Dose mínima efetiva de fosfina no controle da broca-da-raiz do cajueiro, Marshallius bondari Rosado-Neto (Coleoptera: Curculionidae)

The objective of this research was to determine, in field conditions, the minimal of phosphine effective dose for the cashew root borer control. Three experiments were set up at three different periods: August, October and November, 1994, to control the cashew root borer, Marshallius bondari Rosado-Neto (Coleoptera: Curculionidae), in Piaui State, Brazil. One, two, three and six phosphine tablets of three gram each, per plant were tested. In the August essay, phosphine was inefficient to control the borer. In the October essay, control was achieved using as little as 2 tablets per plant and in November with one tablet per plant to control the adult borers in the soil. Higher efficiency was achieved when treatment was applied far away from the last rain, in other words, as soil dries out.