Cause:
Wilsonomyces carpophilus (formerly Coryneum beyerinckii), a fungus that overwinters on infected peach (stone fruit) buds and twigs. When moisture is continuous for at least 24 hours and temperatures are above 36°F, infection can occur in the dormant season. When temperatures are higher during the growing season, shorter periods of moisture are required for germination and infection; for example only 6 hours are needed at 77°F. Spores spread primarily by splashing water and can remain viable several months when dry. Under favorable conditions, spores can be produced from infected buds and stem lesion throughout the growing season. Most cultivars of peach, nectarine, apricot, and almond appear to be very susceptible. Cherry and plum are less susceptible and show only leaf and fruit symptoms when extended periods of moisture are present in late spring and early summer. Can be a problem in eastern districts when over-the-canopy irrigation is used for frost protection.
Symptoms:
Leaves develop small, round, tan to purplish spots that are seldom larger than 0.25 inch wide. Tissue becomes somewhat raised and scurfy and often drops out in dry, warm weather, producing a shothole effect.
Fruit symptoms are similar and can be accompanied by a clear, gummy exudate. Small red fruit spots may be numerous and slightly sunken.
Bud and twig infections darken, the bark tends to rupture in a ring, and some gumming occurs. On current-season and 1-year-old fruiting wood, infections consist of round, reddish spots, which are slightly sunken. Fruit buds often are killed, and fruiting wood may be badly damaged or girdled. Rough, smoky-appearing cankers up to 2 or 3 inches long develop on 2- to 4-year-old wood. These are a source of the overwintering spores. On apricot, buds often are killed, but very few twig infections occur.
This photo shows shothole lesions on the upper left peach, peach leaf curl on upper right peach and powdery mildew on lower peach.
Note the gray lesions with purple borders.
There are many infections on these twigs.
Late season infection of peach, with sporulation of the fungus visible in one of the lesions.
Gumming can occur from shothole spots on fruit.
Cultural
control:
Do not let sprinkler irrigation water to wet tree foliage and fruit.
The cultivars 'Lovell' and 'Muir' are reportedly tolerant.
Remove affected twigs during pruning if practical.
Chemical
control:
Spray at 50% leaf fall in late autumn to help protect leaf scars and again during the dormant season.
Bordeaux 8-8-100.
Bravo Weather Stik at 3.1 to 4.1 pints/A. Do not use more than 20.5 pints/A/season. Good control rating. 12-hr reentry.
Captan 80 WDG at 5 lb/A. For home use but only available with other chemicals in pre-packaged mixes. Moderate control rating. 24-hr reentry.
Copper-based products such as Cuprofix,
Kocide, Nordox, Copper-Count-N or Nu-Cop. Lilly Miller Microcop at 1.5 Tbsp/1 gal water is registered for home use. Good to excellent control rating. 24-hr reentry except Cuprofix, Nordox and Copper-Count N with a 12-hr reentry.
Echo 720 at 3.1 to 4.1 pints/A. Good control rating. 12-hr reentry.
Ziram 76 DF at 6 to 8 lb/A. Good to excellent rating. 48-hr reentry.
Spray again at shuck fall in the spring.
Abound at 11 to 15 fl oz/A. Alternate with fungicides that have a different mode of action. Do not apply more than 4 times/year or 2 sequential sprays. May be applied the day of harvest. Sprayers used for Abound should not be used on apples such as Gala, Cox's Orange Pippin and McIntosh. 4-hr reentry.
Bravo Weather Stik at 3.1 to 4.1 pints/A. Do not use more than 20.5 pints/A/season. Do not apply after shuck split. 12-hr reentry.
Captan 80 WDG at 5 lb/A. For home use but only available with other chemicals in pre-packaged mixes. Good rating when used for same disease on almonds. 24-hr reentry.
Echo 720 at 3.1 to 4.1 pints/A. Do not apply after shuck split. 12-hr reentry.
Gem at 6 to 8 oz/A. Rotate with other fungicides that have different modes of action. Do not apply more than twice consecutively, exceed four (4) applications, 32 oz/A/season, or within 1 day of harvest. Do not use with ogranosilicate surfactants. ‘Concord’ grapes may be injured if accidentally sprayed. 12-hr reentry.
Pristine at 10.5 to 14.5 oz/A. Do not use more than 2 consecutive applications or more than 5 times/year. Can be used day of harvest. 12-hr reentry.
Spectracide Immunox at 0.5 fl oz/gal water. May be applied up to the day of harvest. Do not use more than 7 times per season.
Ziram 76 DF at 6 to 8 lb/A. Do not apply within 30 days of harvest. Good rating when used for same disease on almonds. 48-hr reentry.
Notes:
Sulfur-based products (such as Microthiol Disperss) were ineffective when used for same disease on almonds.
References: Grove, G. G. 2002. Influence of temperature and wetness period on infection of cherry and peach foliage by Wilsonomyces carpophilus. Canadian Journal of Plant Pathology. 24:40-45.
Shaw, D.A., J.E. Adaskaveg, and J.M. Ogawa. 1990. Influence of wetness period and temperature on infection and development of shothole disease of almond caused by Wilsonomyces carpophilus. Phytopathology 80:749-756.
Content edited by:
Jay W. Pscheidt on
January 1, 2009
