More force was required to induce leaf slippage in coleoptiles from corn (Zea mays L. ‘Tenn 5009′) plants grown in the presence of 25 ppmw alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] than in the controls, or in coleoptiles from plants grown in the presence of 25 ppmw alachlor in combination with 150 ppmw 1,8-naphthalic anhydride (hereafter referred to as NA). NA alone reduced the force required to induce leaf slippage below that of all treatments. Incubation for 16 hr in 10 ppmw IAA (indoleacetic acid) did not lower the force required to induce leaf slippage in coleoptiles from plants grown in the presence of 25 ppmw alachlor even though the length of the coleptiles increased 30% more than coleoptiles not receiving the IAA treatment. Percent dry matter, dry matter per 100 plants, and percent protein increased in coleoptiles from alachlor treated plants, while percent cellulose and lignin decreased. The extent of variation in these parameters was lessened when NA was applied in combination with alachlor, with the exception of percent lignin which was further decreased by the combination treatment. Percent hemicellulose was not affected by alachlor, NA, or their combination.

The influence of weeds on crop yield is not only dependent on weed-related factors such as density and time of emergence, but also on environmental and management factors that affect both the weed and crop through time. This study was undertaken to develop the first physiologically based dry bean model that would account for the influence of weed competition. The specific objective was to develop a model that would account for the influence of weed competition on crop yield, and to use this model to test the hypothesis that crop yield losses resulted from competition for photosynthetically active radiation (PAR). To this end, a model that simulated the growth and development of dry bean was developed. The model performed daily calculations and simulated the phenology, leaf area expansion, dry matter production and distribution, and grain yield of dry bean based on weather and management information, but assumed adequate water and nutrients. The model was calibrated without weed competition at two locations and yr, and for these situations, adequately described the growth and development of the crop. Simulations were then run for five common ragweed densities and two times of emergence. Common ragweed leaf area was read into the model from input files and used to simulate weed shading. Shading of the dry bean canopy by common ragweed accounted for about 50 to 70% of the yield losses observed in field studies when weeds emerged with the crop. Weed shading did not account for the yield reduction measured from weeds that emerged at the second trifoliate stage of crop growth. The agreement between model predictions and field studies was consistent with the hypothesis that competition for PAR was a principal factor in weed-crop interaction. The ability to account for differences in weed densities, management, and environmental conditions suggested that modeling was a useful tool for evaluating the interaction among weeds and crops.

Moist-chilled and freshly harvested seeds of redroot pigweed (Amaranthus retroflexus L.) and yellow foxtail [Setaria glauca (L.) Beauv.] were tested for germination responses to soil ammonium and nitrate. A controlled environment was used to simulate overwintering and germination conditions in the field. The results suggest that no alteration of weed germination behavior should be expected in the crop ecosystems studied if ammonium plus nitrification inhibitor replaces other fertilizer systems which result in substantial levels of nitrate in the soil solution. The only germination effect was one of nitrate on unchilled foxtail. Chilling lowered catalase activity in both species.

Growth room and field studies indicated that coating the seeds of oats (Avena sativa L.) with NA (1,8-naphthalic anhydride) at rates of 0.5 to 1% by seed weight significantly reduced the phytotoxicity of barban (4-chloro-2-butynyl m-chlorocarbanilate) applied to the foliage at rates up to 1.2 kg/ha. Complete protection was obtained when barban was applied at 0.4 kg/ha, the highest rate recommended for the control of wild oats (Avena fatua L.) in cereal crops. Treatment of oat seeds with this antidote did not reduce the herbicidal effect of barban on wild oats grown in the same soil. Thus, coating oat seeds with the antidote may allow the use of barban for the selective control of wild oats in oat crops. NA seed treatment also slightly reduced oat injury from diallate [S-(2,3-dichloroallyl)diisopropylthiocarbamate] and triallate [S-(2,3,3-trichloroallyl)diisopropylthiocarbamate].

At early stages of canopy development net carbon exchange (NCE) values for redroot pigweed (Amaranthus retroflexus L.), prickly sida (Sida spinosa L.), and birdsfoot trefoil (Lotus corniculatus L.) were determined in an air-sealed leaf chamber. Regardless of light intensity, temperature, CO2 concentration, or competition level, redroot pigweed had a NCE at least 10 mg CO2/dm2 per hr higher than that of birdsfoot trefoil or prickly sida. On a total leaf area basis, CO2 utilization changed as the heteroculture canopies developed and as the microenvironmental parameters changed. Redroot pigweed's rapid attainment of leaf area and leaf display coupled with a high photosynthetic (P) rate greatly enhance its utilization of available CO2. Direct competition for CO2 does not occur between plants with low and high (P) rates under field conditions because CO2 concentrations are always greater than the CO2 compensation point (r) of plants with low (P) rates. More efficient utilization of available CO2 by weeds such as redroot pigweed with greater (P) capacity contributes to more rapid growth and development of these weeds to the ultimate detriment of a plant such as birdsfoot trefoil with lower (P) capacity.

