Foliar-applied clopyralid was translocated much more readily than chlorsulfuron in the phloem of Tartary buckwheat plants. This result was not due to greater penetration of clopyralid into the treated leaf or to greater retention of chlorsulfuron in the cuticle. Experiments with excised leaf disks indicated that chlorsulfuron was taken up more readily by the leaf tissue and accumulated in the tissue to a higher concentration than clopyralid. Both herbicides effluxed readily from the tissue after transfer to herbicide-free medium, indicating that the accumulation was not due to irreversible binding within the tissue. Chlorsulfuron (2.8 nmol) applied with 14C-sucrose reduced 14C export from the treated leaf. Chlorsulfuron also reduced export of 14C following exposure of the treated leaf to 14CO2 at 6, 12, or 24 h after herbicide application. This effect of chlorsulfuron could be partially reversed by pretreating the plants with a combination of 1 mM valine, leucine, and isoleucine. In similar experiments clopyralid had no effect on assimilate transport. It is concluded that phloem translocation of chlorsulfuron in sensitive species is limited by a rapid, indirect effect on phloem transport that reduces both its own translocation and that of assimilate.

Previous reports have suggested that bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] tolerance among soybean genotypes is the result of differential translocation or metabolism. The basis for tolerance was reexamined using susceptible and tolerant genotypes. Tolerant genotypes (‘Hill’ and ‘Clark 63’) were found to tolerate 100- to 300-fold more bentazon than susceptible genotypes (‘L78–3263’, ‘Hurrelbrink’, and ‘PI 229.342’). Minor differences in absorption and translocation occurred among the genotypes but they did not correlate with tolerance. Tolerant genotypes metabolized 80 to 90% of absorbed bentazon within 24 h, while susceptible genotypes metabolized only 10 to 15%. Two major metabolites, the glycosyl conjugates of 6- and 8-hydroxybentazon, were formed in tolerant genotypes. Susceptible genotypes did not form the hydroxybentazon conjugates but instead produced relatively low levels of two unidentified metabolites. It is concluded that differential bentazon tolerance among soybean genotypes is linked to the ability to form both the 6- and 8-hydroxybentazon conjugates.

Lath-house experiments were conducted to compare the effect of wild oat (Avena fatua L.) competition on two wheat (Triticum aestivum L. ‘Anza’ and T. turgidum durum group ‘Mexicali′) genotypes at three nitrate concentrations. Plants were grown to maturity in pots containing 10 wheat or wild oat plants, or mixtures of 10 wheat and 10, 25, or 50 wild oat plants. Nitrate was supplied in 500 ml Hoagland's solution with 1.5, 7.5, or 15.0 mM nitrate, as K and Ca nitrate, every 4 days. When grown without competition, Anza had more above-ground plant weight and grain yield and less whole-plant percent nitrogen than Mexicali. Wild oat competition caused larger reductions in plant weight and grain yield, and smaller reductions in percent nitrogen for Anza than for Mexicali. Wild oat competition reduced the effectiveness of nitrate in increasing plant weight, grain yield, and whole-plant percent nitrogen of wheat.

We studied the effects of temperature (5, 10, 20, and 30 C) on the phytotoxic activity of decaying quackgrass [Agropyron repens (L.) Beauv.] leaves and rhizomes that were incubated in soils for 0, 1, 2, 4, and 6 weeks. Alfalfa (Medicago sativa L.) seeds were grown for 96 h in water, water extracts of control soils, and water extracts of soil with quackgrass rhizomes or leaves. Dried quackgrass rhizomes and leaves contained water-soluble toxins that inhibited alfalfa seedling development and growth. There was a strong interaction between incubation time and temperature on the development of additional toxins by decomposing quackgrass. High incubation temperature (30 C) accelerated toxin formation and ultimate decay. Intermediate temperature (20 C) delayed toxin formation and decay. Low incubation temperatures (5 C and 10 C) prevented formation of additional toxin. In all extracts of quackgrass and soil that had been incubated for 6 weeks, normal alfalfa seedling number equaled that in water. However, seedling growth varied with incubation temperatures.

