University of Maryland Extension

Apple - Pear Diseases

1) Apple scab and pear scab 

dark spots on apple
Photo: R.W. Samson, Purdue
University, Bugwood.org 
Apple scab

large apple scab lesion
Photo: University of GA Plant Pathology,
University of GA, Bugwood.org
Apple scab

apple scab lesions
Apple scab on leaf

Pear scab on fruit and leaves
Photo: Bruce Watt, University of Maine,
Bugwood.org 
Pear scab

Both are caused by different fungi, but the symptoms and control measures are similar. Foliar lesions often appear first on the undersides of the leaves but can also develop on the upper leaf surfaces as well as on the fruit. At first, the margins of scab lesions appear irregular and the interior area is velvety and olive green to black in color. Within a short time, however, lesion margins become much more defined and the lesion may cause the leaf to curl. Early leaf drop and defoliation can occur. Fruit lesions appear similar to foliar lesions initially, but later appear as slightly raised, russeted, scabby areas. Young leaves are susceptible for about 1 week after emergence or until they are fully expanded, but the fruit remains susceptible throughout most of the growing season. Fruit infections that occur within the first 3 to 4 weeks after petal fall usually cause severe deformities and early fruit drop. Later fruit infections tend to be limited to the surface of the fruit and do not affect the overall quality of the flesh.

Tree Fruits - Pest Control and Spray Schedules

2) Fire blight 

fruit tree with fireblight

Fire blight infected branches

classic shepherds crook
Photo: Ward Upham, Kansas St. Un., Bugwood.org 
Fire blight on apple

Branch killed by fire blight
William Jacobi, Colorado St. Un., Bugwood.org 


A destructive bacterial disease of both apples and pears that destroys blossoms, shoots, and limbs, and sometimes kills whole trees. Infected blossom clusters and shoot tips wilt and then rapidly turn brown and die but remain attached. As the infection spreads into the supporting twig or limb, bark cankers develop and are noticeable by their reddish-brown color and slightly sunken appearance. Where susceptible rootstocks are used, the bacteria from a few infection sites on the scion may pass through otherwise healthy limbs and the trunk without causing symptoms but can initiate a canker on the rootstock that will girdle and kill the tree later in the season or the following spring.

Management: Ugly stub pruning method

3) Powdery mildew 

Apple with powdery mildew damage
Photo: Clemson University, USDA Coop
Ext Slide Series, Bugwood.org 
Powdery mildew damage to fruit

Powdery mildew on leaves
Photo: Un. of GA Plant Pathology,
University of Georgia, Bugwood.org 
Powdery mildew on leaves

Powdery mildew on branch
Powdery mildew infected leaves
Photo: William Brown, bugwood.org

Powdery mildew is a fungal disease of apples that appears early in the season. The fungus overwinters in buds and can appear as early as the pink stage before bloom but is often most visible just after petal fall as the new shoots are rapidly developing. Infected leaves are distorted and covered with white, powdery fungal growth. Mildew can be serious on young trees because it stunts new shoot and branch development. The fungus also can produce a net-like russet on the surface of the fruit, but this is largely cosmetic and does not affect the fruit quality.

Tree Fruits - Pest Control and Spray Schedules

4) Rust diseases of apple (cedar-apple rust, hawthorn rust, and quince rust) 

cedar apple rust on apple tree
Cedar apple rust on apple tree
rust lesions on upper surface of leaf
Cedar apple rust lesions on upper leaf
surface
cedar apple rust lesions lower surface
Cedar apple rust lesions on lower leaf
surface
Cedar apple rust spore close-up
Close-up of cedar apple rust spores

Rust diseases are caused by fungi that complete part of their life cycle on the red cedar (juniper) and part on apple, crab apple, hawthorn, or quince. Cedar-apple and hawthorn rusts produce bright yellow-orange spots on the leaves and fruit. Quince-rust spots develop only on the fruit and are sunken and dark green at first, later becoming purplish. Like apple scab, early season lesions can cause the fruit to be deformed and fall early. Unlike apple scab however, the spores produced on foliar and fruit lesions do not cause more infections on apple but, instead, infect nearby junipers. Rust diseases cause leaf drop and defoliation. 

Tree Fruits - Pest Control and Spray Schedules

5) Sooty blotch and flyspeck 

flyspeck and sooty blotch
Photo: Bruce Watt, University of
Maine, Bugwood.org 
Both sooty blotch and flyspeck
(small dark dots on fruit)
close-up of flyspeck and sooty mold
Close-up of flyspeck and sooty blotch
sooty blotch and San Jose scale
Sooty blotch and San Jose scale

These are two common fungal diseases that develop during the summer. Both affect the fruit finish but neither affects the quality of the fruit flesh to any great degree. Sooty blotch produces dark patches of black fungal growth on the surface of the fruit, sometimes covering most or the entire apple. Flyspeck disease often occurs in conjunction with sooty blotch and looks very much like fly specks on paper i.e., shiny little pinpoints of black fungi appearing in small to large circular groups on the apple skin. Both these diseases begin developing about mid-season and tend to be more common and severe in areas that remain wet for extended periods of time following rain or dew.

Tree Fruits - Pest Control and Spray Schedules

6) Summer rots and spots 

apple with rotten spot
Photo: University of GA Plant Pathology,
Un. of GA, Bugwood.org 
Black rot on apple

Black spots on leaves
Photo: Paul Bachi, Un. of Kentucky
Research and Ed. Center, Bugwood.org 
Black rot spots on apple leaves

large rotten area on apple
Photo: Elizabeth Bush,Va Polytechnic
Ins. and St. Un., Bugwood.org 
Bitter rot and anthracnose on apple

Apples on tree with bitter rot
Photo: Gerald Holmes, CA Polytechnic
St. Un. at San Luis Obispo, Bugwood.org 
Bitter rot and anthracnose on apples

White rot spots on apple
Photo: Un. of GA Plant Pathology,
Un. of GA, Bugwood.org 
Botryosphaeria canker, white rot on apple

 

There are many rots and spots on apples which are caused by a variety of different fungi, all of which are harbored in dead twigs and limbs. Fruit rots can develop in two ways. Primary infections can occur directly through the lenticels on the fruit or through the calyx cup at the tip of the fruit. The rots that develop are usually firm, brown to dark brown in color, and appear as circular, slightly sunken spots that may show concentric rings of color variation. As the rot continues to develop, the flesh decays and, depending on the fungus involved, may remain relatively firm and dry or become soft and watery. Secondary rots occur when pathogens become established in wounds caused by fruit cracking, insect feeding, or hail damage.

Tree Fruits - Pest Control and Spray Schedules

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