Weed-free Maintenance Research Articles

Critical period of weed control in transplanted chilli pepper

Summary Field experiments were conducted from 1991 to 1993 to determine the critical period of weed control in chilli pepper. The maximum weed-infested period ranged between 0.7 and 3.2 weeks after transplanting (WAT) at a 5% yield loss level. To prevent losses in total and marketable yields, weeds should be removed 2.1 or 0.9 WAT respectively. The end of the critical period decreased as the predetermined yield loss level increased from 2.5% to 10%. The minimum weed-free period ranged between 6.7 and 15.3 WAT at a 5% yield loss level depending on crop yield category. The chilli pepper crop required an average of 12.2 weeks of weed-free maintenance to avoid losses above 5%. Using a 5% yield loss level, the duration of the critical period of weed control was 14 weeks in 1991 and 11.2 weeks in 1993, but was shortened to 5.1 weeks in 1992. The results suggest that weeds must be controlled during the first half of the crop's growing season in order to prevent yield losses.

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,...

Competition and control of weeds in soybean

Two field experiments were carried out from 1993 to 1995 to evaluate the critical period of weed control and to develop suitable weed management practices for jungle rice, horse purslane, and cockscomb in soybean. Horse purslane was more competitive during early growth stages (up to 45 days after sowing [DAS]) and cockscomb was more competitive during later growth stages, whereas jungle rice was competitive throughout the growing season. The critical period of weed control was found to be 30 to 45 DAS. Weed-free maintenance up to 45 DAS resulted in a 74% increase in grain yield of soybean over the unweeded control. Keeping soybean weed free for 45 d or allowing weeds to remain in the crop for less than 30 d resulted in no significant yield loss. Sequential application of a reduced rate of soil-applied trifluralin 1.0 kg ha–1(0.67 ×) with postemergence fluazifop 0.75 kg ha–1(0.75 ×) or a reduced rate of soil-applied trifluralin or pendimethalin at 1.0 kg ha–1(0.67 ×) followed by hand hoeing 35 DAS provided better control of a broad spectrum of weeds than a single application of a postemergence herbicide applied at reduced or recommended rates. Integration of reduced rates of soil-applied herbicides with post-emergence herbicides or hand hoeing 35 DAS produced soybean yields similar to the hand-weeded treatment. Compared to the weed-free or integrated weed control, a single application of soil-applied or postemergence herbicide did not control a broad spectrum of weeds and reduced soybean yield.

Wild Proso Millet (Panicum miliaceum) Interference in Dry Beans (Phaseolus vulgaris)

Effects of proso millet interference with irrigated dry beans were evaluated in Nebraska over a 2-yr period. Dry bean yield reduction ranged from 12 to 31% from a wild proso millet density of 10 plants m-2. As density increased, dry bean yield reduction could be predicted with a rectangular hyperbola regression model. Ten wild proso millet plants m-2growing with dry beans produced 14 780 to 21 420 seed m-2. Dry bean yields were reduced 41 and 11% in 1990 and 1991, respectively, when wild proso millet removal was delayed 6 wk after dry bean planting. Four weeks of weed-free maintenance were sufficient to provide dry bean yields comparable to plots kept weed free all season.

Interference of Hogpotato (Hoffmanseggia glauca) with Cotton (Gossypium hirsutum)

The effects of hogpotato interference on cotton and of the crop on the weed were measured under field conditions in four environments. Full-season interference from 105 ± 21 hogpotato plants/m2reduced cotton plant height by 14 to 44%. Conversely, weed dry weight was reduced 54% through full-season interference from cotton. Lint yield reductions in cotton ranged from 31 to 98% following full-season weed interference. Interference during the first 7 weeks of crop growth reduced lint yield by approximately 40%; however, interference after 7 weeks of weed-free maintenance did not affect lint yield. Interference reduced boll size in 3 of 4 yr, lint percent in 2 of 4, and boll number in the only year it was measured. Cotton fiber length, uniformity index, and micronaire were reduced by full-season interference in 1 of 2 yr; however, fiber strength was not affected in either year. Significant use of soil water by hogpotato occurred at 120 cm and deeper in the soil while cotton used water primarily in the upper 75 cm.

