FRUIT NOTES - September 1953 



By the time this copy reaches you Professor 1'. H« Thies, Extension Horticul- 

 turist and Editor of FRUIT NOTES, will be back on the job after his year of service 

 with FAG in Yugoslavia, 



Judging by his reports to the Department of Pomology he has had a very busy 

 and most interesting year helping to solve some of the problems of fruit growing in 

 that country. We shall all welcome his return to assist in solving some of the many 

 problems with which the Massachusetts fruit industry is confronted and to resume 

 editorship of these pages, 



i'HHHHhhhhb;- A, P, Frenclia 



T'E RELATION BETVJEEN BLACK ROT, CANKER & FROG-EYE LEAF SPOT OF APPLES 



The disease is caused by the fungus organism Sphaeropsis malorum which also 

 causes black rot cankers on trunks, branches and twigs and frog-eye spot on the 

 leaves. It is necessary to understand the different forms of this disease to ob- 

 tain satisfactory control and avoid serious losses. 



Black Rot on Fruit usually is noticed first when the apple is half grown 

 but also may be found on smaller apples earlier in the season if conditions for 

 infection are favorable. It starts as a purple discoloration at the calyx end and 

 develops as a circular brown spot made up of concentric rings. Development is off 

 to one side so that the calyx is not in the center of the rotted area but near one 

 edge of it. The rot grows quite rapidly vfhen ripening apples are infected. 



In some localities, the trouble is known as "Brown Rot" because of the brown 

 color of the diseased portion which is aLuost tasteless whereas in "bitter rot" it 

 is bitter. 



Half rotted apples fall to the ground where they continue to rot, dry up 

 into hard black mummies, and begin to produce spores in the autumn and winter, iiifith 

 some varieties, such as Cortland, the rotted applet do not drop to the ground but 

 remain as mummies on the trees. The spores become mature and are ready for dissem- 

 ination at the beginning of the grov^-ing period in spring and dissemination continues 

 through summer. Moisture, either rain or dew is necessary for germination and in- 

 fection. The name Black Rot comes from the black mummified apples. 



Black Rot Cankers are formed on trunks, branches and twigs and, like the 

 mummified apples, are a source of spores and infection in the spring. 



Frog-eye Leaf Spot is an infection on the leaves from overwintered mummies 

 and cankers but seldom from overwintered diseased leaves. Infection takes place as 

 soon as the leaves unfold and continues through summer whenever there is enough 

 moisture for spore germination. The first spots appear about May 1st, are brown, - 

 one-sixteenth to one-eighth inch in diameter, and gradually enlarge to one-fourth 

 inch diameter. There is always a narrow purple ring around each spot, A few spots 

 remain in this condition the rest of the season, sane fall out and cause a shot hole 

 effect, but most of them start a secondary growth of brown crescents, always border- 

 ed with purple on the outer edge, on the margins of the old spots in late July or 

 early August, The crescents run together to form brown concentric rings so that 



