The use of metalaxyl and potassium phosphonate, mounds, and organic and plastic mulches, for the management of Phytophthora root rot of papaya in far northern Queensland

Options for the control of root rot of papaya caused by Phytophthora palmivora were evaluated in two field experiments in far northern Queensland, Australia. In the first experiment, foliar sprays of potassium phosphonate (10 g/L) applied fortnightly reduced the incidence of root rot by 47%. Metalaxyl granules (1.25 g/m2) applied every 6 weeks, and metalaxyl granules (1.25 g/m2) applied at transplanting combined with fortnightly foliar sprays of potassium phosphonate (10 g/L) also provided a level of control. Fortnightly foliar sprays of potassium phosphonate (5 g/L) and monthly foliar sprays of potassium phosphonate (5 and 10 g/L), and fortnightly and monthly soil drenches with potassium phosphonate (1 and 2 g/L) had no significant effect (P > 0.05) on the incidence of root rot. In the second experiment, growing papaya on 0.75 m mounds reduced the incidence of root rot by 38.4% and significantly increased fruit yield. Soil covers of 2 m wide plastic mulch and organic mulch in combination with 0.75 m mounds, further reduced plant losses by 20 and 10%, respectively. Plastic mulch on flat ground was as effective as the mounded treatments in reducing the incidence of root rot and increasing yield