Application of 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) was effective in controlling quackgrass (Agropyron repens) in fields planted to corn. Corn yields were greatly improved by the treatment. Most favorable dates of application were in the fall or in the early spring before planting. Applications after corn planting were much less effective. Favorable rates of application were 2 to 4 lb/A. Rates lower than 2 lb/A were not as effective and rates over 8 lb/A were not required. Atrazine and 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) were generally superior to other triazine analogues used. Greater solubility and greater activity as a foliar spray favors use of atrazine for control of quackgrass.

The influence of 3–amino–1,2,4–triazole (ATA) and eight of its salts or derivatives on defoliation and secondary growth in cotton, the straight growth and respiration of Avena sections, and the respiration of cotton leaf discs were reported in a previous paper.

A typical scotoactive stomatal behavior was noticed in Carissa spinarum L.; Gymnosporia emarginata Laws; Maba buxifolia Cl.; Flacourtia sepiaria Roxb.; Dodonaea viscosa L. and Randia malabarica Lamk. This stomatal behavior was reversed artificially by foliar application of paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) at 100 ppmw or 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] at 2000 ppmw. The size of the stomatal aperture, stomatal conductance and the rates of transpiration were enhanced significantly by the herbicide treatment. The physiological basis for the induction of desiccation and death of plant organs is thought to be the excessive stimulation of stomatal aperture, stomatal conductance and consequently high rates of transpiration observed here. The data suggest that herbicide-induced desiccation is the consequence of inhibition of scotoactive behavior and increased water loss with attendant desiccation and death of leaves.

Establishment and early growth characteristics were defined for sourgrass [Trichachne insularis (L.) Nees], one of the most serious pasture weeds in Hawaii. Optimum germination of sourgrass seeds was obtained in the light at 30 C or with alternating temperatures of 20 and 30 C or 25 and 35 C. Germination in complete darkness was poor except at alternating 25 and 35 C. Sourgrass germinated better than buffelgrass (Cenchrus ciliaris L.) and guineagrass (Panicum maximum Jacq.) at low moisture tension. Sourgrass was capable of emerging from a maximum depth of 5 cm but percent emergence was greatly reduced at planting depths greater than 3 cm. Sourgrass flowering response to photoperiod was day-neutral. Under conditions of adequate moisture, the growth of sourgrass was severely suppressed when grown with buffelgrass, or/or guineagrass. If grazing is restricted, either of these grasses would be useful for controlling sourgrass.

The interaction of chloramben and paraquat on weed control and crop safety in peanuts was examined in a series of experiments. Greenhouse experiments revealed that chloramben was antagonistic toward paraquat on sicklepod and peanut, which are species tolerant to chloramben and sensitive to paraquat Control of Florida beggarweed, a species sensitive to both herbicides, was generally improved with tank mixtures. Similar results were obtained in field studies. Antagonism obtained with tank-mixing chloramben plus paraquat was also obtained by applying chloramben prior to paraquat Studies with 14C-labeled herbicides on Florida beggarweed revealed that chloramben inhibited foliar penetration of paraquat, but paraquat had no effect on foliar penetration of chloramben.

Brownspine pricklypear (Opuntia phaecantha Engelm. & Bigel.) was effectively controlled within 2 yr following application of a 1:1 mixture of 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] and picloram (4-amino-3,5,6-trichloropicolinic acid) at a rate of 0.6 kg ae/ha. Brownspine pricklypear canopy cover and dry weight declined from approximately 23% and 3800 kg/ha to 8% and 1600 kg/ha, respectively. No significant difference in total herbaceous forage dry weight was found between plants growing inside brownspine pricklypear canopy areas and plants growing outside the canopy areas. Differences between areas in species composition were significant in that cool-season grasses dominated the canopy area of the brownspine pricklypear colonies while warm-season grasses dominated the area outside the canopy. Control of brownspine pricklypear will enhance livestock carrying capacity of rangeland in the Rolling Plains of Texas by increasing forage availability but not forage production.

Sown-grass margin strips, historically established to limit pesticide drift and soil erosion, are now also promoted for enhancing floral diversity and associated ecosystem services. To better understand weed community assembly in grass margin strips, we performed floral surveys in 75 sown-grass margin strips in two regions in France and characterized each species using information from trait databases. We hypothesized that traits of dominant species would differ between newly sown-grass margin strips and older strips. Weed species were separated into functional groups based on their traits using multiple correspondence analysis and hierarchical ascendant classification. Functional group trajectories were investigated in sown-grass margin strips that differed in age using a space-for-time substitution approach. We found that geophyte, competitor, and monocotyledon species were more frequent and abundant in grass margin strips than therophyte, ruderal, and dicotyledon species. Results also showed that floral diversity was greatest in grass margin strips of intermediate age. Our findings have implications for optimizing diversity and ecosystem services on land enrolled in conservation programs and suggest that mowing later in the season and periodic soil disturbance can increase floral diversity. The analytical framework that we introduced in this research can also be used to explore weed community assembly in other systems.

