Plant Disease Management Handbook

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Prune and Plum (Prunus spp.) - Russeting

Apple (Malus spp.) - Fruit Russeting

Image related to Peach (Prunus persica)-Russeting

Several problems can be the cause of surface russet on peach.

Jay W. Pscheidt, 2007.

Note the scarred area of the fruit which does not grow deforming the final shape.

OSU Plant Clinic collection, 2012.

Cause Podosphaera pannosa (formerly Sphaerotheca pannosa) and Podosphaera clandestina, fungi that overwinter on infected twigs, shoots, and buds of stone fruits. Leaves are infected as they emerge from the bud. Colonies that develop on leaves produce airborne conidia that infect other leaves and fruit. Fruit are susceptible to infection until pit hardening. Roses are a host of P.

Image related to Peach (Prunus persica)-Powdery Mildew

Several colonies of powdery mildew can be seen on these Elberta peaches.

Photo by Jay W. Pscheidt, 2000

Leaves may become distorted when infections are numerous.

Jay Pscheidt, 2006.

Numerous conidia can be seen on this peach leaf.

Jay Pscheidt, 2006.

The development of rusty spot symptoms from young lesions to russetted fruit, left to right.

Norm Lalancette, 2016.

Cause Plum pox virus (PPV) of which there are several strains. The disease was found in North America for the first time in 1999 in Pennsylvania and has now been detected in New York and Michigan as well as Ontario and Nova Scotia, Canada. Periodic surveys for the virus since 2000 have not found the virus in the Pacific Northwest nursery industry or Oregon's cherry orchards. After 10 years of eradication efforts, Pennsylvania was declared free of the virus in 2009 meeting the requirement of three consecutive years of testing negative.

Image related to Peach (Prunus persica)-Plum Pox (Sharka)

Symptoms of Plum Pox Virus on peach fruit including rings and blotches of uneven color. Courtesy Ontario Ministry of Agriculture, Food and Rural Affairs. © Queen's Printer for Ontario, 2010. Reproduced with permission.

Queen's Printer for Ontario, 2010.

Plum Pox symptoms on peach leaves including yellow rings, lines and vein clearing. Courtesy Ontario Ministry of Agriculture, Food and Rural Affairs. © Queen's Printer for Ontario, 2010. Reproduced with permission.

Queen's Printer for Ontario, 2010.

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Cherry (Prunus spp.) - Nematode, Dagger

Cherry (Prunus spp.) - Nematode, Root-lesion

Cause Taphrina deformans, a fungus. Spores of this fungus overwinter on bark, twigs, and old infected leaves. Infection occurs through bud scales in mid- to late winter just as buds begin to swell. Slow growing shoots and leaves can be infected during cool and wet growing seasons. Maximum susceptibility is between bud break and petal fall. In wet seasons, the fungus continues to cause slight summer infection, particularly west of the Cascade Range.

Image related to Peach (Prunus persica)-Leaf Curl

Sometimes western Oregon can have weather for peach leaf curl well after bud break. Sometimes called late curl or secondary curl. Note that the oldest and newest leaves do not have curl symptoms. Damage is not considered as severe as curl that occurs at bud break.

Jay W. Pscheidt, 2013.

Tree treated for peach leaf curl on the right, non-treated on the left.

Jay W. Pscheidt, 2016.

Without fungicide protection, susceptible trees defoliate in the spring and may die after the next winter.

Jay W. Pscheidt, 2007.

Note the reddish swellings or galls on these peach leaves.

OSU Extension Plant Pathology Slide Collection, 1976.

This is a peach tree grafted with two curl resistant cultivars. Cultivar 'Q 1-8' on the left and the cultivar 'Mary Jane' (with lots of curl) on the right.

Photo by Ed Hoffman, 2003.

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Cherry (Prunus spp.) - Gumming

Species of Prunus, like this peach, often have a flow of resin from pruning cuts which is called gummosis.

Jay W. Pscheidt, 2008.

Cause The specific pathogen(s) in the PNW has not been formally identified but the fungi Cytospora cincta (sexual: Leucostoma cinctum), and the closely related C. leucostoma (sexual: Leucostoma persoonii) have been suggested. Molecular techniques have identified C. pulriova from peach cankers in CA and CO and SC.

Image related to Peach (Prunus persica)-Cytospora Canker

Note the cankered area on the lower portion of this trunk.

Photo by Melodie Putnam, 2001.

This infected peach twig has numerous dark pycnidia of the fungus.

Photo by Melodie Putnam, 2001.

Infected twigs turn brown and eventually gray. Small black fruiting bodies form in the dead tissues.

Photo by Ralph S. Byther

Apples also get Cytospora canker.

Melodie Putnam, 2010.

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Cherry (Prunus spp.) - Crown Gall

Rounded galls near the bottom of the trunk or top of the root crown.

Jay W. Pscheidt, 2007.

Cause The fungi Monilinia fructicola and M. laxa can incite both a blossom blight, a twig and branch dieback, and a fruit rot of several Prunus spp. including many ornamental and fruit trees. Fungi survive year to year on infected twigs, branches, old flower parts, or mummified fruit. Conidia are produced on infected plant debris in the tree when the temperature is above 40°F.

Peaches with brown rot fruit rot showing shriveled fruit and heavy sporulation of Monilinia.

Jay W. Pscheidt, 2007.

Sporulation of fungus on a blighted Suncrest peach flower along with the very start of a twig canker on the stem.

Jay W. Pscheidt, 2017.

Image related to Peach (Prunus persica)-Brown Rot

Rotted peaches mummify and may cling to the tree well into the next growing season.

Photo by Jay W. Pscheidt, 1995.

This shows brown rot of the blossom which results in a twig canker. Note the ooze droplet at the end of the brown cankered area, and sporulation on the blossom.

Photo by Jay W. Pscheidt, 2000.

Note the zones of gray sporulation on the lowest peach.

Photo by Jay W. Pscheidt, 1989.

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Diseases Caused by Pseudomonas syringae

Cherry (Prunus spp.) - Bacterial Canker

Note the dark gumming on the tree trunk and discolored dead cambium where the outer bark has been cut away.

Photo by Iain MacSwann, 1975.

Gumming is associated with bacterial canker formation on branches and twigs, however, other problems can also lead to gumming.

Larry Moore collection.