The suppression of Phytophthora syringae in orchard soil by furalaxyl as a means of controlling fruit rot of apple and pear

Apple orchard soil treated with Aaterra (etridiazole), A5430 (furalaxyl), copper sulphate, LS 74–783 (aluminium tris(ethyl phosphonate)) or water in mid-August 1977 was assayed for Phytophthora syringae by an apple fruit baiting method immediately after fungicide application and at weekly intervals for 8 wk. There was no infection of baits placed in the orchard and this was attributed to low rainfall. When wetted and baited, samples of surface soil caused from 0 to 85% fruit infection depending on the time of sampling and soil treatment. In control soil, fungus activity was low in the first 4 wk, high in the fifth wk and fluctuated widely thereafter. In samples from soils treated with Aaterra, copper sulphate or LS 74–783 activity was first apparent in the fifth wk and then fluctuated roughly in parallel with that of control soil although at generally lower levels. Changing levels of activity were apparently related to air temperature during baiting. No infection of fruits occurred in any samples from soil treated with furalaxyl. Further assays of this soil indicated a complete suppression of P. syringae to at least 10 cm soil depth. Furalaxyl is sufficiently active to be considered as a soil treatment for controlling Phytophthora fruit rot of apple and pear.