Interference of Horsenettle (Solanum carolinense) with Peanuts (Arachis hypogaea)

Duration and density experiments were conducted in the field to measure horsenettle (Solanum carolinenseL. # SOLCA) interference with Spanish and runner-type peanuts (Arachis hypogaeaL. ‘Pronto’ and ‘Florunner′). Spanish peanut yield generally was higher with 6 to 8 weeks of weed-free maintenance. Horsenettle interference for 6 to 8 weeks did not decrease the yield of Spanish peanuts, and interference for 6 weeks did not decrease yields of runner peanuts. Weed-free maintenance for 2 or more weeks allowed increased runner peanut yield when compared to weedy plots. Linear regression predicted a 69 kg/ha Spanish peanut yield increase for each week of weed-free maintenance. Linear regression predicted a Spanish peanut yield reduction of 40 kg/ha for each week of weed interference in 1983, the only year in which the slopes of the regressions were statistically significant Curvilinear equations with the runner-type cultivar predicted an 81 kg/ha yield increase or 96 kg/ha decrease for each week of weed-free maintenance or weed interference, respectively. In 1 of 2 yr, Spanish peanut yield was reduced by horsenettle at a density of 32 plants/10 m of row.

Interference of Silverleaf Nightshade (Solanum elaeagnifolium) on Spanish Peanuts (Arachis hypogaea)1

Abstract Interference of silverleaf nightshade (Solanum elaeagnifolium Cav.) with Pronto spanish peanuts (Arachis hypogaea L.) was evaluated from 1981 through 1983 in a natural occurring weed population. Treatments consisted of weed-free maintenance or weed interference for 0, 4, 8, 12 weeks and for the full season. Silverleaf nightshade stems were counted as a measure of weed regrowth in treatments maintained weed free for 0, 4, and 8 weeks. Contamination of the harvested in-shell peanuts by silverleaf nightshade berries was determined by counting the number of berries passing through the peanut combine. In-shell peanut yields were reduced by an average of 17% when silverleaf nightshade was allowed to interfere with the crop for 4 weeks. Further yield reductions of 53, 66, and 66% were observed in treatments where interference occurred for 8 and 12 weeks and for the full-season, respectively. Regression analysis conducted on yield data of individual years predicts that each week of weed-free maintenance after crop emergence results in an average of 33 to 38 kg/ha yield increase above the unweeded control. Conversely, analyses of yield data averaged over all years indicated that for each week of weed interference there would be approximately a 103 kg/ha decrease in in-shell yield compared to the weed-free control. When yield data were converted to percent of yield of weed-free controls, there was no interaction among years. Regression analysis of the converted data predicts that for each week of weed-free maintenance after crop emergence there would be a 3.7% yield increase compared to the unweeded control and that for each week of weed interference there would be a corresponding yield loss of 4.5%. Silverleaf nightshade stem counts per plot were reduced an average of 18 and 36 percent for treatments maintained weed free for 4 and 8 weeks, respectively. In 1982 analysis of fruit contamination indicated a significant difference between full-season interference and weed-free maintenance for 4 or more weeks. Differences in fruit contamination between 4, 8, and 12 weeks of weed-free maintenance were not significant. In the second year no differences in fruit contamination were observed between the weedy check and the other treatments; however, fruit production after 4 weeks of weed-free maintenance was significantly higher than after 8 and 12 weeks of weed-free maintenance. Peanut quality, disregarding contamination by silverleaf nightshade berries, was not affected by weed interference.

Influence of Shading by Soybeans (Glycine max) on Weed Suppression

Field studies were conducted at Florence and Clemson, South Carolina to measure the influence of soybean [Glycine max(L.) Merr.] planting dates on the length of early-season weed control needed to prevent yield reductions, the rate of shade development, and suppression of annual weeds by soybeans. The rate of shade development was similar for both planting dates during the 9- to 11-week period after planting for Florence and Clemson, respectively. The period of weed-free maintenance required to prevent soybean yield reductions was not affected by planting dates. With cultivation between rows, early- and late-planted soybeans required 3 weeks of weed-free maintenance to achieve maximum yields. Lower weed weights resulted from late than early soybean plantings. At Clemson, 3 weeks of weed-free maintenance for early and late plantings reduced weed weights 97 and 91%, respectively. Weed weights at Florence were reduced 85% with 3 weeks of weed-free maintenance for the late plantings, whereas 5 weeks were required to reduce weed weights 88% for early plantings.

