University of Maryland Extension

Diseases of Stone Fruit

1) Brown Rot, Monilinia fructicola

rotten peach

Brown rot on peach

peach mummy
Peach mummy

Brown Rot is the most common and devastating fruit disease of peaches and nectarines in Maryland. It also attacks plum and cherry. This fungal disease damages blossoms (blossom blight), shoots, small branches, fruit on the tree, and ripening harvested fruit sitting on the kitchen counter. It is spread by wind, water, insects, and humans and can only enter through a wound or lenticel. Many cycles of infection can occur in one growing season. The fungus overwinters on infected, withered fruit known as mummies, on fruit stems and in cankers found on small branches. Warm, rainy weather during the bloom period will greatly increase the inoculum levels. Ripening fruits are most vulnerable to infection. Small, circular brown lesions that expand on ripening fruit can be observed. Tufts of gray spores appear under moist conditions.

Nonchemical management:
• Remove and dispose of fruit mummies from the ground and from trees and always try to remove fruit stems attached to the mummies.
• Handle fruit gently. Insect- and hail-induced injuries and rough handling will help spread the disease. Even rubbing the fuzz on a peach creates a wound opening.
• Harvest prior to full ripeness. Fruit has reached maximum sugar content when background color is all yellow; complete the ripening process for 1 to 2 days indoors.
• A post-harvest 1 to 2 minute dip of fruits in a 10% chlorine bleach solution will kill surface spores.
• Preliminary research suggests that yard waste compost, spread as a thin mulch under trees during the growing season, may reduce brown rot incidence.

Fungicide control:
• A protective fungicide barrier is critical from prebloom through preharvest.
• The critical times to spray are when 5 to 10% of the blooms are open, at full bloom, and about 2    weeks prior to harvest.
• If disease pressure has been high, apply cover sprays, beginning at petal fall.
• Alternate fungicides to slow ability of fungus to build up resistance.
• Organic growers should apply 95% microfine wettable powder sulfur or flowable sulfur with a surfactant. Sulfur, in its gaseous stage, kills the fungus. The finer the sulfur particles the more quickly the gas is produced, and the more effective the fungicidal activity.

Tree Fruits - Pest Control and Spray Schedules

2) Bacterial spot of peach and nectarine, Xanthomonas arboricola pv. pruni

Spotted peach tree leaves

Photo: Gerald Holmes, CA Polytechnic St.
San Luis Obispo, Bugwood.org 

 

spotted peach
Photo: Clemson Un. - USDA Coop.
Extension Slide Series, Bugwood.org

 

This is a difficult and expensive disease to control. Infections occur only when foliage and fruit are wet. Foliar lesions begin as small dark spots. In defense, the leaf quickly walls off the spot and drops the spotted area, leaving a shot-hole. Many infections can make leaves look tattered. Where infections occur on the midvein, leaves turn yellow and often defoliate. Fruit infections cause spotting and cracking of the fruit. The best approach is to choose varieties that are moderately to strongly resistant to this disease.

3) Black knot

black knot on branch

Is a fungal disease that produces large, black, gall-like knots on the limbs and twigs of plum and cherry trees. Infected shoots and limbs should be cut out 6 to 8 inches below the symptoms and destroyed annually when the trees are pruned and before the knots become very large.

Tree Fruits - Pest Control and Spray Schedules

4) Leucostoma canker (also known as Cytospora or Valsa canker)

canker and gummosis on stem
Photo: William M. Brown Jr., Bugwood.org 
Canker on bark with gummosis

A perennial and destructive disease of all stone fruits that produces bark cankers that gradually enlarge and eventually girdle and kill limbs and trees. Amber-colored gum (gummosis) often exudes through the bark around these cankers. The fungus usually invades dead or severely weakened wood first, then advances into healthier wood. Vigorous growth is the best protection against Leucostoma canker, since trees are then better able to defend themselves by limiting the advance of this fungus in limbs and trunks. There are no effective fungicides for Leucostoma canker, so control has to be managed culturally. In Maryland, stone fruit trees should never be pruned before March. When pruning is done, make sure all dead wood and cankers on small limbs are removed. Avoid excessive nitrogen fertilization, so that trees do not suffer from cold winter injury. Where trees develop a dense foliar canopy, water sprouts on the inside of the trees are often weak, thin, and willowy. These will die in early winter and can be readily colonized by the fungus to gain entry into the supporting limb, so remove these before winter begins. Finally, keep peach tree and lesser peach tree borers under control because these insects often provide entry wounds for the Leucostoma fungus.

5) Peach leaf curl, Taphrina deformans

puckered peach tree leaves
Puckered leaves (lower left corner)

close up of peach tree curl
Close-up of peach tree curl

A fungal disease that causes serious defoliation and fruit loss on peaches and nectarines.  This is a common problem that infects peach trees during bud swell and as buds begin to open. It typically occurs, when spring weather is cool and wet as trees come out of dormancy. A similar disease, plum pockets, sometimes occurs on plums. Fungal spores overwinter on twigs. This disease is difficult to control because weather is unpredictable, and no fungicides will control the disease after the buds open. For this reason, the most effective control measure is to routinely apply a fungicide such as a Bordeaux mix or liquid lime sulfur to prevent the disease. Application should occur sometime between the late fall and early spring when the leaves are off of the tree but before the buds being to swell. Thorough coverage of all bark and bud surfaces is important. 

Tree Fruits - Pest Control and Spray Schedules

6) Peach scab, Venturia carpophila

black,scabby spots on peach
Photo: Clemson Un. - USDA Coop. Extension
Slide Series, Bugwood.org

A fungal disease that can be extremely mild or so severe that the crop is ruined by secondary fruit cracking and rot. Infections occur during the first month after petal fall, but the black scabby spots that result may not be apparent for 30 to 40 days, at which time no treatment is available. Sulfur or captan fungicide can be used in three sprays spaced 7 to 10 days apart beginning about 2 weeks after petal fall.

Tree Fruits - Pest Control and Spray Schedules

7) Cherry leafspot, Blumeriella jaapii

small holes in cherry leaves from leaf spotcherry leaf spot yellow leaves
Photo: Ward Upham, Kansas St U. 
Bugwood.org 

A fungal disease that has the potential to totally defoliate cherry trees early in the season so that they are weakened and more likely to be damaged by winter temperatures. Yellowed leaves with reddish-brown spots usually appear in early June. The fungus overwinters on fallen leaves, and good control can be achieved by thoroughly removing all cherry leaves from the planting in the fall.

Tree Fruits - Pest Control and Spray Schedules

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