Competitive crop

Nonchemical or traditional practices, such as weed seed removal, optimal crop seeding rates, crop selection, enhanced crop competitiveness, crop rotation, and mechanical weed control are all important components of an effective weed management program (458,459). In the context of modern intensive chemical herbicide appHcation, nonchemical practices may even represent an innovative approach to weed management and should receive careful consideration. 

Pyrethrins, extracted from the pyre thru in flower (Chrystinrhemum cinerariae-folium), are good knockdown and kill agents against a variety of insects. Supply has been traditionally rather erraiic because of climatic conditions and competition crops. Pyrethmm extract is also relatively expensive, and so searches for alternatives or diluents have been necessary. 

Grass weeds are very difficult to control in the oat crop. Few chemicals are recommended for grass weed control. It is preferable to grow oats where there is no black-grass or wild oat problem. Oats are, however, a very competitive crop against weeds (see Tables 13.6 and 13.7). 

Rye is a very competitive crop with good disease resistance so inputs tend to be lower than for other cereals. A limited range of grass and broad-leaved hetbicides is available (Table 13.6 and Table 13.7) there are a few chemicals with EAMUs in rye. Because rye is tall and often weak-strawed, a growth regulator is required, e.g. ehlormequat (GS 30-31) or trinexapac-ethyl at GS 30-32 or 2-chloroethyl phosphonie acid at late stem extension. 

It is a very competitive crop, though herbicides are still required. There are more restrictions on the nse of some grass weed herbicides in triticale than with the wheat crop. Several broad-leaved weed herbicides are recommended and some have EAMUs in triticale (see Tables 13.6 and 13.7). 

Potatoes are a veiy competitive crop once they meet across the rows, but early weed emergence, which is not controlled, can reduce yields. Weeds can also affect potato quality and ease of harvesting. 

The coconut is a very versatile crop which requires little care. Every part of the coconut pahn is used, and it produces a range of valuable products, many of which contribute to health maintenance and improvement. The coconut industry is founded on producing coconut oil and was the foundation of vegetable oil production for importation by developing industrial economies until other competitive crops entered the market for edible oils. Industrial uses include separation of fatty acids and glycerol, soap production, cosmetics, detergent and biofuels. A recent focus has been on the key nutritional benefits of coconut oil for human health (Fife, 2003). 

Production of nitric phosphates is not expected to expand rapidly ia the near future because the primary phosphate exporters, especially ia North Africa and the United States, have moved to ship upgraded materials, wet-process acid, and ammonium phosphates, ia preference to phosphate rock. The abundant supply of these materials should keep suppHers ia a strong competitive position for at least the short-range future. Moreover, the developiag countries, where nitric phosphates would seem to be appealing for most crops except rice, have already strongly committed to production of urea, a material that blends compatibly with sulfur-based phosphates but not with nitrates. 

What will happen under field conditions is, however, highly uncertain. Laboratory experiments have been conducted under conditions of abundant nutrients and water, ideal temperatures, and no competition among experimental plants. Such conditions are rare in the field. The best prediction is that, whereas increases similar to those found in the laboratory are unlikely under field conditions, increased concentrations of CO2 are likely to ameliorate to some extent the detrimental effects of climate change. However, field-scale experiments under a variety of soils and climates and with several crop plants are needed to provide information on effects of climate change accompanied by higher concentrations of CO2 on agricultural productivity. 

In organic systems the number of hours of hand weeding needs to be reduced, as labour, particularly in the developed countries, is expensive. This can be achieved by competition, the timing of cultivations, adaptation of the rotation nutrient management system and by crop density (Kropff, et al., 2000). Barberi, et al. (2002) experimented with a system of soil disinfection using hot steam to sterilise weed seeds. 

Weeds directly compete with the crop for water, nutrients, light and other growth factors. Competition for water begins when root systems overlap as they absorb water and nutrients (3). Competition for water depends on the rate and completeness with which a plant utilizes the soil water supply (4). Competition for water usually occurs with other forms of competition. For example, competition between weeds and peas (Pisum spp.) centered on light and water depending on weed height (5). 

Estimated Crop Losses from Weed Competition... 

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