Drying Time of Systemic and Protectant Fungicides on Coffee Leaves Exposed to Artificial Rain for the Control of Leaf Rust

The drying time of pesticides on the leaves and the resistance of the deposits to rain removal are essential for success in controlling plant diseases. Because the fungicide application is performed during the rainy season, it is crucial to study the resistance of chemical deposits on the leaf surface for the control of the coffee leaf rust caused by Hemileia vastatrix. Thus, the present work analyzed the effect of an simulated rain (30 min), after several drying time of the deposits, on the removal of (i) copper oxychloride alone and associated to mineral and the adjuvant polyoxyethylene alkylphenol ether and also (ii) before several drying time, on the removal of the epoxiconazol + pyraclostrobin formulation mixed with copper hydroxide and micronutrients applied on coffee leaves, for the control of leaf rust. Around 85% and 45% of the treatments had copper retention > 30% after 120 min and 480 min, respectively, of drying time before the rain. At 480 min, retention of copper oxychloride + 0.75% mineral oil was > 30%, whereas copper oxychloride + adjuvant polyoxyethylene alkylphenol ether at 0.05% and 0.1%, respectively was 40% or higher. When copper oxychloride was added to 0.5% mineral oil at 0.05% to 0.20% of adjuvant polyoxyethylene alkylphenol ether at 480 min of drying time, copper retention was > 30%. When copper oxychloride was added to 0.75% mineral oil, copper retention was > 30% at 0.05% and 0.10 % of adjuvant polyoxyethylene alkylphenol ether. Five of the treatments with copper retention > 50% with 120 min of drying time were reduced to only two (copper oxychloride + 0.75% mineral oil; copper oxychloride + (1.0% mineral oil + 0.1% adjuvant polyoxyethylene alkylphenol ether) with copper retention > 30%, at the drying time of 480 min. All the treatments differed from the control but did not differ between each other for the coffee leaf rust control. The percentage of control ranged from 94.6% to 100% and from 71.3% to 99.5% at 180 min and 480 min of drying time, respectively. Copper retention varied from 32.2% to 55.2% and from 23.7% to 51.5%, at 180 min and 480 min of drying time, respectively, for the best treatments. The treatment with the highest copper retention was copper oxychloride + 0.75% mineral oil, both at 180 min and 480 min of drying time. The best treatments for leaf rust control were not always those with the highest copper retention by the leaves. The highest copper retention by the leaf surface was achieved with copper oxychloride mixed with 0.75% mineral oil; this treatment resulted in > 97% of coffee leaf rust control. Adding adjuvant polyoxyethylene alkylphenol ether to the mixture does not necessarily favor the tenacity and efficiency of the copper oxychloride for the coffee leaf rust control. We concluded that the copper oxychloride acts differently for the coffee leaf rust control, depending on the concentration of added mineral oil and adjuvant polyoxyethylene alkylphenol ether time zero. Pyraclostrobin + epoxiconazol alone or mixed with copper hidroxide controlled 100% of the disease after 30 min, 120 min and 480 min of spraying, but when micronutrients was added to pyraclostrobin + epoxiconazol and copper hidroxide control of coffee leaf rust reached 100% at drying time of 120 and 480 min.