Predominant Weeds Research Articles

Low disturbance seeding suppresses weeds in no‐tillage soyabean

SummaryGermination is a key process in the dynamics of weed populations. In no‐tillage systems, crop seeding is often found to induce seed germination in the seeding strip. In this research, experiments to investigate options for reducing weed seedling establishment were conducted in no‐till soyabean fields located in two sites in south Brazil. A first experiment revealed that a reduction in emergence of some important weed species can be achieved by lowering seeding speed. Further experiments showed the ability of a modified seeder to contribute to an additional reduction in weed establishment. On the modified seeder, coulter discs were equipped with lateral blades, to diminish soil disturbance and to maintain a uniform soil cover by properly cutting the mulch layer. In a field with a high level of residues, the modified seeder, in contrast to the standard seeder, prevented the increase of soil exposure when seeding at high speed. The predominant weeds were annual species. Averaged over all seeding rates, the new equipment led to a 56% reduction in within‐row weed density, compared with the standard seeder. Regardless of seeder type, overall weed density increased with seeding speed, but with the modified seeder, this increase was only half that of the standard seeder. The modified seeder reduced weed biomass by 30% and increased soyabean grain yield by 42%. The research demonstrated that relatively simple changes, like a minor modification to a seeder and a lower seeding speed, can contribute to more diverse and sustainable alternatives to predominantly chemical‐oriented weed management strategies.

Regaining habitats from invasive weeds by planting limited-recruitment endemic trees on an oceanic island: successes and failures 11 years later

The degradation of biodiversity caused by anthropic habitat destruction is a global issue. The recovery of natural habitats from invasive alien weeds in order to conserve endemic ecosystems is especially important on small oceanic islands. Planting of endemic trees may be an effective measure, but a complete restoration process within the island is essential to avoid accidental introduction of invasive aliens. To test planting techniques, we planted two endemic tree species whose regeneration was hindered by alien species on degraded lands on Chichi-jima (Ogasawara Islands) and monitored vegetation changes. During an 11-year period, about half of the Elaeocarpus photiniifolius seedlings survived in gap areas, but all Morus boninensis failed. The E. photiniifolius trees reached a height of 4.7 ± 2.4 m. The restored canopy created a dark environment that greatly reduced the volume of the predominant invasive weeds. These results suggest that E. photiniifolius is suitable for restoration of forests on degraded land and for the suppression of weeds on the island. Low species diversity in the restored forests, however, was a remaining issue to be addressed. Herein we discuss potential improvement measures to facilitate the recovery of species diversity, including other native tree candidates.

Effect of Integrated Weed Management Practices on Plant Height, Number of Tillers in Turmeric During kharif Season

Field experiments were conducted at the Agricultural Research Station, Bhavanisagar of Tamil Nadu Agricultural University, during kharif season of 2012 to evaluate the integrated weed management with pre and post emergence herbicides in turmeric. The experiments were laid out in Randomized block design and replicated thrice. The treatments comprised of different weed management practices wherein PE herbicides viz ., metribuzin 0.7 kg ha ‑1 , pendimethalin 1.0 kg ha ‑1 and atrazine 0.75 kg ha ‑1 followed by either POE fenoxaprop 67 g ha ‑1 + metsulfuron 4 g ha ‑1 (Tank mix) on 45 DAP or HW on 45 and 75 DAP or straw mulch 10 t ha ‑1 on 10 DAP + HW on 75 DAP, all PE oxyfluorfen 0.30 kg ha ‑1 , PE oxadiargyl 0.25 kg ha ‑1 , POE glyphosate 1.03 kg ha ‑1 and 1.54 kg ha ‑1 on 25 DAP followed by HW on 45 and 75 DAP, HW on25, 45 and 75 DAP and unweeded check were imposed. In both the experiments, observations were recorded on plant growth parameters like plant height and plant dry matter production and number of tillers were recorded in kharif season 2012. In the experimental fields, Echinochloa colonum and Digitaria bicornis among grasses, Cyperus rotundus in sedge, Eclipta prostrata and Boerhaavia diffusa under broad leaved weed were the predominant weeds. The grasses constituted the major proportion of the weed flora at all the growth stages of the crop. Slight to moderate phytotoxicity symptoms in turmeric were observed in glyphosate 1.03 and 1.54 kg ha -1 at the time of application of herbicides, however the crop recovered later. Among the weed management treatments imposed, PE metribuzin 0.7 kg ha ­-­1 + HW on 45 and 75 DAP registered higher uptake of nutrient by crop due to effective control of weeds which enhanced the availability of nutrients to crop leading to positive results in respective of growth parameters like plant height, dry matter production and number of tillers plant -1 , during 2012.

