Repetition

The effect of a pesticide application is usually lost quite quickly, and the pesticide must then be applied again. Most crop protection chemicals have to be re-applied every 10-20 days, but some have to be applied more frequently. This is partly because the pesticide tends to be washed off in rain, partly because it is nonpersistent (i.e., it decomposes, preferably into harmless byproducts and residues), and partly because the new parts of rapidly growing plants require protection. In comparison, vertical resistance usually lasts for several years, and horizontal resistance lasts for ever.

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