Contact - a weed-killer that kills only that part of the plant from which it comes into contact;

Residual - a weed-killer that is applied to the soil where it persists for some time, killing weeds as they germinate;

Selective - a weed-killer which, used correctly, causes no injury to the crop or no injury of any economic importance;

Total - non-selective weed-killer. A weed-killer which is used to kill all vegetation as opposed to one used selectively;

Translocated - a weed-killer which is absorbed by the plant and moves about within the plant before killing it.

Hormone - a weed-killer that is similar to substances produced naturally by the plant which regulate the growth of the plant;