are required in the prediction model to describe accurately the response surface of trifluralin diffusion coefficients. With the equation it is possible to predict trifluralin diffusion coefficients for any combination of measured soil parameters as long as they are represented by the range of the variables used in the experiment.

Correlations between herbicide damage and several physiological factors were examined in the field for ponderosa pine (Pinus ponderosa Dougl. ex P&C Lawson) and greenleaf manzanita (Arctostaphylos patula Greene). Pine injury caused by 2,4-D [(2,4-dichlorophenoxy) acetic acid], glyphosate [N-(phosphonomethyl) glycine], or triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid]} was compared to leader growth rate, needle growth rate, predawn xylem potential, daytime xylem potential, and photo synthetic rate occurring on the dates of herbicide application. Shrub injury for each of the three herbicides was compared to predawn xylem potential, daytime xylem potential, and photo synthetic rates. Both species exhibited less injury from herbicide applications made at the end of September than from any applications made from April through October. Comparison of factors highly correlated to herbicide damage indicates that highest herbicide selectivity occurs when pine has ceased growing, the xylem potential of the pine is relatively low (high water stress), and the xylem potential of the manzanita is relatively high.