XIII, A, 5 Reinking: Philippine EcoTwmic-Plant Diseases 243 



the tubers, resulting in the production of the characteristic 

 blackened ring and the consequent rotting. 



Control. — In newly developed sections where potatoes can be 

 grown, the chief precaution to be taken is to keep the bacteria 

 out of the soil. Once the soil becomes heavily infected, it is 

 practically impossible to grow potatoes as a regular crop. Care- 

 ful seed selection will reduce the chances of their introduction. 

 Avoid using seed potatoes from fields or crops known to be 

 diseased. If the source of the seed be not known, all seed 

 potatoes should be carefully examined by cutting a slice from 

 the stem end. If a black ring be found just under the surface 

 or if a rotting have started, such potatoes should be discarded. 

 All wilted plants should b^ dug and burned as soon as discovered. 

 Insects attacking potatoes should be controlled, since they spread 

 the disease. In cases of severe infection, a crop rotation of 

 five years must be practiced. During this rotation no tomatoes, 

 eggplants, peppers, tobacco, or other solanaceous plant should 

 be grown. Diseased tubers should never be stored with the 

 healthy. 



BLACKLEG, OR POTATO STEM ROT: BACILLUS PHYTOPHTHORUS APPEL 



Symptoms. — This disease is probably present in the Philip- 

 pines. The characteristic symptoms of wilting and yellowing 

 of leaves, the blackened rotten stem, and the rotted tubers have 

 been frequently observed. It may be that this disease, as de- 

 scribed here, is the same as the bacterial wilt, only in a diflferent 

 state of development. 



Causal organism.. — No work has been done with the organism. 



Control. — The control is similar to that discussed under bac- 

 terial wilt. 



blight: PHYTOPHTHORA INFESTANS (MONT.) DE BARY 



Symptoms. — This disease has been observed only in the 

 mountain provinces, where it was probably introduced on 

 seed potatoes. Black blotches are produced on the leaves. 

 These spots may have a downy fungus mass growing on the 

 under surface. Diseased stems turn black and rot. A soft 

 ill-smelling rot may be produced in the tubers. 



Causal organism. — The downy growth is made up of much- 

 branched conidiophores with hyaline, lemon-shaped conidia. 



Control. — Spraying with Bordeaux mixture will have to be 

 practiced in severe cases of infection. Crop rotation also should 

 be practiced. 



