In four tests conducted in 2 years, Alternaria cassiae Jurair and Khan effectively controlled sicklepod (Cassia obtusifolia L. ♯ CASOB) as indicated by stand counts of the weed and by soybean [Glycine max (L.) Merr.] yields. The number of sicklepod seedlings was reduced more than 90% within 14 days after foliar applications of A. cassiae conidia were banded (46 cm) at rates of 4.2 and 2.1 kg/ha (9.4 and 4.7 kg/ha broadcast, respectively). One banded application of 0.04 or 0.4 kg/ha (0.09 or 0.9 kg/ha broadcast, respectively) did not satisfactorily control sicklepod. These results indicate that sicklepod control may be enhanced by multiple applications of A. cassiae.

This research was conducted to evaluate the light requirement for redroot and smooth pigweed germination in soil, and how this requirement is affected by germination temperature and seasonal periodicity in seed dormancy. Seed enclosed in nylon mesh bags was buried in the field in December 1993 and 1994 and was recovered throughout the spring and summer of the following year, respectively. Germination was highest with red light or at 30 C. The requirement for red light was more pronounced at 20 vs. 30 C. The saturating fluence of red light was as low as 3 μmol m−2 in buried seed and 1,000 μmol m−2 in unburied control seed, depending on germination temperature. The effect of light and germination temperature pigweed germination also changed throughout the growing season. Our results indicate that light may be a requirement for germination in only the most dormant weed seed in the soil seedbank.

Joint action of the effects of atrazine and mesotrione can lead to synergistic herbicidal activity in broadleaf weed species. The objective of these experiments was to determine if specific rates are required to provide synergistic joint activity between mesotrione and atrazine in both triazine-sensitive (TS) and triazine-resistant (TR) redroot pigweed. Herbicide rates were evaluated in TS and TR redroot pigweed in two experiments: a dose response of mesotrione alone and in mixture with a constant rate of atrazine and a dose response of atrazine alone and in mixture with a constant rate of mesotrione. Results from these experiments revealed that synergism was detected in the TS pigweed when 56 g ai ha−1 mesotrione was mixed with 126 g ai ha−1 atrazine. In the TR pigweed, synergism was detected when mesotrione rate at 10 to 56 g ha−1 was mixed with a constant rate of atrazine at 126 g ha−1. Additionally, when mesotrione was held constant at 10 g ha−1, synergism was detected in mixture with atrazine from 31 to 3556 g ha−1 in TR pigweed. Furthermore, in TR pigweed, analysis of slope deviation across the dose-response curves of mesotrione with and without atrazine revealed a divergence that increased in magnitude as the rate of mesotrione increased. In other words, increased synergism was observed with increased mesotrione rate in the TR pigweed, which was also supported by biomass reduction and atrazine-like injury to the leaves. An additional experiment investigated synergism between mesotrione and bromoxynil in both TS and TR pigweed. Mesotrione at 10 g ha−1 was synergistic when paired with bromoxynil from 70 to 210 g ha−1 in both the TS and the TR pigweed.

The effects of herbicide concentration, adjuvants, and temperature on the phytotoxicity of CGA-82725 {2-propynyl 2-[4-[3,5-dichloro-2-pyridinyl)oxy] phenoxy] propionate}, RO 13-8895 {acetone-O-[D-2-[p-(α,α,α-trifluoro-p-tolyl)-oxy] phenoxy] propionyl] oxime}, and BAS 9052 OH {2-[1-(ethoxyimino)-butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexene-1-one} to large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA] were evaluated. The addition of adjuvants increased the toxicity of BAS 9052 OH at herbicide rates below 0.14 kg ai/ha, whereas the adjuvants had little effect on the activity of CGA-82725 or RO 13-8895. There were no differences among the adjuvants in enhancing grass control with any of the herbicides. Control of large crabgrass with CGA-82725 or BAS 9052 OH was not affected by temperature at the time of spraying; RO 13-8895 was slightly more toxic at 16 C than at 32 C. Soybean [Glycine max (L.) Merr.] had good tolerance to the three herbicides at rates 3 to 10 times those recommended; no differences in tolerance were observed among seven soybean cultivars. Stage of growth and the addition of an emulsifiable oil adjuvant did not affect soybean tolerance to BAS 9052 OH.

