Explanation:

Weeds posses one or more of the following:

abundant seed production; rapid population establishment; seed dormancy;
Weeds are troublesome in many ways. Primarily, they reduce crop yield by competing for water, light, soil nutrients, and space. Other problems associated with weeds in agriculture include:
reduced crop quality by contaminating the commodity; interference with harvest;
serve as hosts for crop diseases or provide shelter for insects to overwinter; limit the choice of crop rotation sequences and cultural practices; and
production of chemical substances which are toxic to crop plants (allelopathy), animals, or humans