Effect of bactericides on population sizes and spread of Clavibacter michiganensis subsp michiganensis on tomatoes in the greenhouse and on disease development and crop yield in the field

Chemical applications, with the exception of mancozeb, reduced population s izes and spread of Clavibacter michiganensis subsp. michiganensis among tom ato seedlings in the greenhouse and impacted subsequent plant development a nd yield in the field. While applications of copper hydroxide, copper hydro xide/mancozeb, copper hydroxide/mancozeb (premixed 12 h before spraying), s treptomycin, and streptomycin/copper hydroxide to seedlings in the greenhou se did not differ significantly from the inoculated control, the trend was for these treatments to increase the survival of inoculated transplants in the field in comparison to the inoculated control. In the field, inoculated controls produced yields that were 63% (1995) and 51% (1996) of those prod uced by uninoculated controls. In both years, with the exception of mancoze b in 1995, all treatments resulted in yields similar to those obtained with the uninoculated control. Plant survival and yield in the field were sever ely affected when transplants had a pathogen population of greater than or equal to 1 x 10(8) CFU/g of tissue. All treatments, with the exception of m ancozeb, limited C. michiganensis subsp. michiganensis populations to <5.0 x 10(5). None of the treatments significantly reduced the incidence of frui t spotting compared with that of the inoculated control.