A gardener finds

To get rid of the weeds efficiently, it can be selectively killed using plant growth hormone regulator called auxins.

Dicot weeds grow by apical shoot meristem growth whereas the grasses usually have the presence of intercalary meristems. When plant growth hormones like auxins is applied, it causes damaging effect on the shoot meristem thus destroying the dicot weeds and has no effect on the lateral meristem keeping grasses intact without a damaging effect. Hence the weeds are selectively destroyed.