xni. A, 4 Reinking: Philippine Economic-Plant Diseases 187 



uniform yellowing of the leaves seems to be due to malnutrition, 

 probably a lack of nitrogen. The yellowing in blotches may be 

 due to the attacks of mites. 



Control. — The disease may be avoided by using healthy stock 

 and by the practice of proper culture methods. In case of insect 

 attacks, these must be controlled by entomological methods. 



DAMPING off: RHIZOCTONIA 



Symptoms. — Seedlings grown in unsterilized soil and in poorly 

 aerated places may be severely attacked, just at the ground sur- 

 face, by this fungus, which first causes a browning of the stem 

 and later a shrinking and weakening of the tissue, causing the 

 plants to fall over and die. The disease is somewhat similar 

 to, but more prevalent than, that produced by a Sclerotium. 



Causal organism. — This organism is a common soil fungus 

 causing a large amount of destruction to tender plants during 

 periods favorable to its spread. It grows well in pure culture, 

 first producing a coarse white mass of mycelium, which later 

 turns brownish and produces a large number of brown sclerotial 

 bodies. No spores have been observed. The fungus penetrates 

 the plant tissues, causing the weakening and death of the cells. 



Control. — Seedlings should be grown in sterilized soil and 

 should be placed where there is plenty of chance for air. 



DAMPING OFF: SCLEROTIUM 



Symptoms. — Seedlings growing in damp and poorly aerated 

 places are frequently attacked by a fungus that causes a rot 

 resulting in damping off. The stem is attacked near the ground 

 and becomes browned, shrunken, and weak, due to cell destruc- 

 tion. Plants in the latter stages of the disease fall over and die. 



Causal organism. — Isolation and inoculation experiments show 

 this disease to be due to a fungus that produces sclerotia. The 

 fungus invades the tissues from the ground. Upon death of 

 the plant small, round, smooth brown sclerotial bodies are pro- 

 duced. These bodies germinate directly by the production of 

 mycelium. No spores have been observed. The same fungus 

 may cause a damping off of coffee seedlings, cacao seedlings, and 

 other plants. In pure culture a dense white growth is first 

 produced, which later gives rise to a large number of round, 

 smooth brown sclerotial bodies. 



Control. — The disease is easily controlled by growing plants 

 in well-aerated places, free from too great humidity. If the 

 soil be heavily infected with the fungus, soil sterilization must 

 be practiced. 