Common Ragweed (Ambrosia artemisiifolia) Interference in Soybeans (Glycine max)

The influence of common ragweed (Ambrosia artemisiifoliaL.) interference on soybean [Glycine max(L.) Merr. ‘Ransom’] yield was studied in the field utilizing naturally occurring weed populations. The damage-threshold population for a full-season, in-row common ragweed infestation was four weeds/10 m of row, which resulted in an 8% yield loss. Soybeans kept weed-free for 2 weeks or longer after emergence in a dry year produced normal yields, but 4 weeks of weed-free maintenance was required when adequate moisture was available early in the growing season. Soybean yield was not reduced by a natural population of common ragweed if the period of interference was limited to 6 weeks or less after crop emergence. By 8 weeks after emergence, common ragweed height averaged 25 cm taller than soybeans, and the weed canopy intercepted 24% of the photosynthetically active radiation.

Influence of Row Spacing, Seeding Rates and Herbicide Systems on the Competitiveness and Yield of Peanuts1

Abstract Peanuts (Arachis hypogaea L. ‘Florunner’), infested with sicklepod (Cassia obtusifolia L.) were grown during 1977 and 1978 in 20.3-, 40.6- and 81.2-cm row widths (on Dothan sandy loam and on Greenville sandy clay loam). The crop was maintained weed-free for 0, 2, or 5 weeks or for the entire growing season. Three herbicidal systems with various intensities were utilized. In 1978, reduced and regular rates of in-row crop seeding were compared. Weed-free maintenance for 5 weeks generally produced yields of peanuts equivalent to those obtained with continuous weeding. Sicklepod green weights were reduced by 28 and 53% in peanuts with row spacings of 40.6 and 20.3 cm, respectively, as compared to standard 81.2 cm spaced rows. Peanuts in close-row patterns yielded about 14% higher than the conventional 81.2 cm row spacing when averaged for all studies. Adjustments of the in-row seeding rate to produce a more normal seed-drop per hectare reduced the yield of peanuts only 1 to 3% and, therefore, did not negate the increased yields produced with close-row spacings.

Studies on Competition between Upland Crops and Weeds : V. The period for weed-free maintenance

The experiment on competition between upland crops and weeds was conducted with four upland crops which were typical in the Kanto plain. And from aspect of the effects of different periods of weed-free maintenance on the crop yields, adequacy of the period for weed-free maintenance hypothesized in the previous report was estimated. 1. In upland rice and soybean cropping plots, plant length of large crab-grass (Digitaria adscendence Henr.) at the plots of 0 and 30 days weed-free maintenance extended up to the upper part of crop canopies which maintained the relative light intensity under 10%. On the other hand, that at the plots of 47 and 58 days weed-free maintenance was limited to the lower part of crop canopies. In peanut cropping plots, even that at the plot of 58 days weed-free maintenance extended up to the upper part of crop canopies. As the plant height of corn was high, even that at the plot of 0 day weed-free maintenance was kept to the lower part of crop canopies. 2. The later the time of competition with weeds started, the smaller the ratio of weed weight to total community weight became. The ratio of weed weight to total community weight in corn was the smallest of all crops, that is, was under 25% at the plot of 0 day weed-free maintenance, and was under 5% at the plots of 30 and 47 days weed-free maintenance. The ratio of weed weight to total community weight in upland rice and soybean was large at the plots of 0 and 30 days weed-free maintenance, but was small at the plots of 47 and 58 days weed-free maintenance. That of peanut was the largest, and was over 30% even at the plot of 58 days weed-free maintenance at harvesting. The amount of weeds at harvesting were little in corn, medium in upland rice and soybean, and much in peanut. And those showed approximately similar results to the ratio of weed weight to total community weight. Namely, the smaller the weed weight to total community weight was, the less the amounts of weeds at harvesting became. 3. Effects of weeds on crop yields were reflected in results of competition between crops and weeds. The yields of upland rice and soybean reduced at the plots of 0 and 30 days weed-free maintenance, as growth of weeds was not diminished greatly by crop canopies. But reduction of yields did not occur at the plots of 47 and 58 days weed-free maintenance, as growth of weeds was diminished greatly by crop canopies. The yields of peanut reduced at all plots of competition with weeds, as weeds grew rampant. In corn, significant reduction of weights of ears did not occur even at the plot of 0 day weed-free maintenance, but weights of stems and leaves reduced. Crop yield reduction due to weeds did not occur at the plots of 30 and 47 days of weed-free maintenance. 4. From above results, it was clear that hypothesis about the period for weed-free maintenance after seeding required to escape crop yield reduction due to weeds had high adequacy.

