Weed control via intercropping with gliricidia: I. cotton crop

The majority of cotton grown commercially in the world has white lint, but recently, there has been a growing interest in colored lint cotton in several countries, including Brazil. The use of naturally-colored fiber reduces chemical pollution. The objective of this paper was to evaluate cotton cultivar fiber yield in response to weed control via intercropping with gliricídia. Cultivars BRS-Verde (greenish fibers), BRS-Rubi (reddish brown fibers), BRS-Safira (brown fibers), and BRS-187 8H (white fibers) were submitted to the following treatments: no hoeing, two hoeings (at 20 and 40 days after transplanting), and cotton intercropped with gliricídia. In the intercropped treatment, gliricídia was planted between rows of cotton plants, using one seedling pit-1, in pits spaced 50.0 cm apart. Twelve weed species predominated in the experiment, many of them belonging to the Poaceae family. Weeds occurred at different frequencies and in a non-uniform manner in the experimental area. Cultivars did not influence weed dry matter. Intercropping with gliricídia reduced weed dry matter but did not prevent reductions in cotton fiber and seed cotton yield, which were higher in hoed plots. Cultivar BRS Safira had the highest fiber yield, but no differences were observed between cultivars regarding to seed cotton yield.

Weed control via intercropping with gliricidia: II. corn crop

A reduction in herbicide use is one of modern agriculture's main interests and several alternatives are being investigated with this objective, including intercropping. Gliricídia (Gliricidia sepium) mulch has no allelopathic effect on corn or beans but significantly decreased the population of some weed species. The objective of this study was to evaluate green ear and grain yield in corn cultivars as a response to weed control achieved via intercropping with gliricidia. A completely randomized block design with five replicates and split-plots was used. Cultivars AG 1051, AG 2060, BRS 2020, and PL 6880 (assigned to plots) were submitted to the following treatments: no hoeing, hoeing (performed at 20 and 40 days after sowing the corn), and corn intercropped with gliricidia. Gliricidia was grown in a transplanting system to ensure uniform germination and fast establishment in the field. Seeding was made in 200-cell trays with one seed per cell (35 mL volume). The plants emerged two to three days after sowing and were transplanted to a permanent site two to three days after emergence. Corn was sown on the same day gliricidia was transplanted. Sixteen weed species occurred at different frequencies, with uneven distribution in the experimental area. Cultivars AG 1051 and AG 2060 were the best with reference to most characteristics employed to evaluate green corn yield. Cultivar AG 1051 provided the highest grain yield. The highest green ear yield and grain yield values were obtained with hoeing. However, the fact that intercropped plots showed intermediate yield between the values obtained for hoed and non-hoed plots indicates that gliricidia was beneficial to corn, and exerted a certain level of weed control.

Effect of cowpea intercropping on weed control and corn yieid

Herbicides have simplified weed control, but the use of herbicides, besides being costly, resulted in the selection of herbicide-resistant weed biotypes and has become an environmental contamination factor. Herbicide use reduction is one of the goals of modern agriculture, with several alternatives being investigated, including intercropping. The objective of this study was to evaluate the effects of cowpea and corn cultivar intercropping on weed control and corn green-ear (immature ears with 80% humidity grains) and grain yield. A completely randomized block design with split-plots and four replications was used. AG 1051, AG 2060 and PL 6880 corn cultivars (assigned to plots) were submitted to the four treatments: no weeding, two hoe-weeding (22 and 41 days after planting), and intercropping with cowpea (BR 14 and IPA 206 cultivars, with indeterminate growth). The cowpea was planted (with corn planting) between the corn rows, in pits 1.0 m apart, with two plants per pit. The corn cultivars did not differ from each other as to weed density (WD), fresh above-ground weed biomass (WB), green-ear yield and grain yields. Higher WD and WB mean values were found in no weeding subplots; lower mean values in two hoe-weeding subplots; and intermediate mean values in intercropped subplots, indicating that cowpea plants had, to a certain extent, control over weeds. The no-weeded plots and the intercropped plots had lower green-ear and grain yields. Although the cowpea cultivars had a certain control over weeds (mean reductions of 22.5 and 18.3%, in terms of green matter density and weight of the above-ground part of weeds, respectively), they also competed against the corn plants, leading to yield reduction (mean reductions of 17.0 and 32% in green ear and grain yield, respectively). The cowpea cultivars did not produce grain, certainly due to the strong competition exerted by the corn and weeds on cowpea plants.

