Arborjet Revolutionary Plant Health Solutions


Winter Moth

Winter Moth, an invasive pest introduced from Europe and the Near East, 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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Winter Moth 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.

Photo A taken by Louis-Michel Nageleisen, Department de la Santa des Forets,
Photo B taken by Hannes Lemme,
Photo C taken by Arborjet, Inc research, b Anette Linnea Rasmussen (


Arborjet recommends a well-timed injection of ACE-jet using either the Tree I.V. or QUIK-jet. ACE-jet should be applied 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, 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.

*Important: Always read and follow label instructions before buying or using these products. The instructions contain important conditions of sale, including limitations of warranty and remedy. TREE-äge® Insecticide is a Restricted Use Pesticide and must only be sold to and applied by a state certified applicator. TREE-äge® is not registered for use in all states. Please check with your state or local extension service prior to buying or using this product. TREE-äge® is a registered trademark of Arborjet, Inc.

When to Treat

Generally, the best seasons for injection are fall and spring, was uptake occurs when trees are transpiring. The environmental conditions that favor uptake are adequate soil moisture and relatively high humidity. Soil temperature should be above 40 degrees F for trunk injection. 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. If treating trees in the summer, it is best to inject in the morning for the quickest uptake. 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.

Use ACE-jet 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.

Another option is to treat with an injection of TREE-äge, 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 a soil drench, bark spray, or chemigation formula.

What to Expect After Treatment

ACE-jet trunk injection in the spring will uptake very quickly and caterpillars will die rapidly. Monitor trees annually to determine the need for a repeat treatment.

Trunk-injected ACE-jet moves rapidly to the growing points in the canopy, where caterpillars feed. Upon ingestion of ACE-jet insecticide, leaf feeding stops and caterpillars die.

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.

AzaSol is not trunk-injected like ACE-jet and TREE-äge, meaning it may have to be applied more frequently to maintain control. Please refer to label instructions for proper usage.

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