MELeaf: A Newsletter From the Horticulture Program, February 23.

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Horticulture Program

MELeaf: A Newsletter From the Horticulture Program, February 23, 2022

In this issue:

Seasonal Considerations for Browntail Moth Management

February is Browntail Moth Awareness Month. The Maine Forest Service recommends following the four Rs – Recognize, Remove, Recruit and Reach Out – to Knockout Browntail Moth. Here is a seasonal breakdown of activities utilizing the four Rs to help nurseries, greenhouses and garden centers manage browntail moth. Taking action now will help you achieve the fifth R: Reduce browntail moth impacts (and itch!) for you, your employees, and customers. 

browntail moth life cycle

Browntail moth life cycle. Click for a larger image

Winter (November-March)

  • Recognize: Learn how to identify winter webs. Webs can look like single leaves hanging onto twigs or fist-sized clumps of leaves tied together tightly with silk. Knowing where nests are can help inform your management decisions.
  • Remove: Use hand snips or extendable pole pruners to remove winter webs within reach from the ground and away from hazards such as powerlines. Protect your eyes and skin from hairs that might be present from past caterpillar activity. After removal, destroy webs by burning or soaking in soapy water for several days, then dispose of the nests in the trash.
  • Recruit: If you don’t have a licensed arborist on staff, hire professional help to remove webs that are out of reach or near hazards. Likewise, if there are trees where it is not practical to remove webs, line up a licensed pesticide applicator to apply an insecticide during the growing season.
  • Reach out: Let your neighbors, town officials and customers know what they can do to help Knock Out Browntail Moth. The more neighbors, businesses and others get together to respond to the problem, the better the results.

Spring (April to June)

  • Recognize: Caterpillars begin to leave nests and feed on many different hosts starting in April. Browntail moth caterpillars have 2 orange dots on the tail end and white tufts of hair along their body. Caterpillars will pupate in June. Both caterpillars and pupa contain irritating hairs and contact should be avoided. Avoid placing plants offered for sale under heavily infested trees.
  • Remove: Inspect plants that are sold and remove caterpillars and pupa from plants offered for sale. Avoid contact with hairs by wearing gloves, long sleeves, long pants and washing after exposure. Wandering caterpillars on buildings, the ground, or other hard surfaces can be washed off with a hose and vacuumed up using a wet/dry vac with a HEPA filter and filled with a few inches of soapy water.
  • Recruit: Have a licensed pesticide applicator treat plants, including those offered for sale and surrounding infested landscape plantings with an appropriate insecticide. Insecticide treatments on landscape plants should take place before mid-May to minimize impacts on trees and shrubs and reduce the presence of toxic caterpillar hairs. Insecticide treatments on plants offered for sale should continue as long as caterpillars are present.
  • Reach out: Educate customers on how to recognize browntail moth caterpillars, how they can reduce exposure to toxic hairs and where to find reliable, accurate management information. Inform customers that the window for insecticide treatment of the caterpillars closes in mid-May.

Summer (July to August)

  • Recognize: Adult moths are out and laying eggs during the summer. Adult moths are attracted to lights at night. Avoid storing plants under lights and consider converting to motion sensitive security lighting to avoid attracting adult moths. Egg masses are usually laid on the underside of leaves and are fuzzy and brown.  
  • Remove: Wash large infestations of moths off plants and buildings with a hose, then vacuum them up with a wet/dry shop vac with a HEPA filter and filled with a few inches of soapy water. Inspect plant material daily and remove any browntail moth adults and egg masses. Drop moths and egg masses into a container with 2-3” of soapy water (wear gloves!).
  • Recruit: Researchers at the University of Maine are trying to develop control strategies for managing the newly hatched caterpillars in August and early September. Reach out to Angela Mech at the University of Maine to see if there are opportunities for assisting with this and other browntail moth research. 
  • Reach out: Encourage customers to avoid attracting adult moths to lights at nighttime. Using lights combined with traps is not effective in reducing populations. Remind customers that there are no effective pesticide treatments for control of the adult moths. 

Fall (September to October)

  • Recognize: Eggs hatch and young caterpillars feed and start to build webs in the late summer and fall.
  • Remove: Take note of plants with feeding activity, clip webs as trees become dormant.
  • Recruit: Plan management strategies for the coming year. Arrange for a licensed arborist to clip webs in taller trees in the winter and line up pesticide applicators for any anticipated spring treatments.
  • Reach out: Assess what management strategies worked well for you and your customers.  Share lessons learned with customers, neighbors, municipalities, the Horticulture Program and the Maine Forest Service.

Spongy Moth: New Name for an Old Pest

The invasive defoliator Lymantria dispar, formerly known as gypsy moth and now known as spongy moth, successfully increased its populations in 2021, with over 55,000 acres of defoliation noted in Maine alone. Overwintering egg masses were observed throughout the state, and the majority of defoliation detected through aerial surveys were most notable in Franklin and southern Oxford counties. 

Region-wide, extensive damage was reported throughout the Northeast, upper Midwest, and Ontario, where drought conditions made these oak dominated areas particularly prone to defoliation. But it is not just oak that the spongy moth enjoys. Over 300 tree species are host for this pest, including conifers. Lymantria dispar is still a federally regulated pest with quarantines established to slow its spread. It’s new common name, the spongy moth, was chosen in part to create a search image for management. One of the best ways to reduce populations and reduce spread is to key into the overwintering egg masses, which look “spongy”, and scrape them off the various surfaces they are laid upon. In areas like Franklin and Oxford counties, egg masses will likely be plentiful and very visible. 

Forest service officials expect that Lymantria dispar, the spongy moth, will return in force in 2022, especially if we experience yet another year of drought conditions conducive to defoliators. The areas affected by spongy moth in 2021 did not coincide with those currently and previously defoliated by browntail moth caterpillar, though that is likely to change if populations of both pests continue to increase and expand. 

Spongy moth egg masses

The spongy egg masses of Lymantria dispar. Karla Salp, Washington State Department of Agriculture,

Green Industry Economic and Education Survey

Do you work in a Maine landscape or nursery business? If so, we need to hear from you! Help us assess the value of the green industry by completing the only survey assessing this important economic sector. Business owners and staff are all encouraged to participate. Every voice matters. If everyone responds, the green industry’s voice will carry more weight in future decisions related to funding and educational outreach. More information and review the survey.

This survey is a collaborative effort between UMaine Cooperative Extension; Maine Department of Agriculture, Conservation and Forestry; and the Maine Landscape and Nursery Association.

Take the Survey

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