The importance of seeds in the reproduction and maintenance of yellow nutsedge (Cyperus esculentus L. # CYPES) populations was evaluated. Isozyme analysis using starch gel electrophoresis was performed on 20 individuals of each of 10 widely separate populations in California. Genetic variation among individuals served as an indicator of the relative importance of asexual and sexual reproduction in each population. Eight enzyme systems were assayed from which 12 loci were resolvable, with four of those loci exhibiting variability. A maximum of four isozyme genotypes appeared in any population; only nine of 81 total potential genotypes were identified. Five populations were isozymically uniform, apparently composed of a single genotype. The remaining five populations were genotypically variable; these frequently deviated strongly from the genotype frequencies expected of a sexually reproducing population. These results indicate that sexually produced seeds are unimportant in the maintenance of yellow nutsedge populations in agricultural environments. Although viable seed may be produced, tubers appear to be the primary mode of reproduction in this species.

Light after treatment was found to be required for the herbicidal activity of nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether) and oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene] following postemergence applications of both herbicides to greenbean (Phaseolus vulgaris L. ‘Spartan Arrow’). The effect of photosynthate and/or light before treatment was investigated. A 24-hr dark period prior to postemergence treatment of the bean seedlings had no effect on herbicidal activity when light followed treatment. The effect of plant pigments on the activity of both herbicides was studied using mutants of corn (Zea mays L.) and soybean [Glycine max (L.) Merr.]. A white mutant of corn was much more resistant to the herbicides than a greenish-yellow mutant or the normal plant. A yellow mutant of soybean was equally as susceptible as the normal type. Studies with radiolabeled foliar applications of both herbicides showed no significant difference in translocation in the light or dark.

Loss in activity of foliar-applied methyl ester of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} occurred under low soil moisture conditions. A loss in control of yellow foxtail [Setaria lutescens (Weigel) Hubb.], wild oats (Avena fatua L.), little-seed canarygrass (Phalaris minor Retz.), and barnyardgrass [Echinochloa crus-galli (L.) Beauv.], was observed under greenhouse and growth chamber conditions. When soil was maintained at 2 to 3% above wilting point as compared to near field capacity, herbicide activity was decreased by 15 to 50%. High soil moisture (at or above 67% of field capacity) for at least 2 to 4 days following treatment was needed to achieve maximum effectiveness of the herbicide. Daily furrow irrigations for a period of 10 days following treatment of barnyardgrass in the field resulted in highest activity as compared to that under single irrigation regimes within the 10-day period. The effect of low soil moisture was minimized by increased rates of herbicide application. Hoe-29152 {methyl-2-[4-(4-trifluoromethylphenoxy)phenoxy] propanoate} showed similar losses in activity associated with low soil moisture. No consistent changes in uptake or translocation of 14C-labeled diclofop could be detected in association with altered soil moisture status.

Glyphosate-resistant rigid ryegrass has been identified in California, but research has yet to elucidate the resistance mechanism. The objectives of this study were to examine the differences between sensitive and resistant rigid ryegrass in absorption and distribution of glyphosate, in vivo and in vitro absorption by chloroplasts, and shikimic acid accumulation after glyphosate treatment. Foliar absorption and distribution of 14C-glyphosate did not differ 1 to 3 d after treatment (DAT) between the susceptible (S) and resistant (R) biotypes. Absorption of 14C-glyphosate by isolated chloroplasts also did not differ between the S and R biotypes. After foliar application of 14C-glyphosate, chloroplasts were isolated from treated leaves from both biotypes. Accumulation of 14C-glyphosate in the chloroplasts did not differ between the two biotypes. Shikimic acid level increased significantly in the S biotype after treatment with glyphosate at 2.24 kg ai ha−1 to levels 10-fold greater than in the R biotype 11 DAT. Shikimic acid in the germination media at 2 to 5 mM did not affect seed germination of S and R biotypes but drastically decreased the length of coleoptiles of both at 5 DAT. Thus, biotype differences in sensitivity or metabolism of shikimic acid do not explain differences in sensitivity to glyphosate.

In Arkansas isopropyl N–(3–chlorophenyl)carbamate (CIPC) is recommended for controlling barnyardgrass (Echinochloa crusgalli (L.) Beauv.) in rice. Method and depth of seeding, time of application, and water management after treatment are critical when using CIPC to control barnyardgrass in rice. Rice is very susceptible to CIPC when roots of the seedlings contact the herbicide. A herbicide that is more selective and less sensitive to management and environment is needed to replace CIPC.

