Common ragweed (2n=36), giant ragweed (2n = 24), and their reciprocal F1 hybrids (2n = 30) were analyzed for a number of traits. Hybrids of the type giant ragweed♀ × common ragweed♂ were obtained via immature embryo culture. The analyses revealed a surprising contribution of the pollen parent for features such as biomass, leaf area, and specific leaf area. Leaf morphology, however, was similar to the maternal parent. One plant, originating from crosses of the type common ragweed♀ × giant ragweed♂, developed abnormally and cytological analysis revealed the presence of 24 chromosomes in its somatic cells. Probably this plant had an androgenetic origin.

Kudzu (Pueraria lobata Ohwi # PUELO) was grown from seeds in controlled-environment chambers at 350, 675, or 1000 μl·1−1 CO2. Biomass and leaf area production, morphological characteristics, and growth analysis components were determined at 14, 24, 45, and 60 days after emergence. At 60 days, plants grown at 1000 μl·1−1 CO2 had 51% more biomass, 58% longer stems, and 50% more branches than plants grown at 350 μl·1−1 CO2. Plants grown at 675 μl·1−1 CO2 were intermediate. Growth analysis components indicated that CO2 enrichment increased growth by compounding effects due to increased net assimilation rates and increased leaf area duration. Relative growth rates were not significantly affected. The large CO2-induced increase in stem height versus stem diameter is in marked contrast to previously reported responses of woody erect growth forms. Possible ecological implications for competitive abilities are discussed.

Greenhouse, growth chamber, and laboratory studies were conducted to determine anatomical and morphological characteristics and cultural practices limiting the distribution of cogongrass, torpedograss, and johnsongrass in the United States. Cogongrass did not produce axillary buds along most of the rhizome nor regenerate when apical six-node-long rhizome segments were buried deeper than 8 cm. Both torpedograss and johnsongrass produced axillary buds along the entire lengths of their rhizomes. Torpedograss shoot emergence decreased at burial depths between 8 and 16 cm. Shoot emergence from johnsongrass rhizomes was not affected by burial as deep as 16 cm. Rhizomes of all three species were tolerant of desiccation. Cogongrass grew better in soil at pH 4.7 than in soil at pH 6.7, whereas torpedograss and johnsongrass grew equally well in either pH. It is postulated that cogongrass spread is limited by lack of axillary bud formation on most of the rhizome and the inability of rhizomes to send up new shoots if buried deeper than 8 cm. These factors could account for the intolerance of cogongrass to cultivation. Torpedograss appears to spread only vegetatively due to the lack of viable seed production.

Native Polyacrylamide gel electrophoresis (PAGE) and enzyme activity staining were used to identify possible progenitor species of velvetleaf (Abutilon theophrasti Medic. # ABUTH). Multiple forms of superoxide dismutase activity were observed in each of the plants surveyed. Three enzyme forms were common to all the species and bio types while one form was different in the velvetleaf biotypes compared to the other species. Multiple forms of peroxidase activity were also detected. The three velvetleaf biotypes possessed identical enzyme forms with minimal similarity to peroxidase forms found in the other species. Multiple forms of esterase activity separated as two nonoverlapping groups. A slowly migrating group was observed in all the velvetleaf biotypes and a more rapidly migrating group characterized the remaining Abutilon species. The results of this study indicated that the progenitors of velvetleaf were not among the species surveyed and suggested that the progenitors may no longer be extant.

Interference from broadleaf signalgrass at a density of 180 plants/m2 reduced rough rice yields of ‘Bond’ a maximum of 48% at 95 days after rice emergence and reduced yields of ‘Mars' a maximum of 21% from season-long interference. Interference durations of 40 days or longer reduced the panicles/m2, culms/m2, and plant height of rice. Straw dry weight of Bond and Mars was reduced 41 and 26%, respectively, from season-long interference. Increased durations of weed interference did not affect the number of spikelets/panicle, percent filled spikelets, rough kernel weight, or head rice yield of either cultivar. Broadleaf signalgrass produced less dry weight and fewer panicles/m2 when grown with Mars than with Bond.

