Herbicide treatments were applied to established alfalfa (Medicago sativa L.) in 1969 and 1970 to determine winter annual weed control efficacy, crop tolerance, and influence on alfalfa yield and protein. Common chickweed (Stellaria media (L.) Cyrillo) was the predominant species in both years. Excellent weed control was achieved in 1969 with 2-sec-butylamino-4-ethylamino-6-methoxy-s-triazine (GS 14254) at 1.7 kg/ha, 2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl]amino]-2-methyl-propionitrile (cyanazine) at 4.5 kg/ha, 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) at 1.7 kg/ha, and 3-tert-butyl-5-chloro-6-methyluracil (terbacil) at 1.1 kg/ha. Several other treatments also significantly reduced weed yields. All herbicides significantly reduced weed yields in 1970. First harvest alfalfa yields in 1969 were not increased significantly despite the excellent weed control afforded by several treatments. Second harvest alfalfa yields did not differ significantly, however, weeds were not a problem in the regrowth. In 1970 four of the 19 treatments did yield significantly more than control plots. Alfalfa protein was not altered by any of the treatments either year.

Rice vampireweed belongs to the Orobanchaceae and is found in Africa and Australia. It is a hemiparasitic weed of lowland rice genotypes and causes losses of 40 to 100% of rice grain yield. Our study addressed the genetic diversity of rice vampireweed in Benin and Senegal. The specific objectives of this research were to study the genetic diversity of rice vampireweed accessions in Benin and Senegal and the relationship between the different genotypes of rice vampireweed through agroecological areas. To achieve these objectives, the genetic diversity of rice vampireweed accessions using the AFLP technique was studied. Based on our results, dendrogram classification has distinguished four different genetic groups. The populations of Benin and Senegal are genetically diverse. Substantial genetic differentiation (GST) exists among agroecological areas within Benin and Senegal (GST = 0.17). The high genetic diversity of rice vampireweed in Benin and Senegal presents a challenge for the development of resistant rice germplasm.

The rapid expansion of the plant bioeconomy is creating strong economic incentives to distribute novel plant material, including transgenic cultivars, exotic species, and species that were formerly constrained to small geographical areas, at large geographical scales. Such introductions carry with them the risk of invasive spread of the introduced species (Simberloff and Alexander 1998). Deployment of plant species for biofuel production offers a clear example of the benefits and risks associated with the new bioeconomy (Raghu et al. 2006).

In a measure aimed at reducing U.S. dependence upon foreign petroleum reserves for energy production, President Bush announced the Advanced Energy Initiative (AEI) in his 2006 State of the Union address. This initiative provides federal funding and guidelines for the development of renewable energy sources, including plant biofuels. The objectives of the AEI, though admirable, have the potential to create a conflict with Executive Order 13112, which states that “[Federal agencies shall] not authorize, fund, or carry out actions that it believes are likely to cause or promote the introduction or spread of invasive species in the United States or elsewhere unless, pursuant to guidelines that it has prescribed, the agency has determined and made public its determination that the benefits of such actions clearly outweigh the potential harm caused by invasive species; and that all feasible and prudent measures to minimize risk of harm will be taken in conjunction with the actions.”

In tobacco (Nicotiana tabacum L. 'Speight G-28′) exposed to benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) vapors from treated soil, the leaves formed after treatment were shortened, narrowed, distorted in shape, and had an abnormal vein pattern. The leaves that had developed before treatment did not have these symptoms. More leaves developed on treated than on untreated plants. The height of treated plants was reduced and many axillary buds became active prematurely. The injured leaves, in general, had fewer epidermal cells, stomata, and trichomes per unit surface area; a smaller volume of intercellular space; and were thicker than those of untreated plants. Many of the meristematic cells in the leaf primordia and shoot apex of treated plants contained large and distorted nuclei and were oriented in improper planes. The plate meristems established by activity of the marginal meristems gave rise to a mass of undifferentiating parenchyma cells in the mesophyll of the young leaves. There was little formation of the palisade or spongy mesophyll layers, but enlargement of the undifferentiating cells caused a radial expansion of the lamina.