Benchmark Study: I. Introduction, Weed Population, and Management Trends from the Benchmark Survey 2010

Almost 1,650 corn, cotton, and soybean growers in 22 states participated in a 2010 telephone survey to determine their attitudes with regard to which weed species were most problematic in glyphosate-resistant (GR) crop production systems for corn, cotton, and soybean. The survey is a follow-up to a previous 2005 to 2006 survey that utilized a smaller set of growers from fewer states. In general, growers continued to estimate weed populations as low and few challenges have been created following adoption of GR cropping systems. Pigweed and foxtail species were dominant overall, whereas other species were more commodity and state specific. Corn, cotton, and soybean growers cited velvetleaf, annual morningglory, and waterhemp, respectively, as predominant weeds. Growers in the South region were more likely to report pigweed and waterhemp (Amaranthus spp.), whereas growers in the East and West reported horseweed. When growers were asked with which GR weeds they had experienced personally, horseweed was reported in all regions, but growers in the South more frequently reported pigweed, whereas growers in the East and West regions more frequently reported waterhemp. Comparisons with the previous 2005 survey indicated that more growers believed they were experiencing GR weeds and were more aware of specific examples in their state. In particular, the Amaranthus complex was of greatest concern in continuously cropped soybean and cotton.

Effect of Pre-Emergence Herbicides on Weed Control in Jatropha (Jatropha Curcas L.) Nursery

Nursery experiments were carried out to evaluate two different pre-emergence herbicides on germination, seedling growth and weed control efficiency of Jatropha nursery. Three days after sowing, pre-emergence herbicides viz. pendimethalin (30% EC) and fluchloralin (45% EC) were applied at different concentrations on the nursery bags using rose cane. Twenty days after application of herbicides, observations were made on germination percentage and 45 days after application of herbicides, parameters like number of predominant weeds (broad leaved, grasses and sedges), weed dry weight(g), weed control efficiency (%), germination (%), root length (cm), shoot length (cm) and dry matter production (g seedling-5) of Jatropha seedling in each treatment were recorded. The results revealed that the compatibility of application of pre-emergence herbicide of pendimethalin @ 0.05% - 0.10% can be used effectively to control broad leaved weeds, without impairing the germination and seedling growth of Jatropha curcas.

Effects of local landscape richness on in-field weed metrics across the Great Britain scale

Weeds sit at the crux of issues of arable biodiversity and productivity. We test whether the effects of a simple local landscape richness score are apparent on in-field data for the predominant weeds, in the seedbank and as standing weeds, across the Great Britain (GB) scale. We test two hypotheses: (H1) that in-field weed species richness is positively related to local landscape richness around arable fields; and (H2) that in-field weed abundance is positively related to local landscape richness. We maintain H1, but find little evidence of a consistent effect of local landscape on the species richness of in-field weeds. Convincing evidence for local landscape richness affecting weed abundance lead us to accept H2 as a working hypothesis for in-field weed abundance. However, we have no mechanism to explain why in-field weed abundance should be linked to off-field landscape features, as expectations for farmer management intensity and local bee abundance affecting weed abundance were not significant.The effects of landscape on weed abundance were consistent across the GB scale dataset despite systematic sources of error due to cropping and regional differences. These results suggest that local landscape might be managed to achieve goals of changing in-field weed abundance at policy-relevant scales.

