Chemical Weed Management Research Articles

Effect of weed-management practices on yield and economics of sesame (Sesamum indicum)-based intercropping systems

The present investigation was conducted during the rainy (kharif) season of 2015 and 2016 at Kanpur, Uttar Pradesh, to study the effect of weed management on yield and economics of sesame (Sesamum indicum L.)- based intercropping system. The experiment comprising 12 treatments was laid out in a factorial randomized block design, replicated 4 times. Sesame + blackgram [Vigna mungo (L.) Hepper] intercropping system in 8 : 2 ra- tio (7.17) had the lowest weed population during both the years and on an average, recorded significantly lowest fresh (11.01) and dry weight (3.71) of weeds. The grain yield of sesame was found significantly in the sesame + blackgram (8 : 2) intercropping system during 2015 and 2016. The grain yield of maize (Zea mays L.) and blackgram was maximum in sesame + maize/blackgram under 8 : 2 row ratio and reduced drastically in intercrop- ping sesame + maize and blackgram under 4 : 1 ratio in the 2 years of study. The sesame-equivalent yield was significantly higher under intercropping of sesame + blackgram (8 : 2) over rest of the intercropping treatments. The sesame + blackgram (8 : 2) intercropping treatment was found significantly superior in terms of economics, viz. gross income ( 48.80 103/ha), net returns ( 26.82 103/ha) and benefit: cost ratio (2.22) on mean basis compared to the remaining intercropping systems, during both years. Among the weed-management practices, hand-weeding reduced the total weeds significantly compared to chemical weed-management practices, followed by alachlor (0.375 kg/ha) and pendimethalin (1.0 kg/ha) respectively. Significant reduction in fresh and dry weight of weeds/m2 was recorded with the hand-weeding. Among the chemical weed-management practices, alachlor treatment resulted in significantly lower fresh and dry-weight of weeds/m2 compared to pendimethalin treatment in both the years. The hand-weeding had a positive effect on grain of sesame with maize and blackgram, sesame equivalent yield, gross income, net income and B: C ratio, which was noted significant response over pendimethalin and alachlor weeding in both years of study. In chemical weed management, post-emergence appliciton of alachlor was found significantly superior over pre-emergence pendimethalin in the 2 years of study.

Herbicide resistant rice (Oryza sativa L.): Global implications for weedy rice and weed management*

SummaryRice cultivars resistant to broad‐spectrum herbicides have been developed and their commercial release is imminent, especially for imidazolinone and glufosinate resistant varieties in the USA and Latin America. Glyphosate‐resistant rice should follow within a few years. Rice growers throughout the world could benefit from the introduction of herbicide‐resistant rice cultivars that would allow in‐crop, selective control of weedy Oryza species. Other perceived benefits are the possibility to control ‘hard‐to‐kill’ weed species and weed populations that have already evolved resistance to herbicides currently used in rice production, especially those of the Echinochloa species complex. Weed management could also be improved by more efficient post‐emergence control. Introduction of herbicide resistant rice could also bring areas heavily infested with weedy rice that have been abandoned back to rice production, allow longer term crop rotations, reduce consumption of fossil fuels, promote the replacement of traditional chemicals by more environmentally benign products, and provide more rice grain without adding new land to production. There are also concerns, however, about the impact of releasing herbicide‐resistant rice on weed problems. Of most concern is the possibility of rapid transfer of the resistance trait to compatible weedy Oryza species. Development of such herbicide resistant weedy rice populations would substantially limit the chemical weed management options for farmers. Herbicide‐resistant rice volunteers also could become problematic, and added selection pressure to weed populations could aggravate already serious weed resistance problems. Because of the risk of weedy Oryza species becoming resistant to broad‐spectrum herbicides, mitigating measures to prevent gene flow, eventually attainable by both conventional breeding and molecular genetics, have been proposed. With commercialisation of the first herbicide resistant varieties planned for 2001, these mitigating measures will not be available for use with this first generation of herbicide resistant rice products. Release of herbicide resistant rice should depend on a thorough risk assessment especially in areas infested with con‐specific weedy rice or intercrossing weedy Oryza species. Regulators will have to balance risks and benefits based on local needs and conditions before allowing commercialisation of herbicide‐resistant rice varieties. If accepted, these varieties should be considered as components of integrated weed management, and a rational herbicide use and weedy rice control should be promoted to prevent losing this novel tool.

