Spring Outlook for Stem Rust This Year : USDA ARS

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Spring Outlook for Stem Rust This Year

Stem Rust Outlook for Spring 2013Dr. Bill Pfender, USDA-ARS
INFORMATION ON RUST FOR WINTER/SPRING 2012-2013
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 2012-2013 have resulted in moderate carryover of rust in some Willamette Valley fields. Individual fields may have higher or lower 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.

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 2013 was higher than in 10 of the last 16 years, but lower than 5 of those years. It is similar to levels we saw in March of 2000. This means the 2013 stem rust epidemic could start relatively early this year, especially if we have warm weather in April and May. It is important to scout your fields and determine your actual conditions, because individual fields may have higher or lower levels than we observe in our plots.

Year	Spring rust level at Hyslop*
1998	10.0 pustules / ft of row
1999	0.2 pustules / ft of row
2000	4.0 pustules / ft of row
2001	0.2 pustules / ft of row
2002	12.0 pustules / ft of row
2003	0.2 pustules / ft of row
2004	0.2 pustules / ft of row
2005	22.4 pustules / ft of row
2006	0.05 pustules / ft of row
2007	0.07 pustules / ft of row
2008	0.2 pustules / ft of row
2009	0.05 pustules / ft of row
2010	0.1 pustules / ft of row
2011	6.0 pustules / ft of row
2012	0.05 pustules / ft of row
2013	2.6 pustules / ft of row
* -Active rust pustules per ft. of row in September-planted, first-year perennial ryegrass plots on 3/15

Stem Rust on Perennial Ryegrass

RUST DISEASE ESTIMATION IN 2013

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 2013 growing season. It is available on the Grass stem rust Estimator page, starting about April 1. At the website you can also look at rust model runs from some prior years and locations, which may help you gauge this year's rust development against your previous experience with the disease.