Absorption, translocation, and metabolism of foliar-applied ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulphonate] were studied to explain field observations showing differences in susceptibility among sugarbeet (Beta vulgaris L.), common ragweed (Ambrosia artemisiifolia L.), redroot pigweed (Amaranthus retroflexus L.), and common lambsquarters (Chenopodium album L.). In laboratory studies, two- to four-leaf seedlings of the highly susceptible species, redroot pigweed and common lambsquarter, absorbed greater amounts of 14C-ethofumesate from foliar application than the moderately susceptible common ragweed and tolerant sugarbeet. Sugarbeet translocated very little 14C from treated foliage to untreated plant tissue. All weed species translocated 14C-ethofumesate to untreated leaf tissue when 14C-ethofumesate was applied to seedlings at the two-leaf stage. Ethofumesate was translocated basipetally to the stem and root of two-leaf redroot pigweed and common lambsquarter seedlings. A high percentage of the 14C was found in the water-soluble fraction in sugarbeet seedlings, indicating inactivation. The amount of metabolites recovered in the non-polar fraction depended on the stage of plant growth. Total photosynthesis and respiration in redroot pigweed was inhibited 4 h after foliar application and did not recover after 96 h. Uptake and evolution of CO2 were also inhibited in sugarbeet leaves, but they recovered rapidly, depending on age of plant at treatment. The stage of plant development was the key factor determining species response to foliar treatments of ethofumesate in terms of absorption, metabolism, and total photosynthesis and respiration.

Sand shinnery oak (Quercus havardii Rydb.) was controlled by both picloram (4-amino-3,5,6-trichloropicolinic acid) and tebuthiuron (N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} in the Rolling Plains vegetational region of Texas. Tebuthiuron provided acceptable control of sand shinnery oak at rates of 0.6 to 1.1 kg/ha, but 2.2 kg/ha of picloram was required to give comparable results. Tebuthiuron pellets applied at 0.6 kg/ha controlled 79% of the sand shinnery oak within 30 to 67 months after application. Applied at 1.1 kg/ha, tebuthiuron controlled 91% (average for three locations). No differences were found between formulations of a given herbicide.

The effects of soil-applied and stem-injected herbicidal techniques of forest conversion on soil moisture, pine establishment and understory vegetation were determined in an Appalachian hardwood forest. Grid applications of fenuron (1,1-dimethyl-3-phenylurea) at 11.2 kg/ha were as effective in killing tops and controlling sprouting of hardwood species as the injection application with 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] and fuel oil. Survival of white pine (Pinus strobus L.) was higher with 5.6 kg/ha than with 11.2 kg/ha of fenuron pellets. The growth in height of pines growing under reduced competition was considerably greater than for pines growing in competition with hardwoods. During the second growing season after treatment significantly more soil moisture was present in the plots treated with fenuron and 2,4,5-T than in the untreated ones. Herbaceous vegetation and understory woody plants increased after the herbicide treatments. The third season following herbicide treatment twenty-seven species were recorded on the treated areas that were not present on the untreated control areas.

The control of greasewood [Sarcobatus vermiculatus (Hook.) Torr.] and salt rabbitbrush [Chrysothamnus nauseosus ssp. consimilis (Greene) Hall and Clem.] was investigated with application of 2,4-D [(2,4-dichlorophenoxy)acetic acid] and a mixture of 2,4-D and picloram (4-amino-3,5,6-trichloropicolinic acid). The herbicides were applied at 2-week intervals from May 1 to August 1. Greasewood had accelerated shoot growth and was most susceptible to application of 2,4-D during June. Accelerated shoot growth and maximum susceptibility to 2,4-D of salt rabbitbrush began in June and extended into July. Mortality of greasewood and salt rabbitbrush from 2,4-D at 2.2 kg/ha applied at optimum dates averaged 72 and 87%, respectively. The picloram/2,4-D mixture was more effective for greasewood control than 2,4-D alone in 1 yr at very early and late application dates on a xeric site and only at the last date of application on a mesic site. Reapplication of 2,4-D at 2.2 and 3.3 kg/ha in June to partially controlled stands gave excellent control of both greasewood and rabbitbrush.

