Pests are vulnerable in winter, giving gardeners an opportunity.

Editor’s note: This article has been updated from its original text.

January is the pinnacle of winter. Although the days are starting to get longer, the frigid air has a tight grip on the season, reminding us that spring is still months away. Winter is the time for sleep. The perennials have died back, the trees have lost their leaves and the garden that was a bustle of activity in August is now silent.

In winter, we forget the challenges of cutworms in the early spring and the potato beetle we faced in the summer. We neglect pests in general, imagining them to have just gone away. In reality, they’re asleep too. The pests we encountered over the summer have gone into hibernation or diapause not far from the food source they once enjoyed. At this stage they’re vulnerable, which gives us an advantage and the opportunity to implement controls.

Winter pest management

Winter management strategies are not an instant solution to the problems in your garden, but they will give you a head start on the season to come. This approach works with the natural system, which is exactly what we are aiming for – long term effects that will continue to work after the initial implementation and require little to no maintenance.

Knowledge is key, so let’s refresh our memories about which pests were in the garden so we may address the problems over the winter to give our gardens a better chance this spring. Who attacked your plants this past season and where are they now?

PestHost PlantsDamageOverwintering Sites
AphidsA wide range of annuals, perennials, fruit and vegetables found throughout North AmericaAphids are sap sucking insects that will cause foliage to distort and leaves to eventually drop. Aphids excrete a substance called honey dew which encourages black sooty mold reducing photosynthesis and weakens the plant.Found throughout North America. Adult Aphids overwinter on host plants in and around the garden. Host weeds include; Thistle, field bindweed, lambsquarters, grasses and mustard. In some cases aphids overwinter as eggs on the terminals of fruit trees.
Potato BeetlePotatoes, tomatoes, eggplant, petunias. Beetles will defoliate plants very quickly, ultimately killing the plant.In the soil as adults in most states and Canada. The adults are usually found around the edges of fields and wooded areas under brush and leaf debris.
CutwormSeedlings and starts of vegetables and annuals. Found Throughout N. AmericaCutworms are present in the early season feeding on new transplants or seedlings. They chew through stems at ground level. Many vegetable starts can be devoured in a night. The destruction resembling a small clear-cut forest.On the Pacific Coast and in Southern U.S. Cutworms are found as caterpillars in the soil of raised beds, gardens, pastures and weedy areas. In colder climates they will migrate in as adults as the temperatures warm.
Cabbage MaggotCabbage family crops; Cabbage, Broccoli, Cauliflower, mustards and radishesMaggots tunnel in roots causing plants to pale and wilt. This can kill the plants directly or provide opportunity for other disease organisms to move in.As pupae in the soil close to plants in the cabbage family and related weeds. Throughout the northern U.S. And Canada.
Mexican Bean BeetleCowpeas, lima beans, snap beans, soybeans. Found East of the Mississippi as well as Arizona, Utah and NebraskaAdults and juveniles will feed on the underside of leaves causing a lacy appearance and ultimately defoliation. As adults under brush and leaves in wooded areas adjoining fields/gardens and in the soybean refuse. Found in most States east of the Rocky Mountains.

Don't throw out the good with the bad.

The allies of your garden such as ladybugs, syrphid flies, ground beetles and parasitic wasps will also stick close to a successful environment. We want to encourage their presence. When you are implementing controls of any kind the aim should be BALANCE not elimination. Balance is achieved through diversity and established thresholds. Diversity means having a broad spectrum of plant variety and insect species.

Plant diversity = insect diversity

Thresholds are a predetermined level of pests that we can manage without severely impacting a crop. For example, a low level of aphids is necessary to keep ladybugs and other aphid predators active in your garden. We need to conduct our garden cleanup with this in mind, approaching the activity with all aspects of the natural system considered.

Follow these guidelines to ensure that you are addressing the problem while not eliminating your allies in the garden.

Winter control guidelines for beneficial insects:

  • Leave healthy, standing, hollow-stemmed plants such as dill, amaranth and elderberry as refuge spots for ladybugs and solitary bees.
  • Rocks and logs strategically placed in the garden for aesthetic effect make excellent refuge for predatory beetles.
  • Wait until spring to cut back ornamental grasses. These perennials are ideal locations for overwintering bumblebees.
  • Create small piles of maple leaves, brush or untreated grass clippings for ground beetles and other terrestrial predators.
  • Add fresh compost to beds to boost beneficial microbes and predatory mites.

Winter control guidelines for pest control:

  • Inspect and remove plant material in the garden where known pests existed. Check the leaves of kale, cabbages and Brussels sprouts for aphids. If found, remove material and dispose into the garbage, not the compost pile.
  • Pull any remaining carrots, onions and rutabagas. Check for root maggots and dispose of those in the garbage.
  • In asparagus patches, remove remaining plant debris where asparagus beetle or aphids are overwintering.
  • Turn the soil lightly to expose any soil dwelling cutworms, potato beetle and grubs to the birds. You can even go so far as to scatter bird seed to encourage types that eat both insects and seed.
  • Collect any ground and rove beetles. Gently transport them to the composter and place under the material.
  • Clean your greenhouse with mild bleach solution to kill any fungus spores. If the structure is wood, follow up the bleach solution with horticultural oil painted onto all exposed wood. This will suffocate the spider mite, thrips and other tiny pests who are hibernating in the cracks and crevices.
  • Clean garden tools with mild bleach solution and your pruners with rubbing alcohol to kill any spores or diseases that could be transferred.
  • In the greenhouse, give your pots and trays “feet” so there is an inch or 2 of space between the bottoms and the table. This will eliminate habitat for sowbugs and encourage airflow.
  • Education is the key

    When spring arrives and the first of the plants start to bloom, get out there and have a look around. The more you know the better equipped you will be. Check for plants that are struggling, these will be the first to be hit by pests. Notice which plants are thriving. What is it that makes them so successful? Learn which insects inhabit your garden to determine what you may be missing and take the steps to encourage the missing ones in.

    Educating yourself leads to a greater level of intimacy with your garden and a clearer understanding of how it all works. Learning today prepares you for tomorrow.

    Colorado State University
    University of Florida
    Rodales Organic Life

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