Species of green algae seldom grew as well in two-species cultures with other green algae, or with blue-green algae, as when cultured alone. Several species of algae apparently excreted one or more substances into the medium which inhibited the growth of the second species. Inhibition of growth of green algae was particularly great in two-species cultures with the blue-green algae, Oscillatoria rubescens Decandolle, Anabaena flos-aquae (Lyngbye) Breb., Microcystis aeruginosa Kutz., and Coccochloris peniocystis (Kutz.) Dr. and Daily. Green algae also failed to grow at normal rates in media prepared from filtrates of water from ponds which contained blooms of blue-green algae. Inhibitory substances are apparently an important factor in the development and persistence of relatively unialgal blooms of various species.

The influence of moisture stress intensity and duration, as well as tank mixtures with pendimethalin, which mitigated the antagonistic effects of drought, on fenoxaprop efficacy were evaluated. In growth chamber tests, specific soil matric potential (Ψm) levels of −0.01 to −1 MPa were imposed and maintained using a polyethylene glycol semipermeable membrane system. Moisture stress was alleviated by irrigation 48 or 96 h after herbicide treatment. Fenoxaprop efficacy was influenced by moisture stress intensity, posttreatment stress duration, and application rate. Under conditions of mild stress (Ψ ≥ −0.2 MPa), both increased application rate and irrigation 48 h after treatment alleviated the effects of drought on fenoxaprop efficacy. Under moderate stress (Ψm = −4.4 MPa), the antagonistic effects of drought were alleviated by a combination of increased rate and irrigation 48 h after treatment However, under more severe stress (Ψm ≤ −0.8 MPa), irrigation coupled with increased rate did not increase crabgrass control above 50%. Where irrigation within 48 h of treatment is not feasible, tank mixes of fenoxaprop with pendimethalin were shown to enhance smooth crabgrass control. Field lysimeter tests indicated that under moisture stress, Ψm of −0.7 MPa, smooth crabgrass shoot dry weight was reduced 65 to 94% with tank-mix combinations of ≥ 0.27 kg ai ha−1 fenoxaprop plus ≥ 2.2 kg ai ha−1 pendimethalin. These rate combinations were shown to be synergistic and able to alleviate the antagonistic effect of moisture stress on fenoxaprop efficacy.

The absorption, translocation, and metabolism of 14C-profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine] and 14C-dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine) in sorghum [Sorghum bicolor (L.) Moench ‘RS6–12′], barnyardgrass [Echinochloa crus-galli (L.) Beauv.], soybean [Glycine max (L.) Merr. ‘Dare’], and Palmer amaranth (Amaranthus palmeri S. Wats.) were determined after treatment with 14C-labeled herbicides in nutrient solution for 24 hr at 16 or 38 C. 14C-profluralin accumulated in roots to a greater extent at 16 C, while metabolism was greatest at 38 C. Very little 14C-profluralin was translocated to the tops of plants. Conversely, 14C-dinitramine accumulated in the tops of plants to a greater extent at 38 C. Metabolism was not greatly affected by temperature. These effects may relate to excess toxicity of profluralin at 16 C and dinitramine at 38 C in species which normally exhibit resistance to the herbicides.

Plumeless thistle is a European Asteraceae naturalized in Argentina, where it is a troublesome pasture and range weed. A European weevil (Rhinocyllus conicus) was imported for biocontrol of this thistle. Oviposition patterns, egg to adult survival, and the weevil's effect on the production of achenes by thistles were monitored over 2 yr. The oviposition period did not begin simultaneously in all thistle populations, but finished in late November. Egg to larvae survival was 63% and egg to adult survival was approximately 50%. No important egg predators were detected. The weevils destroyed 80% of the propagules per capitulum and showed a slight tendency to adapt to the plumeless thistle cycle.