Fall, spring, or late-summer applications of glyphosate, paraquat, sethoxydim, and HOE-39866 were investigated in field trials for no-tillage renovation of endophyte fungus-infected tall fescue pastures. Only spring or late-summer applications of glyphosate at 1.68 and 2.52 kg ae ha−1 consistently provided greater than 80% visual tall fescue control. However, none of the herbicide treatments significantly reduced final percent endophyte fungus infection levels after the pasture was reestablished. High final infection levels were due to regrowth from underground rhizomes of old tall fescue sod that survived the herbicide treatments.

The phenetic relationships of green foxtail [Setaria viridis var. viridis (L.) Beauv.] and its allies were examined by numerical and chemotaxonomic methods. Correlation coefficients and taxonomic distances based on quantitative data from 31 characters displayed close phenetic similarities among green foxtail, its varieties and foxtail millet [S. italica (L.) Beauv.]. Isolation and separation of 35 alcohol-soluble compounds by two dimensional paper chromatography supported the numerical comparisons. By combining all characters examined, the resulting cluster analysis displayed the closest similarity between robust white (S. viridis var. robusta-alba Schreiber), robust purple (S. viridis var. robusta-purpurea Schreiber) and giant green foxtail [S. viridis var. major (Gaudin.) Posp.] indicating that the robust foxtails may be subvarieties of giant green foxtail rather than of green foxtail. The numerical, morphological and chemical comparisons support the proposed phylogeny of the Old World foxtails and indicate green foxtail as the probable center of ancestorial origin.

Greenhouse and laboratory experiments were conducted to determine the physiological basis for differential tolerance of four Zea mays L. hybrids to RPA 201772. Differences in Zea mays tolerance were quantified by determining the herbicide rate required to injure and reduce Z. mays height 50% (GR50). GR50 values indicated that the Z. mays hybrids ‘Pioneer 3751’ and ‘Pioneer 3737’ were less tolerant to RPA 201772 than the hybrids ‘Pioneer 3394’ and ‘Pioneer 3963.’ Experiments using 14C-RPA 201772 were conducted to determine if hybrid sensitivity was due to differential uptake, translocation, or metabolism of the herbicide. Differences in hybrid tolerance were primarily due to differential herbicide metabolism rates. The time required for 50% inactivation (T½) of RPA 201772 was 42 and 52 h for the more tolerant hybrids and 66 and 93 h for the more sensitive hybrids. Increased uptake of RPA 201772 was also a contributing factor to the sensitivity of one of the hybrids.

Greenhouse experiments were conducted to evaluate the effect of the fungus Dactylaria higginsii on the interference of Cyperus rotundus (purple nutsedge) with Lycopersicon esculentum (tomato ‘Agroset'). Cyperus rotundus plants established from tubers were planted at initial densities equivalent to 40, 80, 160, and 320 tubers m−2 with L. esculentum in 35-cm-diam pots. Cyperus rotundus plants were inoculated by spraying with a spore suspension of D. higginsii containing 0.5% Metamucil as a carrier. The treatments were Metamucil only, 104 conidia ml−1 + Metamucil, or 106 conidia ml−1 + Metamucil. In the absence of D. higginsii, C. rotundus at densities of 80, 160, and 320 tubers m−2 reduced L. esculentum yield by 14, 68, and 70%, respectively. In contrast, yield of L. esculentum treated with D. higginsii at 106 conidia ml−1 was equal to that in the weed-free control. The rate of disease increase (r G) was higher in treatments with 106 conidia ml−1 (r G = 0.126 to 0.136) compared to 104 conidia ml−1 (r G = 0.046 to 0.050). At 106 conidia ml−1D. higginsii reduced the interference from C. rotundus, controlled C. rotundus better, and increased L. esculentum yield compared to the weedy checks.

Fresh and stored dandelion (Taraxacum officinale Weber) seeds were studied to determine the germination response to a range of constant and alternating temperature regimes on thermogradient plates. Germination was initiated over a wide range of temperatures. Maximum germination of fresh seed occurred at an alternating temperature of 20 C for 16 hr and 10 C for 8 hr. Seed stored for 30 days germinated best at 20 C for 16 hr and 15 C for 8 hr. In addition to the shift in germination requirement, dormancy increased during the 30-day storage, especially at −15 C.

