GRAPES AND OTHER SMALL ERTJITS 5 



Black mold rot in its commonest form is a black, watery, odorous 

 decay occurring usually at the centers of the bunches. It is character- 

 ized chiefly by the presence of masses of spores that appear black on 

 casual examination but are actually dark purplish brown. Because 

 of this color and the general appearance of a nest of affected berries, 

 the disease is often called sooty mold or smut. The mycelium is 

 usually so scant as not to be evident except under a hand lens. 



CAUSAL FACTORS 



Black mold rot is caused by the fungus Aspergillus niger, which also 

 attacks many other fruits, including peaches, citrus fruits, and pome- 

 granates. In the regions where it occurs, the spores of the fungus seem 

 to be everywhere and able to cause infection when favorable conditions 

 are furnished. The most important of such conditions are skin breaks 

 and leakage of juice; hence, as noted earlier, the rot occurs most often 

 on those varieties that form tight bunches. 



The spores are borne in small clusters or heads that are easily seen 

 by the aid of a hand lens. There is no covering around the clumps of 

 spores, as in rhizopus. The mycelium is white, but, unlike that of gray 

 mold and rhizopus, it is almost always scant. 



Black mold rot is primarily a field disease, but it is sometimes found 

 on grapes as they reach the market. Its development is favored by 

 high temperatures (70° to 100° F.); hence its presence on grapes on 

 arrival at the market is probably a good indication that the rot was 

 present when the grapes were packed and escaped the notice of the 

 packers or that inadequate transit refrigeration was furnished. 



CONTROL MEASURES 



Investigations have been made relative to methods of controlling 

 the disease in the vineyard, but no effective measures have been 

 developed. Tliinning the grapes on the bunches has been practiced 

 by some vineyardists. For transit control, careful handling, prompt 

 movement of shipments, and temperatures of 40° to 50° F. are fully 

 as important with this disease as with gray mold rot, rhizopus rot, and 

 blue moid rot. The usual sulphur dioxide fumigation is also helpful 

 in controlling the disease in transit (7, 9, 32). 



BLACK ROT 



(Guignardia bidwellii (Ell.) Via^a ana Ravaz) 



OCCURRENCE, SYMPTOMS, AND EFFECTS 



Black rot occurs in all the grape-growing regions of the United 

 States except California. It is widespread in Europe, and, wherever 

 found, is one of the most serious diseases with which grape growers 

 have to contend. It is rarely seen on fruit on the market. 



Black rot attacks all the green parts of the vine, producing (1) 

 reddish-brown, irregularly shaped spots on the leaves; (2) small, dark- 

 colored cankers on the canes, the fruit stems and the petioles, and veins 

 of the leaves; and (3) a rot of the fruit. The latter appears at first as 

 a minute blanched area that soon turns darker, becomes sunken, 

 enlarges rapidly, and in about a week turns the whole fruit into a 

 hard, shrivelled, black mummy. During the earlier stages the center 



