DISEASES OF CULTIVATED PLANTS 539 



the leaf spot of the celery. The spots of this Cercospora have an 

 angular appearance, as with Isariopsis, from the fact that the small 

 veins act as barriers to the fungus, as it spreads within the leaf, 

 giving sometimes something of a checkerboard appearance to the 

 surface of the affected leaf. The last two kinds of leaf diseases 

 here mentioned are easily distinguished. 



The Cercospora belongs to a group of fungi that is not diffi- 

 cult to check with fungicides, as repeated tests have shown with a 

 common species upon the beet, and therefore the treatment which 

 should be given for anthracnose or rust will meet the demands of 

 the leaf blotch. (N. J. E. S. B. 151.) 



Leaf Spot on Beans and Cowpeas. This trouble was first ob- 

 served on lima beans, but has since also been found on other varie- 

 ties of beans and also on cowpeas. It has been much more destruc- 

 tive on lima beans and cowpeas, and seemed to be quite common in 

 Delaware wherever these plants are grown. The trouble occurs on 

 the leaves and often so seriously injures them as to kill or greatly 

 weaken the growing plants. On lima beans, the disease appears 

 when the plants are about a foot high and continues to increase 

 with the new growth. So far as my observation goes the pods are 

 never diseased. Often reddish spots are found on the pods of lima 

 beans. 



Fungous Leaf Spot. The fungus occurs on the leaflets of 

 beans and cowpeas as irregular or sometimes circular rusty brown 

 areas. These spots become with age lighter in color in the center, but 

 the margin is still darker in color. This is true on the cowpeas as well 

 as on the beans. The spots are for a considerable time sterile, and 

 no spores of the fungus can at this time be found, though often 

 various saprophytic fungi may be found growing on the spots. 



No work has been done to try and control these various diseases 

 by spraying. There seems to be no doubt but that the Bordeaux 

 mixture properly applied would give beneficial results. Another 

 suggestion perhaps fully as practical for the gardener or farmer 

 is always to destroy diseased vines by fire at the end of the season. 

 In this way many spores that remain in the tissue of the plant will 

 be destroyed and the danger from infection next year much 

 lessened. 



Bean Rust. The true rust of beans is, like the anthracnose, a 

 fungous disease. It differs from the anthracnose, however, in many 

 important respects. The most important difference from the grow- 

 ers' point of view is that it is a much less common and destructive 

 disease. It occurs only on the leaves of the bean, rarely on the 

 stems and pods. Except in very severe cases, it does not materially 

 injure the leaves. 



The rust fungus (Uromyces appendiculaius) sends its mycclial 

 threads into the tissues of the bean leaf there to secure nourish- 

 ment for its own growth and development. From the ends of the 

 threads that come to the surface at certain spots, spores are formed. 

 These are of two kinds; the summer spores, brown and forming 

 powdery specks on the underside of the leaf which readily rub off 



