536 INSECTS AFFECTING VEGETATION 



the seed, as in the case of the anthracnose, remain there dormant 

 throughout the winter. With the germination of the seed in the 

 spring the bacteria also begin to multiply and find their way to 

 healthy beans and so the infection spreads. 



No method of treating the seed to prevent the blight has yet 

 been proposed and properly tested. Professor Barlow has demon- 

 strated that the bacteria are readily killed by exposure for ten min- 

 utes to water heated to 122 F., w r hile dry beans can endure such a 

 temperature for some time without injury. While this gives some 

 promise of success the treatment is open to many of the objections 

 raised in the case of the anthracnose. 



The sorting of seed affected with anthracnose has been shown 

 to be highly desirable. Its value in the case of seed affected with 

 blight is very questionable. Owing to the fact that blight-affected 

 seeds are often not discolored, it is manifestly impossible to sort 

 them from the healthy ones. The safest method is to discard all 

 seed known to have come from fields that showed the disease. 



In regard to these practices Professor Barlow says : A field where 

 beans have sickened with this disease is unfit for growing beans for 

 at least one season, as the germ lives over at least one winter in the 

 stems and leaves left on the ground. How long such a field may 

 remain infected is unknown, for we do not yet know whether the 

 germ can live and increase in the soil where no beans are growing, 

 although this is probable. Bean straw from infected fields may be 

 burned. If it is fed to animals or used in bedding, the manure 

 should be returned to the field on which the beans grew, and not 

 spread on fields as yet free from the disease. 



At the New Jersey Experiment Station, a professor has experi- 

 mented for a number of years with several spray mixtures for the 

 prevention of bean blight. The Bordeaux mixture of the strength 

 recommended for the anthracnose has been found to be very satis- 

 factory. Probably a larger number of applications will be neces- 

 sary for the blight than for the anthracnose. 



The Bean Leaf Spot. To this disease of the bean, much 

 more common than generally supposed, is to be charged much of 

 the trouble ascribed to other fungi. This is the Isariopsis griseola, 

 that for the lack of a common name may be called the bean leaf 

 spot. It is quite different from the other bean diseases, in being 

 confined chiefly to the foliage, where it produces numerous spots, 

 usually small and angular, without any colored border. The fun- 

 gus itself forms a gray, mouldy covering upon the under surface 

 of the spot where the spores are produced in vast numbers. From 

 the superficial nature of the spore production, it is safe to conclude 

 that this fungus is amenable to the ordinary treatment for similar 

 diseases. The direct testing in this instance appears to be lacking. 



The Bean Leaf Blotch. This is not uncommon in the United 

 States, but as it only affects the foliage the crop is shortened only 

 indirectly. This disease produces patches of a brown color upon 

 the leaves, causing them to become useless and fall away as in 

 other kinds of cercosporas, like that of the violet leaf spot and 



