XIII, A. 4 Reinking: Philvppine Economic-Plant Diseases 211 



over the surface. The fungus grows well in pure culture, pro- 

 ducing on sterile potato cylinders, a dense white mycelium with 

 conidia, sporangia, and chlamydospores. 



Control. — All diseased portions should be carefully cut out, 

 down to the healthy tissue, and burned. Disinfection of the 

 knives used for cutting with a 2 per cent formalin solution 

 is recommended. A careful inspection of the plantation should 

 be kept up so that the cankers can be cut out when they first 

 appear. All wounds made by cutting out the diseased cortex 

 should be painted with a coal-tar preparation, care being taken 

 not to paint the cambium layer at the edges of the cut surface. 

 Cacao should never be planted with or near Hevea rubber. In 

 severe cases of the disease it might be advisable to spray the 

 trunks of young trees with Bordeaux mixture. This cannot 

 be done with tapping trees. The humidity of the plantation 

 should be lessened by admitting air and sunlight through the 

 removal of intercrops, thinning out by pruning and planting 

 according to the regulation distance, which will permit a ready 

 aeration. All diseased trees and rubber trash should be burned 

 as soon as possible to avoid the spread of Phytophthora spores. 

 It might be advisable to obtain a large blast torch for this 

 purpose. 



LEAF SPOT: HELMINTHOSPORIUM HEVEAE FETCH 



Symptoms. — Leaves of nursery plants a meter or more high 

 may become spotted, but no serious damage has been observed. 

 The spots may be thickly scattered over the leaf surface. When 

 young they are minute, having purple centers with a lighter 

 purple haze about the edges; older spots are circular, 3 to 5 

 millimeters in diameter, with white semitransparent centers 

 bordered with a purplish ring. The disease has been observed 

 on seedling plants only. 



Causal organism. — The spores are produced on both surfaces 

 of the leaf, but are more abundant on the lower surface. They 

 are cymbiform, browTi, and from eight to eleven septate. The 

 conidiophores are scattered, simple, brownish, and septate. 



Control. — Since the disease is not serious and never has been 

 obser\^ed to cause defoliation, no control has been found necessary. 

 If severe cases of infection should arise, spraying with Bordeaux 

 mixture would control the disease. 



PHYSIOLOGICAL TROUBLE 



Sijmptoms. — This diseased condition is sometimes spoken 

 of as brov^m bast. The external appearance of such trees is 

 usually normal. Internal characters may be normal, but fre- 



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