In Ontario and Manitoba, where dry beans are predominantly grown, anthracnose (Colletotrichum lindemuthianum) infection has caused yield and seed quality losses in dry beans for years. Looking back, Chris Gillard, dry bean agronomy and pest management specialist at the University of Guelph’s campus in Ridgetown, Ontario, says a major anthracnose infestation from Race 23 occurred in Ontario in 1977. That caused all sorts of problems with 18 percent of dry bean seed stock infected, a ban on the commercial crop in the US, and very strict seed inspections implemented.
Then in 2004, the new Race 73 was found in Ontario, “And we are still questioning the extent of its impact on the crop, because I don’t think we know it at this point,” says Gillard.
Since 2005, a national anthracnose project has been conducting studies in Manitoba and Ontario to develop a rapid anthracnose test, update Integrated Pest Management (IPM) strategies and develop new breeding solutions based on pyramiding of genes. Gillard is collaborating alongside Dr. Bob Conner with Agriculture and Agri-Food Canada (AAFC) at Morden, Manitoba, Dr. Parthiba Balasubramanian with AAFC Lethbridge, in Alberta, and Dr. Greg Boland at the University of Guelph. Gillard presented a summary of the findings at the 8th Canadian Pulse Research Workshop in Calgary, in early November 2010, which was organized by the Alberta Pulse Growers.
In 2010, anthracnose was present in most white bean fields in all varieties except T9903. T9903 is unique because it was thought to be one of the few varieties with resistance to Race 73, but in late 2010, anthracnose infection was found on T9903, as well. Gillard also reports that the white bean supply may be limited in Ontario in 2011 because of the prevalence of anthracnose-infected seed. “That leads us to the question, have we accomplished anything in the last five years since we launched this project?”
To kick things off, the project conducted a survey of commercial fields to determine the predominant races. Between 2005 and 2007, the predominant race was Race 73, accounting for 96.2 percent of the isolates submitted between 2005 and 2007. In the US, Race 73 is dominant as well.
Gillard explains that understanding the predominant races helps plant breeders develop resistant varieties, a difficult process given the many different types of dry beans. The plant breeders working on the project are using five different resistant genes that they are crossing into seven different market classes of beans. The breeders have developed some breeding lines and eventually hope to introduce new varieties. But the challenges include breeding for not only disease resistance, but also good agronomics and good canning quality, while trying to pyramid the genes to help slow down resistance breakdown and a shift in disease races. “The obvious benefit is that producers can get inexpensive, long-term control of anthracnose, especially with pyramided genes,” says Gillard. He explains that genetics is one of the pillars of an IPM strategy, with the others being clean seed, cultural control and chemical control.
The second IPM strategy of clean seed requires due diligence by the seed industry. Minimizing disease in the seed supply is possible with dryland seed production in Idaho, where climate, furrow irrigation and state inspections produce clean seed “practically all the time.”
Limited seed multiplication part of the problem
In Ontario, local seed multiplication is now limited. In the past, there were three years of multiplication from Idaho-produced seed, but multiplication has now dropped to only one. Gillard says local seed production also should be coupled with strict seed inspection, with the information provided to commercial growers. “With Canadian Food Inspection Agency (CFIA) getting out of seed inspections and the private sector taking over, the private inspectors need to have the teeth to toss the bad seedlots so they never make it to commercial production. If there are no teeth there, there will be a downfall in the Ontario seed production system.”
Part of the inspection process is to have a test for anthracnose. Dr. Chen, a postdoctoral fellow involved in the anthracnose project, has developed two polymerase chain reaction (PCR) tests and has spent a considerable amount of time trying to develop a quantitative test. A quantitative test is better because it can measure the level of infection, rather than just whether the pathogen is present. The goal is to measure infection levels between 0.001 and 0.1 percent. “Anything below that and I think we can control it with seed treatments,” says Gillard. “And anything above that we can see the infection clearly on the seed coat. We need a seed test that can help screen seedlots for disease.”
Several studies were also conducted to determine the survival of anthracnose. In an overwintering study (still ongoing), Gillard explains anthracnose survived on stem and pod tissue for at least 16 months, and on seed tissue for at least six months. The pathogen survived much longer on the stems and pods than on the seeds, and survival was much longer on infected tissue at Morden, Manitoba, than at Exeter, Ontario.
Survival was also greater for residue placed on the soil surface compared to residue buried 15 centimetres (six inches) in the soil.
Do not spread the disease
The project also looked at how the disease is spread in the crop. A disease transmission study was conducted using common agricultural materials (leather, rubber, painted metal and denim) that were soaked in a concentrated anthracnose spore solution, and then passed through wet and dry bean canopies. The results found both man and machines were capable of moving the disease due to walking or driving through a field.
Infection occurred at the Manitoba site in 2007, at the Ontario site in 2008, and at both sites in 2009. When infection occurred, it was in all treatments in both the wet and dry crop canopies, except the control treatment. The degree of disease transmission was influenced by the humidity in the crop canopy at a site, and differences in the humidity between sites. “While there were some differences, we got pretty good disease transmission for all of them. That’s important when you have growers out in the middle of the field in the middle of the summer trying to spray these crops and walking through these crops and transmitting the disease through the field.”
To disinfect these materials, a 10 percent bleach solution (0.525 percent sodium hypochlorite) was found to be the most effective, followed by chlorine dioxide (Aquacare) and chloroxylenol (Dettol).
Fungicide treatments help
As well, several studies were conducted to determine the efficacy and timing of chemical controls. Gillard presented results showing the economic return for the chemical treatments, rather than just yield or quality. “Economics capture the whole results. This disease impacts yield and quality, and economics takes into account the gross returns, yield and quality losses and also the cost of the treatment.”
The seed treatment DCT (diazinon + captan + thiophanate-methyl), the standard used for the last 30 years, was superior to Apron Maxx (fludioxonil + metalaxyl-M). The addition of Dynasty (azoxystrobin) to Apron Maxx provided results better than DCT. “When we combined Dynasty and Apron Maxx, the returns were equal to DCT and produced a product that had a much higher acceptance rate for growers.”
The best seed treatments suppressed disease symptoms for approximately 45 days after planting, which suggests the need for later-season controls, such as foliar fungicides.
Foliar fungicides were also found to be effective in providing in-crop disease suppression. Gillard reports a late vegetative (V6) application timing of either Headline (pyraclostrobin) or Quadris (azoxystrobin) fungicide gave the best disease control at low disease levels, while an early to mid-flower application timing (R1 to R2) gave the best disease control under moderate to high disease scenarios. A late timing at 10 days after full flower (R4) consistently provided the poorest results.
A sequential fungicide application at early (R1) and full flower (R2), though, consistently provided better results, compared to any single application timing. “What we typically find is that it is difficult for a grower to pick the timing of a single application. A sequential application with two applications gives him a broader window of control and more success.”
Gillard says that growers can use the information to build a more sustainable dry bean production system.
“I think we have made some progress over the last 30 years, but we can’t just rely on one pillar to control the disease. We can’t rely on just genetics to control the disease. Cultural control is limited for what we can do with the disease. Clean seed is getting difficult to source, unless you source it from Idaho. Idaho seed typically costs 50 percent more than local seed. And chemical control is working well but we are relying on it too much. We’re using strobilurin fungicides too often and too much, and I am concerned about resistance. We have to use all the tools we can to help manage the disease.”