Two studies were conducted to determine if selected grass and dicot species had an allelopathic interaction with pecan (Carya illinoinensis Wangenh. C. Koch). Leachate from pots with established grasses or dicots was used to irrigate container-grown pecan trees. Leachates from bermudagrass [Cynodon dactylon (L.) Pers.], tall fescue (Festuca arundinacea Shreb. cv. Kentucky 31), redroot pigweed (Amaranthus retroflexus L.), and cutleaf evening primrose (Oenothera laciniata Hill) reduced leaf area and leaf dry weight about 20% compared to the controls. Bermudagrass, tall fescue, and primrose leachate decreased pecan root weight 17%, trunk weight 22%, and total tree dry weight 19% compared to the control. In a second study, trees were 10% shorter than the control when irrigated with bermudagrass or pigweed leachate.
Michael W. Smith, Margaret E. Wolf, Becky S. Cheary, and Becky L. Carroll
Francis M. Itulya, Vasey N. Mwaja, and John B. Masiunas
Field experiments were conducted in 1992 and 1993 to determine the effect of N fertility, cropping system, redroot pigweed (Amaranthus retroflexus L.) density, and harvesting frequency on collard (Brassica oleracea var. acephala D.C) and cowpea [Vigna unguiculata (L.) Walp.] growth. The N fertilization regimes were 0, 80, 160, and 240 kg·ha-1, applied as urea in a split application. Four weeks after crop planting, redroot pigweed was seeded at 0, 300, and 1200 seeds/m2. Between weeks 6 and 12, collard leaves were harvested at 1- to 3-week intervals. Year, N fertility, and cropping system interacted to determine collard leaf number and mass. For example, in 1992, with N at 160 kg·ha-1, collards intercropped had more total leaf mass than those monocropped. Pigweed density had no effect on collard yields, which were greatest from the 3-week harvest frequency. Cropping system and pigweed density interacted to determine cowpea vine length, shoot dry mass, and branching. The high density of pigweed caused a 56% reduction of cowpea dry mass in 1992.
Joseph N. Aguyoh, John B. Masiunas, and Catherine Eastman
Integrated weed management strategies maintain sub-threshold levels of weeds. The remaining weeds may impact the feeding and habitation patterns of both potato leafhoppers and bean leaf beetles in a snap bean agroecosystem. The objective of our study was to determine the effect of interference between snap beans (Phaseolus vulgaris L.) and either redroot pigweed (Amaranthus retroflexus L.) or large crabgrass (Digitaria sanguinalis L.) on populations of potato leafhopper [Empoasca fabae (Harris)] and bean leaf beetle [Cerotoma trifurcata (Forster)]. Plots were seeded with redroot pigweed or large crabgrass at either the same time as snap bean planting (early) or when snap bean had one trifoliate leaf open (late). The weed density averaged two plants per meter of row. Bean leaf beetle populations, snap bean pod damage, and leaf defoliation were lower in weed-free plots compared to those with either early emerging pigweed or crabgrass. Leafhopper nymphs and adults were 31% to 34% less in plots with crabgrass emerging with snap beans compared to those in weed-free snap bean plots. Thus, the effect of sub-threshold densities of pigweed and crabgrass on insect pests in snap bean varied depending on the species and should be considered when deciding to integrate weed management approaches.
Darren E. Robinson, Kristen McNaughton, and Nader Soltani
pigweed ( Amaranthus retroflexus L.), common ragweed ( Ambrosia artemisiifolia L.), common lambsquarters ( Chenopodium album L.), and eastern black nightshade ( Solanum ptycanthum Dun.). Napropamide, trifluralin, chlorthal dimethyl, and s
Inga A. Zasada, Clyde L. Elmore, Lani E. Yakabe, and James D. MacDonald
arvensis L.), redroot pigweed ( Amaranthus retroflexus L.), common purslane ( Portulaca oleracea L.), annual bluegrass ( Poa annua L.) and cheeseweed ( Malva parviflora L.) (Valley Seed Co., Fresno, CA) were treated in a similar manner. Three samples
Guangyao Wang, Mathieu Ngouajio, and Darryl D. Warncke
cropping for weed management: A review Renewable Agr. Food Systems 19 187 198 Haramoto, E.R. Gallandt, E.R. 2005 Brassica cover cropping: II. Effects on growth and interference of green bean ( Phaseolus vulgaris ) and redroot pigweed ( Amaranthus
Harry Bottenberg, John Masiunas, Catherine Eastman, and Darin Eastburn
Field studies were conducted to determine insect and plant pathogen management effects on weed competitiveness and crop yield and to evaluate weed management impacts on insect pests, diseases, and crop yield. At similar densities, redroot pigweed (Amaranthus retroflexus L.) reduced snapbean (Phaseolus vulgaris L.) and cabbage (Brassica oleracea L. var capitata) yield more than that of common purslane (Portulaca oleracea L.), a low growing weed. In 1995, diamondback moth [Plutella xylostella (L.)] was greater on cabbage growing in plots with purslane than in plots of cabbage growing without weeds. Imported cabbageworm [Pieris rapae (L.)] was greater on cabbage growing in plots with either purslane or pigweed than when growing alone. However, the amount of feeding damage to cabbage was similar across treatments. Disease incidence was low, but fungicide treatments made redroot pigweed more competitive with snapbean, reducing yield in 1995.
