150 Tips: 3 Common Garden Pests

For the sake of the planet, we will not be sharing some of the tips and techniques recommended by MSHS in the distant past for dealing with common garden pests. Arsenic, formaldehyde, powdered strychnine, DDT and many other chemicals were on the menu for gardeners in the early to mid-20th century. That said, gardeners also understood early on that nature had its own ways of controlling troublesome pests.

Encourage birds in your garden for pest control. In 1913, the Rev. Rett E. Olmstead of Excelsior sang the praises of birds as a way to reduce insect populations, particularly in fruit orchards. Caterpillars, cinch bugs, flies and other insects are food for birds. Recent research has confirmed the role beneficial insects also play in reducing populations of pests.

Here are some recommendations we endorse for a few common garden pests. (For more on garden pests, check out this blog post on vegetable garden pests or this one on the value of insectary gardens.

cut worm curled up next to plant stalk

Cut worms will shear a plant off at the base.

Use physical barriers to repel cut worms. Cut worms are so discouraging. One day your cabbages, potatoes, corn or other vegetables are looking great. The next, they’re munched off at the stem. Installing cardboard (cut up toilet paper rolls are a good option) in a circle around the base of the plant, buried two inches underground has been recommended for more than 100 years by hort society experts to thwart cut worms. The University of Minnesota Extension has other tips for identifying and dealing with cut worms.

Treat scale insects with a toothbrush (and more). Scale is among the most frustrating common garden pests to deal with. They don’t even look like bugs, resembling growths of the branches of a plant for much of the year. But a bad infestation can kill a tree. Scale may infest maples, elms, conifers, oaks, dogwood, spirea and more, but the biggest concern recently has been with magnolia scale. Don Engebretson described how he deals with this pest in a recent article in Northern Gardener. In the early 1900s, hort society experts recommended removing the scales (the growths on the branches of trees) with a tooth brush. That will not work for a serious infestation. In 1998, long-time Plant Health columnist Kathy Widin recommended starting with horticultural oils to deal with soft scales. Serious infestations can be treated with insecticides, such as carbaryl (Seven) or malathion. Whenever you use an pesticide, follow directions carefully for timing and rate of application.

3 japanese beetles attacking hollyhock file

Japanese beetles attack a variety of plants, including hollyhocks.

Pick Japanese beetles and watch for reinforcements. Japanese beetles have been in Minnesota for more than 50 years. They are a persistent pest and can wreck havoc on roses, green beans, grapes, birch trees and about 300 other plants. They usually arrive in late June and are around for about eight weeks. The beetles overwinter as grubs in your lawn, which is why it’s often recommended to treat the grubs. To control the beetles, Northern Gardener has recommended going out every morning and picking them off plants and dropping them in soapy water. In 2002, Kathy Widin recommended gardeners choose plants beetles are less likely to destroy, such as elderberry, lilacs, junipers, pines and spruces. It’s worth noting that the winsome fly, a parasite of Japanese beetles, have also arrived in Minnesota and may help reduce numbers. Our editor spotted several beetles infected with winsome flies in 2021. Speaking of Japanese beetles . . .

Japanese Beetle traps are a no-go. While some gardeners use traps that lure beetles via scent and sexual atttractant, this method is often too effective and actually attracts beetles from neighbors and beyond, bringing more in than killing. For this reason, it’s usually better to stick with the traditional method of hand-picking beetles into a tub of soapy water, according to Bud Markhart in a 2012 article

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