Weed Control and Yield Comparisons of Twin- and Single-Row Glyphosate-Resistant Cotton Production Systems

A 2-yr field study was conducted during 2007 and 2008 at Stoneville, MS, to determine the effect of twin-row (two rows 38 cm apart on 102-cm beds) and single-row (on 102-cm beds) patterns and glyphosate POST applications with and without fluometuron + S-metolachlor PRE on cotton canopy closure, weed control, and lint yield in two cultivars (‘DP117B2RF’, early maturity, hairy leaf; ‘DP164B2RF’, mid to full maturity, smooth leaf) under an irrigated environment. The experiment was conducted in a split–split plot arrangement of treatments in a randomized complete block design with row pattern as the main plot, cultivars as the subplot, and herbicide programs as the subsubplot. Cotton canopy closed 2 wk earlier in the twin-row pattern compared to the single-row pattern. Canopy closure was unaffected by cultivars and herbicide programs. Control of nine predominant weeds was sufficient (≥ 95%) to support cotton production. Total weed dry biomass was reduced by 35% in twin rows compared to the single-row pattern, 15% in DP117B2RF compared to DP164B2RF cultivar, and ≥ 97% with glyphosate early POST (EPOST), EPOST followed by (fb) mid-season POST (MPOST), EPOST fb MPOST fb late POST (LPOST) following PRE herbicides or three applications of glyphosate POST only without PRE herbicides compared to no herbicide. Cotton grown in twin-row pattern produced 6% higher lint yield than single-row cotton. Cultivar DP117B2RF produced 23% higher lint yield than cultivar DP164B2RF. Lint yields were higher with glyphosate EPOST fb MPOST, EPOST fb MPOST fb LPOST following PRE herbicides or three applications of glyphosate POST only without PRE herbicides (1,210 to 1,230 kg/ha) compared to glyphosate EPOST following PRE herbicides (1,130 kg/ha). These results demonstrated that cotton grown in twin-rows closed canopy early and produced higher lint yields than cotton grown in single-rows.

Evaluation of mulching, stale seedbed, hand weeding and hoeing for weed control in organic garden pea (Pisum sativum sub sp. Hortens L.)

Weeds are often recognized as the principal biotic constraint to organic crop production. Development of suitable weed control measures is, therefore, a prerequisite for profitable organic farming. A field experiment was conducted during the winter season of 2003–2004 and 2004–2005 in the Indian Himalayas to evaluate the effect of mulching, stale seedbed, hand weeding and hoeing on weeds and yield of organic garden pea (Pisum sativum sub sp. Hortens L.). The weed population ranged from 249–477 m−2, and Polygonum plebejum L. (34%), Melilotus indica L. (31%) and Avena ludoviciana Dur. (17%) were the predominant weeds in the experimental field. Season long weed-crop competition reduced the green pod yield of garden pea by 74% in 2003–2004 and 93% in 2004–2005. All the weed control treatments significantly reduced the population and biomass of weeds resulting in significant increase in green pod yield of garden pea compared to unweeded control. The highest weed control efficiency (84% reduction in weed biomass) was achieved with hand weeding 30 and 60 days after sowing (DAS) closely followed by stale seedbed coupled with one hand weeding (77%). Both these treatments produced significantly higher green pod yield compared to other treatments in both the years. In 2003–2004, hand weeding (30 and 60 DAS) recorded the highest gross margin (Indian Rupees 115,400 ha−1) closely followed by stale seedbed coupled with one hand weeding (Indian Rupees 109,700 ha−1). In the second year, however, the latter treatment gave the highest gross margin (Indian Rupees 56,900 ha−1) compared to other treatments.

Control de malezas en batata [Ipomoea batatas (L.) Lam.

