Insect damage is to be expected in a pollinator-friendly garden. Butterfly and moth larvae (caterpillars) will eat the leaves of their host plants. Leaf-cutter bees will cut holes in leaves. In many cases, a problem will resolve itself when beneficial insects, birds or other predators respond to increased numbers of an insect that is one of their foods. Ignoring, or even appreciating, this insect damage is often the best approach.
There is no doubt that pesticides kill pollinators. In an ideal world, there would be no pesticide use anywhere near a pollinator-friendly garden. However, in the real world there are insects, often invasive pests from Europe and Asia that can severely damage or kill landscape plants. As these plants, particularly the trees and shrubs, are a significant investment in money and time, it is understandable that homeowners want to protect them. The following eight requirements are designed so that, if needed, pesticides can be applied in a manner that minimizes the risks to pollinators.
Identify the specific pest before taking any action. Is a pesticide needed or will the plant survive without any intervention?
The term “pesticide” includes any substance used to control pests and is a broad term that includes insecticides (targeting insects), fungicides (targeting fungal diseases), and herbicides (targeting weeds). All of these substances, even herbicides such as glyphosate, can kill or injure pollinators. Pesticides should never be applied unless they are necessary to maintain plant health. Using preventive cover sprays, where pesticides are sprayed several times a year on a calendar basis, has been shown to create more pest problems than it solves. Not only do cover sprays create potential for pesticide runoff and increased human and pet exposure, they actually create pest problems by suppressing predators, parasitoids and diseases that keep plant pests under control. It is common to see outbreaks of spider mites, aphids and scale insects where pesticides are used. Only spray one plant at a time, and only if it is necessary.
It is important to follow label instructions so that the pesticide is applied in an effective manner while minimizing risk to the environment and the person applying it.
If it is necessary to use a pesticide, it should be done according to label directions using low impact products, such as horticultural oil or insecticidal soap. This webpage provides detailed information on low impact pesticides along with when they are best applied to minimize pollinator impact.
The primary reason tree care professionals and property owners use pesticides is because of the devastating impact of invasive pests from Europe and Asia. Invasive pests multiply and sometimes completely destroy North American plants species for two reasons: (1) our North American plants may lack natural defenses (resistance) to invasive pests from Europe or Asia, and (2) invasive pest populations may build rapidly because we do not have the right predators and parasitoids to control them as in their native habitat. Sometimes, controlling these pests may require the use of more toxic agents, including systemic pesticides. A systemic pesticide is absorbed throughout the plant so that all parts of the plants become toxic to insects, including pollinators. This webpage provides detailed information on the best management practices (BMPs) for controlling the most common of these pests while minimizing risk to pollinators. The article also includes information on protecting trees and shrubs from some specific native insects that sometimes cause problems.
Never spray plants in bloom or nearly ready to bloom. It is clear to most people that insecticides sprayed onto open flowers can be highly toxic to bees, even if they are sprayed early in the morning or at night when bees are not present. However, some may not realize insecticides sprayed in the two-week period before a plant flowers can also be toxic to bees.
Some key points about pollinator biology are good to remember if you have to use a pesticide, even if you are only treating one or two trees, shrubs or perennials. First, most bees and other pollinators forage during the day, so if you can spray at night or in the early morning, you can reduce the risk of accidentally spraying them. Second, pollinators are attracted to flowers. Anything that has flowers or is about to flower is a higher risk than a plant that is past bloom. If you can remove the flowers by mowing or pruning from around the treated plant, and anywhere your application may drift, you can significantly reduce risk to bees and other pollinators.
Fogging or spraying for mosquitoes or biting flies around the yard and garden with an insecticide can be very harmful to pollinators. Even if flowering plants are avoided and applications are made after sunset, insecticides applied as a fog or mist can drift onto flowering plants within 100 meters or more depending on the wind speed and direction. The insecticide drift could contaminate pollen and nectar collected by bees for several days or weeks after it is applied, and the residue on leaves can be toxic to caterpillars for weeks or months. Caterpillars of some species of butterflies are extremely sensitive to insecticide residue on leaves.
The most widely used insecticides for grub infestations of lawns are neonicotinoid insecticides, which are toxic to pollinators if they are sprayed over flowers. If lawns are mowed first to remove any weed flowers, or if there are no flowers in the lawn, it is unlikely that grub control products will be harmful to bees unless there is some spray drift onto flowers. More information on grub control in lawns.
Most or all of requirements 2, 4, 5, 6, 7, and 8 were copied, with permission, from the Michigan State Extension – Pollination website. The authors of that website are David Smitley, MSU Entomology; Diane Brown, Rebecca Finneran and Erwin Elsner, MSU Extension; Joy Landis, MSU IPM; Paula Shrewsbury, Univ. of MD Entomology; Daniel Herms, The Davey Tree Expert Company, Kent, OH; and Cristi L. Palmer, IR-4 Project-Rutgers - May 1, 2019
Last updated May 11, 2021