Nitrogen doses and weed control via intercropping with gliricidia for corn production

Many studies have demonstrated the beneficial influence of nitrogen doses on corn dry grain yield and green ear yield. Due to a growing concern with environmental degradation, many agricultural practices, adopted in the past, are being reexamined. With regard to weed control, strategies that employ mechanical control, including intercrops, are being the object of renewed interest. The purpose of this study was to evaluate the effects of the application of nitrogen doses (0, 40, 80, and 120 kg N ha-1; as ammonium sulfate) and weed control on the growth, green ear yield, and grain yield of the AG 1051 corn cultivar. A randomized block experimental design with split-plots and nine replications was adopted. In addition to nitrogen rates, the AG 1051 cultivar was submitted to the following treatments, applied to subplots: no weeding, two hoeings (at 20 and 40 days after sowing), and intercropping with gliricídia (Gliricidia sepium). Gliricidia was sowed at corn planting, between the corn rows, using two seedlings per pit, in pits spaced 0.30 m apart. Gliricidia did not provide weed control, and gave plant growth, green ear yield and grain yield values similar to the no weeding treatment. However, regarding the number of mature ears got, intercropping with gliricidia did not differ from the two-hoeing treatment. Weed control did not have an effect on plant height and number of marketable, husked green ears, with the application of 120 kg N ha-1; indicating that nitrogen improved the corn's competitive ability. The two-hoeing treatment provided the best means for total green ears weight, number of marketable husked ears, both unhusked and husked marketable ear weight, grain yield and its components than the other treatments. Nitrogen application increased corn growth, green ear yield, and grain yield, as well as weed green biomass, but reduced the stand and growth of gliricidia.

Critical period for weed control in potatoes in the Huambo Province (Angola)

The effects of different weed management periods on potatoes were studied in three areas (Bailundo, Chianga and Calenga) of the central highlands of Angola and in three cropping seasons, from June 2005 to May 2007. Six weed-management treatments were used to identify critical periods of competition and to allow the development of more precise management recommendations. Total potato yield ranged from about 22 t ha-1 in weed-free plots to about 3 t ha-1 with no weed control a yield loss of 86%. Major weed species Galinsoga parviflora, Cyperus esculentus, Bidens biternata, Amaranthus hybridus, Nicandra physaloides, Portulaca oleracea and Datura stramonium differed from area to area. The species G. parviflora dominated the weed flora in all three areas 73, 97 and 72 plants m² 50 days after crop emergence in Bailundo, Chianga and Calenga respectively, in dry season trials; while C. esculentus was also present in Chianga and Calenga, with an average density of ca 30 plants m-2 in dry season trials. Gompertz and logistic equations were fitted to data representing increasing periods of weed-free growth and weed interference, respectively. Critical periods for weed control, with a 95% weed-free total yield, were estimated from 26 to 66 and from 20 to 61 days after emergence for the rainy and dry seasons, respectively. Weed competition before or after these critical periods had negligible effects on crop yield.

Weed control in corn via intercropping with gliricidia sown by broadcasting

There has been interest in reducing the use of herbicides for weed control in order to decrease environmental degradation problems. The objective of this study was to evaluate the effects of gliricidia planting density sown by broadcasting and intercopping on green ear and corn grain yield as well as on weed control. A randomized block design with split-plots and five replicates were adopted. Cultivars AG 1051, BM 2022, and BM 3061, assigned to plots, were submitted to the following treatments: no hoeing, two hoeings (at 20 and 40 days after sowing), and intercropped with gliricidia sown at densities of 10 and 20 seeds m-2. Thirty weed species occurred in the experiment area, with Cucumis anguria as the most frequent ones. Cultivar BM 2022 was the best for the total number of ears (TNE) and number (NMHE) and weight of marketable husked ears. Together with cultivar AG 1051, this cultivar had the highest total weight and marketable unhusked ear weight (MUEW). However, the cultivars did not differ with respect to grain yield (GY). The highest green ear and corn grain yield and weed control percentages were obtained with two hoeings; in MUEW, NMHE and GY, intercropping provided intermediate means in comparison with those obtained in hoed and non-hoed plots, indicating that gliricidia was partially beneficial to corn. Increased gliricidia seeding density heightened the benefits to corn (TNE and MUEW). The lack of hoeing produced the poorest green ear and grain yields.

