Minnesota Plant Diseases. 329 



the tissues soften and become discolored. The fungus threads 

 form black, velvety masses in the center of the spot and these 

 masses increase rapidly in size until large mold-like patches are 

 produced. The dark spores are pinched off of the threads 

 which are formed in a loose arrangement on the surface of the 

 fruit. This parasite is a sac fungus of the black fungus group 

 but the sac spores are very uncommon. 



Bordeaux mixture has proved successful in combating this 

 disease. The first treatment should be given when the flower 

 buds open and should be repeated at intervals of two weeks. 



Early blight of potatoes (Macrosporium solani Ell. et Mart.}. 

 This disease is easily mistaken for the ordinary or "late blight," 

 but has an entirely different cause. It affects early crops and 

 is in general found early in the season. The general symptoms 

 are those of premature ripening of the plants. The leaves turn 

 yellow toward the edge, curl up and finally become dark 

 brown. The entire plant is weakened and may die early, giving 

 the appearance of early ripening. The fungus is similar if not 

 identical with black rot of tomatoes. 



Vigorous plants are said to withstand the attack, so that 

 careful cultivation has been recommended. Bordeaux mixture 

 applied early in the season is also an effective preventive. 



The sterile-fungus rot of garden plants (Species of Rhizoc- 

 tonia). All kinds of garden plants are affected by a rot which 

 attacks the roots or lower stem and which frequently causes the 

 death of a great many plants. The classification of this fungus 

 cannot at present be determined, since it has never been found 

 to produce spores. It is therefore called a sterile fungus, though 

 it is of course possible that spores are formed under unusual and 

 rare conditions. The fungus produces tufts of threads on the 

 infected parts of the host plant. These thread tufts are usually 

 brown or blackish. The threads are brown and branch irreg- 

 ularly in forking fashion and often break up into lengths 

 which may germinate in the fashion of spores, but these lengths 

 are not considered real spores. The following list will show 

 some though not all of the plants attacked by this fungus 

 in the United States : bean, beet, carrot, celery, cabbage, cauli- 

 flower, lettuce, potato, radish, rhubarb, ornamental asparagus, 

 china aster, sweet william, coreopsis, and violet. In many cases 



