Winter Moth

Winter Moth causes severe defoliation of hardwood trees. 

Winter Moth is appropriately named, as adult moths are generally active from November through January.  The larvae begin feeding early on developing leaves; severe infestations will cause noticeable tree defoliation.  In June, they drop to the ground to pupate in the soil until the fall.  Canadian research has shown that four consecutive years of defoliation can ultimately lead to tree mortality.

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  • Common Symptoms
    • Early detection of Winter Moth is difficult, as the first instar larvae begin feeding while the pre-formed leaf is still in the bud. The first symptoms will be visible only after buds break and leaves unfurl, revealing small feeding holes in the leaves; at this point, the larvae are still generally too small to be seen. Over the early weeks of the spring, the feeding damage on the leaf will become more obvious and the caterpillars may grow to a visible size. The caterpillars may also be seen descending from the canopy on silken threads. Extensive populations of Winter Moth can cause severe defoliation of the tree.

    • Arborjet recommends a well-timed injection of ACE-jet when the larvae are actively feeding. ACE-jet is compatible with MIN-jet Iron for a 2-in-1 application of insect control and nutrition. ACE-jet moves quickly and easily to the leaves, and provides rapid treatment.

      Another option is to treat with an injection of TREE-äge or G4, which can control Winter Moth for up to two years. TREE-äge can be injected as long as the soil temperature is above 40 degrees F and below 90 degrees F.

      Lastly, AzaSol may be used as an injection during the Spring, or soil drench, bark spray in the Fall.

    When To Treat
    • Generally, the best seasons for injection are fall and spring, while trees are transpiring. The environmental conditions that favor uptake are adequate soil moisture and relatively high humidity, and the soil temperature should be above 40 degrees F.. Hot weather or dry soil conditions will result in a reduced rate of uptake, so trees should be watered if applications occur when soil is extremely dry.Tree health will also affect treatment efficacy, so assess tree health prior to treating. For example, a declining tree (>50% canopy dieback) is a poor candidate for treatment.

      When using ACE-jet it is best to treat in early spring, before buds break, when Winter Moth outbreaks are expected. Alternatively, treat when leaf injury first appears, or when caterpillars are first observed. One application is sufficient to control Winter Moth. ACE-jet remains active to protect the tree canopy for approximately 3 to 5 weeks.

      If you decide to treat with an injection of TREE-äge or G4, which can control Winter Moth for up to two years. TREE-äge can be injected as long as the soil temperature is above 40 degrees F and below 90 degrees F.


    What To Expect After Treatment
    • ACE-jet trunk injection in the spring will act very quickly and caterpillars will die rapidly. Monitor trees annually to determine the need for a repeat treatment.

      TREE-äge may work more slowly through the tree’s vascular system but will have a longer residual protection time than ACE-jet, making it ideal for multi-season protection. You will still want to monitor the tree’s overall health to see if reapplication is necessary.

    References And Photo Credits
    • Main photo taken by Hannes Lemme, Bavarian State Research Center for Agriculture,

      Larval stage taken by Louis-Michel Nageleisen, Département de la Santé des Forêts,

      Treated and Untreated taken by Arborjet Inc. research, by Anette Linnea Rasmussen ( )

©2016 Arborjet, Inc. Important: Always read and follow label instructions. Some crop protection products may not be registered for sale or use in all states or counties. Please check with your state or local extension service to ensure registration status. TREE-äge® Insecticide is a Restricted Use Pesticide and must only be sold to and used by a state certified applicator or by persons under their direct supervision.  TREE-äge® is a registered trademark of Arborjet, Inc.