Extent and Economics of Biological Control of Tetranychus urticae and Trialeurodes vaporariorum in Danish Glasshouses1

A survey was conducted among Danish tomato and cucumber growers concerning the use of biological and chemical control in Danish glasshouse crops in 1982. The survey revealed a widespread use of biological control of Tetranychus urticae and Trialeurodes vaporariorum on glasshouse crops of cucumber and tomato (87 and 77 % of the area, respectively). The growers estimated biological control to be cheaper than chemical control, and showed a pronounced preference for biological control (82 % of the replies). In cucumber crops, the area on which biological control was uninterrupted throughout the growing season was greater than in tomato crops, despite the fact that more chemical applications against other pests and diseases were necessary on cucumber crops. A list of the pesticides most commonly used in glasshouses in conjunction with successful biological control of spider mite is presented. Guidelines for biological and chemical control of spider mite on cucumber and whitefly on tomato are given.