What Should I Do About Caterpillars?
Just as plants have peak seasons, so do pests. Aphids rule the spring, beetles reign in early summer, but late summer and fall are the season of the caterpillar. Many different types of caterpillars can currently be found munching on tree, shrub, and vegetable leaves in our area and their numbers are likely to increase in the coming weeks.
In many cases caterpillars can be left alone, causing little lasting damage to plants, but there are some situations where control is needed. If you find caterpillars in your yard or garden, don’t automatically reach for the insect spray. Take a minute to put the situation in perspective to determine if there is a need to do anything or if you should simply let nature take its course.
Often referred to as worms, caterpillars are the immature life stage of butterflies and moths. Caterpillars have chewing mouth parts, which they use to feed on plant foliage, leaving behind ragged holes in leaves. They also leave behind plenty of poop. Technically known as “frass”, caterpillar poop are small, hard pellets that range in color from brown to black and can be found on and under plants upon which caterpillars are feeding. Some caterpillars, such as fall webworms, also produce silk and are able to web leaves together or produce large tents to protect themselves as they feed.
Gardeners are often reluctant to leave caterpillars untreated. Perhaps we are haunted by memories of Eric Carle’s The Very Hungry Caterpillar and fear, that if left alone, caterpillars will soon devour everything in sight. In reality this is highly unlikely since most caterpillars are extremely picky eaters. In most cases, when you find caterpillars on a plant in your garden they will only be able to feed on plants of same type, and you do not have to worry about them spreading to everything in your yard. For example, tomato hornworms can devour tomato plants and may feed on their close relatives, pepper and eggplant, but they will not spread to melons, squash, corn, cabbage, parsley or other vegetables and herbs.
Should You Intervene?
Whether or not you should do anything about caterpillars in your yard depends on what they are eating. For healthy, established perennials, trees, and shrubs losing a portion of their leaves is not a problem, especially this late in the growing season. Because of this, treating caterpillars on ornamental plants is typically only necessary on small or recently planted plants that are still getting established.
In vegetable gardens, feeding damage is less tolerated since missing leaves mean less produce. Plus, who wants to eat caterpillars with their cabbage? If caterpillars are noticed on vegetables or herbs, control measures should be taken as soon as possible.
Caterpillars have several predators, including parasitic wasps, lacewings, spiders, and birds. In a healthy landscape, these predators often keep caterpillar populations in check naturally. They can also help provide control in vegetable gardens but usually not enough to preclude the need for human intervention.
Controlling caterpillars can be as simple as picking them off the host plant and squishing them or dropping them in a bucket of soapy water to drown. If you would rather not take such a hands-on approach, insecticides are available to control caterpillars, including several organic products. Advantages of using organic pesticides include that they are less harmful to beneficial insects and break down quickly so are less likely to leave behind residues. Organic insecticides for caterpillar control include those containing the active ingredient B.t., spinosad, pyrethrin, neem oil or azadirachtin.
To determine the active ingredient in any pesticide product check the label, which will also tell you how long you have to wait after spraying to harvest edible crops. When using any pesticide be sure to read and follow all label directions. Avoid spraying open blossoms as this increases the risk of impacting pollinators. If bees are actively working flowering plants in the area wait until late evening to spray, after bees have returned to the hive.
Learn more about controlling caterpillars:
- Organic pest control products: click here
- Controlling caterpillars in vegetable gardens
- Controlling caterpillars on trees and shrubs: click here
- Caterpillars that feed on trees and shrubs, NCSU fact sheet: click here
- What you can learn from a pesticide label: click here
Learn more about common caterpillars found in NC gardens and landscapes:
- Tomato hornworms
- Fall webworms
- Orange striped oakworms
- Azalea caterpillars, greenstriped mapleworms and more!
Use Extension Search to find research based information from Cooperative Extension systems across the U.S.
Visit your local Cooperative Extension center to learn more about gardening and landscape care. Find your county Extension center or post your questions to be answered online via Extension’s ‘Ask an Expert’ widget.
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