Corn cultivar intercropping with arboreal legumes for weed control

Gliricidia (Gliricidia sepium) seedlings are usually beneficial to corn crops when planted between corn rows. The objective of this work was to assess the effects of corn intercropped with gliricidia and "sabiá" (Mimosa caesalpiniifolia), a species native to the Brazilian northeastern region, on weed control and corn green ear and grain yields. The experiment was carried out at Estação Experimental da Universidade Federal Rural do Semi-Árido - UFERSA (Mossoró, State of Rio Grande do Norte, Brazil). The experimental design consisted of randomized complete blocks (multifactorial design) with five replications, arranged in split-plots. The plots consisted of corn cultivars AG1051 and BM 2022; subplot treatments (six) were no-hoeing, twice-hoeing (at 20 and 40 days after sowing) and intercropping with gliricidia and "sabiá", either directly sown or transplanted, simultaneously with corn sowing. The intercropped leguminous plants were spaced 0.40 m from each other, and directly seeded or transplanted (30-day-old seedlings) in between two 1 m-spaced corn rows. Twenty three weed species were identified during the experiment. Gliricidia seedlings were superior to "sabiá" seedlings with regard to plant height and survival rate. The highest corn green ear and grain yields were found for twice-hoed subplots, while the lowest yield was found for no-hoed or intercropped subplots. However, grain yield values in intercropped treatments did not differ from grain yield values in hoed plots. In addition, marketable husked green ear mean weights did not differ between twice-hoed subplots and subplots directly seeded with gliricidia and "sabiá". Such results indicated that corn benefited from the intercropping system, but intercropping with gliricidia and "sabiá" transplanted resulted in lower benefits than with the direct sowing of those species.

Weed control in corn and weed sample size for growth evaluations

The objectives of this study were to evaluate baby corn yield, green corn yield, and grain yield in corn cultivar BM 3061, with weed control achieved via a combination of hoeing and intercropping with gliricidia, and determine how sample size influences weed growth evaluation accuracy. A randomized block design with ten replicates was used. The cultivar was submitted to the following treatments: A = hoeings at 20 and 40 days after corn sowing (DACS), B = hoeing at 20 DACS + gliricidia sowing after hoeing, C = gliricidia sowing together with corn sowing + hoeing at 40 DACS, D = gliricidia sowing together with corn sowing, and E = no hoeing. Gliricidia was sown at a density of 30 viable seeds m-2. After harvesting the mature ears, the area of each plot was divided into eight sampling units measuring 1.2 m² each to evaluate weed growth (above-ground dry biomass). Treatment A provided the highest baby corn, green corn, and grain yields. Treatment B did not differ from treatment A with respect to the yield values for the three products, and was equivalent to treatment C for green corn yield, but was superior to C with regard to baby corn weight and grain yield. Treatments D and E provided similar yields and were inferior to the other treatments. Therefore, treatment B is a promising one. The relation between coefficient of experimental variation (CV) and sample size (S) to evaluate growth of the above-ground part of the weeds was given by the equation CV = 37.57 S-0.15, i.e., CV decreased as S increased. The optimal sample size indicated by this equation was 4.3 m².

Chemical control of morning glory as a function of water restriction levels

Among the herbicides recommended for the dry season and registered to sugarcane crop, amicarbazone, isoxaflutole and the association diuron + hexazinone + sulfomethuron-methyl can be highlighted. These are pre-emergence herbicides efficient against broad-leaved weeds. Morning glory causes large losses in infested sugarcane fields by bending the stalks and interfering in harvesting. In this study the effectiveness of pre-emergence herbicides for two species of morning glory (Ipomoea hederifolia and Ipomoea grandifolia) was evaluated. Treatments were arranged in completely randomized factorial design (4 x 7). There were four periods of water restriction (0, 30, 60 and 90 days), seven chemical treatments [diuron + hexazinone + sulfometuron-methyl (1387 + 391 + 33.35 g a.i. ha-1), diuron + hexazinone + sulfometuron-methyl (1507.5 + 425 + 36.25 g a.i. ha-1), diuron + hexazinone + sulfometuron-methyl (1658.25 + 467.5 + 39.87 g a.i. ha-1), diuron + hexazinone + sulfometuron­methyl (1809 + 510 + 43.5 g a.i. ha-1), amicarbazone (1190 g a.i. ha-1), amicarbazone + isoxaflutole (840 + 82.5 g a.i. ha-1)] and a control with no application. At 7, 14, 21 and 28 days after the restoration of moisture, control was visually evaluated. After the final evaluation, the dry mass of morning glories was measured. At 90 days of water restriction, diuron + hexazinone + sulfometuron-methyl was more effective to control I. hederifolia than the amicarbazone + isoxaflutole tank mixture. The four diuron + hexazinone + sulfometuron­methyl doses have reduced morning glory dry mass to zero; whereas treatments with amicarbazone have not. The most effective treatment for morning glory control was diuron + hexazinone + sulfometuron-methyl. This result may be due to a possible synergistic interaction.