Studies on Competition between Upland Crops and Weeds : IV. Change of light environment in crop canopies and hypothesis about the period for weed-free maintenance

The changes of light environment in crop canopies were investigated with four upland crops which were typical in the Kanto plain. And, the growth of competitive weeds was made clear clear, then we hypothesized about the period for weed-free maintenance after seeding required to escape crop yield reduction due to weeds. 1. The start of shading the surface of the ground by crop canopies after seeding was earliest in corn, but reduction of relative light intensity under crop was slow, and the degree of shading was small. The start of shading by soybean was a little late as compared with that of corn, but reduction of relative light intensity was rapid, and the degree of shading was large. The start of shading was the latest in peanut, but reduction of relative light intensity was the most rapid and the degree of shading was large as well as soybean. The characteristics of shading in upland rice were medium among these crops. 2. High negative correlation was found between logarithms of relative light intensity in the center of crop-rows on the surface of the ground and the number of days after seeding, then the regression lines were obtained. From these regression lines, the times when relative light intensity reduced under 20% were estimated, that is, about 76, 78, 63 and 71 days after seeding in upland rice, peanut, soybean and corn, respectively. And similarly, the times when reduced under 10%, were about 89, 86 and 73 days after seeding in upland rice, peanut and soybean, respectively. Reduction under 10% was not found in corn. 3. The linear regression was obtained between logarithms of relative light intensity in the center of crop-rows on the surface of the ground and LAI. From these regression lines, LAIs at the time when relative light intensity reduced under 20% or 10%, were estimated, that is, 4.9 or 6.6, 2.7 or 3.7, 2.3 or 3.3 and 5.2, in upland rice, peanut, soybean and corn, respectively. 4. At the time when relative light in the center of crop-rows on the surface of the ground reduced under 20% or 10%, the space of 40 or 30 cm-high from the surface of the ground in upland rice, 20 or 15 cm-high in peanut, 60 or 50 cm-high in soybean and 100 cm-high in corn kept the same value of relative light intensity, respectively. 5. In the early summer season when relative light intensitywas reduced by crop canopies, plant length or main stem length of weeds was 1-2, 7-13, 16-28, 39-52 cm in large crab-grass (Digitaria adscendens Henr.), 1-2, 6-12, 12-26, 20-43 cm in Chufa (Cyperus microiria Steud.), and 1>, 4-14, 9-25, 17-33 cm in common purslane (Portulaca oleracea L.)at 10, 20, 30, 40 days after seeding, respectively. 6. From above results. we build up hypothesis about the period for weed-free maintenance after seeding required to escape crop yield reduction due to weeds, as follows. Growth of large crab-grass is greatly diminished at the condition of relative light intensity under 10%. The relative light intensity in crop canopies reduced under 10% at the time of about 89 days after seeding, and the space of 30 cm-high was the same value in upland rice. On the other hand, plant length of large crab-grass grew about 30 cm at the time of 30 days after weed seeding. Therefore, 59 days which went back from 89 days to 30 days were estimated as the period for weed-free maintenance, in the community of upland rice and large crab-grass. It was expected that the growth of large crab-grass which emerged on and after 59 days after crop seeding was greatly diminished by crop canopies. The relative light intensity did not reduce under 10% in corn, but from its characteristics, less than 30 days were estimated, as the period for weed-free maintenance. The period for weed-free maintenance were estimated shorter in common purslane or Chufa. Their growth are greatly diminished at the condition of relative light intensity under 20%.

