Leaf rust, caused by Hemileia vastatrix, is the most important coffee disease. Alternative methods of management of this disease that are less damaging to the environment than fungicide applications are urgently needed. This study aimed at evaluating the effect of foliar applications of potassium silicate (PS) solutions at concentrations of 0, 8, 20, 40, and 60 g/L, at pHs 5.5 and 10.5, on sporulation intensity of H. vastatrix (SI), total number of pustules (TNP) per leaf, and on coffee leaf rust severity. The effect of the applications of PS at the selected rates, of copper oxychloride (7.5 g/L), and of sterile distilled water at pH 5.5, 7.5, and 10.5 on the inhibition of H. vastatrix uredospores germination was also tested and the foliar concentration of silicon (Si) and potassium (K) was determined. A quadratic regression model best described the effect of PS applications, at pH 5.5 or 10.5, on SI, TNP, and severity. The relationship between SI, TNP, or severity and PS applications, at pH 5.5 or 10.5, was linear and negative. Si concentration in leaves increased as the concentration of PS solutions utilized (at pH 5.5) increased from 0 to 60 g/L. There was no effect of PS applications, at pH 10.5, on Si concentration in leaves. K concentration did not change as the PS rates increased from 0 to 60 g/L, both at pHs 5.5 and 10.5. A linear regression model adequately described the relationship of inhibition of uredospores germination versus PS concentrations at the three pHs values. Copper oxychloride significantly reduced uredospore germination as compared with the PS applications. The results from this study highlight the possibility of using PS spray, in a more alkaline pH, as a treatment for reducing coffee leaf rust intensity.
Coffea arabica; Hemileia vastatrix; mineral nutrition
