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Wednesday, May 25, 2005

Challenges and Opportunities for Integrated Weed Management

Resume of Paper: Challenges and opportunities for integrated weed management (Buhler, D. D. 2002, Weed Science 50:273-280)

Integrated weed management emphasizes combination of technique and knowledge that consider the cause of weed problems rather than react to problems after they occur. Weed management is more than control of existing weed problems and places greater emphasis on preventing weed reproduction, reducing weed emergence after planting, and minimize weed competition with the crop.

IWM considers how the complex biological interaction between weed and cropping practice can be exploited in weed management system. IWM system is to create cropping systems unfavorable for weeds and to minimize the effect of the weed that survive. Elements of IWM system are as follows:

Prevention. IWM will most successfully in situations in which humans are the vector or have direct control over the seed source through community action. Seed purity and noxious weed laws are examples of successful weed prevention programs.

Thresholds and weed management. The economic threshold is most commonly described and is defined as the weed density at which the cost of control equals the value of the crops that would be lost due to interference if the weeds were left in the field. At weed densities below the economic threshold, it is recommended that weeds be left in the field because net return would be higher than if they were controlled.

Interactions of weeds with other pests. It is an important element of IWM, in recent review of insect-weed interaction there were 3 type of mechanism for interaction (a) trophic relationships, in which weed act as a food source for insect pest or predator (b) habitat alterations by the weed that increase or suppress insect infestations, and (c) Change in non target pest population due to control tactics.

Crop rotation. Rotation is an integrative practice that combines differences in planting dates and growth period, till age practice, life cycles, competitive characteristics, and weed control practices to disturb regeneration niches of weed species and prevent the buildup of adapted weed species.

Intercropping. Competitive suppression of weed can take a very different from with intercropping than in crop monocultures. Increasing the complexity of a cropping system by interplanting species of differing growth forms, phenologies, and physiologies can create different patterns of resource availability, especially light to weeds.

Crop competitiveness. Enhancing the ability of a crop to compete with weed can be accomplished by providing the best possible environment for crop growth combined with practices that reduce the density and vigor of weeds. Practices such as narrow row spacing, increased plan density, appropriate time planting, and fertility management are capable of shifting the competitive balance to favor crops over weeds.

Cover and smother crops. The goal is to replace an unmanageable wed population with manageable cover crop. Two major type of cover crop that can be used for weed control: (a) of season cover crops, to produce sufficient plan residue or allelochemicals to create an unfavorable environment for weed seed germination and establishment and , (b) smother crop ( a cover crop grown during part or all of the cropping season), to displace weeds from the harvested crop through resource competition.

Tillage and cultivation. Tillage for seed bed preparation can reduce densities of annual weed population, especially if planting is delayed to allow weed seed germination prior to final seed bed preparation and cultivation between rows can provide weed control as well.

Fertility management. The effect of weed may be reducing by management strategies that maximize nutrient uptake by crops and minimize nutrient availability to weeds.

Organic amendments and the concept of weed suppressive soils. In addition to enhancing soil properties, organic amendments of soils may effect weed seed survival, emergence, growth, and reproduction. Because germination and early growth of many weed species are strongly dependent on soil nutrient concentration. The concept of "Weed suppressive soils" suggested possible farming practise which the microbiology community composition and activity are altered to deplete the weed seed bank, reduce probabilities of weed seedling establishment, and reduce weed growth and competitive ability. It suggested that this might be accomplished by managing residue and microbial activity to increase seed decay potential within the residue zone.

Edaphic factors, weed patchiness, and site specific management. Pay attention on association between soil properties and weed species abundance in the field also important in seed management. Variations in the associations over years were substantial and were attributed to differences in agronomic practise, weed control practise and environmental variation from time to time. One way to deal with weed patchines is to develop methods to detect or map weed and use that information to direct herbicide application spatially. Principles of weed management and biology will need to be applied more precisely, as much attention will need to be given to where control practice are applied as to what applied and when it is applied.