xiii. A, 5 Reinking: Philippine Economic-Plant Diseases 229 



PACHYRRHIZUS EROSUS (LINN.) URB. (PAGHYRRHIZUS ANGULATUS 

 RICH.). SINCAMAS 



bust: phakospora pachyrhizi sydow 



Symptoms. — The under surface of the leaves is covered with 

 small, raised brown rust sori. Frequently a brownish white 

 dust of spores is produced over the leaf surface. The disease 

 may be severe, causing defoliation. 



PHASEOLUS SPP. BEANS 

 bacteria blight: pseudomonas phaseoli erw. smith 



Symptoms. — This well-known disease is common and destruc- 

 tive on Phaseolus vulgaris Linn, and on Phaseolus lunutiis Linn. 

 Leaves, stems, and pods are attacked. Characteristic, irregular 

 brownish spots with water-soaked edges are produced on the 

 leaves. These spots may spread rapidly, killing the entire leaf. 

 During dry weather spots become papery and brittle. The or- 

 ganism attacks pods, forming a characteristic watery spot, and 

 also works down into the seed, thus infecting the latter. Entire 

 fields of beans, especially those not acclimated, may be destroyed 

 (Plate XIV, fig. 2) . 



Catisal organism. — The bacteria causing this disease gain en- 

 trance primarily through injuries. They are found in great 

 abundance in the leaf veins, from which they can be seen to 

 exude in large numbers when the leaf is sectioned and examined 

 under the microscope. 



Control. — The disease is spread by the use of diseased seed. 

 Since it is difficult to detect all cases of seed infection, only seed 

 collected from healthy pods should be planted. Crop rotation 

 should be practiced in severe cases of infection. 



blight: rhizoctonia 



Symptoms. — Beans may be severely affected with a blight dis- 

 cussed under soy beans. Phaseolus calcaratus Roxb. and Doli- 

 chos uniflorus Lam. are especially susceptible when planted too 

 thickly and allowed to spread over the ground. Thin planting 

 and training vines to poles, when possible, will reduce the disease 

 attacks. 



blight; sclerotium 



Symptoms. — A dense white growth of mycelium may be pro- 

 duced on the stems of plants. As the mycelium spreads to the 

 leaves, the latter are killed, after showing the same character- 

 istic symptoms as discussed under the Rhizoctonia blight. 



