Winter moth, Operophtera brumata, is a relatively unique species of Lepidopteran. The adult stage is active during the winter making it very noticeable. The larvae are voracious and are capable of destroying all buds on an entire tree. Successive years of heavy damage can kill trees, and has been responsible for 40% mortality in some stands of red oaks in Nova Scotia. Larvae disperse themselves with long silken threads used to move with the wind.
Winter moth can be a challenging insect to achieve acceptable levels of control on. A major challenge that must be considered when implementing winter moth treatment programs is during prolonged late winter/spring weather with fluctuating temperatures. These types of springs can lead to inconsistent development of winter moth life cycle, requiring additional treatments to cover longer durations to achieve high levels of control.
When using Lepitect, use the highest dosage rate and during prolonged spring periods reapply a second application 30-45 days later. Use Mectinite or Lepitect Infusible as tree injection treatments for trees that cannot be treated with foliar sprays or other systemic options.
Insecticide sprays can be used to treat for the caterpillar stage beginning at bud break in early spring, however, do not use insecticides that are toxic to bees and other pollinators while trees are in flower. Sprays should target the earliest instar stage possible as sprays become less effective on larger caterpillars. For severe infestations consider applying at least one foliar spray and a systemic option to carry longer residual length of control and to avoid gaps in coverage.
Other Treatment Practices
- Eggs are laid in hard to reach areas such as bark crevices and under lichens. Therefore a dormant spray of horticultural oil will not fully control this insect.
- Although natural controls have been attempted, they have only provided marginal control on a region wide scale and should not be relied on to protect individual high value trees. Control is further hampered because larvae disperse themselves with long silken threads, which move them to previously controlled areas.
The larvae spin silky strands that allow them to disperse themselves and move between hosts. This means that even if a tree is treated with an insecticide, it could still potentially be infested. With larvae feeding in the actively growing buds, achieving adequate control with a canopy spray is challenging. Furthermore, often the host trees are prohibitively large or in areas where spraying is challenging. These situations are where systemic treatments can provide value.
One challenge that must be considered when implementing winter moth treatment programs is during prolonged late winter/spring weather with fluctuating temperatures. These types of springs can lead to inconsistent development of winter moth life cycle, requiring additional treatments to cover longer durations to achieve high levels of control.
Signs of Damage
- Thin canopy due to larvae feeding on buds
- Partial leaf emergence
- Complete defoliation if warm temperatures are delayed in spring
- Branch death after successive years of infestation
- Tree death if complete defoliation occurs in successive years, especially when coupled with abiotic stress
- Leaves can webbed together or folded over by the early instar caterpillars
- Brown or tan male moths can be seen in November to January
- Female is dark and wingless and rather immobile
- Green caterpillar-like larvae are about 1” long when fully developed with white stripes down their sides and back
- Small green eggs that turn orange or pink in late fall and early winter, these are very difficult to find
Photo: Rainbow Ecoscience
Photo: Wikimedia Commons
Trees At Risk
Many species are affected by winter moth. Preferable species include:
- Oaks (Quercus spp.)
- Maples (Acer spp.)
- Flowering plum
- Flowering pear
- Apple (Malus spp.)
Additionally, winter moth will attack numerous shrub species including blueberry and deciduous azaleas.
- Moths (the adult stage) emerge from the soil usually in late November and can be active into January.
- After mating, the female deposits an egg cluster on tree trunks and branches, in bark crevices, under bark scales, under loose lichen, or elsewhere.
- Eggs hatch when temperatures are near 55 degrees.
- Larvae emerge and spin long silken strands which allow them to move with the wind and travel large distances. This is called “ballooning."
- After landing on a host they feed until June, and then fall to the ground to pupate until emerging again in November.
Always refer to product label for rates and approved uses. Some images courtesy of forestryimages.org or Wikimedia Commons. Use of the images does not imply endorsement of treatments.