I'm just back from attending a pollinator gardening workshop at UC Davis for UCCE Master Gardeners. The news about our bees is not good. The most recent research on the decline of the bee population worldwide cites a combination of probable causes: viruses, mites, pesticides, insect growth hormone regulators, unnatural toxins and malnutrition. Master Gardeners are being urged to teach and encourage home gardeners to assist bees to remain healthy. Home gardeners may not have the means to control for virus or mite infestations, but we can limit or curtail the use of pesticides, insect growth hormone regulators and unnatural toxins that are harmful to bees in our gardens and we can provide food, water and shelter for bees.
This is the first of two columns on how to help keep bees healthy. Before we discuss planting a bee-friendly garden, we gardeners need to review our use of pesticides, even those labeled as nontoxic to bees, in our own gardens, The most crucial step in creating a healthy bee garden is to eliminate the use of all broad-spectrum insecticides, especially systemic insecticides that move into plant tissues, pollen and nectar. Neonicotinoids or neonics (including imidacloprid, clothianidin) target sap-sucking insects (aphids, whiteflies, mealybugs, scales, glassy-winged sharpshooters). Insect growth hormone regulators interfere with or halt the stages of insect metamorphosis when treated plant tissue is ingested. Bee larvae that are fed pollen from plants treated with insect growth hormone regulators never become adult bees. Systemic pyrethroids kill mainly chewing insects (cutworms, beetles, caterpillars), above and below ground. Some are extremely long-lasting and kill on contact as well, so they can kill bees that walk over the pyrethroid residue.
We must read all pesticide labels carefully and then research the active ingredients listed. Before applying any pesticide, even less-toxic products like horticultural oil, neem oil, or insecticidal soap, go to the experts. One of the best sources for pesticide information is the UC Davis Integrated Pest Management website, www.ipm.ucdavis.edu. Enter either the pest name or the host plant name to find least toxic control methods. Some pesticides are listed as well with their toxicity levels. The Fresno County Master Gardeners have a hot line for gardening questions, 9 a.m.-noon, Monday-Friday, (559) 241-7534. They can access the latest research for you.
There will be a lot to learn and educated choices to make. If our hackberry tree is full of woolly hackberry aphids creating a huge mess of sticky litter, do we apply a soil drench of imidacloprid (Bayer's Merit is one brand)? Yes, we can. Hackberry trees do not attract bees. However, we'll need to find other control methods for citrus scales and crape myrtle aphids since citrus and crape myrtles are favorite bee trees. Do we spray imidacloprid? Never. Its effect as a spray lasts only a couple of weeks, and it is highly toxic to flying bees when sprayed. Good information from the experts helps maintain healthy bee populations.