Field experiments were conducted for 3 yr to determine the effect of various biological and physical factors on the operation of the weed-sensing Detectspray system. Plant detection is achieved by sensors measuring differential reflectance of red and near-infrared wavelengths of light from green plants, crop residues, and soil. Weed detection was greatly reduced 70 to 80 min after sunrise and before sunset when operated at lat 50°N because of reduced solar irradiance. Tall, dense-standing crop stubble limited detection of small weeds at the soil surface. Weed detection varied with plant species. Canola with three to four leaves consistently was detected, but wheat or green foxtail usually required five to six leaves to be detected. Small weeds were detected if present at densities greater than 70 plants m−2. Growers and commercial applicators need to be aware of the limitations of the Detectspray system to use it effectively to control weeds with concurrent reductions in herbicide use.

Based on bioassays of soil samples from field plots, the rate of disappearance of 5-amino-4-chloro-2-phenyl-3 (2H)-pyridazinone (pyrazon) was estimated with a multiple regression equation. Within a limited geographic region, pyrazon residues were directly related to the organic matter content of soil and inversely related to rainfall during the growing season. The bacteria population increased with the presence of pyrazon in soil at soil temperatures ranging from 4.5 to 29.5 C, indicating a wide capability of microbiological utilization of the herbicide in soil. There was no evidence that soil bacteria or actinomycetes were adversely affected by pyrazon. Thin layer chromatography of ethanol extracts of soil containing 3H-phenyl-labeled and 14C-pyridazinone-labeled pyrazon revealed that pyrazon is dephenylated to 5-amino-4-chloro-3-pyridazinone. In a sandy loam soil, less than 10% of the herbicide was degraded to 5-amino-4-chloro-3-pyridazinone after 10 weeks at 21 C.

Biannual applications of hexazinone have been applied in many lowbush blueberry fields in Nova Scotia for more than 30 years. Persistent reliance on a single herbicide chemistry may have selected for hexazinone-resistant red sorrel. The recommended rate of hexazinone (1.92 kg ai ha−1) no longer controls red sorrel in many growing regions. Six levels of hexazinone (0, 0.48, 0.96, 1.92, 3.84, and 7.68 kg ai ha−1) were applied to red sorrel plants grown in a greenhouse from seeds collected from three commercial fields and a no blueberry area to determine if they were hexazinone resistant. Red sorrel from two sites where hexazinone had not been applied regularly died at the 0.96 kg ai ha−1 rate of hexazinone whereas red sorrel from two commercial fields survived at 7.68 kg ai ha−1. It is concluded that red sorrel is hexazinone-resistant in some wild blueberry fields. A portion of the psbA gene was sequenced and it was determined that resistant plants had a Phe to Val substitution at position 255 in the D1 protein. This is the first recorded instance of hexazinone resistance in a perennial broadleaf weed in blueberry fields.

Many substitutions in the herbicide target enzyme acetohydroxyacid synthase (AHAS) confer whole-plant resistance and may reduce plant fitness. This study was done to determine the impact of different watering and temperature regimes on the germination, growth, and seed production of eastern black nightshade populations resistant (R) to AHAS inhibitors as conferred by an Ala205Val substitution in their AHAS. Growth and reproductive ability of four R and four susceptible (S) populations were determined in growth-cabinet and greenhouse studies. The R populations had lower total berry and viable seed production per plant than S under optimal conditions because of slower berry maturation. Seed production of both S and R populations decreased under lower or higher than optimal watering regimes; however, this reduction was more pronounced for the S populations so that seed production was comparable across S and R. The R populations had significantly higher germination and vegetative growth under cooler alternating temperature regimes. Although there were no differences between R and S plants under stress conditions, under optimal growth conditions, the Ala205Val substitution comes at a significant cost in eastern black nightshade. Under optimal growth conditions and in the absence of herbicide selection, S populations should eventually dominate over R; however, the lack of fitness differences under stress conditions could enhance the persistence of the R individuals.

Crop tolerance (CT), the crop's ability to endure or avoid competitive stress from weeds, varies between old and modern dent corn hybrids; however, this hypothesis has not been tested in sweet corn. Three modern sweet corn hybrids, known to vary in canopy density, were subjected to a range of wild-proso millet densities under irrigated conditions in Washington and primarily rain-fed conditions in Illinois. A path analysis was used to identify relationships among CT and specific canopy properties important to competitive interactions. Crop tolerance varied among hybrids in three of four site–years. Sweet corn hybrid ‘Spirit’ suffered higher yield losses than hybrids ‘WHT2801’ and ‘GH2547’. Generally higher yield loss parameter estimates in Illinois, compared with Washington, suggests CT may have more to offer for weed management in the north-central than north-western United States. Path analysis indicated that wild-proso millet biomass and seedling population density were both important factors driving yield loss in canopy-sparse Spirit, whereas only early season wild-proso millet population density contributed to yield loss of canopy-dense WHT2801 and GH2547. Differential tolerance to weed interference exists among commercially available sweet corn hybrids.

