Photo: Lamb's-Quarters in Southwestern Montana. © 2020 Delena Norris-Tull
Vertebrates as Biocontrol Agents
Summaries of the research and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, July 2020.
Within this website, in the section on Innovative Solutions, refer to the research on, and recent uses of grazing animals, including both livestock and bison, to control noxious weeds.
Fish as Biocontrol Agents
In 1963, researchers at Auburn University and the US Bureau of Sport Fisheries and Wildlife Fish Experiment Station, in Arkansas, received permission to import grass carp, to conduct experiments on its potential to control aquatic weeds, especially hydrilla. Grass carp is an herbivorous fish from eastern Russia and China (Biss, 2018). The research team determined that grass carp would eat several times its weight in aquatic weeds. The fish ate large enough quantities to warrant a very controlled introduction into Florida. From 1970 to 1984, grass carp were cautiously introduced in various Florida locations, but the fish started to reproduce. To prevent the fish from over-populating Florida waters and becoming invasive itself, the researchers developed a triploid fish, with extra chromosome numbers, that rendered the fish infertile. The triploid fish has been successful in reducing populations of several invasive aquatic plants, including hydrilla, chara (an algae), pondweed, southern naiad (native but considered a weed in some areas), and Brazilian elodea. While the fish does not completely obviate the need to use herbicides, chemical use can be reduced significantly, by enabling pond and lake owners to use herbicides as little as once in five years.
Birds as Biocontrol Agents
A worthwhile area for additional research is on the value of birds in controlling noxious weeds. Seed eating birds, including many species of sparrows, juncos, goldfinches, pine siskins, redpolls, towhees, grosbeaks, horned larks, cowbirds, meadow larks, doves, quail, blackbirds, and crows, will eat the seeds of noxious weeds in quantities significant enough to be useful in weed control. And many birds consume pests.
A USDA report (Judd 1898) over 100 years ago showed that weed seeds commonly eaten by birds were ragweed (Ambrosia artemisiifolia), wild lettuce (Lactuca spp.), bull thistle (Carduus vulgare and other species), pigeon grass (Setaria pumila, formerly Choetocloa glauca and C. viridis), smartweeds, bindweed, knotweed (Polygonum species, some native and some invasive), crab grass (Digitaria sanguinalis, formerly Panicum sanguinale), lamb’s-quarters (Chenopodium album), pigweed (Amaranthus species, some native and some invasive), nutgrass (Cyperus rotundus) and other sedges. The survey noted that birds eat prodigious amounts of weed seeds daily, and thus are important in controlling the spread of weeds. One study included examination of the stomachs of 4,000 sparrows from across the USA and Canada, research that would not be considered ethical today. But that study proved that, not only do these birds eat very large numbers of weed seeds (from 300 to 1000 seeds daily), they have a strong preference for those seeds, and do little damage to grains. Of 19 native sparrows collected in the area south of Washington, D.C., only two had eaten grain, and they had eaten only one grain seed each. Ironically, the English sparrow, a non-native bird often considered invasive, is particularly efficient at eating weeds seeds. In contrast to native sparrows, English sparrows do consume significant amounts of grain seeds, but they also consume large numbers of weed seeds, particularly crab grass, Indian goosegrass (Eleusine indica), and dandelions. Several native sparrows and goldfinches also consume dandelion seeds. A researcher that examined the stomachs of tree sparrows in Iowa estimated that these birds consume weed seed almost exclusively, and that they destroy about 1,750,000 pounds of weed seeds over one winter.
Birds also eat large numbers of insects, including many considered pests in crops. University of California-Berkeley researcher, Julie Jedlcka, conducted an experiment that demonstrated that bluebirds are significant consumers of beet armyworm, an insect pest in vineyards. A Humboldt State University wildlife ecologist, Matt Johnson, conducted research that demonstrated that birds benefit coffee farms, by consuming significant amounts of coffee berry borers (Berger, 2012).
Baumgartner, et al., 2019, examined the benefits birds have for farming and for reduction of noxious weeds. They produced a booklet listing which birds eat which insect and rodent pests. They found that in 90% of 118 bird studies, birds benefitted crops, either by reducing insect or rodent pests in crops, or by consuming large amounts of noxious weed seeds. The research also demonstrated that hawks and owls reduce the impact of pest birds that eat fruit. In addition, they found that some pest birds are beneficial to some crops. For example, starlings consume large amounts of grass grubs in pastures. “Globally,… birds eat about 28 million tons of insects per year” (Baumgartner, et al., 2019). The research also demonstrated that having natural habitats and nesting boxes and perches close to, or within, farming areas increases the beneficial impacts of birds. Their booklet provides much practical information on how to encourage beneficial birds to visit crops, and how to safely discourage pest birds. Some birds are useful in pollinating crops.
The chemicals used to control insect pests and weeds also reduce the supply of insects and seeds for insect-eating and seed-eating birds. A number of chemicals harm birds. In particular, cholinesterase inhibitors, ingredients in organophosphate and carbamate pesticides, and the neonicotinoid insecticide imidacloprid and chlorpyrifos cause declines in bird populations (Baumgartner, et al., 2019). Anticoagulant rodenticides can poison predatory wildlife. Thus, chemical use can conflict with the use of birds as weed and pest control agents.
Within this website, refer to the section on Herbicides for more information on the detrimental effects of herbicides.
References:
Next section on Biocontrol:
Links to return to other reports on Biocontrol Agents:
Vertebrates as Biocontrol Agents
Summaries of the research and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, July 2020.
Within this website, in the section on Innovative Solutions, refer to the research on, and recent uses of grazing animals, including both livestock and bison, to control noxious weeds.
