92 PROTECTION OF PLANTS, 1921-22 



Symptoms 



During the season the leaves are the only parts attacked. The first sign 

 of the disease is a small yellowish spot with a slightly watersoaked margin. The 

 spot enlarges until it is from 1-8 to 1-4 of an inch in diameter and variations in 

 the growth rate of the fungus give rise to concentric markings in the spots. The 

 whole becomes dried out and brownish-black and it frequently happens that the 

 central part of the lesion falls out giving rise to a modified "shot-hole" effect. 

 When the disease is severe owing to suitable infection conditions several spots 

 may coalesce. Under these circumstances the foliage is considerably reduced 

 and at times very few mature leaflets will have any chlorophyll-bearing tissue 

 with which to function in manufacturing food for plant growth and tuber deve- 

 lopment. Persistence of these conditions will involve the premature death of 

 the vines. 



The stems are not affected until late in the season and it is in debris from 

 vines and leaves that the fungus overwinters. 



Life History 



The fungus may overwinter as mycelium in old lesions in plant debris or as 

 spores but there is no known perfect stage. Under moist conditions, spores 

 which have overwintered or have developed from over-wintered mycelium, in- 

 fect leaves causing the characteristic spots. On these dead spots the fungus pro- 

 duces many conidiophores bearing racquet-shaped, multicellular spores. These, 

 when washed or blown to other leaflets, germinate rapidly if moisture be pres- 

 ent and so the disease is spread throughout the season. 



Other Hosts 



AUernaria solani may also attack the tomato. 



Control 



The only method of control is consistent spraying with Bordeaux as for 

 Late Blight. 



(b) Wilt or Fusarlose 



Luckily this disease, caused by Fusarium oxysporum Schlect, is not of 

 serious economic importance here since the causal organism is best suited to 

 sandy loam and a hot growing season. It is common in Pennsylvania, Ohio, 

 Michigan, Indiana, South Dakota, etc., and it is sometimes severe in south- 

 eastern New York. The fungus is to be found in our sandy-loam soils and pota- 

 toes are attacked but wilting to any marked extent does not often occur. 



