GRAPES AKD OTHER SMALL FRUITS 9 



weeks in cold storage. Another type of infection commonly observed 

 after rains is slip skin, described on page 9. 



CAUSAL FACTORS 



In the early stages of the disease, the causal fungus (Boirytis sp.) 

 is present in the rotted tissue but may not be evident on the outside. 

 Later on, it grows to the surface, forming a cottony, white mass which 

 eventually becomes gray through the production of immense numbers 

 of spores and a slight darkening of the mycelium. It is this gray 

 appearance (pi. 3, A) that gives the fungus its common name and 

 serves to distinguish it from others commonly found on fruits. 



In the vineyard it often seems to develop from the inside of the 

 bunch outward, and in some instances apparently results from the 

 spread of the fungus from diseased stems. More often it results 

 from infection by spores at places where juice escapes when berries 

 are broken by the pressure developed as the bunch grows and the 

 berries are crowded closer together. This is especially true in varie- 

 ties that form tight bunches, such as Zinfandel, Burger, and occasion- 

 ally Alicante Bouschet, all of which at times are seriously damaged 

 by the rot while the bunches are hanging on the vine. During wet, 

 cool seasons in California, especially in the bay counties, gray mold 

 is sometimes found causing a decay of the flowers and flower stems 

 and a little later of the young berries. It is possible that the fungus 

 spreads to the larger stems at this time but soon becomes dormant, 

 only to revive on the packed fruit in transit or in storage and there 

 cause further decay of both stems and berries. 



In the vineyard and in storage gray mold and possibly other fungi 

 sometimes form a shallow surface infection on grapes that is called 

 slip skin (pi. 5, E, F). In such infections the mold spreads through 

 the skin and the flesh just beneath it but does not appear on the 

 surface. The condition usually develops after a rain and is common 

 on late Emperors during wet autumns. 



In wet weather gray mold rot is a serious disease because the fungus 

 and its spores are more common then on vines and fruit, and spore 

 germination is increased. When rains occur at or just before harvest- 

 time they cause the skin of the fruit to crack and thus make it more 

 susceptible to attack by gray mold and other decay organisms. The 

 initial infections with gray mold usually take place in the vineyard 

 and later develop into rot in transit and storage. In seasons when 

 grapes are not subjected to rains or foggy weather during harvest, 

 gray mold rot is much less common after harvest. Cool weather 

 does not check the rot, but seems to favor it because gray mold is 

 able to grow at temperatures that seriously limit the growth of other 

 fimgi that may be present. 



In transit and storage, as in the field, conditions most directly 

 affecting the development and spread of gray mold rot are water on 

 the fruit and an^ easy entrance through the skin. Water may be 

 present on fruit picked and loaded during times of heavy rain or dew, 

 or it may condense there because of a moist atmosphere and fluctua- 

 tions in temperatures in the car or storage room. An easy entrance 

 into the fruit may be furnished by injuries resulting from careless 

 handling or too much handling prior to loading, from rough handling 



118834° — 39 2 