Transplanted tomatoes (Lycopersicon esculentum Mill. ‘Springset’) kept weed free for 36 days after transplanting, or weeded from the 24th day after transplanting, gave yields equal to those that had been kept weed free throughout the growing season. Conversely, when weeds were allowed to remain in the crop for more than 24 days after transplanting, yields were progressively reduced. Therefore, the ‘critical period’ of weed interference in tomatoes was between 24 and 36 days after transplanting. The yield of tomatoes was reduced significantly when only 5% of the weeds were allowed to remain in the plots longer than 21 days after transplanting. Weed interference appeared to have little, if any, effect on tomato juice quality as measured by color, consistency, and flavor.

An indigenous soil-borne fungus was isolated from infected seeds and seedlings of Texas gourd [Cucurbita texana (A.) Gray] and evaluated as a mycoherbicide. The pathogen was identified as Fusarium solani App. & Wr. f. sp. cucurbitae Snyd. & Hans. Only Cucurbita species were susceptible in host range tests. Ample quantities of microconidia for greenhouse and field plot inoculum were produced in shake culture on Richards' solution. Granular inoculum for field plot tests was produced in 5% (w/w) cornmeal/sand medium. In controlled-environment experiments, inoculated Texas gourd seedlings were killed over a range of air temperatures from 16 to 40 C. Optimum air temperature for disease development was 26 to 30 C. Complete kill of 4- and 8-cm-tall seedlings was achieved after 3 weeks when sprayed until runoff with a microconidial suspension containing 2.0 × 106 spores/ml. Texas gourd seedlings were effectively controlled in field plots (99% maximum) with liquid or granular inoculum. Soil samples from infested plots indicated that the fungus persists up to 12 months in a fine sandy loam, but after 12 months inoculum levels were insufficient to cause disease on seedlings grown under optimum conditions for disease development.

The parasitic purple witchweed [Striga hermonthica (Del.) Benth.] is a serious constraint to maize production in sub-Saharan Africa, especially in poor soils. Various Striga spp. control measures have been developed, but these have not been assessed in an integrated system. This study was conducted to evaluate a set of promising technologies for S. hermonthica management in western Kenya. We evaluated three maize genotypes either intercropped with peanut (Arachis hypogaea L.), soybean [Glycine max (L.) Merr.], or silverleaf desmodium [Desmodium uncinatum (Jacq.) DC] or as a sole crop at two locations under artificial S. hermonthica infestation and at three locations under natural S. hermonthica infestation between 2011 and 2013. Combined ANOVA showed significant (P<0.05) cropping system and cropping system by environment interactions for most traits measured. Grain yield was highest for maize grown in soybean rotation (3,672 kg ha−1) under artificial infestation and in D. uncinatum and peanut cropping systems (3,203 kg ha−1 and 3,193 kg ha−1) under natural infestation. Grain yield was highest for the Striga spp.-resistant hybrid under both methods of infestation. A lower number of emerged S. hermonthica plants per square meter were recorded at 10 and 12 wk after planting on maize grown under D. uncinatum in the artificial S. hermonthica infestation. A combination of herbicide-resistant maize varieties intercropped with legumes was a more effective method for S. hermonthica control than individual-component technologies. Herbicide-resistant and Striga spp.-resistant maize integrated with legumes would help reduce the Striga spp. seedbank in the soil. Farmers should be encouraged to adopt an integrated approach to control Striga spp. for better maize yields.

Allelopathic effects of lantana (Lantana camara L. ♯3 LANCA) residues (root, shoot), foliar leachates, and the soil (where lantana was grown) on milkweedvine (Morrenia odorata Lindl. ♯3 MONOD) seed germination and growth over a 30-day period were examined. Foliar leachates or the soil collected from the field where lantana had been growing had no effect on the final germination percentage or the seedling growth of milkweedvine. Incorporation of dried lantana shoot or root material into soil had no effect on the final percentage germination but caused significant reductions in milkweedvine growth over a 30-day test period. Roots were more inhibitory than shoots. Fifty percent of milkweedvine seedlings died within 15 days after germination at 1% (w/w) dried lantana root incorporation into the soil, and higher concentrations increased seedling death. Lantana roots incorporated into the soil produced foliar symptoms such as wilting and desiccation, whereas lantana shoots incorporated into the soil produced yellowing of the foliage of milkweedvine. Allelopathic activity of lantana residues was still strong even after decomposition of lantana residues for 4 weeks prior to the planting of milkweedvine seeds.