The influence of management practices at a system level is rarely studied in weed science, even though weed communities respond to the cumulative effect of farm management systems. On-farm visits and detailed grower surveys were used to objectively classify 59 Indiana tomato fields into management systems. Fields were chosen to represent a range of practices used to grow conventional and organic tomatoes. Multivariate statistical analyses identified five distinct management systems based primarily on differences in hours spent hand-weeding, use of plastic mulch, irrigation, row spacing, and whether tomatoes were staked. Farmers generally reported many more hours of hand-weeding for organically managed fields than for fields in the other groups. This finding may reflect a trade-off between the use of herbicides and the need for hand-weeding. However, some organically managed fields were grouped with conventional fresh market fields, suggesting that management practices besides herbicide inputs can be used to reduce hand-weeding. Although some fresh market fields used to produce organic or conventional tomatoes had similar management systems, there was little overlap between fields in fresh market or processing tomato production. Further research is needed to determine underlying relationships among management systems and weed control in Indiana tomato production.

The rust pathogen, Puccinia thlaspeos, is used for biocontrol of dyer's woad. Rust infection results in chlorotic leaves and abnormal flower and seed production of this noxious weed during its second year of growth. Auxin-like and cytokinin-like activity of healthy and infected plants (roots, shoots, and leaves) were determined during different growth stages. These samples were analyzed by use of the mung-bean rooting bioassay (auxin-like activity) and the soybean-callus bioassay (cytokinin-like activity). Rooting activity in the mung-bean bioassay was significantly higher in the infected-root extracts from Harvest 1 (rosette stage) compared with the healthy-root extracts and significantly higher in the healthy-shoot extracts from Harvest 2 (bolting plants) compared with infected-shoot extracts. Infected plants collected during Harvest 1 had greatly reduced cytokinin-like activity in the roots, shoots, and leaves compared with the healthy plants. Cytokinin-like activity increased slightly in the infected plants collected in subsequent harvests, with the highest activity recorded in root extracts. The results suggest potential ways that the rust-causing fungal pathogen is able to influence some physiologic processes in dyer's woad and so affect its growth.

Experiments were conducted with isolated protoplasts of wild oat (Avena fatua L. # AVEFA) and isolated chloroplasts of wild oat and wheat (Triticum aestivum L.), to determine if the methyl sulfate salt of difenzoquat (1,2-dimethyl-3,5-diphenyl-1H-pyrazolium) might influence photoreactions in these species. Difenzoquat did not affect CO2 fixation, uncoupled electron transport, or proton uptake. At concentrations of 0.5 mM and 1 mM, difenzoquat caused a slight, but statistically significant, inhibition of photophosphorylation. Experiments assaying coupled electron transport indicated that inhibition of photophosphorylation occurred not through uncoupling, but by an energy-transfer inhibition. This same effect was observed in isolated mitocondria of both species, with about 50% inhibition of state 3 respiration rates occurring with 10 μM difenzoquat. However, no important differentials were observed in the relative susceptibilities of wheat and wild oat mitochondria. Difenzoquat also functioned as a weak autooxidizing electron acceptor in photosynthetic electron transport. Therefore, difenzoquat-induced leaf chlorosis and necrosis may result from a bipyridilium-type electron acceptor activity if sufficient herbicide is absorbed.

The effects of hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4 (1H, 3H)-dione] and its metabolites, A [3-(4-hydroxycyclohexyl)-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4 (1H,3H)-dione], B [3-cyclohexyl-6-(methylamino)-1-methyl-1,3,5-triazine-2,4 (1H,3H)-dione], C [3-(4-hydroxycyclohexyl)-6-(methylamino)-1-methyl-1,3,5-triazine-2,4 (1H,3H)-dione], D [3-cyclohexyl-1-methyl-1,3,5-triazine-2,4,6 (1H, 3H,5H)-trione], and E [3-(4-hydroxycy clohexyl)-1-methyl-1,3,5-triazine-2,4,6 (1H,3H,5H)-trione], on photosynthesis of loblolly pine primary needle segments were studied using a bioassay technique. Hexazinone, at concentrations equal to or greater than 1.0 × 10-6 M, inhibited photosynthesis, while 1.0 × 10-8 M and 1.0 × 10-7 M concentrations increased photosynthesis. Metabolite B at 1.0 × 10-4 M also inhibited photosynthesis. Metabolites A, C, D, and E did not affect photosynthesis at 1.0 × 10-4 in pine needle segments. The bioassay proved simple and useful for determining effects of certain herbicides and metabolites on photosynthesis.

