Evaluation of a mechanical dispenser and interplant bridges on the dispersal and efficacy of the predator, Phytoseiulus persimilis (Acari: Phytoseiidae) in greenhouse cut roses

Adequate distribution of natural enemies is necessary for successful augmentative biological control. In California greenhouse cut roses produced using the bent shoot system, the predatory mite Phytoseiulus persimils is widely used for control of the phytophagous mite Tetranychus urticae. One purported advantage of the bent shoot method is that the dense foliage of the lower canopy creates interplant bridges that facilitate predator movement. However, gaps in lower canopy interplant contact can occur in young plants or can result from varietal growth habit or seasonal cessation of growth in established plants. We observed an average of 1.63 ± 0.10 interplant contacts in the lower canopy across five rose varieties, with the average lower canopy gap being 3.52 ± 0.42 cm wide. We evaluated the use of interplant bridges of plastic flagging tape as a method to enhance dispersal of the P. persimilis predator. We determined that about three times as many predators moved from the plant on which they were released to adjacent plants when those plants were connected by bridges compared to those that were not. Finally, we tested the use of interplant bridges and a mechanical dispenser to determine if the use of a dispersal aid could enhance the efficacy of biological control. After 3 weeks in the greenhouse the number of leaves infested with T. urticae was reduced by approximately 50% using interplant bridges or a mechanical dispenser in comparison to controls without dispersal aid, although there was no difference between dispersal methods.