Glyphosate tolerant volunteer corn control at two development stages

The loss of grains during the harvest of glyphosate tolerant corn may generate volunteer plants, which can interfere in the conventional or glyphosate crop in succession. The current work aim to evaluate the control of the volunteer corn glyphosate tolerant under two weed stages. Aimed to evaluate the control of volunteer glyphosate tolerant corn in two stages of development. There were conducted two experiments with hybrid 2B688 HR (lepidoptera and glyphosate tolerant), the application were at V5 and V8 stage. The experiment was randomized block design with four replicates, using the treatments: haloxyfop at 25, 50 and 62 g ha-1 alone and associated with 2,4-D at 670 g ha-1 or fluroxypyr at 200 g ha-1. The standard was clethodim at 84 g ha-1 with 2,4-D and fluroxypyr at same rates. The applications of haloxyfop and clethodim both isolated or in a mixture with 2,4-D and fluroxypyr at V5 stage showed total control (100%) at 32 and 39 days after the application, except for haloxyfop + 2,4-D (25 + 670 g ha-1) mixture, which did not provided adequate control. At V8 stage, haloxyfop + 2,4-D (50 + 670 g ha-1) and haloxyfop + 2,4-D (62 + 670 g ha-1) mixtures took up to 6 and 10 days or longer to reach adequate to excellent control, when compared to haloxyfop isolated applications in the same doses, respectively. Either isolated clethodim or mixed with 2, 4-D and fluroxypyr did not show adequate control. The treatments showed efficient control on volunteer corn plants at V5 stage, except for haloxyfop + 2, 4-D (25 + 670 g ha-1) mixture. At V8 stage applications, haloxyfop either isolated or mixture with fluroxypyr demonstrated excellent control on every evaluated dose. The mixture with 2, 4-D can reduce haloxyfop efficiency at low doses. Clethodim alone or mixed with 2,4-D or furoxypyr did not provide acceptable level of control.

Use of grass carp (Ctenopharyngodon idella) as a biological control agent for submerged aquatic macrophytes

This study aimed to evaluate feed preference and control efficacy of grass carp (Ctenopharyngodon idella) on the aquatic macrophytes Ceratophyllum demersum, Egeria densa and Egeria najas. An experiment was carried out at mesocosms conditions with 2,000 liters capacity and water residence time of 2.8 days. C. demersum, E. densa e E. najas biomasses were offered individually with sixty g and coupled in similar quantities of 30 g of each species, evaluated during 81 days, envolving 6 treatments. (1 - C. demersum, 2 - E. najas, 3 -E. densa, 4 - C. demersum + E. najas, 5 - C. demersum + E. densa and 6 - E. najas + E. densa). When offered individually, E. najas and C. demersum presented the same predation rate by grass carp, which was higher than E. densa predation rate. When plants were tested in pairs, the order of feed preference was C. demersum > E. najas > E. densa. E. najas and C. demersum percentage control ranged from 73 to 83%. No relation between biomass consumption and grass carp body weight gain was observed, probably due to differences in nutritional quality among macrophyte species according to fish necessities. Therefore, it is concluded that the use of grass carp is one excellent technique to control submersed macrophytes in Brazil.

Selectivity of chemical weed control systems in conventional cotton

Cotton is highly susceptible to the interference imposed by weed community, being therefore essential to adopt control measures ensuring the crop yield. Herbicides are the primary method of weed control in large-scale areas of production, and usually more than one herbicide application is necessary due to the extensive crop cycle. This study aimed to evaluate the selectivity of different chemical weed control systems for conventional cotton. The experiment took place in the field in a randomized block design, with twenty nine treatments and four replications in a split plot layout (adjacent double check). Results showed that triple mixtures in pre-emergence increased the chance of observing reductions in the cotton yield. To avoid reductions in crop yield, users should proceed to a maximum mixture of two herbicides in pre-emergence, followed by S-metolachlor over the top, followed by one post-emergence mixture application of pyrithiobac-sodium + trifloxysulfuron-sodium.

