xiii. A, 5 Reinking: Philippine Economic-Plant Diseases 255 



amount of trash in fields. This practice will greatly lessen the 

 conditions that are favorable for the hibernation and reproduc- 

 tion of fungi and insects. Clean culture is little practiced in 

 the Philippines. It is one of the essentials of good agriculture 

 and should be practiced in the culture of coconuts, abaca, citrus, 

 cacao, coffee, and all other crops when possible. Plantations 

 in which this method of agriculture is practiced obtain higher 

 yields due not only to better culture, but also to the reduction 

 of fungus and insect attacks. 



DISEASB-RESISTANT VARIETIES 



Certain varieties of plants are less affected by disease than 

 are other varieties. Control of plant diseases by the use of 

 disease-resistant varieties is the cheapest and best method, if 

 such varieties can be obtained. It is not always possible to 

 produce varieties that will resist disease, but the grower should 

 select those varieties that are least subject to attack. Different 

 species of coffee show marked degrees of resistance to rust. 

 Coffea arabica Linn, is severely affected, while the robusta and 

 liberica types are less attacked. Resistance of other plants has 

 been pointed out, and whenever possible these varieties should 

 be planted, 



SOIL STERILIZATION 



For the control of a large number of fungi specific measures 

 can be carried out on a practical basis. The soil of the tropics 

 contains many soil fungi, some of which are highly destructive 

 to young, tender plant growths. These fungi, as before dis- 

 cussed, include the following: Rhizoctonia, Phytophthora nico- 

 tianae Breda de Haan, Pythium debaryanum Hesse, Sclerotium 

 and Fusarium. All may cause large destruction by damping off 

 seedlings grown in seed beds. This trouble can be easily avoided 

 by soil sterilization. The soil used for the production of seed- 

 lings should be sterilized. No practical method of soil steriliza- 

 tion for large areas of soil has been devised. Soil sterilization 

 consists primarily of two methods, namely, by heating the soil 

 directly and by the use of disinfectants. 



DIRECT-HEATING METHOD 



For the Philippines the best method of soil sterilization by 

 heat consists merely in heating the soil on a piece of sheet iron 

 (Plate XXI, fig. 1). A piece of sheet iron 95 centimeters by 

 160 centimeters is raised about 50 centimeters above the ground 

 by means of iron posts. Moist garden soil is shoveled on the 

 sheet iron, and a fire is built underneath. In this way the soil 



