Development of improved disease management for powdery mildew on mango trees in Israel

Powdery mildew, caused by Pseudoidium anacardii (formerly Oidium mangiferae Berthet), attacks panicles, young fruits, and leaves of mango trees; it may cause considerable crop loss. Mango is the only known host of this pathogen. Disease management in Israel has not been investigated extensively; it is based on field observations by the Agricultural Extension Service, which instructs growers to spray at 14-d intervals, starting from the beginning of bloom when the first flowers appear in the orchard, or after rain events; rain events during flowering promote development of the disease. The present study found that fungicides applied to panicles at 10-d intervals after they reached a length of 5 or 10 cm improved disease control compared with spraying at 14-d intervals. Earlier applications did not improve disease control; later applications, beginning at the first-open-flower stage, were less effective. Foliar sprays applied before rain events provided better disease control than spraying after the rain. In Israel, about 30 fungicides against mango powdery mildew are registered, but no comparative trials for fungicide efficacy have been conducted in recent years. Efficacy trials showed that the most effective fungicides were penconazole, myclobutanil, tetraconazole, and an improved formulation of mineral oil. A tank mixture of systemic fungicide with a reduced sulfur content (up to 60%) was as effective as, or slightly more so than each component applied alone, and provided 70–90% protection compared with control untreated trees. QoI fungicides (strobilurins) were less effective and less consistent. Where there was an existing infection on panicles, two consecutive applications of sulfur or mineral oil, combined with systemic fungicides, suppressed the fungus and inhibited powdery mildew development. The main findings of the present study were implemented by growers and currently are used to develop improved disease management.