\ 1 8 THE POTATO 



EARLY BLIGHT, ' OR LEAF SPOT DISEASE (Macro- 

 sporium solani}. It is a fungus disease which appears 

 usually in June to July, or ahead of the late blight. It 

 does not generally attack vigorous plants. It spreads 

 in warmer, drier weather than the late blight. It forms 

 circular brown spots with target-like markings on 

 the leaves. It enters the leaf through tissues weak- 

 ened by other agents, as flea-beetles, etc. It does not 

 attack the tubers directly, and never causes them to rot. 



Preventives. i. Spraying with Bordeaux mixture. 



2. Selection of vigorous varieties. 



3. Better tillage and fertilization. 



POTATO ROSETTE {Rhizoctonia solani.*} This dis- 

 ease has been known since 1842, but it is only recently 

 that it has caused considerable trouble. It is now well 

 established all over the country, and in some places 90 

 per cent, of the tubers appear to be affected by it. It 

 tends to cause the formation of an abnormal number of 

 small tubers of no value. The stems show discolored 

 decaying areas above ground and brown dead areas be- 

 low, and the leaves tend to grow in rosette-like clusters. 

 The resting spores live for several years in the soil, and 

 the methods of infection are by seed potatoes, beet and 

 mangold roots, dead potato stems, and some weeds; 

 hence, fields should be kept clean. The disease at- 

 tacks beets, mangolds, and clover. Soaking the seed 

 in formalin will destroy the spores on the potatoes, but 

 is of no value if the soil is infected. Planting sound 



1 Vt. Bui. 49, pp. 91-96; Bui. 72, pp 16-25. U. S. D. A. Farmers' Bui. 15, pp. 

 4, 5; Bui. 91, p. 5. (N. Y.) Geneva Bui. 123, p. 236. N. H. Bui. 45, pp. 50, 56. 

 Tex. Bui. 42, p. 923. 



* (N. Y.) Cornell and Geneva Bui. 186. Col. Bui. 69, 70. Ohio Bui. 139, 145. 



