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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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
Source: Mary Ann Hansen, Virginia Polytechnic Institute and State University,
Bramble Disease - Spur Blight - Articles Articles
Red and purple raspberries are more affected by spur blight, Didymella applanata, than black raspberries. Blackberries appear to be immune. 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
Plum Pox Virus - Replanting Stone Fruit in Sites Previously Affected by PPV
Plum Pox Virus - Replanting Stone Fruit in Sites Previously Affected by PPV - Articles Articles
Lifting the PPV quarantine in Pennsylvania offered the opportunity for a “fresh start” and growers must plan carefully to get the most from their investment. More
Source: SCRI-Dundee , Scottish Crop Research Institute,
Strawberry Disease - Red Stele - Articles Articles
Red stele, or red core, Phytophthora fragariae, is the most serious disease of strawberry in areas with cool, moist soil conditions. 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
Stone Fruit Disease - Prunus Stem Pitting
Stone Fruit Disease - Prunus Stem Pitting - Articles Articles
Prunus stem pitting, caused by the tomato ringspot virus, is an important disease of all stone fruits. It is also called prune brownline and constriction disease. More
Blueberry Disease - Powdery Mildew, Not Symptoms You’d Expect
Blueberry Disease - Powdery Mildew, Not Symptoms You’d Expect - Articles Articles
Powdery mildew, a warm-weather high-humidity disease, is present in some blueberry plantings. Lowbush, highbush, and rabbiteye blueberries are all affected. 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
Photo by Kathy Demchak.
Strawberry Disease - Powdery Mildew - Articles Articles
Powdery mildew, Sphaerotheca macularis, occurs on a wide range of hosts and almost everywhere the strawberry is grown. 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
Source: André Bolay, St. Fédér. de Recherches Agronomiques de Changins,
Raspberry Disease - Phytophthora Root Rot - Articles Articles
Phytophthora root rot, Phytophthora species, is now regarded as a major cause of declining red raspberry plantings. 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
Source: Howard F. Schwartz, Colorado State University,
Pear Disease - Pear Scab - Articles Articles
Pear scab resembles apple scab in nearly all respects and is caused by the closely related fungus Venturia pirina. More
Source: A Jones.
Pear Disease - Pear Leaf Spot Fungus - Articles Articles
The pear leaf spot fungus, Mycosphaerella pyri, infects the leaves of pear, quince, and occasionally apple trees. Numerous leaf spots can produce defoliation. More
Each lesion may have dozens of spots, resulting in extensive defoliation. Photo by K. Peter.
Pear Disease - Leaf Blight and Fruit Spot - Articles Articles
Leaf blight and fruit spot is caused by the fungus Fabraea maculata, which infects the leaves, fruit, and shoots of pear and quince trees and the leaves of apple trees. 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