Plant Disease Identification and Control

Information on plant disease identification and control, including rot, freeze damage, rust, blight, mold, scales, bacteria, viruses, fungus, wilt, mildew, gall, mites, moths and cankers. Tips on integrated pest management and herbicide summaries.

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Hail damaged fruit need protection from fruit rots. Photo: T. Ford, Penn State
Managing Fruit Rots This Season - News News

Managing Fruit Rots This Season


Fungicide re-applications are necessary since several inches of rain have fallen the last few days. Management considerations are discussed for mitigating pome and stone fruit rots. More
Tree Fruit Disease Toolbox - Fungicide Resistance Management
Tree Fruit Disease Toolbox - Fungicide Resistance Management - Articles Articles
Resistance has sometimes resulted in pest-management-program failures. Below are presented tactics to help delay resistance to fungicides. More
Tiny, black, spherical structures are produced on stalks above the white mold. Each of these contains thousands of spores that are released to float in the air. Photo by K. Peter.
Stone Fruit Disease - Rhizopus Rot - Articles Articles

Stone Fruit Disease - Rhizopus Rot

Kari A. Peter, Ph.D.

Rhizopus rot, caused by Rhizopus nigricans, can be very destructive to harvested fruit. More
Source: Mary Ann Hansen, Virginia Polytechnic Institute and State University,
Apple Disease - Blossom End Rot - Articles Articles

Apple Disease - Blossom End Rot

Kari A. Peter, Ph.D.

Blossom end rot of apple, is caused by various fungi (Sclerotinia sclerotiorum, Botrytis cinerea, Botrysphaeria obtusa) just before or during petal fall. More
Protect tart cherries during bloom to prevent cherry leaf spot infection.
Tree Fruit Diseases - Spring Control Strategies - Articles Articles
May is the battleground month for disease management: be on alert for apple scab, fire blight, powdery mildew, rust, cherry leaf spot, brown rot, and bacterial spot infection conditions. More
Orchard IPM - Apple Scab Scouting and Management
Orchard IPM - Apple Scab Scouting and Management - Articles Articles

Orchard IPM - Apple Scab Scouting and Management

Kari A. Peter, Ph.D., Tianna DuPont

Make sure you know where apple scab overwinters, how to monitor, and when it is most likely to appear. More
Be sure to protect your fruit from rots: bitter rot on Red Delicious. (Photo credit: K. Peter)
Tree Fruit Diseases - Managing Pre- and Postharvest Rots - Articles Articles
A big disease concern is keeping fruit free of rots as they are nearing the home stretch of the season. More
External rot is first visible as small, slightly sunken, brown spots that may be surrounded by a red halo. As the decayed area expands, the core becomes rotten and eventually the entire fruit. Photo by K. Peter.
Apple Disease - White Rot - Articles Articles

Apple Disease - White Rot

Kari A. Peter, Ph.D.

The white rot fungus, Botryosphaeria dothidea, often referred to as “Bot rot” or Botryosphaeria rot, is most important on apple trees, but it also attacks crabapple, pear, grape, and chestnut. More
Necrotic leaf blotch, which is a physiological disorder and not a disease, has been manifesting throughout the area and is predominantly seen on the leaves of Golden Delicious, as well as those cultivars with Golden Delicious as a parent.
Tree Fruit Diseases - Preharvest - Articles Articles

Tree Fruit Diseases - Preharvest

Kari A. Peter, Ph.D.

Management is discussed for controlling the physiological disorder necrotic leaf blotch on apple and for pre-harvest peach diseases. More
Pear Disease - Stony Pit
Pear Disease - Stony Pit - Articles Articles

Pear Disease - Stony Pit

Kari A. Peter, Ph.D.

Stony pit of pear is presumed to be caused by a destructive virus, but the virus has not been isolated. Affected fruit are unsightly and unmarketable. More
Photo by K. Peter.
Pear Disease - Sooty Mold - Articles Articles

Pear Disease - Sooty Mold

Kari A. Peter, Ph.D.

Sooty mold fungi of the genus Capnodium cause an unsightly blackening over the surface of fruit and leaves. More
Spores of the fungi are windblown into and throughout the orchard; fruit infection can occur any time after petal fall but is most prevalent in mid- to late summer. Photo by K. Peter.
Apple Diseases - Sooty Blotch and Flyspeck - Articles Articles
Affecting apple, crabapple, and pear trees, sooty blotch and flyspeck of apple are separate diseases, but both are normally present on the same fruit. More
Rusty spot is recognized only on the fruit. The earliest symptoms on young green fruit appear as small, orange-tan spots. K. Peter.
Peach Disease - Rusty Spot - Articles Articles

Peach Disease - Rusty Spot

Kari A. Peter, Ph.D.

