Text B. WHY HERBICIDES DON'T ALWAYS WORK

Дата добавления: 2014-11-12; просмотров: 600

1. Chemical weed control is important in growing many crops to get high yields, but herbicides don't always work. There are some reasons for this.

2. Weed control with chemicals is affected by things that can be arranged into three groups: selection, application and environment¹.

3. Selecting the proper chemical to control the weeds that are present is probably one of the most important things. To do this properly one should know specific weed species that are found or are likely to be found in the crop grown. Then one should choose the herbicide or a mixture of herbicides, to control those weeds.

4. Improper application is another common reason for herbicide failure². Properly working machines for the application of the herbicides, the right rate per acre and good timing are the things that must be paid attention to minimize the possibility of failure.

5. A pre-emergence herbicide must be placed evenly³ on the surface of the soil. For the chemical to move into the germination zone of the weeds, rainfall is required within seven to ten days after application.

6. Some herbicides are volatile⁴. They must be incorporated⁵ into the soil just after spraying. If this is not done the herbicide effectiveness will be reduced.

7. Post-emergence herbicides should be applied after the weeds come up.

8. Growers should carefully prepare the machines for the application of the herbicides. If they use some herbicides at a time⁶, the chemicals must be mixed thoroughly.

9. The right rate of chemical application per acre is also very important. Applying too low rates of the chemical may allow weeds to grow. Too high rates can cause the injury⁷ of the growing crop.

10. Timing of the application is another factor of herbicide effectiveness. Some must be applied about ten weeks before planting, while others should be applied two weeks before planting.

11. Environmental conditions affecting herbicide effectiveness cannot usually be controlled, but information about them can be helpful.

12. As has already been said rainfall is necessary for the action of pre-emergence surface-applied herbicides.

13. Strong winds may cause uneven herbicide spraying. With volatile herbicides winds and high temperatures may cause a loss of the chemical.

14. Soil structure, moisture and organic matter content also affect the effectiveness of the herbicides.

15. Weed species, stage of growth and life cycle must also be taken into consideration in applying the herbicides. Young weeds, for instance, are easier to control than old ones. Biennial weeds are easier controlled in the rosette stage⁸ than in the seed-formation stage while perennial weeds are usually controlled in the seedling stage before the extensive root system is developed.

Notes and commentaries:

¹environment– навколишнє середовище ²failure– неуспіх, невдача ³evenly– рівномірно ⁴volatile– летючий ⁵to incorporate– вносити (добрива) ⁶at a time-одночасно, за один раз ⁷injury– шкода, пошкодження ⁸rosette stage– стадія розетки (розпластане прикореневе листя)

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