In order to evaluate the effect of potassium silicate spray on the control of coffee leaf rust and coffee yield, an experiment was conducted during the 2005/2006 and 2006/2007 growing seasons on Coffea arabica cv. Catuaí Vermelho IAC 144, in a location situated at an elevation of 850 m in Coimbra, Minas Gerais, Brazil. The treatments consisted of: 1 -potassium silicate; 2 -potassium silicate + copper hydroxide; 3 -copper hydroxide; 4 -epoxiconazole formulated with pyraclostrobin and 5 -control treatment. Six applications of potassium silicate and copper hydroxide were made twice per month from December to March of each year. Two applications of the systemic fungicide were done in December and March of each year. Potassium silicate alone or in combination with copper hydroxide was not efficient in reducing coffee leaf rust incidence and increasing yield under high incidence of coffee leaf rust.

This study documents an experiment that was undertaken in growing seasons on Coffea arabica cv. 'Catua ı Vermelho IAC 144' that sought to evaluate the effects of various calcium silicate rates combined with the fungicide triadimenol on the incidence of coffee leaf rust. The experimental design was a randomized complete block in a split plot with five treatments (with varied calcium silicate rates and with or without triadimenol) and four replications. Each experimental unit (split plot) consisted of seven coffee plants (14 m 2 ), which were the central five plants used for the evaluations. Calcium silicate (CS) and lime (L) were used according to the following mixtures (M): M1: 0% CS and 100% L; M2: 25% CS and 75% L; M3: 50% CS and 50% L; M4: 75% CS and 25% L; and M5: 100% CS and 0% L. The leaf Si concentration did not increase as CS rates increased in the soil. There was no reduction in the area under rust progress curve (AURPC) as the rates of CS increased in the soil. During the growing seasons incidence reached 94, 96 and 92% on plants that did not receive triadimenol, respectively, whereas the incidence did not exceed 6, 38 and 16%, respectively, for those plants that did. For yield, no interaction was observed between the calcium silicate rates and with or without triadimenol. The yield increased by 117% for plants receiving triadimenol compared with those that did not. The 3-year experiments indicated that soil amendment with calcium silicate had no effect on either reducing coffee leaf rust incidence or increasing yield. Conversely, as expected, coffee leaf rust symptoms were dramatically reduced on plants sprayed with triadimenol, and this was accompanied by a significant gain in yield.