Influence of Row Spacing on Weed Competition by Cotton

When planted with narrow (53 cm) row spacing, cotton (Gossypium hirsutumL.) ‘McNair 210’ produced maximum yields with as little as 6 weeks of weed-free maintenance. With wider row spacing (79 and 106 cm), however, 10 and 14 weeks of weed-free maintenance were required for maximum yield. When weeds were allowed to grow in cotton for more than 2 to 4 weeks after planting, yield reductions occurred. This tolerance period did not differ with row widths of 53, 79, or 106 cm.

Competition of Florida Beggarweed and Sicklepod with Peanuts II. Effects of Cultivation, Weeds, and SADH

When peanuts (Arachis hypogaeaL.) were not kept weed-free, a single cultivation 4 weeks after emergence increased yields substantially over those of non-cultivated peanuts. Cultivation had no effect, however, when peanuts were maintained weed-free for 4 or 8 weeks. The length of the weed-free periods, cultivation, and the presence or absence of peanuts all strongly influenced the density of the sicklepod (Cassia obtusifoliaL.) plants which grew above the canopy of peanut foliage. Peanut foliage, which was released from weed-free maintenance at 8 weeks but then competed with sicklepod until harvest, reduced the green weight of sicklepod 95 to 98% thus illustrating the competitive capacity of the peanut plant. Moderate stands of Florida beggarweed [Desmodium tortuosum(Sw.) DC] did not markedly affect yield of peanuts. Application of a growth regulator, succinic acid, 2,2-dimethylhydrazide (SADH), did not influence weed competition or yield of in-shell peanuts consistently at any of the three locations. Quality analyses showed that treatment variables did not modify the taste of peanuts; however, in some experiments, components of the market grade of in-shell peanuts were changed by SADH, cultivation, length of the weed-free period, and cultivation X length of the weed-free period.

Competition of Florida Beggarweed and Sicklepod with Peanuts I. Effects of Periods of Weed-free Maintenance or Weed Competition

Peanut (Arachis hypogaeaL. ‘Tifspan’ or ‘Florunner’) yields were not reduced when the crop was maintained free of Florida beggarweed [Desmodium tortuosum(Sw.) DC.] or sicklepod (Cassia obtusifoliaL.) for 4 weeks after crop emergence and when vigorous crop growth was maintained for the remainder of the season. Sometimes weed-free maintenance for only 2 weeks resulted in near-normal yields, which indicated that the canopy of peanut leaves effectively suppressed the weeds. Conversely, these weeds had to compete with peanuts for more than 10 weeks before crop yield was reduced. Weeds that overtopped the peanuts at harvest emerged during the first 6 weeks after planting.

Influence of Nitrogen on Weed Competition in Cotton

Cotton maintained free of annual grass and broadleaf weeds for 6 or more weeks after emergence in 1969 produced maximum yields, whereas in 1970 and 1971, 8 or more weeks of weed-free maintenance were required. Nitrogen applications at planting of 67 and 100 kg/ha did not influence the weed-free requirement of cotton in any year. Cotton yields were not reduced in 1969 when weeds were allowed to compete for 4 or 2 weeks. In 1970 and 1971 weed competition for 7 or fewer weeks did not result in yield reductions. Nitrogen did not affect the competitive relationship between cotton and weeds in 1969 and 1971. In 1970, however, cotton tolerated only 6 weeks of competition at the zero nitrogen rate, whereas it tolerated 7 weeks of competition at the 67 and 100 kg/ha nitrogen rates. Height and stem diameter of cotton were less reliable indicators of the crop-weed relationship than was yield. Neither height nor stem diameter of cotton revealed a consistent difference in the competitive relationship at the three nitrogen rates.