Effects of nonchemical weed control on weed and seedbank demography in ridge-tilled fields were simulated to examine long-term effects on weed population dynamics. Ridge tillage entails active seedbank management, including removal of much of the seedbank from the crop growth zone (ridge) to the interridge zone (furrow) at planting, and other seedbank manipulations. Dynamics of simulated yellow foxtail and velvetleaf populations were sharply sensitive to the rate of seed removal from the ridge. Variation in winter seed survival, ridge plant demography (emergence, survival, and seed production), and seed survival in the furrow after removal from the ridge also had strong effects on simulated dynamics. To prevent rapid population growth in a simulated corn-soybean rotation, very effective control of seedlings emerging with each crop was necessary to offset seed production from seedlings emerging after ridge rebuilding in corn years. Dynamics of both species were highly sensitive to cultivation efficiency. Effective “rescue” weed control must be available to prevent sharp increases in weed seedbanks during years when cultivation is ineffective.

Adaxial and abaxial epidermal surfaces of johnsongrass leaves were studied to determine which cells contribute to leaf microroughness. Cork-silica cell (CSC) pairs, three types of prickles, macrohairs, bicellular trichomes, stomata, and ordinary short and long epidermal cells were found and described. CSC pairs made up about 22% of all cells and probably contribute more to microroughness than any other single type because each cork cell produces 11 ± 3 wax filaments that are up to 100 μm long. Bicellular trichomes represented 4 to 5% of the total cells but decreased leaf roughness by secreting a type of mucilage that covers microscopic wax crystals. Stomatal complexes comprised 15 to 18% of all cells and contributed to leaf roughness because they are slightly recessed below the leaf surface. Long prickles occur primarily over veins and represent less than 1% of all cells. Small prickles were present primarily on adaxial surfaces and represent only 3% of all cells. Macrohairs were the largest appendages, 237 ± 104 μm, but they represent far less than 1% of all cells and occur primarily over veins. Ordinary short cells comprised 6 to 13% of all cells. Long cells were most common (41%) of all cells. Short and long cells contribute to leaf roughness because the surface is often convex. A typical johnsongrass leaf may contain more than 25 million appendages on each surface that increase the roughness already caused by epicuticular wax crystals.

In greenhouse studies root absorption after postemergence applications of cyanazine 2-[[4-chloro-6-(ethylamino)-s-triazine-2-yl] amino]-2-methylpropionitrile enhanced phytotoxicity to fall panicum (Panicum dichotomiflorum Michx.), green foxtail (Setaria viridis L.), and corn (Zea mays L.). Less 14C-cyanazine was taken up by the foliage of corn than by the weed species. A lower concentration of parent cyanazine in corn leaves was also evident. The addition of a phytobland oil to the treatment solution increased foliar cyanazine absorption 1 and 5 days following treatment. Although rapid metabolism occurred in corn roots, the large amount of cyanazine absorbed via the root system resulted in internal concentrations of parent cyanazine similar to that observed in the weed species. Cyanazine translocation was mainly acropetal from the point of application. The basis of selectivity is not solely based on the differential foliar uptake of cyanazine, but also on the proportion taken up by the foliage and roots. Under conditions favoring uptake by roots, the margin of selectivity may be reduced.

The metabolism of three 14C-ring-labeled herbicides, atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], chloramben (3-amino-2,5-dichlorobenzoic acid), and dicamba (3,6-dichloro-o-anisic acid) was studied in the earthworm, Lumbricus terrestris L., taken from plots treated with these herbicides for the past 10 yr and from control plots treated with no herbicides. For the two benzoic acid herbicides, acetone extracts of sand and earthworms from untreated plots contained more unmetabolized herbicide than similar extracts of sand and earthworms from treated plots, indicating a net enhancement of metabolism in worms from treated plots. For atrazine, the amount of unchanged herbicide in the acetone extracts of earthworm and sand were nearly equivalent. Finally, the relative metabolic stability of the three herbicides in decreasing order in earthworms from both control and untreated plots was chloramben>atrazine>dicamba.

