Asevere outbreak of fireblight occurred in Bartlett pear orchards in the northern Sacramento Valley during 1971. It developed in orchards where growers had followed a thorough blight control program using streptomycin sprays (12 to 18 applications per season) exclusively during 1970 and 1971. Blight samples from these orchards were collected and checked for streptomycin resistance in May 1971. The pathogen in many of these samples was shown to be highly resistant to streptomycin. This newly developed resistance to streptomycin in the Sacramento Valley apparently accounted for the failure to control blight in 1971 with streptomycin programs that had performed successfully in 1970.

Cooperators included Heringer Enterprises, Hart-Carter Spray Corp., and the C. E. Sullivan Ranch.