A continuous-flow system was designed for the culture of aquatic weeds in the laboratory and used to examine the effects of low concentrations of terbutryn [N-(1,1-dimethylethyl)-N′-ethyl-6-(methylthio)-1,3,5-triazine-2,4-diamine] and diquat cation (6,7-dihydrodipyrido [1,2-:2′,1′-c] pyrazinediium ion) on algae (epiphyton) growing on surfaces of common elodea (Elodea canadensis L. C. Rich # ELDCA). Terbutryn did not affect the density of the epiphytic algal community, although development of the diatom component was favored at the highest concentration (50 μg/L). Diquat cation stimulated the growth of the epiphyton, particularly the diatoms, at concentrations as low as 5 μg/L. Possible reasons for this response included hormesis, differential tolerance to diquat, and facultative heterotrophy.

Mature achenes from tansy ragwort (Senecio jacobaea L. ♯3 SENJA) capitula borne on lower branches had greater average dry weights and higher percentage germination than those closer to the apex, but these higher averages were obtained because more achenes in these samples were filled. Physiological maturity was attained in ray achenes 21 days past flowering (DPF), 24 DPF in peripheral disk achenes, and 27 DPF in central disk achenes. Maximum germination occurred at 18 DPF in ray and peripheral disk achenes and at 21 DPF in central disk achenes. Neither achene type was shown to have innate dormancy. Disk and ray achenes germinated most rapidly at alternating temperatures of 30/20 C.

Definitions and properties of light, the effects of light on plant growth and physiological processes, and methodology and terminology for the measurement and reporting of light are reviewed. Alternatives to photometric methods now generally used in studies of the effects of light on plants in weed research are proposed. For studies of leaf energy budgets and plant water relations, the irradiance may be appropriately measured with radiometric methods and the data reported as W [watts] m-2. For studies of photosynthesis, the photosynthetic photon flux density may be measured and the data reported as μE [einsteins] m-2 s-1 or μmol [μmoles of photons] m-2 s-1. Different types of instruments are described and sources for these instruments are provided.

Alternaria crassa, a mycoherbicide for jimsonweed control, was tested for differential effects on growth, infectivity, and phenolic metabolism of two field-collected jimsonweed varieties. Seeds from field-grown red- and green-stemmed jimsonweed varieties were grown in the greenhouse and spores were applied in aqueous solutions. Infection studies showed no significant differences between the two weed varieties when tested at various growth stages from cotyledonary to 8–leaf stage at 2.5 × 104 spores ml−1. Spore dose response tests with A. crassa spores (6.25 to 100 x 103 spores ml−1) showed no significant varietal differences in disease ratings. Extractable phenylalanine ammonia-lyase activity increased nearly equally (2- to 3-fold above control) in both varieties (8- to 9-leaf stage) 48 to 72 h after treatment with 5 × 104 spores ml−1. The only significant differences between treated varieties occurred 72 h after treatment. Exposure to A. crassa lowered total ethanol-soluble phenolic levels in both varieties 72 h after treatment. Spectrophotometric scans (400 to 700 nm) of ethanol extracts (72 h after treatment) indicated that infection caused some absorbance increases, especially in red-stemmed jimsonweed. Anthocyanin content was about 11-fold higher in red-stemmed than green-stemmed jimsonweed, and A. crassa treatment slightly increased the anthocyanin absorption peak of the red-stemmed variety.