Fall panicum (Panicum dichotomiflorum Michx.) and witchgrass (Panicum capillare L.) emerged in naturally infested fields as early as April 30 and May 14, respectively. The shortest period between seeding and emergence was during the warmest period of the growing season. The number of days from emergence to heading decreased progressively for later seedings. After emergence witchgrass formed seedheads about 7 days earlier than fall panicum. Fall panicum emerging in the middle of July and witchgrass seedlings emerging July 25 produced mature seeds in the fall, shaded or not. Plant height, tiller number, and yield of both grasses were highest for plants emerging in May and June. Decreased light intensity delayed seed emergence, heading, and maturity of both grasses. Plant height, yields, number of tillers, and number of panicles also were decreased by shading. Fall panicum was a coarser plant than witchgrass and produced more tillers and panicles than witchgrass. Fall panicum and witchgrass seedlings emerging between June 23 and July 7 produced the most vigorous fast growing plants.

An oat (Avena sativa L. ‘Dal’) primary root bioassay procedure was used to study the persistence of eight dinitroaniline herbicides in soil. Sensitivity of the bioassay to the herbicides depended on the length of time roots were exposed to the herbicide treatments. Root inhibition increased with time of exposure. Herbicide persistence was studied under growth chamber, greenhouse, and field conditions. The herbicides remained biologically active the longest under dry and cool soil conditions. At 5 C, little change in herbicide activity was observed over an 8-month period. Under greenhouse conditions, the herbicides in wet soil dissipated rapidly, as compared with those in dry soil. Soil samples taken from depths of 0 to 7.5 cm and from 7.5 to 15 cm in the field showed that the herbicides were retained primarily in the surface 7.5 cm. Small amounts were found from 7.5 to 15 cm only shortly after the herbicides were applied. Dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine) was the only herbicide tested of which soil residues from spring field applications were not detected the following fall.

In leaching studies utilizing slotted columns of soil and redroot pigweed (Amaranthus retroflexus L.) bioassay, 2,4-bis(isopropylamino)-6-methylmercapto-s-triazine (prometryne was leached to a greater depth in the coarse-textured sandy soils than in the fine-textured clay soils. There was little correlation between the depths of leaching and the amount of water used to leach the herbicide. Prometryne formulated as an emulsifiable concentrate was leached to a greater depth than the wettable powder and the granules. The 14C-pro-metryne was much more strongly adsorbed to a clay soil than to loam and silt loam soils. Volatility studies, using cotton (Gossypium hirsutum L.) plants to assay for vapor injury, showed the vapor loss of prometryne was greater from a metal surface than from a soil surface. Injury from prometryne vapors was greater with silt loam and sandy loam soils than clay soils. Cotton plants exposed 1 week after emergence were more severely injured by prometryne vapors than cotton plants exposed at emergence or 2 and 3 weeks after emergence. The vapor injury from prometryne formulated as a wettable powder or an emulsifiable concentrate was greater from granules. Prometryne vapor injury was increased as soil moisture and temperature was increased. Vapor injury to leaves of cotton was characterized by interveinal chlorosis while injury from root uptake was characterized by veinal chlorosis.

Goatsrue is an introduced perennial plant which has proven to have great invasive potential, leading to its classification as a noxious weed in many states and at the federal level. Very little research has been done on its basic biology. Physical dormancy of mature goatsrue seed was tested through scarification with sulfuric acid for up to 60 min resulting in 100% germination. Comparison of dormancy for 26-yr-old and 6-mo-old goatsrue seed indicated that aged seeds had reduced dormancy levels compared to newly harvested seeds. Maximum germination was similar among the 6-mo old and 26-yr-old seed lots, suggesting no loss of viability had occurred in seed stored dry for 26 yr. Goatsrue seedling emergence was inversely related to burial depth, and decreased as burial depth increased. Emergence of seed buried at 0.5 to 3.0 cm soil depth was 93 to 87%, respectively, and no emergence occurred from 12 and 14 cm. When the soil seed bank of five goatsrue-infested areas was sampled, the largest density of seeds found was 74,609 seeds m−2 while the lowest was 14,832 seeds m−2. Viability and dormancy of seeds recovered from the soil seed bank survey ranged from 91 to 100% and 80 to 93%, respectively. Management, which reduces the soil seed bank and controls emerging seedlings, is as essential as control of mature goatsrue plants in order to avoid seedling establishment and reinvasion of a location.