Se establecieron experimentos de campo con batata en Juana Díaz y Gurabo, Puerto Rico, para determinar alternativas de control de malezas utilizando cubierta plástica y secuencias de herbicidas. Al mismo tiempo este experimento proveyó datos sobre eficacia y fitotoxicidad de dimethenamid en batata y sobre la fitotoxicidad de dimethenamid y clomazone en nuevas líneas de batata. Los tratamientos en el experimento de secuencia de herbicidas fueron 1) plástico y paraquat a la dosis de 0.56 kg ia/ha; 2) ametryn a 6 kg ia/ha y sethoxydim a 0.45 kg ia/ha; 3) clomazone a 1.12 kg ia/ha y sethoxydim a 0.45 kg ia/ha; 4) dimethenamid a 1.68 kg ia/ha y sethoxydim a 0.45 kg ia/ha; 5) clomazone a 1.12 kg ia/ha y clethodim a 0.11 kg ia/ha; y 6) clomazone a 1.12 kg ia/ha y clethodim a 0.22 kg ia/ha. Las malezas comunes fueron arrocino (Echinochloa colona) y coquí (Cyperus rotundus), bledo (Amaranthus dubius) y cohítre (Commelina diffusa). La interacción tratamiento de herbicidas por localidad fue significativa para el parámetro de rendimiento de batata. En Juana Díaz, el rendimiento de batata fue mayor que en Gurabo en todos los tratamientos, excepto en el de plástico seguido por paraquat. Cuando se utilizó dimethenamid seguido por sethoxydim, el rendimiento fue 9,614 kg/ha menor que cuando se utilizó clomazone seguido por sethoxydim. En Gurabo, no se observaron diferencias en densidad de malezas ni en el rendimiento de batata con los herbicidas evaluados. Dimethenamid controló las malezas igual que el tratamiento de clomazone y no hubo diferencias en rendimiento de batata en ninguno de los tratamientos de herbicidas. En el experimento de líneas de batata no se observó fitotoxicidad por los herbicidas en ninguna de las líneas evaluadas.

Tratamientos de herbicidas presiembra y postemergentes para el control de malezas en siembra directa y de trasplante de calabaza (Cucurbita moschata)

En 2000 y 2001 se realizaron dos experimentos de campo en la Estación Experimental Agrícola de Corozal, Puerto Rico, para evaluar cuatro tratamientos de herbicidas en siembra directa y de trasplante de calabaza [Cucurbita moschata Duchesne (Poir)] cv. Soler. Los tratamientos de herbicidas fueron 1) glifosato (1.75 L/ha) presiembra; 2) glifosato (1.75 L/ha, presiembra en secuencia con sethoxydim (0.31 kg ¡a/ha) postemergente de cinco a nueve semanas después de la siembra; 3) clomazone (0.50 kg ¡a/ha) presiembra; 4) mezcla de clomazone (0.50 kg ¡a/ha) + glifosato (1.75 L/ha) presiembra; y 5) control manual con azada. Las malezas predominantes en el área experimental fueron pendejuelo [Digitaría sanguinalis (L.) Scop.], arrocino [Echinochloa colona (L.) Link], leche vana (Euphorbia heterophylla L.), y quinino del pobre (Phyllanthus niruri L.). La densidad de gramíneas y el total de malezas fueron mayores en el 2000 que en el 2001, a las tres y seis semanas después de la siembra. Durante el 2000, la densidad de gramíneas y el total de malezas a las tres semanas fue menor con el uso de clomazone presiembra, solo o en mezclas con glifosato, que con el glifosato solo. No hubo diferencias significativas (P < 0.05) entre tratamientos de herbicidas para las densidades de malezas durante el 2001. El cultivo manual con azada fue más efectivo en reducir las gramíneas y el total de malezas que el glifosato solo como presiembra durante 2001. Las diferencias en el peso seco de malezas al final de la cosecha, así como las diferencias en los rendimientos de calabaza, no fueron significativas entre los tratamientos de herbicidas. En ambos años, la calabaza trasplantada produjo un rendimiento mayor que la calabaza de siembra directa, lo que indica que la calabaza trasplantada puede competir mejor con las bajas densidades de malezas (dos vs. 23 plantas por 0.5 m2) encontradas, dada la ventaja de las plántulas de establecerse antes que las malezas.

