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Late season fungicides needed to protect against fruit rot in storage. Photo: K. Peter, Penn State
Apple Disease, Pre- and Post-harvest - Keep Apples Free From Fruit Rot - Articles Articles
Management considerations are discussed for mitigating pome fruit rots before and after harvesting. More
Figure 1. Lodged corn seen from a distance.
Corn rootworms Suspected of Resistance to Bt Corn Varieties Discovered - Articles Articles
Western corn rootworms that developed resistance to some Bt corn varieties may now be a problem in PA. 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
Plum Pox Virus
Plum Pox Virus - Articles Articles

Plum Pox Virus

Kari A. Peter, Ph.D.

Plum pox virus (PPV), or Sharka, is a viral disease that infects not only plum but other economically important Prunus species. More
Young galls are light in color and with age become dark and hard, ½ inch to 3 or 4 inches in diameter. Photo by B. Butler.
Tree Fruit Disease - Crown Gall - Articles Articles

Tree Fruit Disease - Crown Gall

Kari A. Peter, Ph.D.

Crown gall is caused by a bacterium, Agrobacterium tumefaciens, and affects apples, pears, quince, peaches, nectarines, apricots, plums, and cherries. More
Source: K. Yoder.
Apple Disease - Brooks Fruit Spot - Articles Articles

Apple Disease - Brooks Fruit Spot

Kari A. Peter, Ph.D.

Caused by the fungus Mycosphaerella pomi, Brooks fruit spot is also known as Phoma fruit spot. The disease attacks apple and crabapple trees and is rarely found in well-sprayed orchards. 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
A characteristic symptom of shoot blight is the bending of terminal growth into the shape of a shepherd’s crook. Photo by K. Peter.
Apple Disease - Fire Blight - Articles Articles

Apple Disease - Fire Blight

Kari A. Peter, Ph.D.

Fire blight, Erwinia amylovora, is a destructive disease that can attack some 75 species of plants of the rose family. More
Source: Joseph OBrien, USDA Forest Service, Bugwood.org
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: William M. Brown Jr., Bugwood.org
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, Bugwood.org
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
Source: Mike Schomaker, Colorado State Forest Service, Bugwood.org
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: Mary Ann Hansen, Virginia Polytechnic Institute and State University, Bugwood.org
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
Source: John Hartman, University of Kentucky, Bugwood.org
Apple Disease - Blister Spot on Crispin (Mutsu) - Articles Articles
Crispin apples are highly susceptible to blister spot bacterial infection, Pseudomonas syringae, about 2 weeks after petal fall for a period of 2 to 4 weeks. More
Photo by G. Moorman
Plum Disease - Black Knot - Articles Articles

Plum Disease - Black Knot

Kari A. Peter, Ph.D.

Black knot of plum, caused by the fungus Dibotryon morbosum, is well-named because of the characteristic black, warty knots it forms on branches of infected trees. More
Source: H.J. Larsen, Bugwood.org
Apple Disease - Apple Union Necrosis and Decline - Articles Articles
Apple union necrosis, caused by tomato ringspot virus, affects the graft union of apple trees, resulting in gradual tree decline. More
Source: University of Georgia Plant Pathology, University of Georgia, Bugwood.org
Peach Disease - Anthracnose - Articles Articles

Peach Disease - Anthracnose

Kari A. Peter, Ph.D.

Most years, anthracnose, caused by two Colletotrichum species, is considered a minor disease of peach. If left unchecked, this disease that attacks peach fruit can cause serious fruit rot infection. More
Source: Dalphy O.C. Harteveld; Apple and Pear Australia Ltd. Used under Creative Commons 2.0 license: creativecommons.org/licenses/by/2.0/legalcode
Apple Disease - Alternaria Leaf Blotch - Articles Articles
Alternaria leaf blotch, caused by Alternaria mali, is a disease that affects apple leaves. More
Photo by K. Peter.
Tree Fruit Disease - Alternaria Rot - Articles Articles

Tree Fruit Disease - Alternaria Rot

Kari A. Peter, Ph.D.

Alternaria rot, Alternaria alternata, is a common fungus found on stone and pome fruit. The disease can occur during preharvest and postharvest. 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
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
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
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
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
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