Treatment of quackgrass with glyphosate [N-(phosphonomethyl) glycine] in the greenhouse did not influence the toxicity of decaying quackgrass leaves. The highest toxic effect was noted after 1 week of decay on the soil surface.

The effects of chloracetamides on protein synthesis were studied both in vivo and in vitro. Four chloracetamide herbicides, alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide], metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], CDAA (N–N-diallyl-2-chloroacetamide), and propachlor (2-chloro-N-isopropylacetanilide) were tested for inhibition of [3H]-leucine incorporation into protein. Incorporation of 3H-leucine into trichloroacetic acid (TCA)-insoluble protein was inhibited in oat (Avena sativa L. ‘Victory’) seedlings grown in sand culture and treated 12 h at 1 × 10−4M with these chloracetamides. The herbicides were also tested in a cell-free protein synthesizing system containing polyribosomes purified from oat root cytoplasm. These herbicides had no effect on the rates of polypeptide elongation nor on the synthesis of specific polypeptides when herbicides (1 × 10−4M) were added directly to the system. Polypeptide formation was inhibited 89% when 1 × 10−4M cycloheximide was added during translation. Cytoplasmic polyribosomes were isolated from oat roots treated 12 h with 1 × 10−4M herbicide. Translation rates and products were not altered when these polyribosomes were added to the in vitro system. Protein synthesis is inhibited when tested in an in vivo system; however, the inhibition does not occur during the translation of mRNA into protein.

The antagonism of the methyl ester of haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy propanoic acid} by bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one-2,2-dioxide] was evaluated through studies of absorption and translocation in yellow foxtail [Setaria lutescens (Weig. ex Stuntz.) Hubb. # SETLU]. Leaf penetration of haloxyfop was reduced 37% in the presence of bentazon. Bentazon had no effect on translocation from the treated leaf. Direct chemical interactions and contact activity by bentazon do not account for the reduced uptake of haloxyfop. Experimental evidence shows the benzothiadiazione structural class of chemistry to be general antagonists of absorption for foliarly applied herbicides.

Black nightshade was subjected to two degrees of water stress by adding polyethylene glycol 20,000 (PEG) to the nutrient solution 5 d before treatment with glyphosate. The ED50 values for glyphosate, determined from dose-response curves, demonstrated that both degrees of water stress strongly increased the ED50, with and without the surfactant Ethomeen T/25 in the spray solution. The surfactant reduced the ED50 5-, 4.6-, and 6.9-fold at 0, 15, and 20% PEG, respectively. A 14C study demonstrated that unstressed plants absorbed 22% of applied glyphosate. Without surfactant, water stress reduced foliar absorption 2.2-fold at 15% PEG and 4.5-fold at 20% PEG. With surfactant, the foliar absorption was 35% of the applied amount in unstressed and water-stressed plants. The surfactant and PEG reduced the translocation efficiency of glyphosate. The surfactant had the most pronounced influence and reduced the translocation efficiency 1.5-fold at 0% PEG, 2.2-fold at 15% PEG, and 1.8-fold at 20% PEG. Induction or removal of water stress 24 h after glyphosate treatment indicated that plant growth rate is positively correlated with glyphosate efficacy. It was concluded that the surfactant can overcome the adverse influence of water stress on foliar absorption of glyphosate but not the adverse, postapplication influence of water stress on glyphosate efficacy.

