XIII, A, 4 Reinking: Philippine Economic-Plant Diseases 203 



POWDERY mildew: erysiphaceab 



Symptoms. — A white powdery mass may be produced on the 

 leaves. The disease is similar to that discussed under papaya 

 and tomato. 



Causal organism. — Typical conidia and conidiophores of the 

 Erysiphaceae are produced. 



Control. — Powdering with sulphur in severe cases of infec- 

 tion will check the disease, 



DAUCUS CAROTA LINN. CARROT 

 STEM rot: rhizoctonia 

 Symptoms. — During damp weather a stem rot of the carrot 

 may be abundant. The stems are attacked just at and above 

 the ground. Infected stems become brown, shrivel up, and 

 cause the death of the leaf by cutting off the water supply. 



Causal organism. — Isolations and pure culture work showed 

 the causal organism to be a Rhizoctonia. 



Control. — Avoid planting during the excessively rainy season. 



DIOSCOREA ESCULENTA (LOUR.) BXJRKILL. YAMS 

 LEAF spot: cercospora ubi racib., cercospora pachyderma sydow 

 Symptoms. — Leaves may be moderately spotted with spots of 

 the Cercospora type. Little injury is done. 



LEAF spot: ellisiodothis rehmiana theiss et sydow (phyllachora dios- 

 toreae schwein, phyllachora rehmiana theiss et sydow) 



Symptoms. — Shiny black stroma are scattered over infected 

 leaves. Little damage is done. 



rust: uredo dioscoreae (berk, et brm.) fetch., uredo dioscoreae-alatah 



raciborski 



Symptoms. — A common leaf trouble, which at times is serious. 

 Characteristic yellowish rust pustules are developed on the under 

 surface of leaves. 



storage rots: LASIODIPLODIA THEOBROMAE (pat.) GRIFFON et MAUBLANC 



Symptoms. — Storage rots are present in abundance. This rot 

 is characterized by the production of a sooty black mass of 

 spores on the surface of dry-rotted roots. 



Causal organism. — The organism causes a dry rot of a large 

 number of root crops. It is more fully discussed under dry rot 

 of cacao. 



Control. — Avoid injuries in digging. Store in a well-aerated 

 place. All diseased roots should be sorted out and burned. 



A Rhizopu£ may also cause a rot. 



Phoma oleracea Sacc, Gloeosporium macrophomoides Sacc, 

 and Phomopsis dioscoreae Sacc. are found on dead stems. 