Chemical control of different Digitaria insularis populations and management of a glyphosate-resistant population

This study aimed to control different populations of Digitaria insularisby glyphosate herbicide, isolated and mixed, besides the combination of methods (chemical and mechanical) to manage resistant adult plants. Three experiments were conducted, one in pots which were maintained under non-controlled conditions and two under field conditions. In the experiment in pots, twelve populations of D. insularis were sprayed with isolated glyphosate (1.44 and 2.16 kg a.e. ha-1) and mixed (1.44 and 2.16 kg a.e. ha-1) with quizalofop-p tefuryl (0.12 kg i.a. ha-1). The treatment of 1.44 kg a.e. ha-1 of glyphosate plus 0.12 kg a.i. ha-1 of quizalofop was sufficient for adequate control (>95%) of all populations. Population 11 (area of grain production in Itumbiara, GO) was considered sensitive to glyphosate. Others populations were moderately sensitive or tolerant to the herbicide. In the field, the plants of D. insularis of one of the experiments were mowed and, in the other, there were not. Eight treatments with herbicides [isolated glyphosate (1.44 and 2.16 kg a.e. ha-1) and mixed (1.44 and 2.16 kg a.e. ha-1) with quizalofop-p-tefuryl at 0.12 kg a.i. ha-1), clethodim at 0.108 kg a.i. ha-1) or nicosulfuron at 0.06 kg a.i. ha-1)] were assessed, in combination with or without sequential application of the standard treatment, sprayed 15 days after the first application. The combination of the mechanic control with the application of glyphosate (2.16 and 1.44 kg a.e. ha-1) plus quizalofop-p-tefuryl (0.12 kg a.i. ha-1) or clethodim (0.108 kg a.i. ha-1), associated to the sequential application, was the most effective strategy for the management of adult plants of resistant D. insularis.

Weed Control in Maize with Gliricidia Intercropping

One of the very important components in the organic maize production costs refers to spending on weed control. In this research were assessed the effects of maize hybrids (AG 1051 and BR 205) in an intercropping with Gliricidia (Gliricidia sepium) and mechanical hoeing on weed control. The treatments assessed were: A - maize monocropping + two hoeings (20 and 40 days after sowing); B - maize with one hoeing at 20 days + intercropping with gliricidia sowed after hoeing; C - maize sowing intercropped with gliricidia at the time of maize sowing + hoeing at 40 days; D - maize sowing intercropped with gliricidia at the time of maize sowing without hoeing; E - monocropping maize without hoeing. In the intercroppings, gliricidia was sowed in broadcast seeding with 30 viable seeds m-2. Maize hybrids did not differ in their effects on weed growth and grain yield. Treatments A, B and C have reduced weed growth, compared to treatments D and E. The highest grain yield was obtained with treatment A and the lowest with treatment E. It was concluded that intercropping maize and gliricidia is not a good alternative for an integrated weed management in maize crops in the conditions assessed.

INFLUENCE OF PRECIPITATION AND SUGARCANE STRAW IN AMINOCYCLOPYRACHLOR AND INDAZIFLAM CONTROL EFFICIENCY

ABSTRACTThe raw sugarcane harvesting system has changed the dynamics of weed tillage for this crop, changing the predominant weed species and providing a barrier between the herbicide and the soil. Thus, this study has aimed to assess the influence of precipitation and sugarcane straw in the aminocyclopyrachlor and indaziflam herbicides control efficiency for the species Ipomoea trilobaand Euphorbia heterophylla. There were two trials, one for aminocyclopyrachlor and one for the indaziflam, both in the greenhouse at the campus of Faculdade Integrado in the Brazilian city of Campo Mourão, PR. Each experiment consisted of eight treatments with four replications. The treatments consisted of the combination of the presence of straw (10 t ha-1), capillary irrigation and rainfall simulation (20 mm). Assessments of control percentage of I.triloba and E.heterophylla were carried out, as well as the number of plants per pot. The aminocyclopyrachlor and indaziflam herbicides applied directly to the soil were efficient in controlling these species. The 20 mm rainfall simulation or daily irrigation on the straw are indispensable to promote the removal of aminocyclopyrachlor and indaziflam from the straw and provide satisfactory control of I.triloba and E.heterophylla.