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WEEDS

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A weed may be defined as a plant growing where it is not wanted. It means that any plant including a crop plant

may be classified as a weed in certain situations. Host people, howaver, do not cccoidor crop plants to be veeds, regardless of where they are found growing. To most of.. them a weed is a troublesome, wild plant that has inva­ded their fields. Whethor crop plants shou3d be called weeds would dopend largely.on how objectionable they ac­tually are. For example, barley growing in a field of oats that is to be U36d as feed for livestock cculd hard­ly be considered a weed because it ic not objectionable under such conditions. On the contrary, if the same field cf oats is being grown for seed, the mixture would be un­desirable because considerable time and labour Tould be " required in removing the barley seed. In this cat barley would undoubtedly be considered a weed.

Weeds in field crops are objectionable and harmful for a variety of reasons. They reduca the yields of crops as well as their quality. There are weeds which are knosn to be poisonous both to livestock and man. One should also remember that some weed species serve as host plants for certain insects and diseases that attack crops. They may thus act as sources of infection for farm crops.

The adverse effect of weeds on crop production is mainly associated with the decreased economic return from the land. Estimates show that weeds are responsible for an overall reduction of somewhat тоге than 'iO percent in the yield of the major world crops, representing; huge annvO- loss of good supplies, bluch of this loss occure because weeds deprive the crop of water, mineral nutri-

ents and'light which would otherwise he available and so prevent it from producing high yields.

The extent to which yields may be reduced as a result of competition caused by weeds varies greatly. It depends on the competitive ability of the crop grown, on the type of weeds present, on the degree of infestation and on the season the crop is sown or planted at.

There exist different methods of controlling weeds in farm crops. The oldest but still common method is be­ll jved to 00 early and frequent cultivation of the land tfith different types of cultivators and harrows. These implements can be used to advantage in weedy fields of

row crops such as com, potatoes, soybeans, sugar beets, 'cad boons. Crop rotation is another valuable aid in dest­roying weeds since many of thu.i are associated with cer­tain crops. That is why the Dumber of weeds increases,, provided a crop is continuously grown on the same land. Ihej control of weeds through the use o:? chemical herbici­des has expanded considerably. For a herbicide to be ef­fective it should be used at a certain stage of the crop growth when it produces the least or no injury to the crop the rate and method of applying the herbicide being of great importance ай well.

1) prevent... from producing - мешают... производить;

2) to advantage - выгодно.

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