G.D. Leroux, J. Douheret, M. Lanouette, and M. Martel
With growing public concern about environmental quality, farmers must turn to new plant protection alternatives that minimize the use of agrochemicals. Flaming has been practiced for several years as a means of weed control in noncropped areas (railroad, ditches, etc.), but its selectivity toward crops has yet to be defined. Experiments were conducted in the ICG-Propane laboratory at Laval Univ. to determine the temperature needed to kill weeds and the temperature that corn could tolerate. Four weed species were studied: Amaranthus retroflexus, Brassica kaber, Chenopodium album, and Setaria viridis and each species was tested at three growth stages: 0–2, 4–6, and >8 leaves. Corn tolerance was tested at four growth stages: coleoptile, 0–2, 4–6, >8 leaves. All plants were grown in the green-house and were submitted to different combinations of operation speeds and of propane pressures, giving 10 temperature intensities ranging from 110 to 390C. The response of each species was evaluated by measuring its height and dry biomass 2 weeks after treatment. The threshold temperature for corn was below 200C; above this temperature, significant corn injury occurred at all growth stages tested. The corn growth stages most tolerant to heat were coleoptile and >8 leaves. While the most sensitive was 4–6 leaves. All weeds tested were sensitive to heat at 0–2 leaf stage. Amaranthus retroflexus and Chenopodium album were controlled until six leaves with temperatures that were not harmful to corn. Weeds with more than eight leaves needed higher temperature, and control rarely reached 60%. Flaming could be a selective method of weed control if operated at a temperature of 170C. Selectivity can be increased by creating a growth differential between corn and weeds.
Edward Bush, Ann L. Gray, Virginia Thaxton, and Allen Owings
Previous research has shown the effectiveness of prodiamine (FactorÆ)as a preemergent herbicide. The objective of this experiment was to evaluate the efficacy and phytotoxicity of prodiamine applied to several woody ornamental and weed species. Phytotoxicity effects were evaluated on eight ornamental species: azalea (Rhododendron indicum `Mrs. G.G. Gerbing'), dwarf yaupon (Ilex vomitoria `Nana'), dwarf mondograss (Ophiopogon japonicus `Nana'), ixora (Ixora coccinea), lantana (Lantana camara `New Gold'), Southern live oak (Quercus virginiana), weeping fig (Ficus benjamina), and daylily (Hemerocallis fulva). Preemergent herbicide treatments (control-nontreated, 2 lbs aia Factor®, and 4 lbs aia Factor®) were applied to ornamentals twice during the experiment at twelve week intervals. There was a reduction in top dry weight for azalea and dwarf mondograss for both 2 and 4 lbs aia treatments. No significant growth reductions were measured for daylily, dwarf yaupon, ixora, lantana, live oak, and weeping fig. The efficacy experiment consisted of four weed species: barnyardgrass (Echinochloa crusgali), crabgrass (Digitaria sanguinalis), coffeeweed (Sesbania exaltata), and pigweed (Amaranthus retroflexus) and five preemergence herbicide treatments (control-nontreated, control-Rout® at 100 lbs/A, Factor® 1 lb aia, Factor® 2 lbs aia, and a tank mixture of Factor® 1 lb aia plus Gallery® 1 lb aia) applied to bark-filled containers. Twenty-five weed seeds of each species were broadcast over each container following herbicide applications. The high rate of Factor®, Rout®, and the combination of Factor®+Gallery® significantly reduced weed dry weight compared to the control. All preemergence herbicides significantly reduced weed counts and height in a similar manner.
Barbara R. Bingaman and Nick E. Christians
Corn (Zea mays L.) gluten meal (CGM) was evaluated under greenhouse conditions for efficacy on 22 selected monocotyledonous and dicotyledonous weed species. Corn gluten meal was applied at 0, 324, 649, and 973 g·m–2 and as a soil-surface preemergence (PRE) and preplant-incorporated (PPI) weed control product. CGM reduced plant survival, shoot length, and root development of all tested species. Black nightshade (Solanum nigrum L.), common lambsquarters (Chenopodium album L.), creeping bentgrass (Agrostis palustris Huds.), curly dock (Rumex crispus L.), purslane (Portulaca oleracea L.), and redroot pigweed (Amaranthus retroflexus L.) were the most susceptible species. Plant survival and root development for these species were reduced by ≥75%, and shoot length was decreased by >50% when treated PRE and PPI with 324 g CGM/m2. Catchweed bedstraw (Galium aparine L.), dandelion (Taraxacum officinale Weber), giant foxtail (Setaria faberi Herrm.), and smooth crabgrass [Digitaria ischaemum (Schreb.) Schreb. ex Muhl] exhibited survival and shoot length reductions >50% and an 80% reduction in root development when treated with PPI CGM at 324 g·m–2. Barnyardgrass [Echinochloa crus-galli (L.) Beauv.] and velvetleaf (Abutilon theophrasti Medic.) were the least susceptible species showing survival reductions ≤31% when treated with 324 g CGM/m2.