348 DISEASES OF CROP-PLANTS 



of sugar-cane cuttings, and was transferred to sugar-cane, upon 

 which the usual effects were produced. 



L. D. Larsen, in Hawaii, inoculated pineapple cuttings with 

 the spores of this fungus through punctures and by means of a 

 sprayed suspension, obtaining complete infection by both 

 methods and the development of the disease in typical form, the 

 controls remaining healthy. 



Losses. 



In Hawaii, where the existence of an organised pineapple 

 industry allows of observations being made on the subject, the 

 loss of plants in the field due to this disease has been found in 

 different instances to be 23, 27 and 65 per cent. The loss of 

 cuttings during transport has on occasion reached similar figures. 



Control. 



The causative fungus is widely distributed in these islands 

 and in the soil of sugar-cane fields appears to be universally 

 present. It occurs in connection with a pineapple leaf-spot and 

 is the common cause of decay in the ripe fruit after cutting. The 

 fungus can be generally assumed to be present where pineapples 

 are grown, and since large numbers of plants can be raised under 

 these conditions and escape the disease, it is obvious that infec- 

 tion depends on some local factor. What the predisposing causes 

 may be has not been ascertained fmrther than that dry weather 

 after planting seems to favour infection of the sets. This agrees 

 with experience in the parallel case of sugar-cane cuttings, which, 

 according to the writer's experience, are destroyed by Thielaviop- 

 sis only when lack of rain delays their development. The 

 experiments in Hawaii showed that the removal of as few leaves 

 as possible from the sets, and the drying out of the cut ends before 

 planting are effective methods of preventing infection. The 

 use of Bordeaux mixture gave negative results. 



White Leaf-Spot. 

 A leaf-spot which is fairly common in the West Indies has 

 been investigated by L. D. Larsen in Hawaii. It occurs on well- 

 grown plants and its effect on their development is not usually 

 appreciable. It has been shown to be due to the infection of 

 insect and spine punctures, or other injuries, by the fungus 

 Thielaviopsis. Infection and development depend on the pre- 

 valence of moist and cloudy weather or on the shading of the 

 plants. 



Description 4 



Larsen's description is as follows : 



" The spots vary considerably, as regards size, shape and 



