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Natural Controls for Winter Moth

Winter Moth

It’s about to begin. In a couple of weeks here in southern New England, (late November), we’ll start to notice clouds of dull gray brown moths fluttering about at night, attracted to the glow of porch and street lights. Mating season for the Winter Moth, Operophtera brumata, is about to begin as both male and female moths emerge from their pupae. They will procreate into December, or as long as mild enough temperatures prevail.

In our recent research for the best methods to combat this destructive pest (Winter Moth caterpillars devour new plant growth on many of our most highly desirable ornamental trees and shrubs), we came across great news! University of Massachusetts Entomologist Joe Elkinton and his team have solid evidence that a parasitic fly, Cyzenis albicans, is an impressive natural control for Winter Moth. At four test sites where the parasite has been released throughout southeastern MA (Seekonk, Hingham, Falmouth and Wellesley)  populations of winter moth have dramatically decreased. Here is a link to an   article.

Isn’t that fantastic to read? However, while we are waiting for this helpful parasitic fly to move into our neighborhoods, we must begin preventive measures. It is necessary to understand the Winter Moth lifescycle to plan and time your defense.  The first meaure is to apply sticky tree bands around treasured specimens, which trap the females as they adhere and climb up tree trunks, emitting their sex pheromone to attract the males. After the mating scene has occurred, female moths continue to climb to the top of  trees and shrubs and then lay their eggs in the bark and crevices near branches. Adult moths die at this stage.

Other types of botanical controls can be applied over the winter and early spring. In late winter, dormant oil spray can be applied to branches to suffocate the eggs. In early spring, Bacillus thuringiensis a.k.a. BT, a beneficial bacteria, can be used to effectively control the caterpillars as they emerge from their egg sacs and seek nourishment from the young unfurling foliage. Spinosad is another bio insecticide, and is available to homes owner under product labels Monterey Garden Insect Spray and  to licensed pesticide applicators as the product Conserve. Care should be taken to avoid applying Spinosad when bees are active.

Recommended Further Reading

What’s Eating My Plants? I

Tobacco Hornworm

Don’t you just hate this? One day you have a perfectly healthy plant, and the next time you look, the leaves are riddled with holes, or completely gone! Just 2 days ago, I photographed a lovely stand of Nicotiana mutabilis (Flowering Tobacco). As I walked by this morning, I was stunned by totally denuded stalks. On closer inspection, there was a 4″ Tobacco Hornworm chomping away, leaving behind a trail of excrement. Not a pretty picture now.

The Tobacco Hornworm Manduca sexta is the caterpillar of a type of Sphinx Moth or Hawk Moth. It differs from the Tomato Hornworm by having a reddish instead of a black “horn”, and you can also tell the difference by its lateral markings. The Tobacco Hornworm has seven diagonal lines, while the Tomato Hornworm has eight v-shaped markings.

The adult female Sphinx Moth deposits her translucent green eggs on the undersides of leaves of plants in the Solanacea family, especially Nicotiana (Tobacco), and take 2-4 days to hatch. During their larval stage, these Hornworms feed on the foliage, flowers and fruit. They can ingest the toxin Nicotine without ill effects, and their voracious appetites allow them to strip even large plants overnight. Their green bodies camouflage well with the plants they feed on.

Control this pest by handpicking the caterpillars. If you have too large a crop for handpicking, you can use a product like Dipel (Bacillus thuringiensis) or Monterey Garden Spray (Spinosad) on the young larvae. Be on the lookout for hornworms with little white “pills” attached. These white attachments are the eggs of the parasitic Braconid Wasp, which feed on and weaken/kill the unsuspecting hornworm. This biological control is a good example of nature keeping everything in balance.