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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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
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
Scales on new growth and fruit produce deep purplish-red coloration in the tissue. Photo by G. Krawczyk.
Tree Fruit Insect Pest - San Jose Scale - Articles Articles

Tree Fruit Insect Pest - San Jose Scale

Grzegorz (Greg) Krawczyk, Ph.D.

The San Jose scale, Quadraspidiotus perniciosus, is a pest of fruit trees, but it attacks many other trees as well as shrubs. More
Apple rust mites. Photo: David Biddinger
Tree Fruit Mite Pest - Apple Rust Mite - Articles Articles

Tree Fruit Mite Pest - Apple Rust Mite

Grzegorz (Greg) Krawczyk, Ph.D.

Apple rust mite, Aculus schlechtendali, is commonly found, but is rarely an important pest of apple in Pennsylvania. 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
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
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
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
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
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
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
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
The disorder is characterized by irregularly shaped necrotic blotches on the leaves, limited by the veins. Affected leaves turn yellow in about 4 days and subsequently fall off the tree. Photo by K. Peter.
Apple Physiological Disorder - Necrotic Leaf Blotch - Articles Articles
The cause of necrotic leaf blotch of apple is not known, and it is considered a physiological disorder. The disorder is most common on Golden Delicious worldwide. More
The fungus survives in the soil as spores. Populations of these spores in the soil increase one to two months after fruit have been harvested. Photo by K. Peter.
Apple and Pear Disease - Mucor Rot - Articles Articles

Apple and Pear Disease - Mucor Rot

Kari A. Peter, Ph.D.

Mucor rot is a fungal disease of apples and pears. The disease is a postharvest storage problem. More
The fungi enter the developing fruit through an opening in the calyx. Photo by K. Peter.
Apple Disease: Moldy Core - Articles Articles

Apple Disease: Moldy Core

Kari A. Peter, Ph.D.

Moldy core is caused by several different fungal pathogens. Many cultivars of apples are affected, including Delicious, which is very susceptible. More
Protect your fruit: bitter rot on apple can wreak havoc in the orchard. (Photo: K. Peter)
Apple Disease - Rots, Keeping Apples Clean - Articles Articles
A review of managing pre- and postharvest apple fruit rots is discussed. Alternative rot management strategies are included. More
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
Once established in the wound, the fungus can quickly spread from infected fruit to adjacent healthy fruit during storage. Photo by K. Peter.
Apple and Pear Disease - Gray Mold - Articles Articles

Apple and Pear Disease - Gray Mold

Kari A. Peter, Ph.D.

Gray mold, Botrytis cinerea, is the most important postharvest disease of pears and is second to blue mold in importance to apple. 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
Apple and Pear Disease - Fire Blight, Dormant Removal of Cankers
Apple and Pear Disease - Fire Blight, Dormant Removal of Cankers - Articles Articles
When it comes to managing fire blight, the first line of defense is good sanitation, which is removing the overwintering source for the bacteria: cankers. More
Apple Disease Control Toolbox - Fungicide Timing
Apple Disease Control Toolbox - Fungicide Timing - Articles Articles
Timing of a fungicide application in relation to disease development is important for achieving the best results. More
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