 |
 |
|
|
| Wednesday, January 03, 2007 |
|
||||||||
|
||||||||
|
||||||||
|
||||||||
|
Frequently
Asked Questions - Watch for Crown Rust on Oat in Southeast Saskatchewan This Season
What is Crown Rust of oat? To get an answer
to your own question, click here
Crown Rust, also known as leaf rust, is caused by a fungus, Puccinia coronata f.sp. avenae. The Crown Rust fungus is specific to cultivated oat, wild oat, and a few other wild grasses, but will not infect wheat, barley or rye. Crown Rust reduces oat yield and causes thin kernels with low test weight - factors which greatly reduce milling quality. Loss due to disease can reach 100 per cent if infection is early, if it is a susceptible cultivar, and if weather conditions are favourable for the development of fungal spores and their spread. Losses have been more severe in Manitoba compared to Saskatchewan, for the time being at least. The problem area in Saskatchewan is believed to be the southeast. In this region, oat crops are more likely to be exposed to the rust fungus moving in from the south. Symptoms of Crown Rust include orange pustules of spores developing on oat leaves (see photos). Each pustule contains thousands of spores that can be spread to neighbouring plants and produce a new pustule in only seven to 10 days under ideal conditions.
What areas and conditions are of concern? Researchers are warning oat producers to watch for Crown Rust this season. The level of Crown Rust has been increasing in recent years in Manitoba and southeast Saskatchewan. The Crown Rust outbreak in 2005 was one of the most severe in many years. The 2005 season witnessed late planting of oat and humid and warm weather, conditions that were favourable for Crown Rust infection. Furthermore, oat cultivars bred for resistance to Crown Rust are no longer effective at warding off infection, due to the fact that the rust population has developed new races that have overcome the resistance. Since current oat cultivars will no longer be effective at resisting Crown Rust, growers will need to incorporate other management practices to reduce disease risk. Why are our current oat cultivars no longer resistant? Within the rust fungal population, there are a number of different “races” that developed and are specific to oat cultivars carrying certain rust resistant genes. Almost all oat cultivars currently grown on the eastern prairies rely on a single gene for resistance: Pc68. The outbreak of oat rust in 2005 proves this gene is no longer effective. Dr. James Chong, a pathologist with the Cereal Research Centre in Winnipeg, has determined the frequency of the various rust races collected from infected plants. In 2005, 73 per cent of isolates from cultivated oat were virulent against the Pc68 gene, compared to 39 per cent of isolates from 2004, and only 12 per cent in 2003. This is evidence that the rust race that can overcome the Pc68 gene has increased rapidly in the rust population in only a few years. The rust pathogen is not seed or soil-borne. The primary means of infection is from rust spores moving up on air currents from the southern part of the United States. The onset and severity of rust infection in the eastern prairies is dependent on what happens on southern crops. If there is a high proportion of the race virulent against the Pc68 gene in the rust population developing in the U.S., oat crops on the eastern prairies are likely to suffer. The United States Department of Agriculture (USDA) produces a cereal rust bulletin that monitors rust development in the U.S., which is useful in predicting the risk to Canadian crops. Provincial specialists will keep producers and agronomists updated on the risk in 2006 as the season progresses.
Will new oat cultivars with resistance be available soon? Developing Crown Rust resistant cultivars is an ongoing battle for cereal breeders. As soon as new cultivars are developed with specific genes for resistance, it puts pressure on the rust population to develop new races to overcome this resistance. The goal of cereal breeders is to “pyramid” genes for resistance, meaning that several genes are incorporated into one cultivar to extend the breakdown of resistance. Two new cultivars, “Leggett” from Agriculture and Agri-Food Canada in Winnipeg, and “HiFi” from North Dakota State University, have been registered in Canada, but certified seed is not yet available. New sources of resistance have been identified in wild oat collected in Europe, the Middle East and North Africa, and are being incorporated into the breeding programs. Several advanced lines with resistance from the Development Centre, University of Saskatchewan and Agriculture and Agri-Food Canada are in co-op tests during 2006. What can farmers do to protect against Crown Rust? One of the key ways to avoid severe infection is to plant oat crops early. The premise for planting early is that the crop should be advanced enough, by the time rust spores arrive on the eastern prairies, that crops will not suffer significant yield or quality loss. In addition, growers can be more selective in the cultivars they choose to plant. Although most of the cultivars depend solely on gene Pc68 and won’t be effective, a few other cultivars do have other genes. For example, cultivar Leggett was released in 2004, and has Crown Rust resistance because an additional gene is present (Pc94). Leggett will be available in limited quantities in 2006 and widely available by 2007. Cultivar HiFi, developed in North Dakota, also has a different gene (Pc91) which is still effective. HiFi was recommended for registration in 2006. The next best choices are CDC Boyer and CDC Dancer, which are more slow-rusting cultivars. Foliar fungicides are another tool that growers have to manage. There are a number of fungicides available, containing the active ingredients propiconazole and/or trifloxystrobin. Products containing propiconazole include Tilt 250E, Bumper 418EC, and more recently Pivot 418EC. Stratego 250EC (propiconazole and trifloxystrobin) has just been re-instated for use on oat in Canada. The ideal timing for application is to spray at flag leaf emergence to protect the flag leaf. Rust can develop very quickly. Once the flag leaf is covered with spots, it is too late to apply fungicide. The decision whether or not to apply fungicide must take into the account the availability of rust spores moving up from the south, and weather conditions. Spraying fungicide will not be necessary in all years or locations.
Oat production in Saskatchewan is expected to remain strong in 2006. Oat producers need to be aware that Crown Rust may be a problem in oat in 2006. Management practices, as well as crop scouting, should be implemented to reduce risk. Resources: Bailey, K.L., Gossen, B.D. ,Gugel, R.K., Morrall, R.A.A. 2003, Diseases of Field Crops in Canada, CPS Press, Saskatoon, SK. pages 75-77. Chong, J. 2006, Crown Rust in Oat in Western Canada in 2005. Canadian Plant Disease Survey, Volume 86, pages 66-67 (http://www.cps-scp.ca/cpds.htm) Links: USDA Cereal Rust Bulletin (United States Department of Agriculture) Acknowledgements: Penny Pearse, PAg, SAF, Provincial Plant Pathologist | ||||||
|
|
|||||||
|
|||||||