Field experiments were conducted in 1983 and 1984 to measure the interference of wild oat (Avena fatua L. # AVEFA) removed at various stages of development (two to three leaves, two to three tillers, two nodes, and heading), plus treatments with wild oat not removed, and wild oat-free stands on the growth and yield of spring barley (Hordeum vulgare L. ‘Advance’). The final plant density of barley and wild oat was 160 and 170 plants/m2, respectively. Based on aboveground barley biomass and yield, the critical duration of wild oat interference began about the two-node stage and continued until maturity of the barley. Wild oat interference reduced barley biomass, the number of tiller heads/plant, tiller heads/unit area, and tiller grain yield, but not the number or grain yield of the main-stem heads. Wild oat did not affect the soil matric potential or the barley total plant and soil nitrogen contents. However, wild oat did reduce total water and turgor potential in barley at the boot stage of growth, which may have affected tiller head formation.

Structural studies were conducted to evaluate the effects of napropamide on the growth and development of corn roots. At 1.0 and 10.0 μM napropamide, root growth was inhibited severely within 3 days of seed germination. Root diameter within 1 mm of the root apex doubled and numerous lateral root primordia were observed within 10 mm of the meristem tip in treated roots. The number of cortical parenchyma cell files, xylem vessel, and phloem sieve tube strands also significantly increased. Average cortical cell size did not change, regardless of the treatment. A lateral expansion of the meristematic region of the root coincided with a slight reduction in meristem length but resulted in an overall increase in meristem volume. However, enlargement of the meristem occurred despite a reduction in the number of mitotic figures in the root meristem. Treatment of excised root tips for 24 h with 20 μM napropamide reduced the number of mitotic figures 84%.

The basis for differential susceptibility of tolerant rice (Oryza sativa L.), susceptible wild rice (Zizania palustris L.), and susceptible giant burreed (Sparganium eurycarpum Engelm. # SPGEU) to foliar application of 1.1 kg ai/ha of bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] was investigated by evaluating herbicide absorption, translocation, and metabolism. Giant burreed and wild rice absorbed more bentazon than rice at similar growth stages. Less than 10% of the absorbed bentazon was translocated out of the treated leaf of any of the species. Differential tolerance of bentazon among the three species was due to differences in the rate of bentazon metabolism. Rice metabolized 98% of the bentazon retained in the treated leaf 1 day after treatment (DAT), while giant burreed and wild rice metabolized less than 2% of the bentazon retained in the treated leaf 5 DAT.

Cotton, spurred anoda, and velvetleaf were grown in controlled-environment chambers at day/night temperatures of 32/23 or 26/17 C and CO2 concentrations of 350 or 700 ppm. After 5 weeks, CO2 enrichment to 700 ppm increased dry matter accumulation by 38, 26, and 29% in cotton, spurred anoda, and velvetleaf, respectively, at 26/17 C and by 61, 41, and 29% at 32/23 C. Increases in leaf weight accounted for over 80% of the increase in total plant weight in cotton and spurred anoda in both temperature regimes. Leaf area was not increased by CO2 enrichment. The observed increases in dry matter production with CO2 enrichment were caused by increased net assimilation rate. In a second experiment, plants were grown at 350 ppm CO2 and 29/23 C day/night for 17 days before exposure to 700 ppm CO2 at 26/17 C for 1 week. Short-term exposure to high CO2 significantly increased net assimilation rate, dry matter production, total dry weight, leaf dry weight, and specific leaf weight in comparison with plants maintained at 350 ppm CO2 at 26/17 C. Increases in leaf weight in response to short-term CO2 enrichment accounted for 100, 87, and 68% of the observed increase in total plant dry weight of cotton, spurred anoda, and velvetleaf, respectively. Comparisons among the species showed that CO2 enrichment decreased the weed/crop ratio for total dry weight, possibly indicating a potential competitive advantage for cotton under elevated CO2, even at suboptimum temperatures.

