^8 Journal of Agricultural Research VoLxdcno-s 



or relationship to other downy mildews destructive to cereal, forage, and 

 sugar-cane crops in the Orient. 



DISTRIBUTION 



Broadly speaking, the disease is distributed throughout the Philip- 

 pine Islands. Through the personal observation of the writer and through 

 information given by Dr. Reinking, of the College of Agriculture, by 

 his students, and by members of the Bureau of Agriculture, the dis- 

 ease is known to exist in the Cotobato Valley of the Island of Mindanao 

 at the south, in the Islands of Cebu and Occidental Negros, and in the 

 provinces of Batangas, Laguna, Rizal, Cavite, Bulacan, Tarlac, Pam- 

 panga, Nueva Ecija, Pangasinan, Ilocos Norte, la Union, and Isabela in 

 Luzon at the north. In some of these localities the disease appears to 

 have been present for more than lo years, but as yet not enough is 

 known to warrant a discussion of its probable origin. 



DESTRUCTIVENESS 



The disease is unusually destructive. It is impossible for one accus- 

 tomed only to the comparatively light losses occasioned by the maize 

 diseases of the United States com belt to form any conception of the 

 epidemic intensity of the attacks of this downy mildew under favorable 

 conditions, or of the terrible destruction which it occasions (PI. i6). Of 

 the aggregate loss to the $8,820,000 maize crop of the Philippines no 

 estimate can be made, because farmers do not recognize the trouble as 

 a disease but regard it as the result of excessive rain or other unfavorable 

 conditions and accept it with fatalistic resignation. In Laguna and 

 Batangas, however, where maize is a major crop and where the writer 

 has studied the disease in the native fields, losses of 40 to 60 per cent are 

 frequent, and in some cases as high as 82 per cent of infection has been 

 counted. In the experimental and acclimatization plots at the College 

 of Agriculture, where the growing of unacclimatized varieties and the 

 constant presence of actively infecting plants combine to make the con- 

 ditions especially favorable for infection, the losses ordinarily are high. 

 In several beds of United States sweetcorn, planted during the rainy 

 season, every plant was killed before producing any seed. 



The severity of the disease in the individual corn plant varies with con- 

 ditions from the extreme stunting and weakening of the plant resulting 

 in death about one month after planting to the less virulent attacks in 

 spite of which the plant shows a fair growth and ultimately produces a 

 small, more or less poorly formed ear. Even in the few lightly affected 

 cases the grain production is not nearly normal, and in most cases com- 

 plete barrenness or premature destruction occurs, so the aggregate loss in 

 the average field attacked by the mildew is large. In some localities 

 corn growing has been abandoned for the culture of upland rice because 

 of the ravages of the disease. Moreover, this loss can not be offset in part 