Controle de plantas daninhas na cultura do milho-pipoca com herbicidas aplicados em pós-emergência

Objetivou-se avaliar a eficiência de controle de plantas daninhas, a tolerância e a produção de milho-pipoca UFVM2 aos herbicidas atrazine (1.500 g ha-1), foramsulfuron + iodosulfuron methyl sodium + atrazine (15+1+1.500 e 30+2+1.500 g ha-1), foramsulfuron + iodosulfuron methyl sodium (15+1, 30+2, 45+3 e 60+4 g ha-1), nicosulfuron + atrazine (8+1.500 e 16+1.500 g ha-1) e nicosulfuron (16 g ha-1). A aplicação dos herbicidas foi realizada aos 25 dias após a emergência da cultura. As plantas daninhas predominantes na área foram Brachiaria plantaginea, Brachiaria decumbens e Ipomoea spp. Os herbicidas foramsulfuron + iodosulfuron methyl sodium, em todas as doses testadas, proporcionaram maiores índices de toxidez à cultura, aos 7, 14 e 28 dias após a aplicação dos tratamentos (DAA). Todas as combinações de herbicidas proporcionaram controle acima de 90% para B. plantaginea e B. decumbens, aos 28 DAA. O nicosulfuron aplicado isoladamente proporcionou controle de apenas 80% e o atrazine não controlou essas espécies daninhas. Para Ipomoea spp., nenhum tratamento herbicida proporcionou controle equivalente ao da testemunha capinada. A competição das plantas daninhas resultou em menores teores de clorofila total, N, P e K no tecido foliar das plantas de milho-pipoca e menor rendimento de grãos. Para o cultivar UFVM2, as sulfoniluréias isoladas ou associadas ao atrazine não afetaram o estado nutricional da cultura, o rendimento e a capacidade de expansão dos grãos de milho-pipoca.

Use of sicklepod, Senna obtusifolia (L.) Irwin and Barneby, as mulch interplant in cayenne pepper, Capsicum frutescens L., production

The suitability of sicklepod as mulch interplant to smother weeds in the crop interrows and generate mulch in situ in the production of cayenne pepper was investigated on the field in 1997 and 1998 at Ibadan in the dry rainforest of Nigeria. The Senna-interplant treatment was compared with plastic-, grass- and woodchip-mulched treatments, hand weeding control and unweeded control in a randomised complete block design using four replications. Pepper fruit yield from Senna-interplant was similar to those from plastic and grass mulch in 1997, but was significantly (P<0.05) lower in 1998. Uncontrolled weed growth reduced fruit yield by 73% and 78% in 1997 and 1998, respectively, compared to the mean fruit yield from all mulched treatments. Senna-interplant, plastic, grass and woodchip mulch treatments increased the fruit yield by 21%, 36%, 45%, and 11%, respectively, compared to the hand weeding unmulched treatment. Over the two years, the weed control efficiency of the Senna-interplant, plastic, grass and woodchip mulch, and hand weeding treatments relative to unweeded control treatment were 54%, 97%, 27%, 64%, and 88%, respectively. The afternoon temperature of the soil was reduced by the straw mulch types but increased by the plastic mulch. Soil moisture loss was less under all mulch types than in hand weeding and unweeded control treatments. The predominant weeds of the experimental area were Chromolaena odorata (L.) R.M. King & Robinson, Talinum fruticosum (L.) Juss, Synedrella nodiflora Gaertn and Laportea aestuans (L.) ex Miq with relative importance values 9.8%, 8.6%, 8.3%, and 6.3%, respectively. The weed dry weight, topsoil temperature and moisture depletion negatively correlated with the performance of the pepper plants.

Critical period of cropweed competition in rainy season sunflower (Heliunthus annuus)

A field study was carried out at the experimental farm of the Indian Agricultural Research Institute, New Delhi, to determine the critical period of cropLweed competition in sunflower (Helianthus annuus L.) during the rainy (kharif) seasons of 199 5 and 1996. Trianthema portulacastrum L., Digera arvensis Forsk, Acrachne racemosa Ohuy, .Dactyloctenium aegyptium Beauv. and Cyperus rotundus L. were the dominant weed species associated with the crop. Trianthema portulacastrum and Digera arvensis were the predominant weeds. Seed yield loss increased with the increase in the duration of competition and maximum loss (54.6%) occurred due to full season cqmpetition . Seed yield of , sunflower increased significantly with the increase in initial duration of weed free condition up to harvest. Critical period of weed competition was found to be 20 to 49 days after sowing.