Native polyacrylamide gel electrophoresis was used to identify polymorphisms in α- and β-esterases loci and electrophoresis in starch gel to identify polymorphism in malate dehydrogenase (MDH; EC 1.1.1.37) and acid phosphatase (ACP; EC 3.1.3.2) isozymes loci in leaf tissues from samples of horseweed and hairy fleabane populations to determine genetic diversity and population structure. Similar or differential genetic divergence between the two species may guide specific use of herbicides. For samples of plants with high genetic similarity it is possible to adopt similar mechanisms and processes for their control. The proportion of polymorphic loci was 57.14, 50.0, and 53.6%, in samples of horseweed and hairy fleabane, for EST, MDH, and ACP isozymes, respectively. A comparison of the diversity parameters in the two species showed that the number of alleles is similar in the horseweed and hairy fleabane plants. The estimated heterozygosity in horseweed and hairy fleabane was also very close. A relatively low level of population differentiation was detected between horseweed and hairy fleabane (FST = 0.0199), which suggests a substantial genetic exchange among the two species. Accordingly, estimate of gene flow was high (Nm = 12.3172) for the alleles of the loci Est, Mdh, and Acp. The Nei's identity (I) values also was high (I = 0.9561) indicating very high similarity between the two Conyza species. AMOVA showed higher genetic variation within (95%) than among (5%) the two samples. The low genetic structure and high value of genetic identity was an important indication that alleles are exchanged between horseweed and hairy fleabane populations, and provides additional evidence of occurrence of outcrossing between populations or dispersion of samples of one for other site.

Potato exhibits adequate tolerance to preemergence applications of sulfentrazone at rates up to 0.28 kg ai ha−1. Sulfentrazone also controls several troublesome weeds such as common lambsquarters but may be less effective against jimsonweed. Laboratory experiments were conducted to investigate differential tolerance to root-absorbed [14C]sulfentrazone by potato, common lambsquarters, and jimsonweed. Common lambsquarters and jimsonweed absorption of [14C]sulfentrazone g−1 fresh weight was more than twofold that in potato after 24-h exposure. After 48-h exposure, sulfentrazone absorption by common lambsquarters was nearly twofold that in jimsonweed and nearly threefold that in potato. Sulfentrazone movement from roots to shoots was also greater in common lambsquarters than in jimsonweed and potato after 6 h. Both weed species exhibited nearly a twofold increase in sulfentrazone translocation from roots to shoots compared with potato after 12, 24, and 48 h. Minor differences in sulfentrazone metabolism in roots were noted among species after 6 h. Metabolism in roots and shoots was similar in all species after 12, 24, and 48 h. Because the enzyme on which sulfentrazone acts, protoporphyrinogen oxidase, is located in shoot tissue, translocation to shoots is essential for sulfentrazone toxicity. Therefore, differential root absorption and differential translocation of sulfentrazone from roots to shoots are the proposed primary mechanisms of differential sulfentrazone tolerance among potato, common lambsquarters, and jimsonweed.

The uptake, translocation, and fate of (2,4-dichlorophenoxy)acetic acid (2,4-D) were compared in nightflowering catchfly (Silene noctiflora L.) and common lambsquarters (Chenopodium album L.), resistant and susceptible species, respectively. Nightflowering catchfly leaf sections absorbed more 2,4-D from 5 × 10-4 M and 5 × 10-6 M 2,4-D solutions at pH 3.0 than did leaf sections of common lambsquarters. Intact plants of both species accumulated 2,4-D in the stems and leaves below the treated leaf. At 72 hr after treatment, nightflowering catchfly released 2,4-D through the roots into the nutrient solution while common lambsquarters continued to accumulate 2,4-D. Nightflowering catchfly metabolized 2,4-D and the metabolite was recovered in the roots 24 hr after treatment, whereas common lambsquarters did not metabolize 2,4-D.

