218 The Philippine Journal of Science isis 



from seeds of healthy plants. Seedlings should be grown in 

 sterilized soil. Injuring of plants should be avoided during 

 transplanting. All diseased plants should be pulled up and 

 burned. When once the soil becomes infected, a 5-year crop 

 rotation in which no solanaceous plants are grown will have to 

 be practiced. Insects attacking tomatoes undoubtedly are fac- 

 tors in the spread of the disease, so the control of these would 

 be beneficial. The production of disease-enduring varieties 

 would possibly be a means of avoiding the disease. 



DAMPING OFF: RHIZOCTONIA AND PYTHIUM DEBARYANUM HESSE 



Symptoms. — Damping off of seedlings is common with plants 

 grown in unsterilized soil. This is true of all vegetable seed- 

 lings. Plants are attacked just at the surface of the ground. 

 The stem at first is browned, later it shrivels, and then it be- 

 comes black. Diseased plants fall over. 



Causal organism. — A Rhizoctonia and a fungus similar to 

 Pythium debaryanum Hesse are associated with the disease, 

 invading the stem and causing shrinking and death. 



Control. — Seedlings should be grown in sterilized soil. 



POWDERY MILDEW: ERYSIPHACEAE 



Symptoms. — Plants are frequently, during the cold drier sea- 

 son in December, January, and February, entirely covered with 

 a white powdery mildew. The disease may be very severe, 

 causing first the browning and death of the lower, older leaves 

 and finally the death of the plant. The production of fruit is 

 inhibited. 



Causal organism. — The powdery mass is made up of typical 

 conidia and conidiophores of species belonging to the family 

 Erysiphaceae. The mycelium is superficial and only penetrates 

 into the plant by means of haustoria. In no case has the as- 

 cigerous stage been observed. This is true with all powdery 

 mildews studied on economic plants, and it seems to be a general 

 observation throughout the tropics that only the conidial stage 

 is usually produced. 



Control. — Dusting with sulphur or spraying with any standard 

 fungicide will control the disease. 



MANGIFERA INDICA LINN. MANGO 

 LEAF spot: CE31C0SP0RA MANGIFERAE KOORDERS 



Symptoms. — This is a common leaf spot, characteristic of the 

 Cercospora type. It is often abundant and does some damage. 



