About Enviroweather's Sooty Blotch and Flyspeck Progress
By Bill Shane and Mark Longstroth, MSU Extension
About Sooty Blotch and Flyspeck
Overview
Sooty blotch, caused by the fungi Gloeodes and Leptodontidium and flyspeck, caused by Schizothyrium pomi, are two fungal disease complexes of apple and pear common in the humid fruit growing regions of the United States. The diseases can cause significant economic losses due to the unsightly appearance of affected fruit. Fruit with significant symptoms cannot be sold as fresh fruit. Both pathogens colonize the waxy surface of pome fruit but do not penetrate lower layers. Severely affected fruit tend to dehydrate more rapidly in storage compared to unaffected fruit.
The two fungi are found on a wide range of perennial hosts commonly found in the woods, including wild brambles. Spores of the two pathogen groups are available in orchards beginning approximately from late pink bloom growth stage throughout the summer and fall.
Symptoms
Sooty blotch colonies are olive green to black on mature fruit. They may be round or have feathery, diffuse margins, and infection may cover the entire fruit. Symptoms of flyspeck are appropriately described by the name of the disease. Colonies have up to 50 small, shiny black fungal fruiting structures grouped in an irregular to circular pattern.
Disease Cycle
The fungi that cause sooty blotch survive from one season to the next on apple twigs as well as other perennial vegetation with a waxy cuticle. The fungus is dispersed by wind and in windblown rainwater to developing fruit in the spring and early summer. Secondary spread from these primary colonies occurs throughout the summer. Growth of sooty blotch on fruit can begin 2 to 3 weeks after petal fall and a week or two later for flyspeck. Growth of these fungi are favored by temperatures between 65° and 80° F, and wet, humid conditions. Growth does not occur at temperatures above 86°F. It usually takes 20 to 25 days for colonies of sooty blotch to appear on fruit after infection occurs and 3 to 6 weeks for flyspeck.
Management
Control of sooty blotch and flyspeck is achieved through dormant and summer pruning and tree training, which open trees and facilitate drying and fungicide deposition, and through preventive fungicidal sprays. Removal of wild blackberry from the boarder of the orchard can help by eliminating a potential reservoir host.
About the Sooty Blotch and Flyspeck model on Enviro-weather
About the model:
This model is based on work by Brown and Sutton at North Carolina State University. The model is initiated 10 days after petal fall. Enviro-weather will estimate petal fall as 511 degree days base 42 F after January 1st. The user can substitute another date for petal fall if desired.
If a wetting period, rain or heavy dew is 4 hours or more in length, the number of hours is recorded. The first symptoms are expected when the accumulated hours of wetting starting 10 days after petal fall reaches the range of 240 to 290.
The user can elect to enter the date of fungicide application. The model will then track rainfall accumulation following this date. When 2 inches of rainfall have accumulated, and remaining fungicide coverage is expected to be low, the model will again begin to accumulate hour of wetting. Symptoms are expected with 240 hours of additional wetting.
Use of the model:
The model is useful to compare seasons to see how spray program start dates for sooty blotch and flyspeck differ. See the predicted date for 1st fungicide application for these diseases using weather data for the Southwest Michigan Research and Extension Center. Predicted 1st application dates can differ more than 30 days.
Table 1. Predicted 1st symptom date for sooty blotch and flyspeck for the Southwest Michigan Research and Extension Center for five seasons.
| Year | Petal fall date | Predicted 1st symptom date | Days between petal fall and predicted 1st symptom date |
|---|---|---|---|
| 2003 | May 7 | June 20 | 44 |
| 2004 | May 8 | June 17 | 40 |
| 2005 | May 9 | July 16 | 68 |
| 2006 | May 7 | July 2 | 56 |
| 2007 | May 5 | June 29 | 55 |
A typical approach is to use the model to watch the accumulation of hours of wetting and apply an effective fungicide for sooty blotch and flyspeck at or slightly before symptom expression is anticipated. Since orchards, spray equipment, inoculum amounts, and other conditions vary from site to site and year to year this model should be used as a broad outline.
References:
- Brown, E. M. and Sutton, T. B. 1986. Control of sooty blotch and flyspeck of apple with captan, mancozeb, and mancozeb combined with dinocap in dilute and concentrate applications. Plant Disease 70:281-284.
- Rosenberger, D. A. and F. W. Meyer. 2007. Timing summer fungicides to control flyspeck. In: New York Fruit Quarterly. Vol 15 (1).
- Williamson, S. M. and Sutton, T. B. 2000. Sooty blotch and flyspeck of apple: etiology, biology, and control. Plant Disease 84:714-724.
