18 U. S. DEPARTMENT OF AGRICULTURE. 



GRAY MOLD ROT 



OF ARTICHOKE, BEET, CABBAGE, CARROT, CAULIFLOWER, CITRON, LET- 

 TUCE, ONION, PARSNIP, RHUBARB, RUTABAGA, SALSIFY, SHALLOTS, 

 TURNIP, AND OTHER VEGETABLES. 



Cause : A fungus (Botrytis) . 



This is a semi-watery to watery soft rot characterized 

 externally by a gray velvety fungous growth. Frequently 

 there is a slight tinge of green or brown in the gray color of 

 this mold. At times gray to black solid masses known as 

 sclerotia are produced on the affected tissues as in the case 

 of the gray mold rot of onions generally known as "neck 

 rot." 



Gray mold rot can be differentiated from the watery soft 

 rot caused by Sclerotinia by the gray color of the mold and 

 by the absence of a cottony mycelium. 



Gray mold rot can be differentiated from slimy soft rot 

 by the gray fungous growth and by the absence of offensive 

 odors. Rhizopus rot can be differentiated from gray mold 

 rot by its abundant stringy and coarse mycelium, its spo- 

 rangia, and its sour odor. 



In case of doubt as to the identity of a given rot, it is 

 advisable to collect and incubate some material in a warm 

 damp-chamber secured either by wrapping it in paper or 

 by placing it in covered pans. If a mycelium develops 

 within 24 hours, the rot is not slimy soft rot. If a white 

 cottony mycelium develops which later becomes matted, the 

 fungus is probably Sclerotinia. A grayish, powdery fungous 

 growth indicates Botrytis, and a stringy mycelium with 

 sporangia, Rhizopus. The presence of sclerotia will further 

 indicate either Sclerotinia or Botrytis. 



Often the watery soft rot due to Sclerotinia and the gray 

 mold rot due to Botrytis occur either together or^in close 

 succession on the same specimen. 



Gray mold rot does not progress as rapidly as watery 

 soft rot and, like slimy soft rot, may be checked by drying 

 affected tissues, while watery soft rot (due to Sclerotinia) 

 progresses rapidly even under dry atmospheric conditions. 



Infection takes place in the field, in transit, and in storage 

 since the spores of the fungus seem to be everywhere pres- 

 ent. The fungus may develop in the field if moist weather 

 prevails. 



The rot occurs commonly in mature tissues kept in a very 

 humid atmosphere. It attacks frozen or bruised tissues very 

 readily. 



Affected stock may be made marketable if trimmed and 

 kept in a dry, well-ventilated place. It is not safe to store 

 affected stock because it is a menace to healthy stock, the 

 fungus spreading readily from affected to healthy tissues. 



Little is known about the control of this rot, but soil 

 aeration and proper ventilation in transit and storage are 

 preventive measures. The neck rot type of this rot found 



