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Haley Rylander, Anusuya Rangarajan, Ryan M. Maher, Mark G. Hutton, Nicholas W. Rowley, Margaret T. McGrath, and Zachary F. Sexton

, nutrients, and soil moisture), life cycle, and dispersal mechanisms of individual species ( Chauhan et al., 2012 ). Tillage can induce dormancy of annual weed seeds by burying them and/or stimulate germination by bringing them to the soil surface. Tillage

Open access

Dong Sub Kim, Mark Hoffmann, Steven Kim, Bertha A. Scholler, and Steven A. Fennimore

and June 2016 and two tests on weed seed viability during June 2018 and 2019 at Salinas, CA. The experimental units were 24 microplots (1 m 2 ) for all four studies. The Mar. and June 2016 and June 2018 experiments were located at the U.S. Department

Free access

Rakesh S. Chandran and Megh Singh

Depletion of the weed seed bank by stimulating germination during winter months and subsequently exposing the seedlings to adverse air temperatures is a possible means of controlling weeds in small-scale horticultural operations. Johnsongrass [Sorghum halepense (L.) Pers.], hemp sesbania [Sesbania exaltata (Raf.) Rydb. ex A.W. Hill], and barnyardgrass [Echinochloa crus-galli (L.) Beauv.] were seeded in soil trays and maintained for 4 days at 4 or -12 °C, then heated to 32 °C for 4 days using electric heating pads. Germination percentages, after heating soils, were: 55% and 70% for hemp sesbania, 82% and 72% for barnyardgrass, and 45% and 55% for johnsongrass, respectively; for seeds kept at -12 and 4 °C, respectively. Subsequent exposure of seedlings to -12 °C for 7 days killed all seedlings, while exposure to 4 °C killed only 18% to 28%. The temperature regimes of -12 °C for 4 days, and 32 °C for 4 days followed by -12 °C killed 95%, 78%, and 68% of the johnsongrass, hemp sesbania, and barnyardgrass, respectively.

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Mathieu Ngouajio and Milton E. McGiffen Jr.

Organic agriculture is growing in importance worldwide. In the United States, the rate of increase of organic growers was estimated at 12% in 2000. However, many producers are reluctant to undertake the organic transition because of uncertainty of how organic production will affect weed population dynamics and management. The organic transition has a profound impact on the agroecosystem. Changes in soil physical and chemical properties during the transition often impact indirectly insect, disease, and weed dynamics. Greater weed species richness is usually found in organic farms but total weed density and biomass are often smaller under the organic system compared with the conventional system. The improved weed suppression of organic agriculture is probably the result of combined effects of several factors including weed seed predation by soil microorganisms, seedling predation by phytophagus insects, and the physical and allelopathic effects of cover crops.

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Monica Ozores-Hampton, Thomas A. Bewick, Peter Stoffella, Daniel J. Cantliffe, and Thomas A. Obreza

The influence of compost (derived from MSW and biosolids) maturity on seed germination of several weed species was evaluated. A bioassay was developed by extracting 20 g of compost of different maturities with various volumes of water, then measuring germination percentage of ivyleaf morningglory (Ipomoea hederacea) seeds placed on extract-saturated filter paper in a petri dish. A 20 g (dry weight) compost: 50 mL of water generated an extract that produced the widest percentage seed germination variation in response to composts of different maturity. Ivyleaf morningglory, barnyardgrass (Echinochloa crus-galli L.), purslane (Potulaca oleracea L.), and corn (Zea mays L) were selected as plant indicators to determine the compost maturity stage with maximum germination inhibition. Compost 8-week-old decreased percent germination, root growth, and germination index (combines germination rate and root growth), and increased mean days to germination (MDG) of each plant indicator. Immature 8 week-old compost extract effect on MDG and germination percent of 15 weed species was evaluated. Extract from 8-week-old compost inhibited germination in most weed species, except yellow nutsedge (Cyperus esculentus). Compost extracts derided from immature (3-day, 4-, and 8-week-old) compost resulted in delayed and reduced germination percent of important economic weed species.

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Amanda F. Shearin, S. Chris Reberg-Horton, Eric R. Gallandt, and Francis A. Drummond

Seed predators may significantly reduce the weed seedbank. In Maine, one ground beetle species, Harpalus rufipes DeGeer, can consume 90% of the epigeous seeds of certain weeds. H. rufipes is the predominant carabid seed predator in Maine agricultural systems. The mechanisms by which H. rufipes can be promoted are not well understood. Two weed management techniques used by diversified vegetable growers in Maine (cover cropping and cultivation) were evaluated in 2004 for their impact on H. rufipes movement and abundance. H. rufipes individuals (n = 200 plot) were marked and released into 180-m2 plots that were either fallow or cover-cropped. Pitfall traps were installed in each plot to recapture marked beetles. The total recapture rate in fallow plots was 46% less than in cover crop plots. Movement of fallow-released beetles into cover crop plots was 48% higher than movement of cover crop-released beetles into fallow plots. A second study evaluated the impacts of tillage on H. rufipes. Marked beetles (n = 25 plot) were released into 9-m2 plots surrounded by raingutters. Plots were either tilled with a tractor-mounted rotovator to a depth of 15 cm or left undisturbed. There was no significant difference in beetle recapture rates in tilled (32%) vs. untilled (35%) plots, suggesting that beetles are capable of surviving even intensive tillage events. Variation in the number of H. rufipes across farming systems may not be due to tillage, as widely postulated in literature, but is instead a product of vegetative cover. Further research into the impacts of weed management on other life stages of H. rufipes is needed before firm conclusions can be reached.

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Steven A. Fennimore, Milton J. Haar, Rachael E. Goodhue, and Christopher Q. Winterbottom

activated in the soil by sprinkler irrigation according to label directions ( CDMS, 2006 ). Weed control assessments. Weed control was assessed by three methods: 1) weed seed viability bioassays; 2) weed density counts; and 3) timing of handweeding

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Nicole Burkhard, Derek Lynch, David Percival, and Mehdi Sharifi

suppressed by PN and, to a lesser degree, by MC. The difference in weed control by MC between years was a result of weed seeds (predominantly common ragweed) that proliferated in MC in Trial 2, demonstrating the variation of weed seedbank that can occur in

Open access

Mark Hoffmann, Husein A. Ajwa, Becky B. Westerdahl, Steven T. Koike, Mike Stanghellini, Cheryl Wilen, and Steven A. Fennimore

is also shown to have proven activity against soil-borne nematodes ( Wood et al., 2017 ), soil-borne fungal pathogens ( Neubauer et al., 2015 ), and insects ( de Souza et al., 2018 ), and it reduces the viability of weed seeds and weed seed

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Dennis N. Portz and Gail R. Nonnecke

difficult because not all weed species are controlled by labeled herbicides ( Pritts and Handley, 1998 ). Growers can use pre-emergent herbicides to prevent weed seed growth and selective postemergent herbicides to control monocot weeds throughout the season