Abstract

VELANDIA MONSALVE, Jorge; VITERI ROSERO, Silvio Edgar; RUBIO CARDENAS, Nubia Janeth  and  TOVAR DUARTE, Fabián Octavio. Effect of the Potasium Phosphite in Combination with the Fungicide Metalaxyl plus Mancozeb on the Control of Downy Mildew (Peronospora destructor Berk) in Onion Bulb (Allium cepa L.). Rev. Fac. Nac. Agron. Medellín [online]. 2012, vol.65, n.1, pp.6317-6325. ISSN 0304-2847.

Abstract. Peronospora destructor fungi causes considerable loses in the production of onion bulb in the world. Potassium phosphite in combination with the fungicide Metalaxyl + Mancozeb was evaluated for its efficiency in the control of this pathogen in the onion bulb hybrid Yellow Granex. The treatments consisted in one application of potassium phosphite (5 mL L^-1) alternated with one of fungicide (2 g L^-1); two and three consecutive applications of potassium phosphite alternated with one of fungicide; one application of fungicide alternated with one of potassium phosphite; two and three consecutive applications of fungicide alternated with one of potassium phosphite; applications of potassium phosphite and fungicide alone and one control. The experimental design was a complete block randomized with three replicates. The variables evaluated were the incidence and severity of the disease and the number, size and weight of the bulbs of first, second and third class and total bulb weight. The results showed that the applications of potassium phosphite during two consecutive weeks alternated in the third week with one of fungicide and the weekly applications of phosphite alone had highly significant effects on the control of the incidence and severity of P. destructor and significant differences on the weight of the first class bulbs (28.1 and 27.9 t ha^-1) and total bulb weight (55.5 and 52.1 t ha^-1), representing in comparison to the control an increment of 200 and 196% on the weight of the first class bulbs and of 55 and 45,7% on the total bulb weight, respectively. It is concluded that with the potassium phosphite the application of fungicides is reduced and this represents a viable alternative for the ecological management of P. destructor in the production of onion bulb.

Keywords : Integrated control; chemical control; vegetables; pathogen.

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