such evidence was reported at "Bacterial Blight of Rice: Proceedings of the International Workshop on Bacterial Blight of Rice, 14-18 March 1988"  Int. Rice Res. Inst., 1989 - 235pp. at page 91: 

"... If the phages of Xanthomonas oryzae detected in the irrigation canals number> 100/ml, a disease outbreak is expected shortly." and so on.

Related to phages of Xoo, that was an indicator of bacteria in water:

"Immediately after transplanting, the phage population in the fields is low. But if more than 200 phages/ ml are observed, diseased plants must exist in the field. At the time of transplanting, if 50 phages/ml are detected in the irrigation canals, the first disease occurrence is expected on L. oryzoides. If more than 100 phages: ml are detected, the first disease outbreak on rice is expected within 10-14 d. At midtillering, if the phage population is l00/ ml, moderate; and if >1,000/ ml, severe. If the phages detected in the irrigation canals number >100/ml, a disease outbreak is expected shortly. The disease already prevails if the phage population is >1,000/ ml. At maximum tillering, if the phage population in the ricefield water is 500/ ml, moderate; and if >5,000/ ml, severe. When the phage population is regularly >1,000/ml, the disease is widely established in the area. When 1,000-2,000 phages/ml are detected frequently in a wider area, many secondary infection sources already exist and a high possibility of disease is forecast (Mizukami T (1966) Epidemiology of bacterial leaf blight of rice and use of phages of forecasting. Pages 15-32 in Symposium on plant diseases in the Pacific. XIth Pacific Science Congress. Tokyo.). 

The genus Xanthomonas, which mostly comprises phytopathogenic bacteria, is a member of the family Pseudomonadaceae. Among xanthomonads, Xanthomonas oryzae pv. oryzae causes bacterial blight (BB) of rice which is one of the most important diseases of rice in most of the rice growing countries.Restriction fragment length polymorphism and virulence analyses are  used to evaluate the population structure of Xanthomonas oryzae pv. oryzae, the rice bacterial blight pathogen, from several rice-growing countries in Asia. 308 strains of X. oryzae pv. oryzae are collected from China, India, Indonesia, Korea, Malaysia, Nepal, and the Philippines. On the basis of the consensus of three clustering statistics, the collection is categorized in  five clusters. Genetic distances within the five clusters ranged from 0.16 to 0.51, and distances between clusters ranged from 0.48 to 0.64. Three of the five clusters consisted of strains from a single country. . The pathotype of X. oryzae pv. oryzae was determined for 226 strains by inoculating five rice differential cultivars. More than one pathotype  associated with each cluster; however, some pathotypes were associated with only one cluster. Most strains from South Asia (Nepal and India) proved virulent to cultivars containing the bacterial blight resistance gene xa-5, while most strains from other countries were avirulent to xa-5. T