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| stem rust outlook for 2009 |
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Stem Rust Outlook for Spring 2009
Dr. Bill Pfender, USDA-ARS
INFORMATION ON RUST FOR WINTER/SPRING 2008-2009
Epidemics of stem rust on perennial grasses do not have a clear starting time in the spring, but gradually develop from fall and winter infections at a rate that depends on the weather. Mild winters may permit an increase in rust, whereas severely cold winters may greatly reduce overwintering rust populations. Autumn and winter conditions in 2008-2009 have resulted in relatively low carryover of rust in most Willamette Valley fields. Individual fields may have higher rust levels. |
| Since the spring epidemic develops from infections that have survived winter, a warmer winter favors an earlier epidemic because of the resulting larger spring rust population. Surviving rust population also depends on fall planting date - earlier-planted stands tend to carry more rust through the winter than later-planted stands.
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Each spring on March 15, we determine the amount of rust present in stands that were planted in mid-September at Hyslop Farm. The Table below shows that the amount of rust in early-planted perennial ryegrass in March 2008 was slightly higher than what we saw in March 2006 and March 2007. This means the 2008 stem rust epidemic may develop slightly earlier than in 2007, but certainly later than it has in the most severe rust years, such as 2002 and 2005. However, it's important to scout your fields and determine your actual conditions. |
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Year |
Spring rust level at Hyslop* |
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1998 |
10.0 pustules / ft of row |
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1999 |
0.2 pustules / ft of row |
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2000 |
4.0 pustules / ft of row |
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2001 |
0.2 pustules / ft of row |
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2002 |
12.0 pustules / ft of row |
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2003 |
0.2 pustules / ft of row |
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2004 |
0.2 pustules / ft of row |
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2005 |
22.4 pustules / ft of row |
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2006 |
0.05 pustules / ft of row |
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2007 |
0.07 pustules / ft of row |
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2008 |
0.2 pustules / ft of row |
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2009 |
0.2 pustules / ft of row |
| * -Active rust pustules per ft. of row in September-planted, first-year perennial ryegrass plots on 3/15 |
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Stem Rust on Perennial Ryegrass |
RUST DISEASE ESTIMATION IN 2008
Once the spring epidemic has started, the weather continues to play a very important role in determining rust severity. Overnight and early-morning temperatures above 34 F permit infections if the leaves are wet, and the amount of infection increases sharply with warmer temperatures. The amount of time required for a new infection to produce a new crop of rust spores (called generation time or "latent period") is affected by average (day and night) temperatures. Warmer temperatures mean shorter generation times, that is, a more quickly-developing epidemic. The Rust disease model indicating danger of rust development will be updated daily during the 2009 growing season. It is available on the Grass stem rust Estimator page, starting April 1. At the website you can also look at rust model runs from some prior years/locations, which may help you gauge this year's rust development against your previous experience with the disease.
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Last Modified: 03/19/2009
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