Fish as Biocontrol Agents
In 1963, researchers at Auburn University and the US Bureau of Sport Fisheries and Wildlife Fish Experiment Station, in Arkansas, received permission to import grass carp, to conduct experiments on its potential to control aquatic weeds, especially hydrilla. Grass carp is an herbivorous fish from eastern Russia and China (Biss, 2018). The research team determined that grass carp would eat several times its weight in aquatic weeds. The fish ate large enough quantities to warrant a very controlled introduction into Florida. From 1970 to 1984, grass carp were cautiously introduced in various Florida locations, but the fish started to reproduce. To prevent the fish from over-populating Florida waters and becoming invasive itself, the researchers developed a triploid fish, with extra chromosome numbers, that rendered the fish infertile. The triploid fish has been successful in reducing populations of several invasive aquatic plants, including hydrilla, chara (an algae), pondweed, southern naiad (native but considered a weed in some areas), and Brazilian elodea. While the fish does not completely obviate the need to use herbicides, chemical use can be reduced significantly, by enabling pond and lake owners to use herbicides as little as once in five years.
Birds as Biocontrol Agents
A worthwhile area for additional research is on the value of birds in controlling noxious weeds. Seed eating birds, including many species of sparrows, juncos, goldfinches, pine siskins, redpolls, towhees, grosbeaks, horned larks, cowbirds, meadow larks, doves, quail, blackbirds, and crows, will eat the seeds of noxious weeds in quantities significant enough to be useful in weed control. And many birds consume pests.
A USDA report (Judd 1898) over 100 years ago showed that weed seeds commonly eaten by birds were ragweed (Ambrosia artemisiifolia), wild lettuce (Lactuca spp.), bull thistle (Carduus vulgare and other species), pigeon grass (Setaria pumila, formerly Choetocloa glauca and C. viridis), smartweeds, bindweed, knotweed (Polygonum species, some native and some invasive), crab grass (Digitaria sanguinalis, formerly Panicum sanguinale), lamb’s-quarters (Chenopodium album), pigweed (Amaranthus species, some native and some invasive), nutgrass (Cyperus rotundus) and other sedges. The survey noted that birds eat prodigious amounts of weed seeds daily, and thus are important in controlling the spread of weeds. One study included examination of the stomachs of 4,000 sparrows from across the USA and Canada, research that would not be considered ethical today. But that study proved that, not only do these birds eat very large numbers of weed seeds (from 300 to 1000 seeds daily), they have a strong preference for those seeds, and do little damage to grains. Of 19 native sparrows collected in the area south of Washington, D.C., only two had eaten grain, and they had eaten only one grain seed each. Ironically, the English sparrow, a non-native bird often considered invasive, is particularly efficient at eating weeds seeds. In contrast to native sparrows, English sparrows do consume significant amounts of grain seeds, but they also consume large numbers of weed seeds, particularly crab grass, Indian goosegrass (Eleusine indica), and dandelions. Several native sparrows and goldfinches also consume dandelion seeds. A researcher that examined the stomachs of tree sparrows in Iowa estimated that these birds consume weed seed almost exclusively, and that they destroy about 1,750,000 pounds of weed seeds over one winter.
Birds also eat large numbers of insects, including many considered pests in crops. University of California-Berkeley researcher, Julie Jedlcka, conducted an experiment that demonstrated that bluebirds are significant consumers of beet armyworm, an insect pest in vineyards. A Humboldt State University wildlife ecologist, Matt Johnson, conducted research that demonstrated that birds benefit coffee farms, by consuming significant amounts of coffee berry borers (Berger, 2012).
Baumgartner, et al., 2019, examined the benefits birds have for farming and for reduction of noxious weeds. They produced a booklet listing which birds eat which insect and rodent pests. They found that in 90% of 118 bird studies, birds benefitted crops, either by reducing insect or rodent pests in crops, or by consuming large amounts of noxious weed seeds. The research also demonstrated that hawks and owls reduce the impact of pest birds that eat fruit. In addition, they found that some pest birds are beneficial to some crops. For example, starlings consume large amounts of grass grubs in pastures. “Globally,… birds eat about 28 million tons of insects per year” (Baumgartner, et al., 2019). The research also demonstrated that having natural habitats and nesting boxes and perches close to, or within, farming areas increases the beneficial impacts of birds. Their booklet provides much practical information on how to encourage beneficial birds to visit crops, and how to safely discourage pest birds. Some birds are useful in pollinating crops.
The chemicals used to control insect pests and weeds also reduce the supply of insects and seeds for insect-eating and seed-eating birds. A number of chemicals harm birds. In particular, cholinesterase inhibitors, ingredients in organophosphate and carbamate pesticides, and the neonicotinoid insecticide imidacloprid and chlorpyrifos cause declines in bird populations (Baumgartner, et al., 2019). Anticoagulant rodenticides can poison predatory wildlife. Thus, chemical use can conflict with the use of birds as weed and pest control agents.
Within this website, refer to the section on Herbicides for more information on the detrimental effects of herbicides.
References:
- Baumgartner, J., Kross, S., Heath, S. & Connor, S. (Winter, 2019). Supporting beneficial birds and managing pest birds. Wild Farm Alliance.
- Berger, M. (March-April 2012). Controlling pests with birds. Audubon Magazine.
- Biss, J. (May 18, 2018). Grass carp - A biological control to manage pond weeds. Best Management Practices, Invasive Species. University of Florida IFAS Extension.
- Judd, S.D. (1898). Birds as weed destroyers, in Yearbook of the U.S. Department of Agriculture. USDA, National Agricultural Library.
Next section on Biocontrol:
Links to return to other reports on Biocontrol Agents: