Missing the critical window of effectiveness by even 24 hours can result in plant infection and buildup of a significant amount of bacteria for later infections. If the blossom blight is well controlled, the subsequent increase of fire blight in summer is often prevented. To prevent development of streptomycin-resistant strains of the pathogen, no more than 4 applications of streptomycin per season is recommended. Streptomycin is more effective in preventing blossom infection and the management of the shoot blight phase of fire blight should not be attempted with streptomycin. However, application of streptomycin immediately following hail storms is highly recommended.
Bordeaux mixture is recommended for use by growers who had a severe epidemic the previous year.
Bordeaux mixture should be applied at the green tip to quarter inch green stage of flower bud growth. Do not mix bordeaux with other chemicals, and use it as soon as it is prepared. Do not follow bordeaux mixture with streptomycin, and do not concentrate bordeaux mixture greater than 2 times. Bordeaux is not as effective as streptomycin in controlling fire blight. Control sucking insects.