The toxicity, leachability, and site of uptake of the herbicide 2-chloro-2',6'-diethyl-N-(methoxymethyl) acetanilide (hereinafter referred to as CP 50144) were studied in different soils. Two inches of water leached most of the compound to a soil depth of 2 to 3 inches, when applied at rates of 1 and 2 kg/ha. The inherent toxicity of CP 50144 to cotton (Gossypium hirsutum L., var. Acala 4-42) was studied in culture solution. The herbicide was most toxic to cotton when the entire root system of the crop was exposed to soil treated with CP 50144; reduction of weight of seedlings was accompanied by severe inhibition of root growth. On the other hand, only a slight reduction in growth rate was noticed when only the shoot zone of cotton was exposed to the herbicide.

Experiments were conducted in 200-gal concrete tanks to evaluate a large fresh-water snail, Marisa cornuarietis, as a biological aquatic weed control agent. Adult Marisa snails were collected from a canal near Miami, Florida, where a colony had recently become established. These snails are of South American origin and appear identical to those being used in Puerto Rico for biological control of schistosomiasis. The snails controlled Ceratophyllum demersum, Najas guadalupensis, and Potamogeton illinoensis completely and Pistia stratiotes and Alternanthera philoxeroides partially. Eichhornia crassipes was not completely eaten, but its growth and flowering were greatly retarded by the root-pruning action of the snails. Marisa preferred submersed weeds to floating or emersed weeds, but the floating weed Salvinia rotundifolia was eaten nearly as readily as submersed weeds. Little damage was done by Marisa to 4- and 5-week-old rice plants, but younger rice was killed when the snails had no other source of food. A common snail-eating bird, Cassidix mexicanus, was found to be a predator of Marisa in Florida. Except for its possible deletarious effects in rice-growing areas, Marisa was regarded as very promising for control of aquatic weeds at least in confined bodies of water.

Herbicide resistance is an exceptional marker to quantify gene flow. Quantification of pollen-, seed-, and vegetative propagule-mediated gene flow provides key weed biology information. Pollen-mediated gene flow influences the genetic variance within a population, the frequency of multiple or polygenic herbicide resistance, and the evolutionary dynamics of a species. Seed-mediated gene flow predominates in self-pollinating species. Gene flow quantification may enable the estimation of herbicide resistance epicenter, the comparison of the relative importance of gene flow pathways, and prediction of future distribution of resistance traits. Gene flow studies using herbicide resistance also can provide insight into the rates and importance of hybridization.

The disodium salt of 3,6-endoxohexahydrophthalic acid (disodium endothal) and the derivative identified by the manufacturer as the di-N,N′-dimethylococoamine salt of endothal (coded as TD-47) were particularly effective upon submersed species of aquatic vegetation as contact herbicides. Disodium endothal at concentrations of 0.5 to 10.0 ppmw was effective in controlling approximately 50 per cent of the 19 species of plants involved in 270 tests. TD-47 at concentrations of 0.02 to 10.0 ppmw trolled 77 per cent of the 11 plant species in 94 tests.

Algae (Chara, Cladophora, Pithophora, and Spirogyra) were more effectively controlled by TD-47 than by disodium endothal. Although TD-47 was at least 10 times more herbicidal than disodium endothal, it was about 100 times more toxic to fish. Disodium endothal was more than 50 per cent effective on submersed aquatic plants at rates in excess of 2.5 ppmw with a wide margin of safety in fish (4- to 10-fold). Disodium endothal had a median tolerance limit ranging from 95 to 150 ppmw in the aggregate of nine fish species tested extensively. Median tolerance limits for TD-47 ranged from about 0.06 to 0.3 ppmw for five species of fish. TD-47 applied at a concentration lethal to fish (0.3 to 1.0 ppmw) was effective as a dual management tool in controlling vegetation and achieving partial or complete renovation of stunted fish populations.

Young, growing vegetation was most susceptible to control, and best results were achieved at water temperatures exceeding 60 F. Higher rates were required to kill plants as they matured and stands became dense. Endothal liquid formulations were superior to granules in controlling algal mats, floating and emergent plants. Granules were more effective on submersed rooted plants.