Effect of methods of sowing and weed management on yield of chicory (Cichorium intybus)

A field experiment was conducted during Though the weed-management treat- winter season of 1992-93 to study the effect ments barring unweeded control did not dif- of methods of sowing and weed fer significantly among themselves: how- management on weed control and root yield ever, proved superior to the unweeded con- of chicory (Cichorium intybus L.) at Anand. trol for weed density (at 60 days). The dry The soil was loamy sand. Nine treatments weight of weeds was influenced significantly comprised 2 herbicides (trifluralin @ 0.5 by different treatments. Methods of sowing kglha and pendimethalin @ 0.5 kglha both treatments and 2 hand-weeding treatments as pre-emergence), 2 conventional weeding proved effective in reducing dry weight of treatments (hand-weeding at 30 days after weeds. Though the herbicides and 1 hand- sowing and 2 hand-weedings at 30 and 60 weeding treatments significantly reduced days), 2 methods of sowing (line sowing by the dry weight of weeds compared with the seed drill and shallow sowing through unweeded control, these did not show supe- furrow opened by kudali each at 20 and 30 riority to methods of sowing treatment and 2 cm width) along with unweeded control, hand-weedings (broadcast sown). Both the were tried in randomized block design with herbicides found more or less equally effec- 3 replications. Chicory cv. Rexor was tive in controlling Chenopodium album L., sown on 20 November 1992 and harvested Digitaria sanguinalis (L.) Scop. and on 17 April 1993. The crop was uniformly Eragrostis cilianenisis (All.) Link compared fertilized with 100 kg N + 50 kg P,O, + 50 the unweeded treatment. Both herbicides kg &amp;O/ha as basal application in the form significantly reduced the weed density com- of urea, single superphosphate and muriate pared with the unweeded control. Pate1 and of potash respectively. The crop was Upadhyay (1989) noted the effectiveness of irrigated 5 times during the crop season. pendimethalin in reducing the weed density Species-wise weed density was recorded throughout the growth period of chicory. using 0.25 m2 quadrate from randomly Significant differences were observed in selected 2 spots in a plot at 60 days. fresh as well as dry weight of chicory roots However, predominant weeds counted due to different treatments. Significantly separately. In hand-weeding, the count was highest yields of chicory (20,648 kg fresh taken just before the operation and and 4,750 kg dry rootslha) were recorded subsequently the dry weight was recorded. with 2 hand-weedings when compared wxth

Crop-weed competition in summer greengram (Plzaseolus mdiatus)

A field experiment was conducted during 1992 and 1993 to study the crop-weed competition in sununer greengram or mungbean (Phaseolus radiaius L.). Predominant weeds of the experimental field were Chicorium intybus. Cjlnodon daciyion (L.) Pers., Cyperus roiundus L. and Commelinn con~munis L. Grain yield of summer mungbean was reduced by 34.88% due to competition with weed during the first 30 days afler sowing which increased to 49.15% when weeds competed with the crop for the enlire crop season. Grain yield was increased when the initial weed-free duration was extended up to 45 days afler sowing and further increase in the duration of weed free had no beneficial effect on grain yield. Weed emergence afler 45 days afler souring was low and thus smothered by crop. The application of pendimethalin (I kgha) and clomazone (1 kg/ha) also increased grain yield significantly over weedy for first 30, 45 days afler souring and up to harvest. The initial 45 days perioctconsidered to be the critical period with respect to weed-crop competition in mungbean.

