I am not an expert on how best to combat lily leaf beetle. When I find adults, eggs and larvae, my usual response is to bring them into the lab to perform experiments with them (which I suppose is as good a method of control as any, since it removes individuals from the breeding population). When I get questions about how best to control the beetle, I typically refer people to the factsheet prepared by my colleagues at the University of Rhode Island. However, I’ll bet there are many other clever solutions out there. In a contact form submitted at this site today, D. reports that she spreads diatomaceous earth on the soil to kill emerging adults. Diatomaceous earth is the fossilized silica-rich remains of diatoms. It works by interfering with the waxes on an insect’s cuticle, which causes the insect to dry out. It has low mammalian toxicity and poses minimal danger to the environment. Diatomaceous earth is effective against stored-products pests, but when used outdoors, it is washed away by rain and can even be inactivated by heavy dew, so repeated applications would be necessary.
S. from Nova Scotia reports using the usual hand control method but describes it so vividly that it deserves repeating here. She simply picks the adults off the plants “by hand (regularly and slyly with quick hands, as they drop and get lost in the soil below if they sense motion) and squash them. This is not as unpleasant a task as trying to remove the larvae later on, in their dark goo.” (I love that description of the larvae—can’t wait to have my hands covered in dark goo once again!) Getting the adults before they have a chance to lay eggs is perhaps the best way to control the beetles in small gardens, but it’s time consuming and one must be vigilant until egg laying ceases in July.
T. prepares a tea from cigarettes to spray on his lilies. Yes, nicotine is indeed a nasty insecticide. Several other plants with potent chemical defences can also be used. A graduate student at the University of Ottawa tried extract of black pepper (the leaves of the plant though, not the peppercorns), which was quite effective as a repellent. C. from Ottawa tried killing two invasive birds with one stone—by making a tea out of the horrendously invasive dog-strangling vine that was taking over her garden and used it to kill the beetles on her lilies.
Has anyone tried anything else? Are you thinking of trying something new this year? Please share your solutions with us!