Barnyardgrass [Echinochloa crus-galli (L.) Beauv. #4 ECHCG] and pigweeds (mixture of Amaranthus retroflexus L. # AMARE and A. powellii S. Wats. # AMAPO) seeded separately with alfalfa (Medicago sativa L.) in mid-August suppressed alfalfa severely before frost killed them in October and November. Some alfalfa was killed, and yield of alfalfa forage was reduced in each of three harvests the following year. These weeds did not harm alfalfa seeded in mid-September. Downy brome (Bromus tectorum L. # BROTE) and tumble mustard (Sisymbrium altissimum L. # SSYAL) suppressed alfalfa seeded in August and September. They reduced alfalfa stands and reduced yield of alfalfa forage in each of three harvests the following year. Alfalfa seeded August 27 and allowed to compete with a mixture of these species for various periods was injured most by weeds that emerged with the alfalfa and remained uncontrolled until forage harvest in May. These weeds did not reduce alfalfa yields if removed by 36 days after alfalfa emergence. Thereafter, yield decreased as the period of weed interference increased. Interference was most damaging in early spring, when growth of winter annual weeds was rapid and vigorous. Weeds seeded 65 or more days after alfalfa emergence did not reduce alfalfa yields but sometimes produced enough biomass to reduce the quality of the first-cutting alfalfa hay.

Green foxtail [Setaria viridis (L.) Beauv. # SETVI] and proso millet [Panicum miliaceum (L.) #PANMI] growing under high water stress for 3 days before + 3 days after foliar applications of the methyl ester of haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} developed less herbicide injury than plants growing under low water stress. There was a 32% reduction in the retention of haloxyfop sprays by proso millet when growing under high water stress than when growing under low water stress. Haloxyfop spray retention by green foxtail was not affected by the degree of water stress. The translocation of 14C out of 14C-haloxyfop-treated leaves was significantly greater in plants of both species when growing under low water stress than when growing under high water stress. The conversion of 98% of the absorbed 14C-haloxyfop-methyl to 14C-haloxyfop and unidentified polar metabolites occurred in both species within 12 h of application. The green foxtail growing under low water stress contained greater concentrations of 14C-haloxyfop than did plants growing under high water stress. Levels of 14C-haloxyfop were the same in proso millet growing under high and low water stress. The reduced injury of green foxtail and proso millet growing under high water stress from postemergence sprays of haloxyfop can be attributed to a reduction in herbicide translocation in both species, plus a reduction in spray retention by proso millet or changes in the metabolism of the herbicide in green foxtail, which results in a reduction in the concentration of haloxyfop.

A growth room study was conducted to evaluate the effect that timing of application has on the distribution of several herbicides in quackgrass. Uniformly labeled 14C-sucrose and the radiolabeled herbicides glyphosate, sethoxydim, the butyl ester of fluazifop, and the methyl ester of haloxyfop were applied to quackgrass (ranging from the three- to eight-leaf stage) propagated from six-bud rhizome segments. Five days after treatment the plants were harvested, lyophilized, and later sectioned, mapped, and oxidized in preparation for 14C quantification. In most cases, slightly more 14C was translocated to the shoots than to the rhizomes. 14C translocation to the rhizomes was similar at all growth stages. The 14C accumulating in the rhizomes exhibited a nonuniform distribution pattern with more 14C in the distal areas of new rhizomes than in the other areas of the rhizome system. Plants treated with haloxyfop had a more uniform distribution of 14C along their rhizomes than did those treated with fluazifop or sethoxydim.