TD-47 residues were of short duration. The rate of disappearance depended on time and concentration. Detectable residues disappeared within 8 days following application of 0.3 ppmw and within 2 weeks for 0.6 ppmw. However, 1.0 to 3.0 ppmw took up to 25 days to disappear. Some residues were found in fish-food organisms from treated enclosures 3 weeks after application. Fish flesh showed no absorption of endothal-armeens at sublethal concentrations. Intraperitoneal injection of endothal into fish produced a disturbance of the osmoregulation. The physiological effect of endothal was measured by chemical analysis of blood serum.

Four greenhouse trials were conducted to determine the effects of various growth temperatures and soil moistures on dormancy of primary seed of selected strains from two wild oat (Avena fatua L. ssp. fatua (L.) Thell.) varieties. Both higher temperature and lower level of moisture decreased dormancy, temperature having a greater effect than level of soil moisture. The dormancy difference between seed produced on plants grown at 15.6 to 18.3 C in soil with approximately 75% or from 100 to 75% available moisture and at 25.3 to 28.4 C in soil with approximately 25% or from 100 to 25% available moisture ranged between 31 and 100%, dormancy tests being conducted 10 or 14 days after seed maturity. The magnitude of the difference in seed dormancy caused by conditions of growth was affected by strain and variety of wild oat, and by age of seed.

The addition of simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] wettable powder to water solutions of glyphosate [N-(phosphonomethyl)glycine] in greenhouse studies reduced glyphosate activity on quackgrass [Agropyron repens (L.) Beavu.], corn (Zea mays L.), and beans (Phaseolus vulgaris L.). Atrazine [2-chloro-4-(ethylamino)-6-isopropylamino)-s-triazine] wettable powder reduced glyphosate activity on corn. This antagonism was more pronounced at threshold levels of glyphosate and was overcome by increasing the glyphosate rate. Simazine applied to corn through the soil did not reduce the activity of glyphosate applied to the foliage. Glyphosate activity on corn was reduced equally when glyphosate was mixed with 4.2 kg/ha of commercial simazine wettable powder or an equal amount of the inert ingredients used in the commercial product. When mixtures of glyphosate with either the commercial simazine product or the inert ingredients from the commercial product were centrifuged, the amount of phosphorus (used as a measure of glyphosate) in the supernatant was reduced by 10 to 20%. When the supernatants of the various mixtures were applied to bean plants, the reduced phytotoxicity from the mixtures was comparable to the antagonism noted in previous experiments. These data support the conclusion that the reduction in glyphosate phytotoxicity from mixing with atrazine or simazine wettable powders is due to a physical binding within the spray solution rather than from biological interactions within the plant.

Parasitic plants, including the root holoparasites Orobanche spp., cause devastating damage to crops worldwide. Arabidopsis thaliana is widely used as an amenable model plant system to study host–pathogen interactions. Understanding the molecular basis involved in host–parasite interactions will provide practical tools for the detection of genes responsible for incompatibility and resistance responses. In preliminary petri dish experiments, A. thaliana induced seed germination of O. aegyptiaca, O. minor, and O. ramosa at the rate of 87, 72, and 67% of maximum seed germination, respectively. Arabidopsis thaliana induction of O. crenata and O. cumana seeds was negligible (less than 2% of maximum germination). In additional polyethylene bag studies, A. thaliana was parasitized by O. aegyptiaca, O. ramosa, and O. minor resulting in 12, 5, and 2 parasites per host plant, respectively. The results facilitate the use of A. thaliana in host-parasitic plant interaction research.

