Potato. 347 



there may be seen the characteristic browning and drying of the 

 leaf-tissue, rings of a darker color being visible in the affected 

 areas. The edges of the leaves are more generally affected, and 

 as the small, circular spots increase in size they run together 

 and destroy the entire outer portions of the leaf. These then 

 turn yellow and later brown, the edges curl up, and tin ally all 

 the leaflets and the petiole are destroyed. The injury also 

 extends to the stems, and eventually the plant dies. The pota- 

 toes do not rot, but they remain small. The browning of the 

 tissue often begins during July, the trouble being much more 

 severe upon mature plants, and if the weather is moist the 

 trouble appears to increase less rapidly than during a drought. 

 Whether the early blight fungus is capable of entering unin- 

 jured tissue, or whether its entrance is entirely dependent upon 

 the work of the flea-beetle, has not yet been definitely deter- 

 mined, but it is undoubtedly true that the abundance of this 

 insect has considerable influence upon the prevalence of the 

 disease. In some cases the tissue dies apparently without the 

 assistance of insects. 



Treatment. Spraying the vines with the Bordeaux mixture 

 has given fairly good results. The fungicide should be used at 

 least of normal strength, and it appears probable that a 

 stronger mixture is still more beneficial. For very early pota- 

 toes the first application should be made, in Xew York, iri June ; 

 for medium varieties from the first to the middle of July ; while 

 late varieties may not require treatment before the first of 

 August, although this period is rather late, the third week in 

 July being perhaps an average date. Applications should be 

 repeated at intervals of two to four weeks, three treatments 

 being sufficient in seasons favorable to the fungus. If power 

 sprayers are used, each row should receive as much liquid as 

 is thrown by two Vermorel nozzles while the horse is walking 

 across the field. The vines should be very thoroughly treated. 



Rot ; Blight ; Late Blight ; Downy Mildew (Phytopldlwra in- 

 festans, De Bary). Description. Potato blight, or rot, has 

 long been known as the most serious and destructive of all 

 potato troubles. When the weather is warm and moist the 

 disease spreads with great rapidity, so that an entire field may 

 be destroyed in the course of a few days. The first symptom 

 of the malady is the browning of distinct areas upon the potato 