Growth, development, and germination among jointed goatgrass (Aegilops cylindrica Host. # AEGCY) accessions collected from nine western states were not consistently different in field plots near Pullman, WA, or in the greenhouse. Germination percentage and rate of spikelet germination of all accessions produced in the field and greenhouse were consistently high, averaging about 64% and 5.2 (on a unitless scale of 0 to 7), respectively. The Montana accession germinated consistently less than the others. In a separate greenhouse study comparing only the accessions from Colorado and Nebraska, the accession from Colorado averaged 18, 16, and 15% greater net photosynthesis rate (Pn), transpiration rate (E), and stomatal density, respectively, and 21% lower diffusive resistance (rl) than did the accession from Nebraska. However, growth parameters of the Nebraska accession averaged 7 to 35% greater than for the Colorado accession. Overall, the germination, growth, CO2 fixation, and water use among accessions appeared to be similar when jointed goatgrass was grown under Pacific Northwest conditions.

Barley (Hordeum vulgare L. ‘Advance’) and wild oat (Avena fatua L. # AVEFA) were grown in the field in monoculture and mixed culture (additively) to compare their seasonal growth and development. Barley and wild oat tiller and tiller head production were reduced by the interference (higher density) of the other species. Plant height of either species was not affected by interference of the other. Wild oat biomass was reduced more and at an earlier growth stage (two to three tillers) than was barley biomass (heading) in mixed culture. Barley and wild oat grown in monoculture had similar total plant nitrogen content throughput the growing season. Gas exchange and water potential of barley and wild oat in monoculture and mixed culture were similar. All measurements indicated that barley and wild oat grown in monoculture had growth and development patterns that were similar. In mixed culture, however, barley was more competitive with wild oat than wild oat was with barley. Wild oat reduced barley yield component quality and grain yield.

Field experiments were conducted in 1984 and 1985 at Stuttgart, AR, to investigate the interspecific and intraspecific interference of broadleaf signalgrass densities of 0, 10, 50, 100, and 150 plants/m2 with rice. In 1984, significant reductions in rice leaf area index (LAI) occurred 6 weeks after emergence with all broadleaf signalgrass densities. The first reduction in LAI occurred 8 weeks after emergence at the density of 150 plants/m2 in 1985. Densities of 50 plants/m2 or greater reduced rice dry weight 6 weeks after emergence in 1984, and the highest density of 150 plants/m2 reduced rice dry weight 12 weeks after emergence in 1985. Height of rice was reduced by densities of 100 and 150 plants/m2. Linear regression equations indicated that each broadleaf signalgrass plant/m2 reduced rough rice yield 18 kg/ha both years. Growth of broadleaf signalgrass was reduced by interspecific and intraspecific interference. The dry weight of broadleaf signalgrass increased at a decreasing rate at plant densities of 100 to 150/m2 when grown alone in 1984 and 1985, when a quadratic equation best described the response. Regression equations indicated interspecific interference from rice reduced broadleaf signalgrass dry weight an average of 48 and 81% in 1984 and 1985, respectively. The height of broadleaf signalgrass was greater when grown with rice than when grown alone.

Imazaquin {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} absorption, translocation, and toxicity were investigated in yellow nutsedge (Cyperus esculentus L. # CYPES) and purple nutsedge (C. rotundus L. # CYPRO) after foliar treatment. Imazaquin rates from 0.125 to 0.375 kg ai/ha were sprayed on nutsedge plants at the four-leaf stage. Compared to untreated plants, these rates reduced the main shoot growth of yellow nutsedge by 70 to 86% and that of purple nutsedge by 80 to 92% at 28 days after application (DAA). However, the regrowth as measured by tiller production was significantly greater at 0.125 and 0.188 kg/ha rates than at higher rates. The plants treated with 0.313 and 0.375 rates had no rhizomes or tubers at the 28 DAA sampling. In yellow nutsedge, absorption of 14C-imazaquin increased from 36% at 1 DAA to 57% at 8 DAA. of the total absorbed 14C, 12% translocated from the treated area by 8 DAA. Roots and rhizomes accumulated equal amounts of radioactivity. In purple nutsedge, the absorption of imazaquin increased from 17% at 1 DAA to 53% at 8 DAA. Translocation of absorbed 14C in purple nutsedge at 8 DAA was 21%. Rhizomes accumulated significantly greater amounts of 14C than the roots.

