Hello. I read your article about leaf roller on hydrangea. In town (Ottawa) I can watch closely and smash the caterpillars. But at the cottage I’ve lost 5 plants to the infestation because I was not there often enough to address the problem. Is there something nontoxic that I can use… a spray perhaps? I’ve cleaned under the bushes. Thanks you.
Thank you for contacting the Toronto Master Gardeners.
You have been doing all the right things when it comes to controlling this pest. Removing the infected leaves and crushing the caterpillars as well as cleaning up under the shrubs are excellent pest management controls.
According to the University of California “A number of insects eat leafrollers including certain tachinid flies and ichneumonid wasps, which parasitize the larvae. After consuming the leafroller larvae, the braconid wasp forms a white cocoon next to the shriveled up worm inside its nest. A white cocoon is an indication that the parasite is present and might provide control. Lacewing larvae, assassin bugs, and certain beetles also are common predators. Birds sometimes feed on the larvae and pupae, although they usually prefer other insects. These natural enemies often help to keep leafrollers at low, nondamaging levels, but even if natural enemies are present, large outbreaks of leafrollers occasionally occur.”- Leafrollers on Ornamental Fruit Trees
However, if you find that you are losing the war at the cottage against these pests then you may want to try Bacillus thuringiensis. (Bt ). Bt is a naturally occurring bacterium, which is common in some soils, which when applied correctly works as a stomach poison paralyzing the digestive system of the caterpillars and is found to be effective against the larval stages of the leaf rollers. I must mention that it can be difficult to get the spray inside the rolled up leaves. Bt will only affect those insects that actually eat it so timing is crucial.
Bacillus thuringiensis products are highly susceptible to degradation by sunlight, so the best time to spray your garden is early morning or evening. Bt pest control products have a shorter shelf life than most chemical insecticides and should be stored in a cool, dark place. As with all products make sure to read the label carefully before applying.
Good Luck !