Foliar and root absorption and translocation of metribuzin (4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one) by downy brome (Bromus tectorum L. # BROTE) and winter wheat (Triticum aestivum L.) was determined. After a 48-h absorption period, roots of three-week-old downy brome plants had absorbed two times more metribuzin on a total plant fresh weight basis than had roots of winter wheat. Root-absorbed metribuzin was translocated similarly regardless of species with 80% of absorbed 14C accumulating in leaf blades, 10% in the leaf sheaths, and 10% in the roots. After 24 h, leaves of downy brome and winter wheat had absorbed, respectively, 26 and 36% of foliar-applied metribuzin, and absorption increased threefold with the addition of a nonionic surfactant. Translocation of foliar-absorbed metribuzin was primarily towards the apex of the treated leaf. No translocation from the treated leaf to other plant parts occurred with either species. The greater tolerance of winter wheat to metribuzin is due in part to less root absorption of metribuzin by winter wheat than by downy brome.

Field, greenhouse, and laboratory studies were conducted to evaluate the performance of starch xanthide (SX), sludge polymer (SP), and coventional formulations (CF) of benefin [N-butyl-N-ethyl-2,6-dinitro-4-(trifluoromethyl)benzenamine], oxadiazon {3-[2,4-dichloro-5-(1-methylethoxy)phenyl]-5-(1,1-dimethylethyl)-1,3,4-oxadiazol-2-(3H-one}, and prosulfalin {N-[[4-dipropylamino)-3,5-dinitrophenyl] sulfonyl]-5,5-dimethylsulfilimine} for the control of large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA] in Kentucky bluegrass (Poa pratensis L.) turf. Turf injury was greatest with SP oxadiazon and prosulfalin formulations, while SX formulations of oxadiazon and prosulfalin caused decreased and /or delayed injury and provided control comparable to conventional formulations. Coarse SX granules containing prosulfalin caused less turf injury than fine granules, while the opposite effect sometimes occurred with SX oxadiazon. Differences in control were observed in the greenhouse when SX benefin formulations which varied in cross-linking agent and/or degree of substitution were compared to the conventional formulation on sandy and silt loam soils. Benefin SX formulations also demonstrated controlled-release properties, which improved large crabgrass control when compared to the conventional formulation in the greenhouse. This effect was short lived on silt loam but persisted on sand. SX granules cross-linked with Fe3+ extended benefin activity longer than H2O2 cross-linked materials on sandy soil only. Release of 14C-labeled benefin from SX matrices was altered by the extent of water imbibition, solvent characteristics, and granule size.

Livestock losses, mainly to cattle, from Astragalus miser Dougl. ex Hook. (timber milkvetch) have been reported since 1927. The species is found in the northwestern United States and also in Alberta and British Columbia. Recent taxonomic treatment distinguishes eight varieties. The most northern variety (A. miser var. serotinus (Gray) Barneby) and the most southern variety (A. miser var. oblongifolius (Rydb.) Cronq.) are the only two varieties known to cause livestock losses, but all varieties should be regarded as poisonous until it is known they are not. A. miser var. oblongifolius was controlled with 2 lb/A of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) or 2,4,5-trichlorophenoxypropionic acid (silvex). Removal of A. miser increased both cover and frequency of grass species.

Only a few reports have been published on the susceptibility of rabbitbrush (Chrysothamnus spp.) to chemical herbicides (1, 2, 5, 6, 7). From these publications the following conclusions may be made: (a) 2,4–D (2,4–dichlorophenoxyacetic acid) is more effective on rabbitbrush than 2,4,5–T (2,4,5–trichlorophenoxyacetic acid), (b) June applications are generally best, (c) rabbitbrush is more tolerant to growth regulators than big sagebrush (Artemisia tridentata), and (d) resprouting from the stem base is common.