Phytotoxicity of five substituted urea herbicides 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), 3-(p-chlorophenyl)-1,1-dimethylurea (monuron), 3-phenyl-1,1-dimethylurea (fenuron), 3-hexahydro-4,7-methanoindan-5-yl) −1,1-dimethylurea (norea), and 3-(m-trifluoromethylphenyl)-1,1-dimethylurea (fluometuron) at 0, 10, 100, and 1000 ppm were determined in factorial combination at four urea nitrogen levels of 0, 45, 450, and 900 ppm with three Aspergilli: A. niger, A. sydowi, and A. tamarii. Response interactions were apparent, with all three fungi most tolerant for fenuron and least for diuron. Apparent tolerance order of the three intermediates were: A. niger, norea > fluometuron > monuron; A. sydowi, fluometuron > monuron > norea; and A. tamarii, fluometuron > norea > monuron. Oat (Avena sativa L.) bioassay for residual herbicide toxicity indicated significant differences in herbicide degradation rates between these three fungi at 5, 10, and 20 ppm in Eufaula sand. Diuron was more rapidly degraded than monuron at these levels with fluometuron and norea somewhat intermediate. A. niger was most effective in degradation of these herbicides with A. tamarii greater than A. sydowi. High nitrogen levels in soil organic matter amendment generally favored increased rates of urea herbicide degradation.

Citron melon is a monoecious, hairy annual vine commonly found in citrus orchards, and cotton and peanut fields. Information is not available on the effect of various environmental factors on the germination of citron melon. Laboratory and greenhouse experiments were carried out in 2011 and 2012 to determine the effect of light, temperature, salinity, pH, simulated water stress, and depth of sowing on the germination of citron melon. Citron melon germination was affected by various environmental factors. Highest germination was observed at day/night temperatures of 25/20 to 30/25 C regardless of light conditions. At temperatures below 25 C and beyond 35 C, germination declined and was higher under dark condition than light. Germination decreased as osmotic potential became more negative (−0.3 MPa to −1.5 MPa) and salt concentration increased (50 to 350 mM). No germination was observed at > −0.9 MPa and ≥ 300 mM salt concentrations. However, germination was observed over a broad range of pH (3 to 9) and up to 10-cm sowing depths. Seeds sown at the surface did not germinate but maximum germination (88 to 96%) occurred at 2- to 4-cm depth. The results of this study suggest that citron melon can grow in a wide range of climatic conditions and therefore can persist in Florida because of favorable weather and environmental conditions.

Five species of Nymphaeaceae, representing four genera, were collected from various sites in New Jersey and their tissues analyzed for 12 elements. Three species were separated into leaf blades and petioles before the mineral analyses were made. Variations in the concentrations of many elements were noted between these two structures. Except for the petioles of these three species, the N content of the plants appeared to be sufficiently high so that no extra N would be required to prepare composts from them.

Clomazone dissipation in soil was examined in field and laboratory experiments. Field studies suggested a potential for injury to rotational crops such as wheat. Field half-lives were 5 to 29 d (average of 9 field studies was 19 d) for the Etowah clay loam (fine-loamy, siliceous, thermic typic Paleudult) and Lily loam (fine-loamy, siliceous, thermic typic Hapludult) soils. Clomazone had an average half-life of 34 d under lab conditions, indicating slower dissipation in the lab than in the field. Clomazone was moderately adsorbed to soil as indicated by a Kd of about 1, and a Kom of 52 in the two soils.

Fall-planted longspine sandbur began to emerge in April, peaked in late April or May, and continued at low levels through October. During the first year after seeding, 98% of the total seedlings emerged prior to June. Fall-planted puncturevine began to emerge in late April or May and continued through October. Puncturevine emergence was multipeaked and 75% of each season's total emerged prior to mid-July. A similar number of puncturevine seedlings emerged the second and third years after planting as in the first. The emergence pattern for a species was similar each year regardless of how long the seed had lain in the soil. Longspine sandbur required 7 to 13 weeks from emergence to heading and produced approximately 2600, 1300, 180, and 3 spikes per plant when planted in May, June, July, and August, respectively. Puncturevine flowered within 3 to 4 weeks after emergence when temperatures were favorable and produced an average of 5600, 5200, 3600, and 200 burs per plant when planted in May, June, July, and August, respectively.