Literature on the effectiveness of grazing animals (especially cattle, goats, and sheep) in controlling weeds is reviewed. Availability of animals and the ability to fence them onto or off weed infestations are essential. Weeds of pastures are the most suitable subjects for control, although weeds of arable crops, forestry, and waste places are sometimes amenable to control by grazing animals. Although grazing animals themselves often cause weed problems in pasture, adjusting grazing timing or intensity or both can sometimes redress the balance. Increasing sheep or cattle stocking rates prevents animals from grazing selectively and can help control some weeds. Adjusting grazing pressure can also improve the growth of desirable pasture species so that these are more competitive and able to resist invasion of annual or biennial weeds. Introducing a different class of stock, like sheep into a cattle system or goats into a sheep system can control many weeds. Goats are capable of browsing on and controlling spiny or poisonous brush weeds, including gorse and poison ivy, without suffering adverse effects. Examples are given of the use of grazing animals for weed control in crops and forestry.

Literature concerning interactions between herbicides and insects is reviewed. Herbicides can be toxic to insects or can affect them indirectly, such as by destroying food supplies, but they usually can be used with proper application timing without affecting insects adversely. Herbicides and biocontrol insects can interact either favorably or unfavorably depending on the life cycle stage of weed and insect, effect on predatory insects, changes in food quality, mobility of the biocontrol insect, and impact of herbicides on weed growth. Thus, interactions between a biocontrol insect and herbicide can be antagonistic, additive, complementary, or synergistic. Split-plot techniques to evaluate these interactions at an early stage of insect establishment are proposed to improve weed biocontrol.