Minor issue in Pennsylvania and is caused by the same fungus as apple powdery mildew. Loring is a susceptible variety. More
On leaves, cedar-apple rust first appears as small, pale yellow spots on the upper surfaces. The spots enlarge to about 1∕8 inch in diameter. Photo by K. Peter.
Apple Diseases - Rust - Articles Articles

Apple Diseases - Rust

Kari A. Peter, Ph.D.

There are three rust diseases: cedar-apple rust, hawthorn rust, and quince rust. The most common is cedar-apple rust, Gymnosporangium juniperi-virginianae. More
A declining tree with bark removed from graft union to show necrosis. Note numerous rootstock suckers. (Photo: K. Peter)
Apple Disease - Rapid Apple Decline (RAD) or Sudden Apple Decline (SAD)? - Articles Articles
There is a mystery surrounding rapid apple decline/sudden apple decline of young, dwarf apple trees. More
A thermometer that records the maximum and minimum temperature is extremely useful for determining degree hours.
Tree Fruit Diseases - Predicting Infection Periods to Apply Protection - Articles Articles
This article will help you manually determine infection periods for certain diseases. Also included is a table listing coppers available to manage bacterial spot during cover sprays. More
Source: William M. Brown Jr.,
Peach Disease - Powdery Mildew of Peach, Nectarine, and Apricot - Articles Articles
Powdery mildew, Sphaerotheca pannosa, sometimes called rose mildew (it affects some woody ornamentals), is not often serious. More
Source: Bruce Watt, University of Maine,
Stone Fruit Disease - Powdery Mildew of Cherry and Plum - Articles Articles
The disease is caused by Podosphaeria oxyacanthae, one of the common species of the powdery mildew group of fungi. More
On leaves of new shoot growth symptoms of powdery mildew are feltlike, white patches on the margins and lower surfaces. Infected leaves curl upward and soon become covered with a powdery coating of spores. Photo by K. Peter.
Apple Disease - Powdery Mildew - Articles Articles

Apple Disease - Powdery Mildew

Kari A. Peter, Ph.D.

Powdery mildew, caused by the fungus Podosphaera leucotricha, attacks buds, blossoms, leaves, new shoots, and fruit of wild and cultivated apples and crabapples. More
Source: Mike Schomaker, Colorado State Forest Service,
Stone Fruit Disease - Plum Pockets - Articles Articles

Stone Fruit Disease - Plum Pockets

Kari A. Peter, Ph.D.

In the northeastern United States, the most important disease affecting American-type plums is known as plum pockets, or bladder plum. It is caused by Taphrina communis. More
Source: Joseph OBrien, USDA Forest Service,
Plum Disease - Plum Leaf Spot - Articles Articles

Plum Disease - Plum Leaf Spot

Kari A. Peter, Ph.D.

Leaf spot of plums and prune-type plums is caused by the fungus Coccomyces prunophorae. More
Tree Fruit Disease - Phytophthora Collar, Crown and Root Rots - Articles Articles
Phytophthora collar, crown, and root rots, Phytophthora cactorum, continue to be a major cause of tree death in Pennsylvania orchards. These rots can affect both pome and stone fruit. More
Although the fruits remain susceptible through harvest, it is usually only infections that occur during the shuck split to pit hardening stage of development that have an opportunity to show symptoms at harvest. Photo by K. Peter.
Peach Disease - Scab - Articles Articles

Peach Disease - Scab

Kari A. Peter, Ph.D.

Peach scab, Cladosporium carpophilum, is an important disease in warm, humid peach-producing areas of the world. More
Infected leaves, which begin appearing in mid-May, are easily distinguished from healthy leaves in that they are puckered and thicker than normal. Deformed areas are red to yellow at first and then turn brown. Photo by K. Peter.
Peach Disease - Peach Leaf Curl - Articles Articles

Peach Disease - Peach Leaf Curl

Kari A. Peter, Ph.D.

The peach leaf curl fungus, Taphrina deformans, destroys early peach leaves. More
The canker typically exhibits a few pink or coral fruiting structures of the fungus in mid-summer. Photo by S. Weikert.
Apple Disease - Nectria Twig Blight - Articles Articles

Apple Disease - Nectria Twig Blight

Kari A. Peter, Ph.D.

Nectria twig blight, caused by the fungus Nectria cinnabarina, is a minor disease that breaks out occasionally. More
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