264 Diseases of Truck Crops 



depends on weather conditions. It is most prevalent 

 during periods of heavy night dews, or during pro- 

 longed rains, and in hot muggy weather. 



Symptoms. Anthracnose is so characteristic, that 

 it cannot be mistaken for any other disease, except 

 perhaps the blight. In light attacks, the seeds are 

 covered with sunken brown to black specks. These 

 are especially evidenced on the black seeded varieties. 

 In severe attacks, the seeds are covered with deep 

 sunken black spots which are rifted in the center. 

 On the leaves the disease attacks the veins, which 

 become blackened and somewhat shrunken. Fre- 

 quently it attacks the petioles, especially at the point 

 of leaf attachment. In this case the foliage drops off, 

 leaving the bare petioles or stems. Anthracnose on 

 the leaves begins as small, circular, pin-point, dark red 

 spots which enlarge, and later elongate into maroon 

 colored pits, cracks, or cankers (fig. 47 e). On young 

 seedlings the stem rots off a short distance above 

 ground. 



The Organism. Spores are formed on the spots or 

 cankers on all parts affected (fig. 47 f). These are 

 imbedded in a gelatinous substance and can become 

 loosened only by rain splashing or dew. It is at this 

 stage that the disease becomes serious, since it is then 

 spread about from plant to plant. When the spores 

 are lodged on a new bean plant or on a new part of 

 the same plant, infection takes place through the 

 penetration of the germ tube of the germinated 

 spores. It is estimated by Edgerton 1 that from one 

 1 Edgerton, C. A., Louisiana Agr. Expt. Sta. Bui. 119 : 3-55, 1910. 



