The Biological Control of Weeds by Introduced Natural Enemies

Abstract

Man’s activities on this planet have given rise to a variety of problems— not the least of which stem from his intentional or accidental spread of plants which subsequently become “weeds.” In the United States the losses caused by alien and native weeds are believed to equal the combined losses from insects and diseases and to rank second only to those caused by soil erosion (Saunders et al., in King, 1966). For the decade ending in 1960, this meant an annual loss of $5.1 billion (U.S. Dept. of Agr., 1965). Cultural and chemical control practices currently are the main approaches to weed control. Both methods are aimed at removing unwanted plants and reducing real and suspected damage as quickly as possible, a short term approach requiring considerable annual expenditures of resources and energies, yet affording only temporary relief, not lasting weed control. The ever-increasing recognition given to weeds as pests and the concomittant increases in expenditures for their control, have focused attention on the need for effective, low-cost, and long-lasting alternative control methods. Biological control provides one such alternative. Although the natural mortality factors in the environment of a weed have long been considered of prime importance in limiting such a plant’s distribution and abundance, their practical use has not been exploited. Many of our introduced weeds are probably as abundant as they are primarily because the natural enemies that attack them in their native lands are not found in their new home areas. Thus, these natural control factors can be augmented through the classic biological control method of importing the enemies of such weeds. This approach has received little serious consideration by those currently charged with developing and instituting weed control programs.