Spreading dogbane is a common perennial weed in wild blueberry fields. It is highly competitive and spreads rapidly once established. Herbicides can provide effective control of spreading dogbane, but application timing is important. The emergence pattern, ramet height, and flowering time of spreading dogbane were observed in 2008 and 2009, and thermal-based emergence, growth, and development models were developed and used to estimate optimum herbicide application timing. Spreading dogbane emergence and height were described with a three-parameter, sigmoid, nonlinear regression model, whereas flowering was described with a four-parameter, Weibull, nonlinear regression model. Spreading dogbane ramets initiated emergence soon after the biofix date of April 1. Peak emergence tended to occur at 420 growing degree days (GDD). Spreading dogbane reached its peak height by about 558 GDD. The maximum number of flowers per plant was reached at approximately 750 GDD. This study suggested that POST herbicides should be applied between 486 and 535 GDD to maximize efficacy. This time frame occurs after peak emergence and during early floral bud development.

In a 2-yr field study with preplanting-soil-incorporated treatments of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] and metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one], tolerance of soybeans [Glycine max (L.) Merr.] to these herbicides, as measured by seed yield, was increased by increasing the seeding rate one-and-one-half or two times that normally recommended. These results agree with suggestions in the literature that plants can compete for herbicide in the soil, and suggest that increased seeding rates of soybeans can partially reduce the adverse effects of atrazine carryover or excessive metribuzin application.

Five PRE herbicides were applied at below maximum registered use rates to the same bermudagrass turf plots for three consecutive years for large crabgrass and goosegrass control. In most instances, full labeled herbicide rates were needed for acceptable large crabgrass and goosegrass control during the 1st year of treatment. All herbicides controlled large crabgrass but not goosegrass during the 1st year. Weed management programs that utilized the lowest herbicide rates while maintaining ≥ 80% control during the 2nd and 3rd years varied with herbicides. The programs for large crabgrass were prodiamine at 0.8 kg ha−1 the 1st year followed by 0.2 kg ha−1 the 2nd and 3rd years; oryzalin at 2.2 kg ha−1 the 1st year followed by 0.6 kg ha−1 the 2nd and 3rd years; dithiopyr at 0.3 kg ha−1 the 1st year followed by 0.1 kg ha−1 the 2nd and 3rd years; pendimethalin at 1.7 kg ha−1 the 1st year followed by 0.8 kg ha−1 the 2nd and 3rd years; and oxadiazon at 3.4 kg hha−1 the 1st year followed by 2.5 kg ha−1 the 2nd year and 1.7 kg ha−1 the 3rd year. The programs for goosegrass were prodiamine at 0.8 kg ha−1 followed by 0.6 kg ha−1 the 2nd and 0.4 kg ha−1 the 3rd year; dithiopyr at 0.8 kg ha−1 the 1st year followed by 0.4 kg ha−1 the 2nd and 3rd years; pendimethalin at 3.4 kg ha−1 the 1st year followed by 1.7 kg ha−1 the 2nd year and 0.8 kg ha−1 the 3rd year; and oxadiazon at 3.4 kg ha−1 followed by 0.8 kg ha−1 the 2nd and 3rd years. Because goosegrass control with oryzalin at reduced rates was unacceptable during the 1st and 2nd years, this herbicide should not be used in a reduced rate program. The quality of common bermudagrass was not affected by reduced herbicide rates.

A technique was developed for seeding rangelands which are too steep or too rocky to seed by current methods. Hardinggrass (Phalaris tuberosa L. var. stenoptera (Hack.) Hitchc.) and subclover (Trifolium subterraneum L.) were established by seeding immediately after spraying the resident vegetation with 1,1′-dimethyl-4,4′-bipyridinium ion (paraquat). Tested for seeding in sod were single-disk, double-disk, and hoe-type drill openers. The double disk was best adapted to the clay soils most common in the area. A heavy-duty rangeland drill was modified with custom-made, heavy, double-disk openers and equipped with a spray system which sprays either bands or full coverage. The resulting planter will kill weeds, plant seeds, and spread fertilizer any place where a crawler tractor can pull it. Weed-free bands of 6 and 12 inches were compared with full spray coverage. No hardinggrass was established without some weed control. In only 5 of 16 tests over a 5-year period was full-spray coverage superior to the 6-inch band. The 12-inch band or full spray may be preferable on shallow soils or soils of low water-holding capacity. Spraying helped establish subclover but, unlike with hardinggrass, was not critical. Grazing or mowing during the establishment period improved stands of both hardinggrass and subclover. Prolonged weed control made paraquat superior to cultivation by giving better weed control and a firmer seedbed.

