Test of fungicides against Stemphylium vesicarium on pear with or without a warning system

Stemphylium vesicarium causes brown spot of pear. The fungus especially causes severe damage in southern Europe. In recent years the disease is also found in the Netherlands and to a lesser extent in Belgium. Conference is the cultivar most commonly grown in the Netherlands. This cultivar is one of the most susceptible cultivars. A two years experiment was started to test the most promising fungicides against S.vesicarium on Conference. Some of these fungicides were tested together with a warning system in order to reduce the number of sprays. The fungicides that were tested were: thiram, tolylfluanide, difenoconazole, tebuconazole, fludioxonil and trifloxystrobin. Fungicides in a preventive schedule were sprayed weekly from end of bloom until harvest. The fungicides applied according to the warning system were sprayed after an infection moment. Symptoms on leaves and on fruit were counted. The symptoms with S. vesicarium were reduced in the case of the best fungicide by 83% on leaves and 49% on fruit in 2002. The best fungicide reduced the incidence by 100% and 89% on leaves and fruit respectively, the following year. The number of fungicide treatments was reduced by 44% in 2002 and 67% in 2003 when the fungicides were sprayed according to the warning system. In 2002, there was no significant difference in disease incidence between the treatment sprayed weekly and sprayed according to the warning system on leaves and fruit. In 2003, fruit sprayed with fungicides after an infection were significantly more infected than fruit sprayed weekly but less infected than the untreated plots. This might be due to a change in the action threshold from 1000 points in 2002 to 1500 points in 2003.