The effects of chemical pest, disease and weed management practices on the trophic structure of nematode populations in tomato agroecosystems

We assessed the responses of nematode communities to mixtures of insecticides, fungicides and herbicides in a tomato ( Lycopersicon esculentum L.) field experiment. The treatments were: (i) full spectrum of recommended pesticides; including insecticides (carbaryl, endosulfan and esfenvalerate) a fungicide (chlorothalonil) and herbicides (trifluralin and paraquat); (ii) only insecticides; based on applications of the same insecticides and similar doses to the full spectrum treatment; (iii) only fungicides and herbicides; based on similar fungicide and herbicide applications and doses to the full spectrum pesticide use treatment; (iv) control plots which received no pesticide applications. Nematode populations were separated into plant parasites, bacterivores, fungivores, omnivores and predators. The temporal community dynamics of different nematode trophic groups differed with the pesticide applications. Plant-parasitic nematode populations were much higher in the full spectrum pesticide-treated and in the insecticide-treated plots than in control plots. Fungivorous nematode populations were affected adversely by all treatments. Bacterivorous nematode populations were lowest in the full spectrum pesticide-treated plots and the fungicide- and herbicide-treated plots. Predatory nematode populations were lower in the full spectrum pesticide-treated plots than in the control plots.

Role of economic analysis in the evaluation of new dryland technologies

AbstractAn evaluation of agricultural systems often involves multidisciplinary teams that include crop scientists, animal scientists, soil scientists, pest control specialists, agricultural economists, and others. Agricultural economists can improve the technical quality and comprehe nsiveness of agricultural systems research in six major areas: budgeting and investment analyses; whole-farm and institutional factors; risk considerations; aggregate effects on crop and livestock prices; society-wide welfare effects of technical or policy changes; and economic values of environmental and other nonmarket effects. Economic analysis has been part of several successful multidisciplinary research efforts in the United States Pacific Northwest. These have covered soil conservation, integrated pest management, sustainable agriculture, crop rotation choice, and beef ranch management. As an example of institutional influences on economic outcomes, one study showed that the structure and selectivity of United States commodity programs have favored conventional over low-input rotations. Regarding risk management, an appropriate “package system” including conservation tillage, a diversified crop rotation, and adequate chemical weed management was shown both to sustain profitability and to reduce income fluctuations. Properly designed economic analysis can make similar contributions to identifying successful dryl and agricultural technologies throughout the world.

THE USE OF INTERPLANTED COVER CROPS FOR PEST MANAGEMENT IN STRAWBERRIES

Non-chemical methods for weed management are becoming important as fewer herbicides are labelled for use and as the market demands pesticide-free produce. We have studied the use of interplanted cover crops in strawberry plantings as an alternative/supplement to chemical weed management. Several different cover crops (tall fescue, marigold and sudangrass) were seeded between rows of newly planted strawberries in late June as runnering was commencing. An additional seeding of sudangrass was made in late July. For comparison, untreated plots and diphenamid treated plots were included in the experimental design. Measurements were taken throughout the season of soil moisture, light levels, crop nutrient concentrations, nematode numbers in soil and crop roots, runner biomass, and weed composition and biomass. Cover crops were incorporated in late fall and the planting was mulched. The following spring, crop nutrient concentrations, nematode numbers in soil and crop roots, weed composition and biomass, yield, individual fruit size, and aboveground strawberry biomass was assessed. The marigolds were too competitive for moisture to be an effective companion cover crop. The early planting of sudangrass was too tall, and fescue was too competitive for nutrients. The untreated plots contained many more weeds than other treatments, nematode levels were higher in the strawberry roots in these plots, and harvesting fruit was very difficult. The late seeding of sudangrass, however, provided significant weed control while not reducing yield relative to herbicide-treated plots.