Biological control for downy brome
A biological control of downy brome is a step closer to reality.
Downy brome is a winter annual grassy weed spreading across the dry areas of southwestern Saskatchewan and Alberta.
Its spread is helped by a lack of selective herbicides and effective control measures in winter wheat.
Added to these factors is downy brome’s life cycle, which is similar to winter wheat.
Susan Boyetchko of Agriculture Canada’s Saskatoon Research Centre, with money from Saskatchewan Agriculture’s Agriculture Development Fund, recently began a two-year project to evaluate the potential of controlling downy brome with a bioherbicide.
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“Bioherbicides, which are annually applied in high doses over a localized area infested with the target weed, have different modes of action, such as producing physotoxins or plant-growth regulators. They cause diseases on either the foliage or roots of the weeds, resulting in complete kill or suppression. Others inhibit growth and development, or reduce the rate of germination,” she said.
Boyetchko isolated native populations of rhizobacteria, root-colonizing bacteria in the soil, from fields infested with downy brome around Maple Creek, Sask.
She tested hundreds of rhizobacterial strains that grow on or close to the roots to find one that inhibits the development of downy brome.
At the start of the project, little information was available on the importance of soil microorganisms, particularly rhizobacteria and their potential for biological control.
“Not only did we add to the general information about rhizobacteria, we found bacterial strains with the potential to control downy brome and to produce compounds that will control the weed growth,” she said.
Boyetchko is also looking at how rhizobacteria act to control downy brome and at ways to mass produce them to formulate a product that producers can use.
She is also looking into biological control of wild oats and green foxtail, two weeds in which herbicide resistance has been reported.
– Saskatchewan Agriculture
Canola research
The cabbage seed pod weevil, which has been called the wheat midge of canola, has been detected in Alberta, but not in Saskatchewan.
It is a serious oilseed crop pest in the northwestern United States, and was detected in southern Alberta canola fields in 1996. It expanded its range throughout southern Alberta in 1997.
Agriculture Canada research scientists Owen Olfert in Saskatoon and Rick Butts in Lethbridge, Alta. have started a project that focuses on this insect and on lygus bugs, another potential threat to canola production in Western Canada.
“Lygus bug infestations in canola have also increased in severity in 1996 and ’97, with insecticide applications required for its control in Alberta both years” said Olfert.
“Lygus bugs severely infested canola in Saskatchewan at Meadow Lake last year. We know more about the lygus bug because it has been around for years on alfalfa, so we’re familiar with its behavior and control on alfalfa. Its attack on canola is more recent and we want to gain more information about this.”
But the cabbage seed pod weevil is the main focus of the study.
“This insect is taken very seriously in the northwest states. Producers always spray when it appears,” Olfert said. Even light infestations can cause 30 to 40 percent damage.
There are no cabbage seed pod weevil insecticides registered in Canada. In the U.S., some states have chemicals registered but they are expensive.
Much of what Olfert and Butts know about cabbage seed pod weevil is based on research by Joe McCaffrey of the University of Idaho in Moscow. McCaffrey reported the life cycle of the weevil synchronizes with winter canola, which blooms earlier than spring canola.
Olfert is concerned about this because of recent recommendations for early spring planting of canola to increase yields.
Fall-seeded canola, which emerges early, is another recent change in this province. Both practices may provide better situations for the cabbage seed pod weevil.
The weevil behaves somewhat like the wheat midge on wheat. The adult weevil bores a hole in the canola pod, lays eggs inside and when the larvae hatch, they feed on seeds inside the pod.
Olfert’s project aims to determine the geographic extent of weevil infestations on the Prairies, and the biological requirements for survival in this region. Researchers also hope to develop plans for management tactics if their findings indicate control is warranted.
“McCaffery encourages Canadian researchers to include biological control in their efforts. He has found in Idaho that parasites can control up to 40 percent of the weevil population in areas that have not been sprayed with insecticides,” Olfert said.
– Saskatchewan Agriculture
Insecticide resistance
Scientists at Agriculture Canada’s Lethbridge research centre are developing an insecticide resistance management program for the Colorado potato beetle in Western Canada.
The beetle is the most destructive insect pest of potatoes worldwide. In spring, hibernating beetles emerge from the soil and lay several hundred eggs on young potato plants. Hatching larvae feed on plant foliage. Plants under heavy attack are barely able to support their growth requirements and potato yield is reduced.
In many parts of the world, including Eastern Canada, complete reliance on insecticides for control has resulted in resistant beetle populations, said Mark Goettel, an insect pathologist and Christine Noronha, an entomologist, both of the Lethbridge centre.
Where resistance has developed, farmers have been forced to adopt new management programs to save their crops. Alternative controls include propane flamers, plastic-lined trenches, pest resistant transgenic cultivars, trap crops, straw mulch and crop rotations.
“However, as soon as newer insecticides become available, many producers abandon these alternative strategies,” Goettel said. “If this occurs on a wide scale, it is only a matter of time before resistance to these newer chemicals develops.”
To prolong the effective use of chemical controls in Western Canada, an insecticide resistance management program must be implemented, researchers said.
In Manitoba, resistant potato beetles have already shown up. Although resistance hasn’t developed in Alberta, it will if growers rely only on insecticides.
The alternatives used in Eastern Canada might not be as effective here because of agronomic practices and adaptation of the beetle to the western climate. One of the first goals of research is to determine the insect’s phenology -its life cycle, movement within the crop, overwintering habits – in Western Canada.
“Once the phenology is known, the next step will be to determine alternative control methods that can be used together with insecticides. This approach targets the beetles that have survived insecticide treatment and could harbor genes for resistance,” said Noronha.
Researchers are studying the effectiveness of a fungus, Beauveria bassiana, on overwintering adult beetles and on the bug’s soil-dwelling stages. This naturally occurring pathogen of the potato beetle can decimate the insect. It has recently been registered in the U.S. for this use.
Researchers plan to test the fungus against beetles that have survived summer insecticide treatment, said Goettel.
“These beetles migrate out of the fields to high density overwintering sites and treatment of these migrating adults could be a method of contaminating these sites and controlling the overwintering population.
“Another benefit is that there is growing evidence that the inoculum builds up in soil, providing effective control year after year and reducing the numbers of insecticide sprays that need to be applied.”
In the long term, researchers want to integrate the fungus into a comprehensive pest management program, eventually reducing or even eliminating dependence on chemical pesticides.
For now, they stress the potato industry must adopt a balanced control system to defer development of resistance and buy time in the quest for a long-term control of this noxious pest.
– Agriculture Canada