Herbicide resistance has been studied extensively in agronomic crops across North America but is rarely examined in vegetables. It is widely assumed that the limited number of registered herbicides combined with the adoption of diverse weed management strategies in most vegetable crops effectively inhibits the development of resistance. It is difficult to determine whether resistance is truly less common in vegetable crops or whether the lack of reported cases is due to the lack of resources focused on detection. This review highlights incidences of resistance that are thought to have arisen within vegetable crops. It also includes situations in which herbicide-resistant weeds were likely selected for within agronomic crops but became a problem when vegetables were grown in sequence or in adjacent fields. Occurrence of herbicide resistance can have severe consequences for vegetable growers, and resistance management plans should be adopted to limit selection pressure. This review also highlights resistance management techniques that should slow the development and spread of herbicide resistance in vegetable crops.

The effects of non-flooded plastic film mulching cultivation (PM) and polymer-coated urea (PCU) on rice yield, soil properties, and weed diversity were investigated in experimental plots of rice monoculture in Lanxi, China. The combination of PM and PCU increased rice yield. Compared with traditional flooded cultivation, under PM, soil pH remained higher, but decreased soil organic matter, total nitrogen, available phosphorus, and exchangeable potassium in the 0- to 10-cm soil layer. Soil fertility influenced winter weed communities, with hairy bittercress, Asian mazus, and shortawn foxtail being the most abundant species. Multivariate analysis indicated that changes in the winter weed species diversity were primarily due to exchangeable potassium. PCU had no significant influence on weed diversity, while plots without nitrogen fertilizer had higher spring-germinating weed density.

The literature does not reveal any direct information concerning the time of exposure or concentration required of a soil fumigant to kill weed seeds. For specific soils and conditions the appropriate rate of application may be known but this does not represent an actual toxic concentration. This is due to the fact that the toxicity of the fumigant may be decreased due to adsorption of the fumigant by the soil or solution in the soil water. This investigation was carried out to determine what concentration of fumigant is needed for a specific time to produce a given percent control of dormant imbibed seeds.

A knife injector was designed and tested for the application of ethyl-N,N-dipropylthiolcarbamate (EPTC). Performance was good and preliminary tests were encouraging for both preemergence and postemergence applications.

Residues of 2,3,6-trichlorophenylacetic acid (fenac) and 2,6-dichlorobenzonitrile (dichlobenil) were determined in irrigation water flowing over canal-bottom plots treated with the herbicides prior to the entry of water. Concentrations of fenac and dichlobenil in the first water to flow over the entire treated plots were 8.82 and 8.63 ppm, respectively. The bulk of the residues was transported from the plots in a very short time, and safe levels were reached after 1 hr of water flow. The dichlobenil burden, picked up by water as it flowed over the treated plot, was effectively reduced as the water passed over untreated canal soil downstream.

The need for information concerning effects of quality and quantity of light on submerged aquatic plants has been emphasized by the Committee on Aquatic Weed Control at the Southern Weed Conference and by Westman. Factors such as light intensity, water temperature, and depth of water interact with soil fertility to govern the establishment of rooted aquatic vegetation and determine the rate at which it grows.

Results of studies with the herbicide 1-(3-chloro-4-methylphenyl)-3-methyl-2-pyrrolidinone (hereinafter referred to as BV-207) suggest that it interferes appreciably with photosynthesis. A concentration of 10-4 M of BV-207 almost completely inhibited fixation of labelled carbon dioxide by leaf disks of various plants. In addition, carbohydrates protected plants from the phytotoxic action of the chemical. BV-207 was considerably more toxic when plants received light after application of the herbicide, compared with those held in the dark. On the other hand, root growth was inhibited only slightly by BV-207.

Barnyardgrass (Echinochloa crusgalli (L.) Beauv.) is the most serious weed in rice in Arkansas and this and other species of Echinochloa are a serious problem throughout the rice-growing areas of the world. A limited field survey conducted in August 1957 in the Grand Prairie rice-growing region of Arkansas indicated that 27 percent of the rice fields were infested with barnyardgrass. Presumably the yield of rice on these fields could have been increased substantially by controlling the barnyardgrass.

Field experiments were conducted in Louisiana over 2 yr to evaluate the influence of full-season interference from johnsongrass, common cocklebur, or hemp sesbania at densities of 2.5, 0.5, and 2.0 plants m–1 of row, respectively, and simulated insect defoliation of soybean on weed and soybean growth. Defoliation at R2 (full bloom) and R5 (beginning seed development) soybean growth stages was accomplished by removal of zero, one, or two leaflets per soybean trifoliate, which approximated 0, 33, and 66% defoliation, respectively. Height and dry weight of all weeds were not affected by soybean defoliation level or defoliation stage. Soybean height 3 wk after defoliation at R5 was not influenced by weed interference, soybean defoliation level, or defoliation stage in either year. Averaged across soybean defoliation levels and stages in 1994, johnsongrass, common cocklebur, and hemp sesbania reduced soybean yields 30, 15, and 14%, respectively. In 1995, johnsongrass reduced soybean yield 35%. As soybean defoliation level increased, a linear decrease in soybean yield was observed. Averaged across weeds and soybean defoliation stages, 33 and 66% defoliation reduced soybean yield 6 and 20% in 1994 and 12 and 33% in 1995, respectively. Defoliation at R5 resulted in 10% lower yield than defoliation at R2 in one of two years. Yield reduction due to combinations of weeds and soybean defoliation was additive.

The patterns of buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2 imidazolidinone} uptake, translocation, and metabolism, and their potential contribution to crop selectivity, were studied in tolerant alfalfa (Medicago sativa L. ‘Vernal’) and susceptible quackgrass [Agropyron repens (L.) Beauv.]. 14C-Buthidazole was absorbed from a 5-μl droplet by leaves of both alfalfa and quackgrass plants, but did not move basipetally to the roots or nontreated leaves in 14 days. 14C-Buthidazole was absorbed very rapidly from Hoagland's solution by the roots of both species and translocated apoplastically to the leaves. Absorption and translocation of buthidazole did not differ between species, indicating that these processes did not contribute to crop selectivity. The herbicide and five metabolites were present in alfalfa leaf extracts 6 days after treatment. One unidentified metabolite accounted for 40% of the detected radioactivity 6 days after root application. Unmetabolized 14C-buthidazole accounted for 87% of the total radioactivity in quackgrass after 6 days. Metabolites having different chromatographic properties were recovered from the two species. Differential rate and type of metabolism appeared to contribute to buthidazole selectivity between the species.

Greenhouse and field experiments were conducted to evaluate clopyralid formulations and triclopyr ester alone and in mixtures for control of honey mesquite. In the greenhouse the butoxyethyl ester of triclopyr enhanced activity of the monoethanolamine salt of clopyralid when applied as mixtures for total rates of 210 to 630 g ae ha-1. Greenhouse activity of triclopyr was not enhanced with the addition of clopyralid. In the field, 1989 applications of these same formulations, mixtures, and rates were usually synergistic, with each mixture killing more plants than the combined effect of either herbicide applied alone. For example, clopyralid plus triclopyr at 140 plus 140 g ae ha-1 killed 87% of the plants. When applied alone at 140 g ha-1 neither herbicide killed >27% of the plants. Honey mesquite response to the potassium or oleylamine salt of clopyralid was similar to the monoethanolamine salt when applied alone or in mixtures with triclopyr ester. Effectiveness of these mixtures in 1990 was similar to the 1988 and 1989 applications except that two to three times more herbicide was required for high mortality in 1990 because of unfavorable environment and plant growth prior to treatment.

Subirrigated pot-plant systems were developed for greenhouse simulations of field methods being tested for herbicidal control of saltcedar (Tamarix pentandra Pall.). The methods included: over-the-top spraying; soil injection; soil layering, with whole plants transplanted onto the herbicide layer; and soil layering by severing the roots and concomitantly injecting herbicide. Existing foliar application techniques were improved for greenhouse testing of herbicides and results from preliminary tests were apparently similar to literature reports of limited efficacy in the field. Preliminary results from these greenhouse techniques showed that root zone applications, either by soil layering or soil injection, were very effective; stem or foliar applications were less effective.