16 MISC. PUBLICATION 541, U. S. DEPT. OF AGRICULTURE 



On the market bacterial soft rot, downy mildew, heterosporium leaf 

 spot, and white rust are the diseases most frequently observed. 



Damage to the young leaves in the center of the plant caused by 

 feeding of the larvae of the seed-corn maggot (Hylemya cilicrura 

 (Rond.)), the so-called budworm injury, and the holes made in the 

 older leaves by feeding of the spotted cucumber beetle {Diabrotica 

 duodecimpunctata (F.)) constitute important insect injuries noted 

 on the market. 



(See 3, 15, 56, 57, 89, 103, 123, lift.) 



Bacterial Soft Rot 



(Erurinia carotovora (Jones) Holland and other organisms) 



OCCURRENCE, SYMPTOMS, AND EFFECTS 



Bacterial soft rot is one of the most important diseases of vege- 

 tables. It affects a wide variety of different commodities causing 

 losses in the field and serious spoilage of the marketed products. 

 Bacterial soft rot is an important market disease on beets, endive, 

 escarole, lettuce, and spinach among the vegetables included for dis- 

 cussion in the present publication. 



Affected tissues become water-soaked, muddy green, or greasy in 

 appearance (pi. 9, G and D). Rapid softening and disintegration 

 follow so that the decayed tissues soon become wet and mushy. Under 

 moist conditions favorable for development of the rot, the leaf may 

 be completely destroyed and have a putrid odor. In dry air the decay 

 may be checked and the affected tissues become dry and brittle. 



CAUSAL FACTORS 



Bacterial soft rot of vegetable commodities is caused by Erwinia 

 carotovora and other bacterial organisms. These bacteria are found 

 commonly in soils and plant debris. They are spread by contact with 

 farm animals, tools, and insects and by running or splashing water. 

 The market product becomes contaminated with the soft rot bacteria 

 while in the field or during harvesting and packing operations. In- 

 sect punctures and other wounds, disease lesions, or other skin breaks 

 are essential for entrance of the pathogen. 



A combination of high humidity and high temperatures is ideal 

 for the reproduction of the bacteria and the development and spread 

 of the decay. Under humid conditions the most favorable range is 

 approximately 77° to 86° F. Frequently the decay is more important 

 at somewhat lower temperatures (69° to 77°), inasmuch as at these 

 temperatures there is less drying-out than at the higher range. The 

 decay is checked by temperatures of about 40° to 45°. 



CONTROL MEASURES 



The control of transit and market losses caused by bacterial soft 

 rot consists very largely in maintaining low temperatures during 

 transit and moving the commodity promptly through marketing chan- 

 nels after it is unloaded. 



Shipping fresh, high-quality produce that is as free as possible 

 from disease lesions, as well as reduction in the crushing and bruising 



