This work was carried out to verify the effect of precipitation on different copper fungicides application and its efficiency for controling coffee (Coffea arabica) rust caused by Hemileia vastatrix, in the presence or absence of vegetable oil. Cuprous oxide, hydroxide of copper and copper oxicloride, in the proportion of 0.3% of the active ingredient, were sprayed on coffee plants 24 h before inoculation with urediniospores. 60 min after spraying, half of the plants received 20 mm of rain for 6 min; repeated four times at weekly intervals. The other half of the plants did not receive water. Cuprous oxide was more efficient without oil than with oil, contrasting with the results obtained for hydroxide of copper. Adding oil did not improve copper oxicloride action. Rain was not observed to make any significant difference in the incidence and severity of coffee rust among the plants. This suggests that, besides copper compounds being contact products, they showed a certain resistance to the action of the rain, with good characteristics of adherence and/or persistence on the surface of the coffee leaves. The mixture of copper oxicloride with oil, independent of the presence of rain, was efficient in reducing the viability of the spores to 13.5%, indicating the erradication action of this treatment, while the test treatment showed 41.29%. Cuprous oxide with no oil in the absence of the rain also provided no sporulation action, but did not differ from the test plots where rain was present.
