Weeks Of Interference Research Articles

Interference betweenRottboellia cochinchinensisandZea mays

Abstract Field studies conducted over 2 yr in Louisiana determined critical periods of Rottboellia cochinchinensis interference in Zea mays. In a duration of interference study, R. cochinchinensis was allowed to compete with Z. mays for 0 (weed-free, season-long), 2, 4, 6, 8, 10, 12, or 14 (weedy, season-long) wk, after which plots were maintained weed-free for the rest of the growing season. Rottboellia cochinchinensis biomass at time of initial removal increased linearly as weeks of interference increased. For 2 wk of interference, R. cochinchinensis biomass was greater in 1993 than 1994, but for 4 wk or more of interference, biomass was greater the second year indicating environmental conditions were more conducive to R. cochinchinensis growth in 1994. Season-long R. cochinchinensis interference reduced Z. mays height by 18% compared with the weed-free check. For both years, R. cochinchinensis reduced yields 125 kg ha−1 for each week of interference. In weed-free maintenance studies, 0, 2, 4, 6, 8, 10,...

Ivyleaf Morningglory (Ipomoea hederacea) Interference with Cotton (Gossypium hirsutum)

Full-season interference and critical duration of early-season ivyleaf morningglory interference with cotton were measured in experiments at two Oklahoma locations. Densities ranging from 0 to 64 weeds/10 m of row were evaluated for their effects on cotton lint yield, fiber quality, and harvest efficiency. Analyses using linear-linear regression proved superior to linear, curvilinear, and linear-plateau models. Lint yield reductions of 36.9 kg/ha (or 5.9%) were recorded at Perkins for each weed/10 m up to 8.7. At densities greater than 8.7/10 m, yield was reduced an additional 3.0 kg/ha (0.5%) for each additional weed. At Chickasha, lint yield was reduced 29.7 kg/ha (or 3.9%) for each weed/10 m up to 9.0 with an additional lint loss of 3.6 kg/ha (0.7%) for each weed above the density of 9.0/10 m. Yield losses were over 80% before fiber length was also reduced. Mechanical harvest was not possible at densities above 8 weeds/10 m at Chickasha and above 16 weeds/10 m at Perkins. In critical duration experiments conducted at Perkins, lint yield was reduced 52.9 kg/ha (or 11.2%) for each week weed removal was delayed up to 9.5 wk. An additional 1.0 kg/ha (0.2%) was lost for each week of interference after 9.5 wk. At Chickasha, lint yield was reduced 49.0 kg/ha (or 7.8%) for each week of interference up to 11.0 wk with an additional loss of 1.2 kg/ha (0.2%) for each week thereafter.

Interference between triazine‐resistant Brassica napus and Panicum miliaceum

SummaryAtrazine carryover often limits growers to production of atrazine‐tolerant crops the year following application, and allows the increase of triazine‐tolerant weed species such as Panicum miliaceum L. (wild proso millet). Tiriazine‐resistant Brassica napus L. cv. ‘Triton’ (oilseed rape) was tested to characterize the nature of interspecific interference with P. miliaceum. In a greenhouse study, atrazine at 2.2 kg ha−1 depressed oilseed rape fruit (siliqua) number and fruit dry weight, and delayed flowering, but did not significantly affect height or weight of shoots, Oilseed rape fruit weight was reduced at 200 P. miliaceum plants m−2. fruit number and shoot weight were inhibited at 400 weeds m−2. and height was reduced and flowering delayed at 600 weeds m−2. Number and weight of fruits were reduced by one‐third after 8 weeks of interference as compared to oilseed rape grown with the weed for 4 weeks. Oilseed rape height was reduced by 29% and shoot weight by 55% by 600 weeds m−2 and 2–2 kg ha−1 atrazine, while fruit number and weight were reduced by 72%. Oilseed rape shoot weight was reduced by 74% by 600 weeds m−2 for 12 weeks of interference, while fruit number and weight were reduced by 85% and 82%. respectively.In a field study, fluazifop reduced early season P. miliaceum cover by 72%, but did not increase oilseed rape cover. Mid‐season P. miliaceum shoot weight was decreased by 97% by fluazifop and oilseed rape shoot weight was increased by 34%. P. miliaceum control increased oilseed rape biomass by 38% at 89 days, but biomass of oilseed rape sown at 11.2 kg ha−1 with 2.2 kg atrazine ha−1 was not decreased by P. miliaceum interference at 89 days.