Production of native grasses following aerial application of 1.12 kg/ha of 2.4.5-T ((2,4,5-trichlorophenoxy)acetic acid), 2,4,5-T + dicamba (3,6-dichloro-o-anisic acid), or 2,4,5-T + picloram (4-amino-3,5,6-trichloropicolinic acid) (1:) to a south Texas mixed-brush (Prosopis-Acacia) community was significantly increased by all herbicide treatments the year of application, by the herbicide combinations during the second year, but only by 2,4,5-T + picloram the third year after treatment. Moisture-use efficiency based on kg/ha native grass produced/cm precipitation was greastest where the herbicide combinations were applied. Defoliation of woody plants in years of above-average rainfall resulted in favorable grass production responses regardless of herbicide(s). However, range improvement over the 3-yr of study was dependent on maintenance of herbicide effectiveness, especially control of underbrush which resulted only where 2,4,5-T + picloram were applied. Consumption of native grass was a direct function of availability in response to brush control as augmented by rainfall. Forb production was reduced by all herbicides the year of treatment and by 2,4,5-T + picloram the year following application, but was not reduced by any treatment during the third growing season.

We applied (2,4-dichlorophenoxy)acetic acid (2,4-D), (2, 4,5-trichlorophenoxy)acetic acid (2,4,5-T), 4-amino-3,5,6-trichloropicolinic acid (picloram), and 1,1′-dimethyl-4,4′-bipyridinium ion (paraquat) alone and in various combinations by aircraft on arborescent species in Texas and Puerto Rico. Paraquat defoliated trees rapidly but did not give long-term control. Picloram defoliated a greater number of species than the other herbicides and defoliation extended over a longer period. No treatment killed all trees in the mixed forest or prevented regrowth and secondary succession for a period of more than 1 year. Higher herbicide rates were necessary to defoliate woody plants in tropical Puerto Rico than in subtropical Texas.

Responses of Rhizoctonia solani Kuhn to napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide], were evaluated by measuring whole-cell respiration, mitochondrial respiration, ATP synthesis, and membrane leakage. Whole-cell respiration, measured with an O2 electrode, was stimulated in the presence of napropamide at 1.1, 2.2, and 4.4 × 10−5 M. Mitochondrial respiration was stimulated at 1.1 × 10−11 M, but higher concentrations were inhibitory. The addition of 10−5 M napropamide to isolated mitochondria of R. solani resulted in reduced ATP synthesis, measured by the firefly luciferase assay, and in increased membrane permeability as measured by increases in electrical conductivity of filtrates from R. solani grown in culture medium containing napropamide. These results indicate that, under laboratory conditions, napropamide reduced ATP synthesis, caused membrane leakage, and stimulated respiration in R. solani.

In 1979 and 1980, isolates of Alternaria were obtained from diseased leafy spurge (Euphorbia esula L.) plants. The pathogenicity of an Alternaria sp. towards leafy spurge was demonstrated in glasshouse and limited field studies, and the Alternaria is considered to be a potential biological - control agent for leafy spurge. The pathogenicity and cultural characteristics of the fungus suggest its classification as A. tenuissima f. sp. euphorbiae, with isolate Krupinsky 80-3547ss4 (= E. G. Simmons 35-079) as a representative strain.

Measurements of net photosynthesis, chlorophyll a fluorescence and solute leakage were evaluated as techniques for rapid detection of grass tolerance to fenoxaprop-ethyl and sethoxydim. Net photosynthesis measured as net CO2 uptake of the youngest fully expanded leaf of Calamagrostis arundinacea ‘Karl Foerster’ (Feather Reed Grass) detected tolerance to fenoxaprop-ethyl and susceptibility to sethoxydim 4 days after treatment and prior to the observation of visual injury. Sethoxydim reduced photosynthesis compared to untreated controls but fenoxaprop-ethyl did not. Measurements of older leaf (second most recently fully expanded leaf) photosynthesis were less consistent than those of the younger leaf. Chlorophyll a fluorescence of Calamagrostis leaf segments following treatment with fenoxaprop-ethyl and sethoxydim was ineffective for detecting grass tolerance. Solute leakage from leaf discs treated with 50 to 500 μg ml−1 fenoxaprop–ethyl and 10 to 100 μg ml−1 sethoxydim indicated differential tolerance of Calamagrostis and johnsongrass to fenoxaprop–ethyl and centipedegrass and johnsongrass to sethoxydim. Fenoxaprop–ethyl increased solute leakage from susceptible johnsongrass at 100 μg ml−1 while the 500 μg ml−1 concentration was required to cause substantial solute leakage from tolerant Calamagrostis. Sethoxydim caused greater leakage from johnsongrass than from centipedegrass at 50 and 100 μg ml−1. The best potential rapid screening technique was solute leakage measurements.

