Don’t Invite These Pests To The Plant Sale Or Camp!

If you’re one who can’t wait to get into the dirt with spring weather, we can relate! As you get ready to grow, please keep in mind that many pests and pathogens can move with freshly dug and potted plants. Use caution when moving plants with associated soil. Below, we highlight two species that threaten the health of Maine’s forests and move readily in soil and other landscape material, such as mulch.

Winter Moth (Operophtera brumata):

Winter moth was introduced into North America from Europe. It was first recorded in Nova Scotia in the 1930s, appeared in eastern Massachusetts in the early 2000s, has since spread into western Massachusetts and Rhode Island, and is now in coastal Maine from Kittery to Lubec. The larvae of winter moth defoliate deciduous trees and shrubs in early spring. Trees heavily defoliated by winter moth for three or more years can exhibit branch dieback and mortality. The pattern of winter moth defoliation and damage in Maine suggests that humans are largely responsible for its introduction and spread in Maine. It is likely that they moved with landscaping material.

Image: Life stages of winter moth: caterpillar and adult moths.

Larvae hatch in April from eggs laid during the winter on the trunks of host trees. The caterpillars crawl up the trees and burrow into both leaf and flower buds, feeding on the expanding buds and foliage. The larvae also produce silk that they use to “balloon” to new locations. Winter moth larvae are light green to brownish-green inchworms with longitudinal white stripes on each side of the body and are one half inch long when full-grown. Winter moth caterpillars are active from April through early June. Once mature, larvae come down out of the trees on silk threads to pupate in the soil, not only under the trees, but also in the surrounding area. The larvae form small earthen cocoons that resemble clods of dirt. They stay in these cocoons from June to November. During this time is the greatest risk of transporting winter moth to other areas. However, there is a risk of moving eggs and caterpillars other times of the year if you move trees and shrubs from infested areas.

Image: Winter moth cocoons resemble clods of dirt and are difficult to see in the soil around dug plants.

Winter moth caterpillars feed on the leaves of many deciduous trees and shrubs in Maine. Preferred hosts include oak, maple, apple, elm, ash, crabapple, cherry, and blueberry, but the larvae will also feed on many other plants.

Image: Heavy feeding damage from winter moth caterpillars on a oak in South Bristol, ME.

Image: Map of known and likely occurrences of winter moth in Maine.

Jumping Worms (Amynthas spp.):

Image: Jumping worms have a smooth, white or gray clitellum (collar) that fully encircles the worm. The clitellum is also located near the head of the worm, around segments 14-16. Common earthworms have clitellums that are raised and pink and are saddle-shaped. The clitellum of common earthworms is often located in the middle of the worm body, around segments 32-37.

Image: Jumping worms change the soil consistency into loose and dry granular soil full of worm castings (worm poop). Note the depleted leaf litter layer, an important facet of healthy forests.

Amynthas worms, otherwise known as jumping worms, are native to Korea and Japan and are now found in the United States from Maine to South Carolina and west to Wisconsin. Jumping worms were first collected from a Maine greenhouse in 1952, though an established population of this active and damaging pest was not discovered here until about 2014 when two populations were discovered in Augusta (one at the Viles Arboretum) and two populations were found in Portland. Jumping worms are now considered to be widespread in Maine and are found in 13 of the 16 counties.

Image: Many towns in the southern half of Maine have jumping worms.

Jumping worms are an annual species, with the adults dying after the first few hard frosts in late fall. Throughout their one-year life, jumping worms change the soil by rapidly consuming the nutrient-rich leaf litter layer on the forest floor. They turn good soil into grainy, dry worm castings (a.k.a. poop), which cannot provide support for our native plant and tree roots. Other native fungi, invertebrates, and vertebrates relying on the plant and tree diversity of our Maine forests may decline or vacate an area due to the loss of their native host plants. As native species decline, invasive species may take their place and further exacerbate the loss of species diversity.

In early fall, the worms mature into adult worms and begin laying cocoons containing eggs into the soil. Unfortunately, jumping worms are parthenogenetic, meaning they do not need a mate in order to produce fertile offspring. This means that just one cocoon hatching can create an entire population in an area due to self-fertilization of the adults. Cocoons successfully overwinter in Maine and are very difficult to differentiate between soil, making them a problematic pest species.

In nurseries and greenhouses, jumping worms reduce the functionality of soils and planting media and cause severe drought symptoms. These worms and their cocoons may be inadvertently moved to new areas through infested soil, mulch, or compost. Many of Maine's forests are already under pressure from invasive insect pests, invasive plants, pathogens, and diseases. Jumping worms may cause long-term effects on our forests.

Some helpful tips for gifting, moving or selling plants from your dooryard:

• If you are digging plants from your yard, it is important that the plant material is bare root. Make sure to wash all soil off of the roots.
• You can repot these plants using sterilized potting soil and plant pots.
• Be mindful of what soil pests are present in your yard and take appropriate steps to limit their spread.

In addition to jumping worms and winter moth, many other pests, pathogens and invasive plants can move in plants that were dug up from people’s yards.

Find more tips on sharing plants, not pests, from the University of Maine Cooperative Extension.