6 MISC. PUBLICATION 3 4 0, U. S. DEPT. OF AGRICULTURE 



of the spot is light brown with a darker band encircling it (pi. 3, B, C, 

 D, E). This has sometimes caused black rot spots to be mistaken for 

 spots of anthracnose, although in the latter the center is gray rather 

 than brown and is surrounded by a bright-red ring. 



Very early in the development of the disease, numerous brown to 

 black raised specks develop on the surface of the diseased areas (pi. 3, 

 D). These are thespore-producing bodies (pycnidia) of the black rot 

 fungus, and they give affected fruits a characteristic appearance that 

 is of value in diagnosis. 



The disease is rarely seen on fruit on the market and then only in the 

 form of wrinkled, dried-up mummies. It is not known to develop or 

 spread in transit. 



CAUSAL FACTORS 



The fungus Guignardia bidwellii (Ellis) Viala and Kavaz which 

 causes black rot winters over in mummies or in diseased spots on old 

 canes, tendrils, and leaf petioles, and spreads from these places in the 

 spring by means of spores liberated from the fruiting bodies of the 

 fungus. Infection and development of the disease is favored by warm, 

 wet weather and is either checked or entirely prevented by cool, dry 

 weather. 



CONTROL MEASURES 



The chief control measure recommended for black rot is spraying 

 with bordeaux mixture; details concerning spray schedules are given 

 in the publications cited below. It is desirable also to remove black 

 rot mummies at picking time as completely as may be practicable 

 without too much expense 4 (13, 17, 18, 21 22. 26, 27, 28, 52, 53). 



BLUE MOLD ROT 



(Penicillium sp.) 



Blue mold rot is rarely found on small fruits before harvest, but it 

 often damages them quite severely in transit and storage. On all of 

 them it is characterized by the usual scanty growth of mold which is 

 white at first and turns bluish green later. The mold grows along the 

 edges of cracks in the skin or over most of the surface of affected areas. 

 It is also characterized by a slight browning and a soft, more or less 

 watery, mushy condition of affected tissues. 



The rot is more common on grapes than on other small fruits, 

 although it occasionally appears in rather high percentage on rasp- 

 berries, blackberries, and dewberries. It is extremely rare on straw- 

 berries and so far as known does not occur on cranberries. The fungus 

 that causes it is a weak parasite and at least in its first attack is con- 

 fined to fruits crushed by too tight a pack or rough handling. Later 

 when it becomes well established, it seems to be able to spread from 

 affected fruits to sound ones lying in contact with them. On grapes 

 it frequently forms a rather heavy growth on the stems and probably 

 grows from these into the berries by way of the cap stem (pi. 4, ^4). All 

 fruits thoroughly infected with it have a moldy smell and taste (7, 9, 

 32.) 



4 Porter, B. A., and Demaree, J. B. See footnote 3. 