Five field experiments were conducted to evaluate effectiveness of postemergence herbicidal treatments. Amitrole (3-amino-s-triazole) at 1.1 kg ai/ha and picloram (4-amino-3,5,6-trichloropicolinic acid) at 0.6 kg ai/ha reduced stands of common milkweed (Asclepias syriaca L.) for a 4-yr period. Glyphosate [N-(phosphonomethyl)glycine] at 2.2 kg ai/ha reduced stands of milkweed for two to three growing seasons. Glyphosate or amitrole applied in June (early bud stage) more effectively reduced milkweed stands in the second year than did the herbicides when applied in August (post-flowering stage). Treatments of 2,4-D [(2,4-dichlorophenoxy)acetic acid], 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], and dicamba (3,6-dichloro-o-anisic acid) did not reduce stands of common milkweed.

When glyphosate [N-(phosphonomethyl)glycine] was fed through the transpiration stream of excised bean (Phaseolus vulgaris L. ‘Red Kidney’) shoots, it was readily absorbed and transported to the leaves where it inhibited transpiration. Maximum inhibition (40 to 50%) resulted from tissue concentrations of 50 to 3000 nmoles glyphosate/g fresh weight, while transpiration was significantly inhibited (20%) by as little as 15 nmoles/g fresh weight. A combination of 5 X 10-4M tyrosine (Tyr) and 5 x 10-4M phenylalanine (Phe) supplied continuously through the transpiration stream prevented the inhibition of transpiration by glyphosate during the course of 8-h experiments. Tyrosine (10-3M) alone delayed the transpiration response to glyphosate by 2 to 3 h but 10-3M Phe alone did not affect the inhibition by glyphosate. Levels of endogenous Tyr and Phe were about 50% lower in glyphosate-treated leaves than in the controls 6 h after treatment.

Soybean field experiments were conducted to compare weed interference data obtained from small 2.7-m2 plots to that obtained from large 11-m2 plots. Soybean row spacings of 15, 30, 45, and 90 cm were used. Sicklepod, common cocklebur, and soybean biomass as dry matter were harvested from small plots 10 weeks after planting and were compared to weed biomass and soybean seed yield from the large plots. Sicklepod and common cocklebur biomass in small plots increased and soybean biomass decreased as soybean row spacing increased. Soybean biomass was not affected by row spacing when weeds were not present. Sicklepod and common cocklebur biomass in large plots increased and soybean seed yield decreased as soybean row spacing increased. Soybean seed yield was not affected by row spacing when weeds were not present. Comparison of regression coefficients for paired regression lines indicates that soybean biomass from small plots may be substituted for seed yield from large plots as a measure of sicklepod or common cocklebur interference if both size plots use the same soybean row spacing and are irrigated until harvest.

Injury to corn (Zea mays L.) hybrids from butylate (S-ethyl diisobutylthiocarbamate) was investigated as a function of planting depth, soil pH, and temperature. Field and growth chamber studies indicated that the potential for butylate injury increased with increasing planting depth regardless of hybrid. Greenhouse and growth chamber experiments suggested that as soil pH decreased butylate injury increased, depending upon the hybrid. Butylate injury was also a differential response among hybrids, depending on temperature. Certain hybrids may be injured more at higher temperatures and other hybrids more at lower temperatures. Butylate injury to corn, therefore, appears to be due to a three-way interaction, stress x hybrid X butylate.

We collected tubers from greenhouse-grown yellow nutsedge (Cyperus esculentus L.) control plants and plants foliarly-treated with 3.36 kg/ha of disodium methanearsonate (DSMA) or monosodium methanearsonate (MSMA). Where sufficient tubers were produced, they were separated into two classes, large and small. Some of the tubers were analyzed for elemental arsenic, and others were stored at 2 C and planted at various intervals. Vitality of tubers was noted in terms of sprouting and vegetative growth. Tubers collected from treated plants contained significantly more arsenic (4 to 33 ppm) than control tubers (1 ppm). Tubers collected from treated plants and planted without separation sprouted in significantly reduced numbers compared to control tubers. Small tubers contained a significantly higher concentration of arsenic (23 to 33 ppm) than large tubers (4 to 12 ppm). The treatments reduced the vitality of small tubers but had little or no effect on vitality of large tubers.