disease in mature pepper plants. At the Florida Agricultural Experiment 

 Station 5 applications at 200 p. p.m. effectively controlled the disease. 

 Good results were also obtained in Florida when 2 to 4 pounds of a neutral 

 copper fungicide in 100 gallons of water was combined with only 100 to 

 200 p. p.m. of streptomycin. 



DISEASES OF CUCURBITS 



Downy Mildew 



Downy mildew is a destructive disease of cucumber, as well as 

 muskmelon and watermelon, in the Eastern and Southern States. It is 

 usually less damaging in the North Central States and rarely occurs in the 

 Southwest. The causative fungus, Pseudoperonospora cubensis , also 

 attacks pumpkin and squash. 



The disease first appears as a gray-tinged spore mass on older leaves. 

 It causes snaall, angular, yellowish spots, which later increase in number 

 and size. Severely infected leaves turn yellow, then brown, and finally 

 shrivel. Maturing fruits or infected plants fail to color properly, are 

 tasteless, and usually are sunburned. 



Various fungicidal sprays and dusts have proved useful in the past, 

 but effective control with streptomycin has recently been reported. The 

 Florida Agricultural Experiment Station used 7 applications of Agri-mycin 

 at a concentration of 200 p. p.m. of streptomycin to achieve control on 

 cucumbers. Plants were sprayed at 4 to 5 day intervals. The same number 

 of applications of streptomycin (100 p. p.m.) and tribasic copper (2 to 4 

 pounds per 100 gallons of water) proved equally effective. 



Angular Leaf Spot 



Angular leaf spot is serious only in cucumbers. The causal organism, 

 Pseudomonas lachrymans , forms water-soaked spots on leaves and fruits. 

 The spots become angular, turn gray to tan in color, and form an exudate 

 on the lower surface of the leaf. Many of the infected spots loosen and fall 

 out. "Infected fruits show a brown, firm rot which ruins salability. Chances 

 of seedling infection can be reduced by soaking the seed in mercuric 

 chloride, but the treatment may not prevent an occurrence of the disease 

 if conditions favor its development. 



Field-grown cucumber plants at the Agricultural Research Center 

 were protected from angular leaf spot by spraying with either Agri-mycin 

 or Agristrep at a concentration of 400 p. p.m. of streptomycin the day 

 before inoculation. Infection was further reduced to less than 1 infected leaf 

 per plant by additional sprayings on the fifth, tenth, and fifteenth day after 

 inoculation. 



DISEASES OF POTATOES 



Seed-Piece Decay and Blackleg 



Decay of potato seed pieces is caused by various bacteria, including 

 Erwinia atroseptica and Pseudomonas fluorescens . These organisms fre- 

 quently cause heavy losses in field stands and of potatoes in storage. 



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