A method for decision support in pest, disease and/or weed control management is proposed, wherein a forecast regarding the time of an appearance of a pest species, pathogen and/or a weed variety at a forecast location is made in a forecast year on a forecast day (t1) based on the temperature data of the year preceding the forecast year and of the forecast year, wherein the date of a day of the preceding year on which the pest species, pathogen and/or weed variety appeared for the first time at the forecast location is inputted into an evaluation device and stored in a storage device, wherein the temperature data of the preceding year and of the forecast year are transmitted by a temperature measuring device to the evaluation device and stored in the storage device, wherein the evaluation device calculates an accumulated degree day number (Y1) for the forecast day (t1) from the temperature data of the forecast year, wherein the evaluation device determines accumulated degree day numbers of the preceding year from the temperature data of the preceding year and compares the accumulated degree day number (Y1) of the forecast year with the accumulated degree day numbers of the preceding year, wherein the evaluation device, based on this comparison, makes a forecast regarding the time of an appearance of the pest species, pathogen and/or weed variety and a day number difference is displayed on a display device, wherein the day number difference indicates by how many days a forecast date of the appearance of the pest species, pathogen and/or weed variety in the forecast year differs from the date of the day of the preceding year on which the pest species, pathogen and/or weed variety appeared at the forecast location for the first time.