Greenhouse and field experiments were conducted to compare the response of cucumber (Cucumis sativus L. ‘Ashley’), muskmelon (Cucumis melo L. ‘Delicious 51’), watermelon (Citrillus vulgaris L. ‘Charleston Grey’), and three winter squashes (Cucurbita moschata Duch. ex Poir. ‘Butternut’, Cucurbita pepo L. ‘Table Queen’, and Cucurbita maxima Duch. ‘Boston Marrow’) to 3-amino-2,5-dichlorobenzoic acid (chloramben) and six of its analogs (ammonium salt, amide, mixed salts, methyl ester, hydroxy propyl ester, and butoxy ethyl ester). There were little differences among the analogs except the amide was generally nontoxic to all test crops and weeds. Great differences in growth were noted among species. When chloramben was incorporated in the soil, cucumber and watermelon were very susceptible to all analogs except the amide. Muskmelon was tolerant of all analogs. Squashes exhibited variable susceptibility with ‘Butternut’ the least tolerant, ‘Table Queen’ intermediate, and ‘Boston Marrow’ quite tolerant of the analogs. Separation of exposure of the germinating and emerging seedling on the basis of root or shoot showed cucumber to be most susceptible to root exposure but also susceptible to shoot exposure. Muskmelon and ‘Boston Marrow’ squash were susceptible to root exposure but not to shoot exposure. Muskmelon was not susceptible to either hypocotyl or cotyledon exposure, but cucumber was susceptible to both these treatments. All three species were severely injured by postemergence sprays of chloramben.

A yellow nutsedge biotype (Res) from an Arkansas rice field has evolved resistance to acetolactate synthase (ALS)-inhibiting herbicides. The Res biotype previously exhibited cross-resistance to ALS inhibitors from four chemical families (imidazolinone, pyrimidinyl benzoate, sulfonylurea, and triazolopyrimidine). Experiments were conducted to evaluate alternative herbicides (i.e., glyphosate, bentazon, propanil, quinclorac, and 2,4-D) currently labeled in Arkansas rice–soybean production systems. Based on the percentage of aboveground dry weight reduction, control of the yellow nutsedge biotypes with the labeled rate of bentazon, propanil, quinclorac, and 2,4-D was < 44%. Glyphosate (867 g ae ha−1) resulted in 68 and > 94% control of the Res and susceptible yellow nutsedge biotypes, respectively, at 28 d after treatment. Dose-response studies were conducted to estimate the efficacy of glyphosate on the Res biotype, three susceptible yellow nutsedge biotypes, and purple nutsedge. Based on the dry weights, the Res biotype was ≥ 5- and ≥ 1.3-fold less responsive to glyphosate compared to the susceptible biotypes and purple nutsedge, respectively. Differences in absorption and translocation of radiolabeled glyphosate were observed among the yellow nutsedge biotypes and purple nutsedge. The susceptible biotype had less 14C-glyphosate radioactivity in the tissues above the treated leaf and greater radioactivity in tissues below the treated leaf compared to the Res biotype and purple nutsedge. Reduced translocation of glyphosate in tissues below the treated leaf of the Res biotype could be a reason for the lower glyphosate efficacy in the Res biotype. No amino acid substitution that would correspond to glyphosate resistance was found in the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene of the Res biotype. However, an amino acid (serine) addition was detected in the EPSPS gene of the Res biotype; albeit, it is not believed that this addition contributes to lower efficacy of glyphosate in this biotype.

