De curatieve bestrijding van de stromijt Tyrophagus dimidiatus (Acari: Astigmata: Acaridae) op Rhododendron simsii

Tyrophagus mites on ornamentals are usually regarded as secundary pests. In ornamentals, their populations seem to increase clearly during the last years. A comparative control experiment was carried out on azaleas infested by Tyrophagus dimidiatus. The azaleas were treated twice with a week interval, using a knapsack sprayer. Endosulfan, omethoate and abamectine gave a theoretical mortality of 75-80 % two weeks after the retreatment. Four weeks after retreatment abamectine proved to be the most effective with an estimated mortality of 85 %. The efficiency of endosulfan, omethoate, pyridaben, bifenthrin and dicofol after 4 weeks decreased to only 50 to 60 % mortality. Methamidophos, amitraz and to a lower extend methomyl clearly gave an unsatisfactory result. In conclusion, it seems that Tyrophagus mites are quite tolerant to the most currently used pesticides in ornamental cultures. This way, they are capable to fill up the vacuum created by the chemical control of typical leaf pests, which can explain their increased occurence in ornamentals.