The following is from the Johnston County Cooperative Extension Service.
Garden pests create stress not only for plants but also gardeners. They eat leaves, transmit viruses, cause flowers not to open and can even kill plants.
The first thing many gardeners do at the sign of pests is spray. But often, spraying can do more harm to the delicate environment than the pests themselves.
Pollinators such as honeybees depend on flowers for food. As reported by news media for several years now, the honeybee population is rapidly declining. And it is safe to assume that if honeybees are falling in number, so are other pollinators like bumble bees, butterflies, bats and beetles (just to name a few). While few people are monitoring the levels of these other pollinators, scientists and beekeepers all over the world are monitoring honeybees.
To save our pollinators, we must take some precautions before spraying pesticides. First, make sure to correctly identify the problem. Is the pest really affecting the plant, and if so, is it really a problem? Some beneficial insects look just like pest insects. Second, assess the damage. Do the pests really need to be controlled? Are they eating leaves on the plant but leaving the fruit alone? What amount of damage is the insect causing, and is it enough to justify spraying in order to control them? Third, determine if there are cultural control options. Cultural controls include using traps, using beneficial insects, handpicking insects off of plants, etc.
If you have evaluated the situation and spraying is your only option for control, think before you spray. Many pesticides can be extremely toxic to honeybees and other pollinators. Pollinators are attracted to flowering plants. Try to avoid spraying plants when they are in bloom. If pests are harming plants that are in bloom, then treat the plants with pesticide in the evening hours, when the bees are less active.
Pesticide application depends on how the chemical was formulated. Dusts and wettable powders leave a residue that is harmful to pests and pollinators. These types of chemical formulations don’t target specific pests; they are non-selective killers. Solutions and granular pesticides usually aim to target specific pest insects and are less likely to harm the beneficial insects.
The 2013 N.C. Agricultural Chemical Manual lists the relative toxicity of pesticides honeybees. Go to http://ipm.ncsu.edu/agchem/5-toc.pdf.
When protecting plants from pests, give consideration to those insects, birds and mammals that are providing pollination.