inch worms

Asked September 17, 2016, 1:02 PM EDT

How can I exterminate inch worms naturally? Or what chemical can be used on food grade plants.

Lincoln County Oregon

1 Response

Thanks for your question! Here's an answer an OSU faculty member (Neil Bell) gave to a similar question in August 5, 2013:

"State and local agencies have been flooded with calls in recent days concerning localized, often severe defoliation of Oregon white oaks in some areas of the mid-Willamette Valley. Defoliation has also occurred in Douglas-fir and some ornamental plants where they are adjacent to or intermixed with infested oaks. The damage is being caused by the western oak looper (Lambdina fiscellaria somniaria); it is a native moth that historically has had periodic outbreaks in the Willamette Valley.With heavy infestations the trees may be almost completely defoliated. Outbreaks by this insect are not new to the Willamette Valley, they have been reported about every 15 years. The most heavily affected areas this year are consistent with previous outbreaks, and extend from Sheridan south to Monmouth and east to Silverton. During each of the previous outbreaks, Oregon white oaks have been shown to tolerate repeated years of defoliation from this insect with only minor impacts, and tree mortality from the effects of defoliation alone have not been reported. Although affected trees may be completely defoliated, the damage to oaks is usually only minor due to their ability to produce a second flush of leaves in the current year and/or a normal flush the following year since the buds are not affected. Following these outbreaks, populations of the insect collapse due to the combined effects of diseases, natural enemies (parasites and predators), larval starvation, and in some cases adverse weather conditions. Two diseases, a nuclear polyhedrosis virus and a fungal pathogen have been identified as among the most significant natural control agents. In terms of management, non-chemical options are generally the best choice. Infestations of caterpillars on smaller trees can be manually removed by high-pressure sprays or other techniques. Proper cultural care of affected trees also helps to reduce stress and will allow trees to better tolerate and recover from the effects of the defoliation. A number of products are registered for control of western oak looper in Oregon, but products containing Bacillus thuringiensis (Bt) are most commonly used due to their reduced impacts on natural enemies and other non-targets. The spraying of older larvae during late July and August is not recommended as many have already completed their feeding and the Bt formulations must be ingested to have any effect."