Interference and Seed Production by Common Lambsquarters (Chenopodium album) in Soybeans (Glycine max)

Multiple regression and response surface plots were used to analyze the effects of common lambsquarters population density and interference duration on weed growth and soybean seed yield. Under favorable growing conditions in 1986, weed biomass production at all population densities and interference durations was four to five times that produced in 1987, under less favorable conditions. However, there was no significant treatment by year interaction for soybean seed yield reduction by common lambsquarters, and production of each kg/ha weed biomass resulted in an average soybean yield reduction of 0.26 kg/ha. Utilizing 5% yield loss as an arbitrary threshold level, the regression equation predicted a common lambsquarters density threshold of 2 plants/m of row for 5 weeks of interference after crop emergence and 1 plant/m of row for 7 weeks. Seed production by individual common lambsquarters plants was highly correlated (r=0.92) with weed dry weight, and seed production ranged from 30 000 to 176 000 seeds/plant.

Effect of Russian Thistle (Salsola iberica) Interference on Spring Wheat (Triticum aestivum)

The effect of Russian thistle density and duration of interference on spring wheat was investigated in two 3-yr field studies. In the density study, the best fit regression equation predicted a loss in spring wheat yield of 0.5, 0.5, and 0.6% in 1983, 1984, and 1985, respectively, for each percent of the total biomass contributed by Russian thistle. In 1985, when rainfall was 46% below normal, the highest weed density produced greater than 70% of the total plant biomass and reduced yields more than 50%. In contrast, in 1984 when rainfall was 65% above normal, the highest weed density produced less than 20% of the total plant biomass and reduced yields 11%. In the duration study, the predicted yield loss was 2.3 and 0.7% for 1983 and 1984, respectively, for each week of interference. In 1985, yield was not significantly reduced until after 6 weeks of interference. In both studies, spikes/m of row had the highest correlation with yield and were affected the most by weed interference.

Influence of Jerusalem Artichoke (Helianthus tuberosus) Density and Duration of Interference on Soybean (Glycine max) Growth and Yield

The effect of Jerusalem artichoke (Helianthus tuberosusL. # HELTU) density and duration of interference in soybeans [Glycine max(L.) Merr. ‘Hodgson 78’] was investigated in two studies. Jerusalem artichoke densities of 1, 2, and 4 tubers/m of row reduced soybean seed yield by 31, 59, and 71%, respectively. Soybean height, branches/plant, pods/plant, and seed weight were usually reduced by all three weed densities. Soybean leaf area and relative growth rates were reduced by densities of 2 and 4 tubers/m of crop row, and net assimilation rate (NAR) was reduced by 4 tubers/m of crop row. Jerusalem artichoke interference at 4 tubers/m of row for 4, 6, 8, and 20 weeks (full season) reduced soybean yields 9, 10, 38, and 82%, respectively. Branches/plant, pods/plant, and seeds/plant were reduced after 8 weeks of interference. These results suggest that Jerusalem artichoke is highly competitive with soybean and should be controlled within 6 weeks after planting.

Effect of Duration and Type of Natural Weed Infestations on Soybean Yield1

AbstractThe time of weed removal from a crop may be as important as the extent of removal. A 4‐yr field study was conducted at two locations each year to define the extent of soybean [Glycine max(L.) Merr.] yield and population reduction occurring from the presence of natural weed populations. Soil types were Typic Ochraqualfs and Typic Albaqualfs. ‘Williams 79’ soybeans were planted at approximately 30 seeds m− 1of row using 76‐cm spacing between rows. Grass, broadleaf, or grass plus broadleaf weeds were allowed to interfere 0, 1, 2, 3, or 4 weeks, or all season (control), prior to their removal. Weed populations in the control plots ranged from 16 to 148 plants m−2in 1981 and increased to 104 to 1172 plants m−2in 1984. Allowing grass, broadleaf, or grass plus broadleaf weeds to interfere with soybeans for up to 4 weeks did not reduce soybean yields under ample soil moisture conditions. However, under drought conditions or extremely high weed infestations, yield losses with 4 weeks of interference were observed. No differences were found between the competitive effects of grasses or broadleaves on soybean yield with 4 weeks or less of interference. Significant yield reduction occurred every year at both locations when grass plus broadleaf weeds interfered all season. Yield reductions from all‐season grass‐only or broadleaf‐only weed interference occurred most years, but were dependent on location, weed density, and environmental conditions. Soybean populations were reduced where weeds were most dense and were associated with yield decreases.