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Various levels of weed competition were implemented in a second-year well-established strawberry (Fragaria ×ananassa `Jewel') planting by cultivating and hand weed removal for defined periods of time over 3 years. The impact of weeds on subsequent productivity was then determined. Sixteen treatments were established where weeds were allowed to grow for defined periods (0, 1, 2, 3, 4, or 5 months) throughout the growing season. Treatments were maintained in the plots for 3 consecutive years. Spring weed biomass in 1997 had no impact on yield that same year. Weed biomass in 1997 was negatively associated with yield in 1998, although the trend was nonsignificant. However, several individual contrasts were significant. For example, the weed-free control treatment had the highest average yield, while season-long weed competition reduced yield by 14%. The inverse relationship between weed biomass and fruit yield became significant in 1999. For every 100 g·m-2 increase in weed biomass in 1998, fruit yield was reduced by 6% in 1999. Season-long uncontrolled weed growth reduced productivity by 51%. However, several plots with a limited amount of weed competition had higher yields than the continuously weeded control. These data indicate that yields from a well-established strawberry planting may not be vulnerable to a limited amount of weed competition for at least 2 years. Furthermore, data suggest that hand weeding and cultivation on a monthly basis for multiple years may be damaging as well. Growers should direct a majority of their efforts and resources toward controlling weeds in the planting year. Once the planting is well-established, growers may limit the number of times they hand weed to two or three per season.

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Competition from weeds and an interplanted sudangrass [Sorghum bicolor (L.) Moensch, formerly S. sudanense (Piper) Stapf.] cover crop was allowed to occur in newly-planted strawberries (Fragaria ×ananassa Duch.) for varying lengths of time, and at different times during the growing season. Newly planted strawberries were most susceptible to weed and cover crop competition during the first 2 months after planting, as both runnering (stolon formation) and subsequent yield were impacted. In 1994-95, 1 month of weed competition in June reduced yield by 20%, whereas 2 months of weed competition reduced yield by 65%. However, 1 month of uncontrolled weed growth later in the growing season had little to no impact on yield, although weed biomass was much less then. Herbicide (napropamide) use alone was insufficient to prevent weed competition and yield reduction. In our study, yield was reduced 0.67 t·ha-1 or 5.5% for each 100 g·m-2 of weed biomass. The data suggest that it is critical for growers to minimize weed competition early in the planting year when weed growth is greatest. Since an interplanted sudangrass cover crop displaced a portion of the weeds, it could be seeded later in the year to provide some weed suppression without a negative impact on yield. Chemical names used: N, N, Diethyl-2-(1-naphthalenyloxy)-propionamide (napropamide); N-(phosphonomethyl)glycine (glyphosate).

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Abstract

Close plant spacing in bush snap beans (Phaseolus vulgaris L.), sweet corn (Zea mays L.), and onions (Allium cepa L.) resulted in less weed competition, as measured by crop plant reproductive parts, than wider row spacings. Early weed competition was important in all crops but weed competition at any time reduced onion yields significantly. Corn required 2 weeks and bush snap beans 3 weeks of cultivation after emergence to eliminate losses due to weed competition. Fresh weights of weed at harvest time were significantly less (0.8 kg) in plots of bush snap beans at the narrow row spacing than in plots with the medium and wide spacings (2.8 and 2.4 kg) in an 0.81 m2 area.

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The early competitive relationships of sweet corn (Zea mays L.), barnyardgrass (Echinochloa crusgalli (L.) Beauv.), large crabgrass (Digitaria sanguinalis (L.) Scop.), common lambsquarter (Chenopodium album L.), and redroot pigweed (Amaranthus retroflexus L.) during the first 4 weeks of growth were studied in the greenhouse using a modified diallel analysis. Heights of individual plants at 2, 3, and 4 weeks after seeding were measured as well as dry weights at 4 weeks. Analyses indicate that sweet corn was the most competitive species. Barnyardgrass offered the most competition to sweet corn relative to the other weed species which offered much less competition to sweet corn and comparable competition to each other. Competitive relationships remained fairly constant over time with perhaps a slight increase in the competitive ability of crabgrass. A slight increase in compatibility between sweet corn and barnyardgrass, and between crabgrass and pigweed occurred during the 4th week of growth.

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Dry wt of Japanese holly (Ilex crenata (Thunb.) cv. convexa Makino.) decreased significantly as the density of competing weed species increased. One redroot pigweed plant (Amaranthus retroflexus L.) reduced the dry wt of Japanese holly by 47% in 2.4 liter and 30% in 6.0 liter containers and 1 plant of large crabgrass (Digitaria sanguinales (L.) Scop.) caused reductions in dry wt of Japanese holly of 60% in 2.4 liter and 35% in 6.0 liter containers.

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The objective of this study was to identify a sweetpotato canopy type ideally suited to suppress weed growth. With this knowledge, breeders could select sweetpotatoes that require less weed control. Diverse canopy types, ranging from upright, short-internode bunch types to long-internode trailing types, were compared in a split-plot design (hand-weeded and weed treatments). We also included lines with deeply lobed leaves (palmate) and more entire-leaf types. Our results show no significant differences between lines for total ground surface area covered after 6 weeks of growth, no differences in weed dry weight at harvest and few differences in canopy dry weight at harvest. Total ground surface area covered correlated positively with total yield, and weed dry weight correlated negatively to total yield. We were unable to identify individual lines that yield better when pressured with weeds compared to the hand-weeded control, but we were able to identify lines that yield poorly when pressured with weeds compared to the hand-weeded control. These results demonstrate the difficulty in categorically identifying a superior canopy.

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The relationships between canopy density of three perennial weed species (Potentilla pacifica Howell, Aster subspicatus Nees, and Lotus corniculatus L.) and `Mcfarlin' and `Stevens' cranberry (Vaccinium macrocarpon Ait.) yield and fruit quality were evaluated. Yield was more severely affected by weed interferences than fruit size or color. Best-fit regression equations for the effects of weed density on yield, fruit size, and color were linear or quadratic polynomials with a strong linear component. For each bog, the slope of the linear relationship between yield and weed density was more negative as the mean yield of weed-free controls increased. `Stevens' fruit size and yield were more sensitive and fruit color was less sensitive to changes in P. pacifica population density than those of `McFarlin'.

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Studies established the critical period for eastern black nightshade (nightshade) (Solanum ptycanthum Dun.) competition in pea (Pisum sativum L.) and determined the effect of N fertility on pea and nightshade growth. In 1992, pea yields were most affected when nightshade was established at planting and remained for 4 or 6 weeks, while in 1993, competition for 6 weeks caused the greatest reduction in pea yields. In a sand culture study, pea biomass and N content were not affected by three N levels (2.1, 21, and 210 mg·L-1). Nightshade plants were five to six times larger in the highest N treatment than at lower N levels. Nitrogen content of nightshade was 0.76% at 2.1 ppm N and 3.22% at 210 ppm N. Choosing soils with low N levels or reducing the N rates used in pea may decrease nightshade interference and berry contamination of pea.

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weed control of mixed systems may be related to greater competition provided by the CC and allelopathic activities of radish, possibly as a result of the glucosinolate content reported for radish and other members of the Brassicaceae family ( Morra and

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Hemp ( Cannabis sativa ) is a new crop for producers in the United States, and information on weed competition in relation to crop quality and yield is limited. After decades of prohibition, the 2018 Farm Bill allowed for cultivation of hemp

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