Biological Control of Rangeland Weeds

Abstract

Weedy forbs and brush cost America's range managers at least $1.7 billion/year. Biological controls, or "the planned use of living organisms to reduce the vigor, reproductive capacity, density, or effect of weeds," should be considered and included in pragmatic integrated weed management systems for rangelands. Various approaches to biocontrol under that definition are discussed. These include foreign exploration and introduction of exotic insects, notes, and plant pathogens as biocontrol agents; augmentation of native biocontrol agents, especially plant pathogens; grazing systems; and positive and aversion conditioning for various classes of livestock to use against troublesome weeds or brush or to avoid palatable poisonous weeds. USDA's Agricultural Research Service has at least nine laboratories, worldwide, devoted to research on various aspects of biocontrol of exotic and native rangeland weeds. The usual goal of biocontrol is to improve ecological systems by using biotic agents to restore target plant species to lesser competitive intensities or to negate their effects so that they do not overwhelm plant communities or cause damage to livestock. The usual results of biocontrol are: improved agricultural production, improved ecosystem functions and status in terms of species richness and diversity of plant and animal communities, and improved protection of rare species. Regardless of whether target weeds are introduced or native, researchers must make balanced evaluations of risks, benefits, and the potential for success in developing biological control programs.

Ecological effects of selected invasive plants and their nature based management approaches

“…Prior to late 1800's only mechanical control of weeds was used in agriculture (Bell, 2015) but for over years, weed control mechanisms such as biological control and Integrated Pest Management (IPM) have been recommended to complement the traditional control methods for improved performance (Altieri, 1994). Among the goals of biological control of weeds are to improve ecosystems by using living organisms and to manage target weedy plants to lesser competitive intensities so that they do not stress native plant communities or cause damage to livestock (Quimby et al, 1991).…”

“…According to Quimby et al (1991), livestock's differential grazing habits, preferences and selectiveness for instance, as a biological control, allows for selective grazing pressure on palatable problematic weeds which might result into effective control. While in PRs, maintenance of biodiversity through ecological friendly methods is crucial, IPM might represent an important sustainable weed control tool.…”

“…The most imminent shortfall of mechanical control of weeds is that, most invasive seeds remains in the soil, hence, posing a risk of future invasions (Personal observation). One of the major challenge over biological control of weeds have been a rising concern on the potential damage to both threatened and endangered native forage plants closely related to a targeted weedy plant (Turner, 1985in Quimby et al, 1991. Although to date there is no known intentional introduction of weed biological control agent that has caused harm to any known endangered plant (Quimby et al, 1991), the potential is imminent (Turner, 1985in Quimby et al, 1991.…”

“…One of the major challenge over biological control of weeds have been a rising concern on the potential damage to both threatened and endangered native forage plants closely related to a targeted weedy plant (Turner, 1985in Quimby et al, 1991. Although to date there is no known intentional introduction of weed biological control agent that has caused harm to any known endangered plant (Quimby et al, 1991), the potential is imminent (Turner, 1985in Quimby et al, 1991. Therefore, care must be observed to introduce biological agents that will provide the greatest benefit with the least risk of harming the receiving community.…”

“…Recently, there have been an increasing concern on the use of weed control mechanisms such as biological control and Integrated Pest Management (IPM) as complements to the traditional control methods for improved performance (Altieri, 1994). Although biological control of weeds have raised a concern due to its potential damage to untargeted native forage plants and plants closely related to a targeted weedy plant (Turner, 1985in Quimby et al, 1991, to date there is no known intentional introduction of weed biological control agent that has caused harm to any known native forage plant (Quimby et al, 1991). Therefore utilizing two forage plants; Cynodon dactylon and Desmodium species presents environmentally friendly methods for the management of both T. minuta and G. cordifolia.…”