The Norman Transcript


August 9, 2013

Bagworms are abundant this year

NORMAN — After a few dry summers, it is now time for the triumphant return of many pests, specifically bagworms. Bagworms have a very wide host range. They are common on juniper and cedar, but I’ve seen them on redbuds, roses and bald cypress this year. Apparently, bagworms will feed on more than 128 different plant species.

Bagworms cause damage by feeding on the tree or shrub and can completely defoliate smaller shrubs. The bagworm eggs begin hatching from old bags in late April to early May.

At this time, the larvae begin feeding to construct the bag. The bags are typically small and upright early in the season. As the larvae of the bagworm grow, so does the bag, which consists of plant material and silk.

The bag will typically reach about 11⁄2 to 2 inches in length.

The mature larvae will fasten the bag to the plant with silk. In August, pupation occurs, where the larvae matures to a pupa inside the bag.

In August and September, male bagworms emerge to mate with the females, who happen to be wingless adults inside the bag. After mating, females lay hundreds of white eggs inside the old pupal case to begin the cycle again next year.

Bagworms are best treated when eggs hatch and the larvae first emerge, typically April or early May. Products containing the soil-borne bacteria Bt (Bacillus thuringiensis) can be applied to the foliage of the plant at this time. Bt is only harmful to larvae of moth or butterflies, but it must be ingested by the pest.

You may have to reapply frequently, especially after rain or heavy dew. Once the springtime window for treatment has passed, the best method is removing bags by hand and squishing them.

If you have questions about treating bagworms or other plant questions, a Cleveland County Master Gardener can help. Call 321-4774 or email to speak with someone at our Master Gardener desk.

Tracey Payton Miller is Cleveland County’s horticulture extension educator for the Oklahoma Cooperative Extension.

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