Studies suggest that disturbance-induced reductions in soil seedbank density are diminished by periods of water scarcity after soil disturbance; however, this hypothesis has yet to be tested. The objectives of this study were (1) to determine the effects of increasing time between soil disturbance and flood irrigation on disturbance-induced reductions in soil seedbank density, and (2) to identify specific soil moisture levels that cause seedbank reductions under flood irrigation. Weed species in this study were junglerice, Palmer amaranth, and yellow foxtail. For Objective 1, artificial seedbanks with known numbers of seeds were disturbed 10, 3, or 0 d prior to flood irrigations under field conditions. For Objective 2, seeds were buried in soil mesocosms that were hydrated to specific soil water potentials (flooded, 0 kPa, −30 kPa, −60 kPa, and −180 kPa) and placed in laboratory conditions favorable for germination. For both objectives, seeds were recovered to determine the percentages of buried seeds that survived the disturbance or moisture treatments. Results for the field study indicated that soil disturbances reduced seedbank persistence of Palmer amaranth but did not affect seedbank persistence of junglerice and yellow foxtail. Disturbance-induced reductions in seedbank density were greatest when soil was disturbed 0 and 3 d prior to flood irrigations. For the laboratory study, results showed that waterlogged soil was not required for seedbank losses because rates of seedbank persistence were greater in saturated soils (0 kPa and flooded) compared to the lower moisture levels. These studies indicate that delays in irrigation can reduce the seedbank reduction potentials of soil disturbance events. Further, irrigation timing effects on disturbed soil seedbanks are likely to occur in all irrigation systems, including those that reduce the amount of water applied compared to flood irrigation.

The effects of time of precipitation and soil type on runoff losses of cyanazine and metolachlor were studied using a tilted-bed, microplot system. Two silt loam soils, Bosket and Dubbs, and a Sharkey silty clay were evaluated. Rainfall (22 mm h−1) was simulated at 0, 2, and 14 days after treatment (DAT). Time of precipitation did not impact herbicide losses or any of the runoff parameters evaluated in this study. Water runoff occurred sooner and in greater quantities from the surfaces of Bosket and Dubbs silt loam soils than from the surface of Sharkey silty clay. Runoff losses of cyanazine did not vary by soil type. Soil drying produced large cracks in Sharkey silty clay, which greatly reduced runoff in this soil. Combined runoff and leachate losses were highest from Dubbs silt loam. Runoff losses of metolachlor were not affected by soil type. However, regression analyses indicated that time of precipitation and soil type interacted to affect initial metolachlor concentration. At 14 DAT, initial metolachlor concentration was highest in runoff from Sharkey soil. Time of precipitation ranked with respect to initial metolachlor concentration in runoff from Bosket and Dubbs silt loam soils were 0 > 2 > 14 DAT and 0 = 2 > 14 DAT, respectively.

The spread and dominance of the invasive native hay-scented fern in the understory is one of the most significant changes that has affected the forest ecosystems in the northeastern United States in the last century. We studied changes in the distribution and dynamics of hay-scented fern at a large scale over a 10-yr period in Pennsylvania. The study included 56 stands covering 1,009 ha in two ecoregions. Hay-scented fern was more widely distributed and occurred at higher densities in the Allegheny Plateau ecoregion vs. the Ridge and Valley. Hay-scented fern abundance was positively associated with overstory red maple abundance in both ecoregions. After overstory removal, the density and distribution of hay-scented fern tended to increase and remain at elevated levels in stands that were not treated with herbicide. Herbicide treatments resulted in temporary reductions in fern densities and created a “window of opportunity” for the establishment of tree regeneration.

In controlled-environment chambers, the scentless plant bug Niesthrea louisianica Sailer damaged reproductive structures of velvetleaf (Abutilon theophrasti Medik. # ABUTH) and reduced viable seed production by 98 to 99%, in comparison with insect-free control plants. The insect completed its life cycle on velvetleaf in two temperature regimes simulating warm growing-season conditions in Mississippi (29/23 C day/night) and Minnesota (24/18 C). Feeding by N. louisianica delayed flowering, capsule development, and capsule and seed maturation in biotypes of velvetleaf from Mississippi and Minnesota, in both temperature regimes. Numbers and weights of capsules and seed were lower in the infested plants. Augmentation of natural populations of N. louisianica to increase population density early in the growing season might be effective in reducing velvetleaf seed production.

In field practice much of the application of herbicides to local infestations of bermudagrass (Cynodon dactylon L.) is done by hand on a spray-to-wet basis. With a fixed concentration of active ingredient in the spray mixture the dosage is determined by the volume used in wetting a particular stand of grass. The amount of herbicide deposited on the weed foliage may be affected by the addition of surfactants to the spray mixture. In orchards and vineyards where the tolerance of the crop to the herbicide is limited, variations in the stand may lead to local overdosage and injury to the trees and vines.