Cotton (Gossypium hirsutum L. ‘Westburn M’) was grown for 2 yr at two locations with full-season interference from buffalobur (Solanum rostratum Dunal ♯ SOLCU) at densities ranging from 0 to 64 plants/10 m of row. Dry weight of buffalobur harvested increased by 0.063 to 0.303 kg/plot for each additional weed/10 m of row. Intraspecific competition among buffalobur plants was observed at the higher weed densities. Cotton plant height was reduced by 16 and 32 buffalobur plants/10 m of row (or more) at Tipton and Perkins, OK, respectively, when compared with cotton grown under weed-free conditions. The threshold densities at which initial lint yield reductions occurred were 8 buffalobur plants/10 m of row in 1982 and 1983 at Tipton and 32 and 2 plants/10 m of row at Perkins in 1982 and 1983, respectively. Lint yields were reduced curvilinearly from 6 to 18 kg/ha for each additional buffalobur plant/10 m of row. Fiber quality was not significantly influenced by weed density when analyzed over all experiments; however, 50% span length, uniformity index, and micronaire were adversely affected in some environments.

Effects of three diphenylether herbicides [2,4-dichlorophenyl-p-nitrophenyl ether (nitrofen); 2,4,6-trichlorophenyl-4′-nitrophenyl ether (hereinafter referred to as MC-1478); and 2,4′-dinitro-4-trifluoromethyl-diphenylether (hereinafter referred to as C-6989)] were measured on phosphorylation and electron transport in spinach (Spinacia oleracea L.) chloroplasts, and mung bean (Phaseolus aureus L., var. Jumbo) and white potato tuber (Solarium tuberosum L.) mitochondria. All of the diphenylethers acted primarily as inhibitors of chloroplast noncyclic electron transport, and the coupled photophosphorylation. The compounds ranked in the following decreasing order of inhibitory effectiveness: MC-1478 ≥ C-6989 >> nitrofen. A site of action close to light reaction II was suggested. At high molar concentrations, marginal interference with cyclic electron transport or phosphorylation was obtained. In mitochondria, MC-1478 and nitrofen acted primarily as electron transport inhibitors with malate, NADH, and succinate as substrates. MC-1478 was a slightly stronger inhibitor than nitrofen. Only slight stimulation of ADP-limited oxygen uptake was obtained during the oxidation of NADH and succinate; whereas, strong inhibition of oxygen uptake was obtained with malate. C-6989 also weakly stimulated ADP-limited oxygen uptake with NADH and succinate but differed from the two chlorinated diphenylethers in that electron transport was not inhibited when ADP was present in excess. Interference with ATP generation could be one of the mechanisms through which the phytotoxicity of diphenylether herbicides is expressed.

Persistence of 1.12, 2.24, and 3.36 kg/ha of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] applied preemergence to corn (Zea mays L. ‘Funk's 4761′) was determined in three soils, each providing a range of pH from 5 to 7. Samples of surface soil from each plot were collected at intervals after atrazine application until there was no evidence of phytotoxicity to oat (Avena sativa L. ‘Florida 501′) in bioassay. Persistence (Y50) was defined as the number of days following atrazine application until bioassay indicated 50% relative growth of oats (no atrazine = 100% growth). This period ranged from 24 to 178 days, depending upon soil type, pH, and atrazine rate. Persistence of atrazine increased with increasing soil pH. The effect of soil pH was essentially the same at each atrazine rate and did not vary appreciably with years in a given soil. In McLaurin sandy loam, atrazine persisted 8 to 9 days longer with each unit increase in soil pH. In Hartsells fine sandy loam and Decatur silt loam, atrazine persistence increased 9 to 13 days and 29 days, respectively, with each unit pH.