A fungal pathogen, Colletotrichum gloeosporioides (Penz.) Sacc. f. sp. malvae, isolated from anthracnose symptoms of round-leaved mallow (Malva pusilla Sm.), was shown in greenhouse tests to be host specific to Malva spp. and velvetleaf (Abutilon theophrasti Medic. #3 ABUTH), and only with slight attack on hollyhock [Althaea rosea (L.) Cav. # ALGRO], Malope trifida Cav., and Venice mallow (Hibiscus trionum L. # HIBTR). Round-leaved mallow plants inoculated with a spore suspension of the fungus were killed after 17 to 20 days. It was less pathogenic on velvetleaf with 60 to 70% attack. The fungus can readily be cultured and field tests from 1982 to 1987 resulted in excellent control of round-leaved mallow under natural conditions. Therefore, it has good potential for biological control of round-leaved mallow in field crops.

Dyers woad (Isatis tinctoria L. # ISATI) has greatly expanded on rangelands in the Intermountain region. Herbicidal and tillage controls are not feasible on rangelands. Better knowledge of the biology of this species could help in the development of biological controls. We examined characteristics that could assist in this effort. Seed viability remained high and relatively stable, but germination decreased over a 10-month period. The seed dispersal pattern of dyers woad was best described by a negative exponential model (log10 y = 1.92-0.02x; r2=0.60), where y equals seeds/m2 and x = distance from mother plant (cm). The root system of dyers woad is dominated by a taproot with some laterals in the upper 30 cm of the soil profile. Survivorship of experimentally established populations monitored over 2 yr showed constriction at two stages: 1) germination and establishment, and 2) young rosette. The latter stage should be targeted for biological control.

Greenhouse, growth chamber, and field studies were conducted to determine effects of temperature on the potential of cogongrass (Imperata cylindrica L. Beauv. # IMPCY) and torpedograss (Panicum repens L. # PANRE) to spread beyond present distribution in the Lower Coastal Plains of Southeastern United States. Johnsongrass [Sorghum halepense (L.) Pers. # SORHA] was included in the study for comparative purposes. Growth of each species was greater with day/night temperature regimes of 30/25 C than with 27/22 or 24/18 C. Apical six-node-long rhizome fragments of all three species were killed by a 24-h exposure to −4.5 C. Johnsongrass produced at least three to five times more dry matter than either cogongrass or torpedograss. Order of interspecific competitiveness under 30/25, 27/22, and 24/18 C day/night temperature regimes was johnsongrass > torpedograss > cogongrass. After 2 yr, johnsongrass and torpedograss competition reduced common bermudagrass [Cyndon dactylon (L.) Pers. # CYNDA] yield by 99 and 37%, respectively, while cogongrass competition did not affect common bermudagrass yield. It is concluded that cogongrass and torpedograss are unlikely to spread into more temperate regions of the United States. However, both species are apt to become even more widespread and troublesome in the Lower Coastal Plains of Southeastern United States.

In common milkweed, the development of subterranean root buds on excised root segments, following emergence from the parent root, is characterized by development of nodes and internodes followed by internode expansion. Transverse sections of root buds reveal that bicollateral vascular bundles as well as leaf traces and gaps are well developed in buds from 3-month-old plants. Strands of xylem and phloem connect the parent root and root bud in both inhibited and noninhibited root buds. Pitted primary tracheary elements, characteristic of developmentally advanced primary xylem, are present in these traces. The occurrence of a well-developed vascular system throughout the root bud and between the parent root and bud provides evidence that retardation of growth of inhibited root buds in common milkweed is not caused by anatomical constraints.