Gas chromatographic analysis of benzene extracts was used to study the effects of temperature and relative humidity on the degradation and volatilization of 2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide (alachlor) in the soil. The relative humidity of a closed system had little effect on alachlor retention in air dry Sawyer fine sandy loam at 22 C, but had a pronounced effect when soil temperature was 38 C or higher. At 0% relative humidity (38 C or 46 C) alachlor was degraded to 2-chloro-2′,6′-diethylacetanilide. Decomposition, which also occurred in 5 N aqueous HCl, was attributed to acidic soil water film surfaces. As relative humidity within the system increased, the rate of degradation decreased, apparently because condensation of water vapor increased the thickness of the soil water film and decreased the surface acidity. At 38 C, minimum loss was noted at 31% relative humidity, and at 46 C, minimum loss was found at 79% relative humidity. The increased loss of alachlor at relative humidities above these critical points was attributed to volatility and not to chemical degradation.

Field studies using area-of-influence techniques were conducted in 1987 and 1988 to evaluate soybean growth and yield, and to predict soybean yield losses from photographs of jimsonweed and common cocklebur canopies. Differences in weed competitiveness within the 100-cm area of influence were induced by dates of soybean planting, locations, weed species, and years. Soybean yield losses within the first 20-cm interval from weeds correlated well with yield of all soybean plants within 100 cm of weeds (r2 = 0.86). Soybean growth responses as a function of distance from weeds were best described by complex polynomials, but simple linear functions, based on a data point from soybean plants nearest a weed and from the average of plants 60 to 100 cm from a weed, closely approximately actual yield losses (r2 = 0.96). Soybean yield losses were highly correlated (r2 = 0.84) with leaf area of weeds as viewed from directly above the weed-crop canopy. Weed canopy diameter, measured from overhead photographs 8 weeks after soybean emergence, also correlated well with soybean yield losses (r2= 0.82), but correlation with actual weed leaf area was not significant (r2 = 0.31).

Field experiments were conducted in 1982 and 1983 on a Dothan sandy loam (Plinthic Paleudult) at Headland, AL, to investigate minimum-tillage production of peanuts (Arachis hypogaea L.). The experiments included two peanut varieties: a) ‘Pronto’ (an earlier maturing Spanish type), and b) ‘Florunner’ (a later maturing runner type). Two row-spacing patterns were used: a) conventional 91-cm rows, and b) a modified twin 18-cm row pattern. A constant seeding rate (140 kg/ha) was used regardless of row spacing. Six herbicide systems were evaluated within each combination of variety and row spacing. The Florunner variety outyielded the Pronto variety across both years and weed management systems. Modified twin 18-cm rows outyielded conventional 91-cm rows across years and peanut varieties. Two of the six weed management systems were successful: 1) paraquat (1,1’-dimethyl-4,4’-bipyridinium ion) + oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) (preemergence), paraquat (ground cracking), naptalam (N-1-naphthylphthalamic acid) + dinoseb (2-sec-butyl-4,6-dinitrophenol) (postemergence); and 2) paraquat + pendimethalin [N-(1-ethylpropyl-3,4-dimethyl-2,6-dinitrobenzenamine] (preemergence), acetochlor [2-chloro-N(ethoxymethyl)-6’-ethyl-o-acetotoluidide] + dinoseb (ground cracking), and cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazine-2-yl]amino]-2-methylpropionitrile} (early postdirected spray). Both systems provided the best overall control of Texas panicum (Panicum texanum Buckl. ♯ PANTE), Florida beggarweed [Desmodium tortuosum (Sw.) DC. ♯ DEDTO], and sicklepod (Cassia obtusifolia L. ♯ CASOB) and were acceptable for use in minimum-tillage peanut production.

