Bull's eye rot

Bull's eye rot

Bull's eye rot, Golden Delicious

Bull's eye rot, Red Delicious

Bull's eye rot, Golden Delicious

Bull's eye rot, Golden Delicious

Market Diseases of Apples, Pears, and Quinces
Bull's-Eye Rot

Pezicula malicorticis (Jacks.) Nannf.

Occurrence and importance
Bull's-eye rot at times causes serious losses in apples grown in Washington, Oregon, and British Columbia. The disease occurs in practically all of the irrigated districts east of the Cascade Range, and on fruits grown in the more humid irrigated districts west of the Cascade Range.

Bull's-eye rot infections occur in the orchard, becoming established in the fruits at any stage of development from petal fall onward. The rot usually begins at open lenticels and develops slowly at cold-storage temperatures, appearing on the fruits late in the storage season, during transit, and on the market. The rot does not spread from one fruit to another. All varieties are susceptible, but the rot is most frequently seen on Winesap, Yellow Newtown, Delicious, and Golden Delicious.

The disease has been reported as occurring on apples in Idaho, Maine, Michigan, Pennsylvania, and West Virginia, but bull's-eye rot is usually not a problem in these states.

Symptoms
Bull's-eye rot occurs at open lenticels or at breaks in the skin. The rot spots may be only specks, but most of them are 1/2 to 1 inch across by the time they reach the market. They may occur singly or may be numerous. They may be pale yellowish cream or uniformly brown, but are most often brown with a pale center that forms a bull's-eye (top two photos). The spots are flat to sunken, and the rotted tissues are relatively firm. The skin over the surface does not break easily under slight pressure. The rot may be shallow or nearly as deep as wide. In the deeper rots the penetration is more or less U-shaped. Ordinarily the decayed tissues are somewhat mealy and do not separate readily from the healthy tissues. Spore-bearing tufts of the causal fungus may or may not be present on the surface of the rot, but when present are short, wet, and cream-colored and protrude through the skin.

Bull's-eye rot closely resembles fisheye rot, but can be distinguished from it by being less firm and having a mealy texture. In fisheye rot the surface is tougher, and the decayed tissues are dry and stringy. Fisheye rot may be accompanied by mold, consisting of white cobweb-like strands spreading over the surface of the fruits.

Bull's-eye rot may also be confused with side rot at times, but generally they can be distinguished by close examination. The skin over areas affected with side rot is very tender and breaks readily under slight pressure. Side rot is usually shallow, saucershaped, and wet, and is easily scooped out from the healthy tissues.

Causal factors
The causal fungus of this disease has been reclassified since the last revision of this publication. The perfect stage has been renamed Pezicula malicorticis (Jacks.) Nannf., and the imperfect (asexual) stage has become Cryptosporiopsis curvispora (Pk.) Gremmen.

The fungus attacks the trees, producing cankers on the branches. Spores of the asexual stage of the fungus develop on the cankers and are carried to the fruits by dripping or blowing water during rain storms.

Control measures
A fungicidal spray program in the orchard is the best method for controlling bull's-eye rot. The recommendations of the State extension service or experiment station should be followed in such a program. Bull's-eye rot can also be reduced by cooling the fruits rapidly and maintaining a temperature range of 31° to 32 °F to hold ripening to a minimum.

Where tree props and rainy weather interfere with fall spraying, losses from the disease can be minimized by use of bull's-eye rot forecast technique. This consists of holding samples of apples from grower-lots at 65° to 70 °F and high relative humidity to hasten the development of bull's-eye rot from incipient infections. Lots of fruits showing a potential for bull's-eye rot after 30 days under these conditions should be marketed early in the storage season.