12 MISC. PUBLICATION 16 8, U.S. DEPT. OP AGEICULTUEE 



the growing season. Much of the diseased fruit drops before picking 

 time, but that which arrives on the market suffers seriously from the 

 disfiguring effect of the blotch spots and occasionally also from rots 

 occurring as secondary infection by other fungi. Blue mold and 

 the black-rot fungus are most commonly found associated with blotch 

 in this way. On the market, blotch causes more loss than bitter 

 rot and less than scab, yet the fungus develops and spreads very 

 little, if at all, in transit and storage. 



CAUSAL FACTORS 



Blotch is caused by the fungus PhyJlosticta solitaria^ which attacks 

 the leaves, fruit spurs, and twigs of the apple. The latter two are 

 the sources from which infection spreads in the spring to other parts 

 of the tree. Blotch spots on the fruit have already been described. 

 On the leaves the disease appears as small, nearly white spots on 

 the blades, and as dark, sunken, oval areas on the midribs and leaf 

 stems. 



During the first year after infection occurs on the twigs and fruit 

 spurs, blotch occurs as black blisterlike spots. During the second 

 year the spots assume a light tan color in the older or central por- 

 tion, with a dark border denoting the extent of the second year's 

 growth. Beginning with the third year the cankers appear as ir- 

 regularly roughened areas resulting from a gradual sloughing of 

 the dead parts by growth of the bark beneath them. 



CONTROL MEASURES 



Blotch can be controlled by spraying three times at 3-week inter- 

 vals, beginning about 3 weeks after the petals fall. In regions 

 where the disease has not been destructive, lime-sulphur is recom- 

 mended for the first application and Bordeaux mixture for the later 

 ones, in order to avoid spray injury to the fruit. Where the attack 

 is severe or likely to be so, Bordeaux mixture should be used in all 

 three applications. Spraying for blotch ihav well be combined with 

 that for bitter rot. {10, 11, 22, 75, 77, 78, 79, 87, 100, IIJ^, m, IJ^B, 

 183, 188, 195, 206, 207, 208, 209.) 



BLUE-MOLD ROT 



{Penicillium expansum (Lk.) ex Thorn) 



Blue-mold rot is the most common and usually the most destructive 

 of all the rots found on apples, pears, and quinces in transit, in 

 storage, or on the market. It occurs on all varieties of these fruits 

 from all parts of the country. 



The rot appears as soft, w^atery spots of a light brown to pale 

 straw color, which show all possible variations in size and may 

 occur on any part of the fruit, "the spots are shallow at first, but 

 extend deeper very rapidly, in fact, just about as rapidly as they 

 increase in diameter on the surface, so that by the time the rot 

 reaches the core it has involved a third or more of the fruit. Whether 

 or not a surface growth of blue mold develops will depend very 

 largely on temperature and moisture conditions and very little on 