Twelve populations of eastern black nightshade from different locations in Ontario are resistant to imazethapyr. This study aimed at determining the molecular basis of resistance in these populations and the activity of the resistant acetohydroxyacid synthase (AHAS) enzyme compared to that of the sensitive AHAS in response to different herbicides and branched-chain amino acid concentration. The results of partial AHAS sequencing indicated that all resistant populations had a cytosine331 to thymine substitution coding for an alanine205 to valine substitution. In vitro AHAS enzyme assays of one resistant population showed that the specific activity of the resistant enzyme was 56% less than that of the susceptible enzyme. AHAS from the resistant population was 72-, 70-, and 64-fold less sensitive than that of the susceptible population to imazethapyr, imazamox, and primisulfuron, respectively. Furthermore, the resistant enzyme was less sensitive to feedback inhibition from branched-chain amino acids compared to the susceptible enzyme. Results confirmed that resistance in resistant populations of eastern black nightshade was conferred by target-site modification and that the Ala205Val substitution alters the kinetics and regulation of branched-chain amino acid biosynthesis.

Tall morningglory is an annual broadleaf vine and a problem weed in manyannual and perennial crops in several countries including the United States.A better understanding of the germination biology of tall morningglory wouldfacilitate the development of better control strategies for this weed.Experiments were conducted under greenhouse and laboratory conditions toevaluate the effects of various environmental factors, such as temperature,light, planting depth, pH, osmotic and salt stress, and flooding duration,on the germination of tall morningglory. The results suggested that theoptimum day/night temperature range for the germination of tall morningglorywas 20/12.5 to 35/25 C and maximum germination (89%) was observed at 30/20C. Temperature higher and lower than the optimum range significantly reducedgermination. Alternate light and dark did not have any adverse effect on thegermination of tall morningglory seeds. The germination was 10% at anosmotic stress of −0.3 and −0.4 MPa, and above that, no germination wasobserved. Tall morningglory showed some tolerance to salt stress. Thegermination was 40% and 12% at salt concentrations of 50 mM and 200 mM,respectively. Germination was affected by pH levels, and maximum germinationoccurred at pH 6, whereas above or below that level, germination wassignificantly reduced. Maximum germination of seeds was 83 and 94% when sownat 0 and 2 cm depth in soil, within a week of sowing; however, germinationwas significantly reduced to 76% when placed at a depth of 4 cm or deeper.Under no flooding treatment, 87% of seed germinated, but flooding delayedand inhibited the germination of tall morningglory seeds. It is concludedthat several environmental factors affected the germination of tallmorningglory, and this information could help to predict the spread of tallmorningglory in new areas such as Florida.

Seed of corn (Zea mays L., var. Texas 28) and cotton (Gossypium hirsutum L., var. Deltapine smooth leaf) were planted in sand and subsequently drenched with solutions of α,α,α trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin). The levels of herbicide used inhibited growth of roots and shoots in both crops, but cotton proved more tolerant than corn. The roots failed to elongate normally, but the lateral growth that continued gave the radicle a “club-shaped” appearance, especially in corn. Stained sections of the roots were mounted as permanent slides for study. The cells at the extreme tip of the treated roots were small and dense; many were multinucleate. Immediately behind this region, the cells were abnormally large, thin-walled, and aberrant. A disorganized type of nuclear division was evident. Cell plate and cell wall formation were apparently rare. Although we found no normal sequence of mitosis in cells of treated roots, all stages of mitosis were seen in the untreated roots.

Vegetative propagules of an invasive riparian weed, giant reed, were collected monthly from two Southern California sites and planted in a greenhouse from August 1998 to July 1999. Rooting and emergence frequency of planted pieces and time to emergence, growth rate, and number of developing shoots were recorded; soluble carbohydrates were analyzed. Response variables were regressed against climatic, seasonal, and site effects using a stepwise model. Rhizomes established much more frequently than stems in all months. Time of year of collection was found to be the most important factor determining establishment of all propagule types. The interaction of maximum daily temperature and precipitation at the field sites had a lesser, but significant effect on rooting frequency. The lack of a consistent correlation between any of the response variables and climate or site may indicate broad environmental tolerance. Seasonal patterns in emergence, growth, and soluble carbohydrates suggest that control by shoot removal would be most effective in fall when rhizome carbohydrate reserves are the lowest, resulting in the greatest reduction in regrowth. Chemical control with phloem-mobile herbicides would be most effective in late summer or early fall, when carbohydrates are moving from leaves to belowground structures but prior to natural leaf senescence.