Effect of Copper Sprays on the Epiphytic Populations of Pseudomonas syringae pv. garcae on Coffee in Kenya

In unsprayed plots, the total population of Pseudomonas syringae pv. garcae consisted of copper-resistant and sensitive strains. The cu-resistant strains were “invaders” from sprayed trees. The frequency distributions for the different population density classes (101,102 to 107cfu/g) of the cu-resistant and sensitive strains were not different from the expected normal distribution. The wild-type P s garcae was able to predominate the cu-resistant strains. In sprayed plots, the incidence of P s garcae declined because of the effect of Cu-hydroxide (Kocide 101, 0.7%) sprays on the Cu-sensitive population and Bordeaux mixture (1.0% and 0.5%) on the resistant component, in contrast, sprays of Kocide 101 (0.4%) reduced the frequency of population densities ≥ 103 cfu/g of the Cu-resistant and of the sensitive strain while Bordeaux mixture (0.5%) only reduced the Cu-sensitive population. During the post-spray period, the incidence of the Cu-sensitive P s garcae increased exceeding that in the unsprayed plots and the population density frequencies re-adjusted to a distribution similar to that of the unsprayed plots.