Efeitos de métodos e épocas de controle das plantas daninhas na cultura do milho

Com o objetivo de avaliar os efeitos de diferentes épocas de controle de plantas daninhas, realizado através de capina manual ou aplicação de herbicidas, sobre a produtividade e características agronômicas do milho, foi instalado um experimento na Fazenda Escola "Capão da Onça" (UEPG), em Ponta Grossa-PR, no sistema de plantio direto na palha. O delineamento experimental utilizado foi de blocos ao acaso, em esquema fatorial 2 x 5, com seis repetições. O híbrido utilizado foi XL 212, semeado no dia 11/11/97. Os herbicidas utilizados, com as respectivas épocas de aplicação, foram: atrazine (1400 + 1400 g/ha), aos 2 e 19 dias após a emergência (DAE); atrazine + nicosulfuron (1400 + 12 g/ha), aos 8 DAE; atrazine + nicosulfuron (1600 + 20 g/ha), aos 19 DAE; atrazine + nicosulfuron (1000 + 40 g/ha), aos 26 DAE e nicosulfuron (60 g/ha), aos 31 DAE. As capinas manuais foram efetuadas nestas mesmas épocas. As plantas daninhas predominantes foram Brachiaria plantaginea, Triticum aestivum, Raphanus raphanistrum, Galinsoga parviflora e Richardia brasiliensis. Observou-se que o atraso na época de controle das plantas daninhas, a partir de dez DAE, afetou negativamente as características das plantas avaliadas, mais acentuadamente para o controle com herbicidas. Exceto o peso de 100 grãos, os demais componentes da produção e a produtividade diminuíram com o atraso na época de controle a partir de dez DAE.

Controle de plantas daninhas na cultura da batata

O experimento foi conduzido na Fazenda Escola da UEPG, em Ponta Grossa-PR, em Latossolo Vermelho Escuro de textura média argilosa, com o objetivo de verificar a praticabilidade e a eficiência agronômica dos herbicidas metolachlor e metribuzin + metolachlor no controle de plantas daninhas na cultura da batata. O delineamento experimental foi de blocos ao acaso com nove tratamentos e quatro repetições, quais sejam: metolachlor (1,92; 2,88 e 3,84 kg i.a./ha); metribuzin + metolachlor (0,24 + 1,68; 0,36 + 2,52 e 0,48 + 3,36 kg i.a./ha); metribuzin (0,48 kg i.a./ha); testemunha capinada e testemunha sem capina. O plantio foi realizado em outubro/95 utilizando-se a cultivar Elvira, no espaçamento 0,70 x 0,35 m. As plantas daninhas predominantes foram Brachiaria plantaginea (capim-papuã), Digitaria horizontalis (capim-milhã) e Galinsoga parviflora (fazendeiro). As avaliações foram efetuadas aos 15, 30 e 45 dias após a aplicação dos tratamentos onde verificou-se que foram eficientes os seguintes herbicidas: metolachlor no controle sobre capim-papuã e capim-milhã nas doses de 2,88 e 3,84 kg i.a./ha; a mistura metribuzin + metolachlor no controle sobre capim-papuã e capim-milhã nas doses 0,36 + 2,52 e 0,48 + 3,36 kg i.a./ha; metolachlor (1,92; 2,88 e 3,84 kg i.a./ha) e metribuzin + metolachlor (0,24 + 1,68; 0,36 + 2,52 e 0,48 + 3,36 kg i.a./ha) no controle sobre fazendeiro. Não foram observados efeitos fitotóxicos dos produtos sobre as plantas de batata.

Effects of Preemergence Herbicides on Weed Control and Yield and Vase Life of Leatherleaf Fern

Six preemergence herbicides were applied twice a year at 1x and 2x rates for 2 years to leatherleaf fern [Rumohra adiantiformis (Forst.) Ching] starting from the time of rhizome planting. Predominant weeds present were Cardimine hirsuta, Erechrites hieracifolia, Oxalis stricta, and Phyllanthus tenellus. All herbicides, except pendimethalin and oxadiazon at the 1x rates, reduced weed biomass by 60% to 99% compared to the unweeded control during the fern bed establishment phase (year 1). During that period, hand-weeding times were reduced (51% to 95%) by prodiamine and dithiopyr at both rates, and oxadiazon and pendimethalin at 2x rates. During year 2, herbicides were of greatly reduced benefit due to reduced weed growth caused by the increasingly competitive fern. After 2 years, only 2x dithiopyr-treated plots had reduced yields compared to the hand-weeded controls. Herbicide treatments had no detrimental effects on frond postharvest longevity. In fact, fronds harvested from the 1x isoxaben-treated plots exhibited increased vase life compared to the controls.

