Killing the pests or my plants? Mealys and Scale

[Ray]

Originally Posted by northernorchids

... I've used many of the tips I've read here, but mainly I've used the Bayer systemic when watering. I only use it occasionally now as a preventative.

Generally speaking, preventive application of insecticides should be avoided. Repeated use of the same one is also a potential problem. The combination of the two can be the ideal way to help breed resistant strains.

The better thing to do is be observant, and treat affected plants immediately with an appropriate pesticide, repeating at whatever interval the label recommends (three applications at one-week intervals seems to be pretty standard, to encompass the entire pest life cycle).

If the ailment recurs, repeat the treatment using a pesticide with a different killing action.

One thing more about Merit (imidicloprid - Bayer's most common insecticide): repeated use has been linked to bad mite infestations. I speculate that it is so effective at killing insects - including those that attack mites but not plants - that it wipes out their natural enemies. I have used the stuff without any mite infestations, but the high humidity of a greenhouse environment doesn't favor them anyway.