Vernolate (S-propyl dipropylthiocarbamate) injected into a sandy loam soil controlled a higher percentage of early weeds in soybeans (Glycine max (L.) Merr.) in 2 years out of 3 when compared with incorporated vernolate at the same rate by conventional methods. Late season weed control was enhanced by split applications of herbicides applied postemergence in sequence with vernolate. Chloroxuron (3-[p-(p-chlorophenoxy)phenyl]-1,1-dimethylurea) applied early postemergence plus 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron) or 2,4-bis-(isopropylamino)-6-(methylthio)-s-triazine (prometryne) applied in split applications as late and layby treatments gave the best weed control. Prometryne caused chlorotic veination in the upper leaves of the plants each year. In 1970, when prometryne was applied in sequence with incorporated vernolate, soybean plants were injured 30% compared with only 8% injury when the same herbicide was applied in sequence with injected vernolate at the same rate. The average seed yields were higher from injected vernolate at 1.12 kg/ha than from incorporated vernolate at 2.24 kg/ha. There was no difference in yield when vernolate was incorporated or injected at the same rate. Seed yields from the 3-year average were lower from plots treated with prometryne than from plots treated with linuron or 2-sec-butyl-4,6-dinitrophenol (dinoseb). Generally, the soybean seed quality was lower and seed size smaller when herbicide treatments failed to control weeds throughout the growing season.

Preemergence application of chloramben (3-amino-2,5-dichlorobenzoic acid) at 5.0 and 6.7 kg/ha, chlorbromuron [3-(4-bromo-3-chlorophenyl)-1-methoxy-1-methylurea] at 2.2 kg/ha, and linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] + nitralin [4-(methyl-sulfonyl)-2,6-dinitro-N,N-dipropylaniline] at 1.1 + 1.1 kg/ha controlled 95% or more of the barnyardgrass [Echinochloa crus-galli (L.) Beauv.], common lambsquarters (Chenopodium album L.), red-root pigweed (Amaranthus retroflexus L.), Powell amaranth (A. powellii S. Wats.), and hairy nightshade (Solanum sarachoides Sendt.), but reduced stands and injured direct-seeded asparagus (Asparagus officinalis L. ‘UC-66’). Linuron at 1.1 kg/ha controlled only 84% of the barnyardgrass and metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] at 0.6 kg/ha controlled about 50% of the hairy nightshade. Activated carbon applied at 56 and 112 kg/ha in a 3-cm band over the seeded row protected the asparagus from chloramben at 5.0 kg/ha, chlorbromuron at 2.2 kg/ha, and linuron + nitralin at 1.1 + 1.1 kg/ha. Weed control generally was reduced about 10% in the carbon band, but control was still 85 to 90%. Metribuzin reduced asparagus stands and vigor severely, even when 112 kg/ha of activated carbon was applied.

Near isogenic strains of okra, super okra and normal leaf cotton (Gossypium hirsutum L.) were grown in rows spaced 25, 50, and 100 cm apart and were sprayed with various combinations of trifluralin (α,α,α,trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) and fluometuron [1,1-dimethyl-3-(α,α,α,-trifluoro-m-tolyl)urea]. Neither row spacing nor leaf type had any effect on early season weed control. Late season control was better with normal and okra leaf types than with the super okra leaf type. Weed control was significantly better with additional postemergence application of herbicides than with only preplant and preemergence applications. Although the cotton varied in opening date with herbicide programs there was no difference in total yield.

Experiments were conducted in 1993 and 1994 to determine persistence of pyrithiobac as determined by bioavailability following different application times in a silty clay. Pyrithiobac was applied at PPI, PRE, pinhead square (PHS), and first bloom (FB) application timings. Greenhouse studies were also conducted in 1993 and 1994 to determine pyrithiobac persistence under controlled conditions on a sandy loam soil. Slope comparison indicated no difference in degradation patterns in the field for any application timing of pyrithiobac within years; thus, application timings were combined for 1993 and 1994. Slope comparison also indicated no difference in slope between 1993 and 1994; thus, years were combined to determine pyrithiobac persistence. The initial concentration was 30 ηg g−1. The half-life of pyrithiobac was 62 d in the field. Analysis of covariance indicated no difference in slope for the 1993 and 1994 greenhouse studies, and years were combined to determine the half-life. The initial concentration was 43 η g−1. The half-life was 43 d in the greenhouse study.

Experiments were conducted in order to establish the mechanism by which the synergist MZH 2091 increases metribuzin activity on ivyleaf morningglory. Herbicide absorption and metabolism were compared for plants treated either with 14C-metribuzin alone or with 14C-metribuzin plus nonlabeled MZH 2091. The compounds were applied via the roots for 3 h and the absorption was determined. After the pulse treatment, the plants were grown for additional 0, 3, 6, 9, 12, 21, 45, or 69 h in water, and the metribuzin metabolism was studied in the cotyledons. The synergist did not interfere with herbicide uptake but did strongly inhibit metribuzin metabolism. The pathway of metribuzin metabolism in ivyleaf morningglory is discussed as well as the way it is affected by the synergist MZH 2091.