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Tree Fruit Diseases

Fully developed black knot.

An Introduction to Black Knot

Black knot is a fungal disease, caused by Apiosporina morbosa, that attacks stonefruit species in the genus Prunus. Black knot is known for irregular, thick, black swellings on limbs. Severe infestations can reduce production drastically, reducing infected trees to
a worthless condition in a few years if the disease is not addressed.

Black rot canker on diseased limb.

Black Rot Disease in Apples

Black rot disease, caused by the fungus Botryosphaeria obtusa (Schwein), is concerning to homeowners with apple trees as part of their landscapes. All apple cultivars are susceptible to it, but it appears that McIntosh, Cortland, Empire and Northern Spy varieties are the preferred hosts. It seems that black rot is becoming more of a problem than usual. Normally, protectant apple scab programs would keep black rot in check. But, since incorporating other materials (like sterol inhibitors) that have no effect on these fungi, symptoms were more readily observed in the orchards throughout the state.

Brown rot on maturing stone fruit (cherries).

Brown Rot in Stone Fruit

Brown rot (Monillinia fruticola) is a major disease of stone fruits. All stone fruit(i.e., cherries, plums, apricots, nectarines, peaches) is susceptible to this disease, with sweet cherries being the most susceptible. As the fruit ripens and starts changing color, it becomes more susceptible to infection.

Cherry leaf spot lesions on leaf surface.

Cherry Leaf Spot

Cherry leaf spot is a fungal disease caused by Blumeriella jaapii (Rehm) Arx, formally known
as Coccomyces hiemali. It attacks the leaves, leaf stems, fruit and fruit stems.

Fire blight

Fire Blight on Pome Fruit

Fire blight damage can range from minimal to extremely severe depending on several factors.

Cracked apple from stress.

Fruit Cracking

Cultivar choice and tree care are the best ways to avoid and minimize cracking.

Reddish areas on developing leaves are a symptom of peach leaf curl. (Photo credit: MM Rahman)

Peach Leaf Curl

By applying fungicide in a timely manner, peach leaf curl can be controlled.