280 PLANT DISEASES 



Control. — Can be controlled successfully by the use of bor- 

 deaux mixture, 5-5-50. It is always i)r()fitable to spray at least 

 three times, and in a wet season six or more applications should 

 be made. As the vines increase in size, greater quantities of spray 

 and more nozzles must be used. Use from 40 to 100 gallons of 

 sjiniy mixture per acre. 



Dry- Rot and Wilt {Fusarium oxysporum). — A dry rot of the tuber 

 in storage and wilt of plants in the field. Can be detected in the 

 seed tuber before there is any external appearance by examin- 

 ing a section near the stem end. A black ring or chain of dots 

 near the surface is indicative of the rot. Infection frequently 

 takes place through wounds. 



Control. — Reject all diseased tubers for seed. Practice a 

 rotation in which potatoes are not grown on the soil for at least 

 two years. 



Scab {Oospora scabies). — A scabby and pitted roughness of potato 

 tubers. Lime, ashes or manure added to the soil increases the 

 amount of scab by favoring the growth of the fungus. It has 

 become one of the serious diseases of the potato. 



Control. — Do not plant on land which has grown scabby 

 potatoes. Plant clean seed. If only scabby seed is at hand, soak 

 the uncut tubers in a solution of formalin, 1 pint in 30 gallons 

 of water, for two hours. Drain, cut, and plant in clean soil. Use 

 the formalin solution over and over. The same fungus also 

 attacks beets. 

 Pumpkin. — See under Muskmelon (p. 274). 



Quince. Bl.\ck-rot {Sphceropsis malorum). — A trouble which usually 

 appears at the blossom end of young quince fruits, causing them 

 to become black and hard, with a dry rot of the tissue. The same 

 di.sejuse occurs on apples, which see. 



Blight. — See under Pear Blight (p. 277). 



\j£..KF- AND Fruit-spot. — See Pear-Leaf Blight, which is the same 

 di.sease. 



Hu.sT. — The organism causing this disease is of the same habit and 

 nature as that causing apple rust. 



Control. — As for Apple Rust (p. 264). 

 Radish. White ru.st or Mildew (Albugo candidiis). — A whitish 

 powdery growth on the leaves and petioles, often causing distortion. 



