Enhancing septoria leaf blotch forecasts in winter wheat I: the efect of temperature on the temporal distance between critical rainfall periods and the breaking of the control threshold

In integrated pest management (IPM), pests are controlled when the costs of control correspond with the damage caused by a pest on a monetary scale, implying that low pest levels are left uncontrolled. Several forecast models have been developed in plant pathology to warn farmers before an epidemic occurs to allow timely control. Most of these models do not predict a
control threshold (pest level at which action needs to be taken to prevent economic losses at the farm level) directly making an application in precision agriculture where pesticides and other inputs shall be used precisely where and when they are needed, difcult. Here, we quantifed the temporal distance between critical rainfall periods and the breaking of the control threshold of Z. tritici on winter wheat, as afected by temperature based on data from 52 feld experiments carried out in
Luxembourg between 2005 and 2016. The highest frequency of hours with rain (≥0.1 mm/h) was observed approximately at 300 h before epidemic outbreaks at about 13 °C, at 350 h at 11.5 °C and at about 475 h at about 7.5 °C. A Q10 value of 2.8 was estimated. The knowledge generated here will be used to construct a model that directly forecasts the time at which the control threshold will be reached and thus, when fungicide use is needed according to the standards of IPM with direct applicability in precision agriculture.