Field experiments were conducted from 1997 through 1999 to evaluate interspecific interference between pitted morningglory at 0, 10, 16, and 62 plants m−2 and drill-seeded, glyphosate-resistant soybean as influenced by soybean population and a single glyphosate application of 1.12 kg ai ha−1. Photosynthetic rate of soybean was not influenced by pitted morningglory density or glyphosate use 2 wk after treatment (WAT). Photosynthetic rate of soybean 12 WAT was reduced by 21 and 91% with 62 treated and untreated pitted morningglory plants m−2, respectively, whereas 10 treated and untreated pitted morningglory plants m−2 had no effect on the soybean photosynthetic rate. Pitted morningglory photosynthetic rate 2 and 12 WAT was reduced by 64 and 80%, respectively, when treated with glyphosate. The reduction in the photosynthetic rate of glyphosate-treated pitted morningglory was partially attributed to shading by soybean, whereas untreated plants were fully exposed to sunlight. Glyphosate-treated pitted morningglory at 10 and 16 plants m−2 did not reduce the rate of soybean leaf area index (LAI) accumulation; however, when the density was increased to 62 pitted morningglory plants m−2, soybean LAI decreased from 1.19 to 0.88 for each accumulated 100 growing degree days. Pitted morningglory produced a maximum of 24 million seeds ha−1 in the absence of glyphosate with 217,000 soybean plants ha−1. Pitted morningglory seed production declined with increasing soybean seeding rate in the absence of glyphosate, with a 41% reduction occurring when soybean population increased from 217,000 to 521,000 plants ha−1. Seed production of treated pitted morningglory ranged from 380,000 to 700,000 seeds ha−1. Soybean seed yield was not influenced by pitted morningglory density when treated with glyphosate. Untreated pitted morningglory at 10, 16, and 62 plants m−2 reduced soybean seed yield by 47, 62, and 81%, respectively. Competitiveness of untreated soybean increased with soybean seeding rate, resulting in 22% less yield loss with 521,000 than with 217,000 plants ha−1. Soybean seed yield was not reduced by 10 and 16 glyphosate-treated pitted morningglory plants m−2, but a 9% loss in yield occurred with 62 pitted morningglory plants m−2. Averaged over all pitted morningglory densities, glyphosate-treated pitted morningglory failed to reduce soybean seed yield at each of the three soybean densities. Following a single application of glyphosate, no apparent benefit was noted from increasing the soybean population above 217,000 plants ha−1.

Phytotoxic effects of metabolites from a naturally occurring rhizobacterial isolate, Pseudomonas syringae strain 3366, were determined on downy brome and ‘Hill 81’ winter wheat, along with 10 other weed and crop species. Centrifuged supernatant and concentrated ethyl acetate extracts from aerobic shake cultures of strain 3366 suppressed germination of seeds and reduced root and shoot growth in agar diffusion assays, soil assays, and under field conditions. Generally, root growth was inhibited more than shoot growth. Strain 3366 metabolites applied in soil inhibited all species tested. Crude ethyl acetate extracts in soil inhibited downy brome at concentrations that had little effect on winter wheat. Inhibitory activity was greater in Palouse silt loam (pH 5.8, 3.6% organic matter) than in Shano silt loam (pH 9.0, 0.8% organic matter). Activity of extracted metabolites decreased rapidly in wet soil but remained high in dry soil. Active metabolites were isolated and purified from the ethyl acetate extract using column chromatography, thin-layer chromatography, and crystallization. Chemical analysis revealed the presence of phenazine-1-carboxylic acid, 2-amino phenoxazone, and 2-amino phenol. Activity of these metabolites against downy brome was confirmed in agar assays. Phenazine-1-carboxylic acid, the major identifiable metabolite present in ethyl acetate extracts (20% by weight), inhibited downy brome root growth by 99% at concentrations of 5.7 mg L−1. Production of these metabolites in field soil by live bacteria of strain 3366 was confirmed with thin-layer chromatography.

A method is described in which tissue excised from cotyledons of 10-day-old pumpkin (Cucurbita pepo L. ‘Alabama Gold’) seedlings is floated in the light on a phosphate-based medium suspected of containing a photosynthesis inhibitor. The discs sink in a few hours if photosynthesis is inhibited; otherwise they continue to float. The method is capable of detecting a 0.002 to 0.02 ppm concentration of the herbicide prometryne [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine]. The method could be used both for screening chemicals for potential herbicide use and for monitoring water for pollution by photosynthesis inhibitors.