APPLICATION FRECUENCIES OF CLOROTALONIL FUNGICIDE 82.5 FOR THE HANDLING OF Phytophthora infestans IN THREE POTATO VARIETIES.

Abstract

The objective of this study was to determine the application interval of Clorotalonil 82.5 fungicide for the handling of the Phytophthora infestans fungus in Amigo, Granola and IDIAP-92 potato varieties during the raining season. It was established in Cerro Punta, Chiriqui during the period August to December of 1998. It was utilized a completely randomized block design in a split-plot arrangement with four repetitions. The principal plot was the varieties (Amigo, Granola and IDIAP-92) and the subplot was the application intervals of Clorotalonil 82.5 fungicide with doses of 0.9 kg pc/ha at 3, 6, 9, 12 and 15 days after the emergence (DAE) of the cultivation. Producer practice during the raining season is spaying every three days. In all treatments at 30 DAE (formation of tuber phase), the Metalaxil CT 60 WP fungicide was applied. The effective area of the plot was of 9.0 m². In these plots, measurements of the foliage infection cause by Phytophthora infestans were done weekly using an arbitrary scale expressed in percentage. Cero is equal to healthy plant and 100 are equal to death plant. Eight measurements were done per treatment and the area under disease progress (AUDPC) curve was calculated. Also, commercial yields were recorded as biological efficiency parameters. With applications of Clorotalonil 82.5 fungicide at 6 DAE in IDIAP-92 showed a value of the AUDPC of 825, average commercial yields of 33.25 t/ha and the higher Marginal Return Rate (4327 per cent).