With the long holiday weekend upon us, now is the time to start scouting your trees and shrubs for bagworms.
With the long holiday weekend upon us, now is the time to start scouting your trees and shrubs for bagworms. Widely recognized as a notable pest of eastern red cedar and junipers, bagworms will attack arborvitae, spruce and pine. An array of broadleaf trees, shrubs and ornamentals can also serve as hosts to bagworms. If you had a problem with bagworms last year, then you will probably need to treat again. If you noticed a tree loaded with bags this past fall, then you need to treat them.
Initiation of treatments depends upon the condition of the infested tree(s). If the previous year’s damage was slight, then a single spray application should be applied at the end of June or the first week of July. This delayed application will ensure that all larvae have emerged from the parent bag. If the previous year’s damage was severe, any additional feeding damage could cause further setbacks. In these instances, immediate treatment is needed to preserve tree health. A follow-up treatment may be necessary two to three weeks later to kill worms that emerge later that were not killed in the initial treatment. Small infestations can be picked off by hand once the larvae are large enough to see easily. However, any insecticide spray will be more effective if used on young larvae that are actively feeding. In Kansas, we typically see the first hatch in late May. It is recommended to wait a few weeks after seeing the first larvae emerge to allow those still in the bag to make their appearance. This normally means spraying during the latter half of June.
Insecticides commonly used for controlling bagworms include spinosad (Conserve, Fertilome Borer, Bagworm, Leafminer & Tent Caterpillar Spray), acephate (Acephate, Orthene, Ortho Systemic Insect Killer), and cyfluthrin (Tempo, Bayer Multi-Insect Killer). Controls applied in August are often a waste of time and expense because the larvae are large, tough and may have stopped feeding.
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