Effects of various hand-weeding programmes on yield and components of yield of sweet potato (Ipomoea batatas) grown in the tropical lowlands of Papua New Guinea

SUMMARYThe effects of weed competition, harvest date and cultivar on sweet potato (Ipomoea batatas(L.) Lam.) yield and components of yield were investigated in three factorial experiments planted during the wet seasons of 1984 (Expt 1) and 1986 (Expts 2 and 3) in the tropical lowlands In Expts 1 and 2, the commencement of regular hand-weeding (every 14 days) was delayed for varying lengths of time following planting. In Expt 3, the duration of hand-weeding from planting onwards was varied. The main competing weed species following planting were Cyperus rotundus, C. brevifolius, Euphorbia geniculata and Portulaca oleracea. After canopy closure, E. hirta, Imperata cylindrica, Eleusine indica, Sida rhombifolia, Mollugo pentaphylla and Mimosa invisa were the predominant weeds to emerge and persist. Cultivars differed in their sensitivity to weed competition. In L431 both mean marketable root tuber weight and number of tubers/plant were severely reduced. However, in L44, tuber number was more sensitive than tuber weight: marketable tuber weight was significantly reduced only by prolonged weed competition (no weeding until 56 days after planting (DAP)). In Expts 1 and 2, delaying the commencement of weeding beyond 14 DAP significantly decreased vine weight, total yield and mean number of tubers/plant. In Expt 3, prolonging regular weeding until 14 DAP and longer significantly increased total and marketable tuber yield and mean number of tubers/plant.Effects of weed competition in the early part of the season during the first 28–42 DAP substantially reduced crop production in the later part of the growth cycle (after 110 DAP). This was probably due to a partial suppression of vine growth early on, which reduced tuberous root initiation and thus limited the number of root tubers that could develop in the later stages of crop growth. Hand-weeding during the period 28–42 DAP also appeared to have a detrimental effect on tuber initiation as a result of mechanical root disturbance at this sensitive period of root differentiation. There was also a trend towards lower yields when the crop was regularly hand-weeded after 56 DAP, probably due to disturbance of the vine canopy.The critical period for weed competition commenced at or before 14 DAP, possibly as early as 7 DAP, and did not continue beyond 56 DAP. In order to avoid weed competition and the detrimental mechanical effects of hand-weeding, an optimum hand-weeding programme for sweet potato in the tropical lowlands of will probably involve (i) keeping the crop weedfree for the first 14–21 DAP; (ii) no crop disturbance during the period of maximum tuberous root initiation (from c. 21–28 DAP until 42–56 DAP); (iii) clean weeding at c. 56 DAP; and (iv) minimal or no weeding after 56 DAP. Weeding during the period 7–14 DAP is particularly important.

Weed Control in a Conservation Tillage Rotation in the Texas Blacklands

A field experiment was conducted to evaluate weed control systems in a conservation tillage rotation of grain sorghum [Sorghum bicolor(L.) Moench.] – cotton (Gossypium hirsutumL.) – wheat (Triticum aestivumL.). Herbicide systems included fall and spring/summer inputs of high and low intensity. Tillage regimes were no-till (NT) and reduced-till (RT) systems; the latter included fall primary tillage followed by spring stale seedbed planting. Both tillage systems utilized controlled traffic lanes and wide, raised beds. Effective johnsongrass [Sorghum halepense(L.) Pers. # SORHA] control required intense herbicide inputs at one or both application periods, i.e., in the fall and/or spring/summer. Grain sorghum and cotton yields for the most intense weed control system, which included high inputs in both the fall and spring/summer, were not superior to systems that included high inputs in only one of the two application periods. Seedling johnsongrass emergence occurred before spring planting in RT (but not in NT) in 2 of 3 yr, and control measures were ineffective. After 3 yr, the predominant weeds were johnsongrass and browntop panicum (Panicum fasciculatumSw. # PANFA).