Thanks to everyone who has submitted ideas for solutions over the past two years! Next summer we are going to test some of these ideas in our experimental garden. Madame T writes: "I am in the Montreal area and I had very positive results with coffee grounds. I put about 1 cup directly on top of each new lily as it poked it's head out. There are about 30 lilies in this central bed (called 'The Museum' )and I did not see 1 beetle or any damage at all." Coffee grounds seems to be the front-runner in terms of popularity, so we will make sure to include that treatment in our experimental design.
"In the spring when the Lilies are 1" to 6" tall you put down Beyers Grub Killer around all lily bulbs .
I did it once in April and again in May i only saw about 7 or 8 in April and i got rid of them by hand.
All of my lilies have come up this year and are just wonderful and really big."
I have to point out that grub killer is not available throughout much of Canada, including all of Ontario and Quebec, due to a cosmetics pesticide ban. Where they are available, pesticides should be used with caution, following the instructions on the label.
Rebecca raises an excellent point about home-made concoctions to control lily beetle in her recent comment. I've reproduced that comment here:
"I use three methods to control red lily beetles on my lilies. Constant vigilance is really the most effective. At dawn and dusk, starting in early May and continuing through until July, I patrol for beetles and squish any that I find. It’s especially satisfying to catch two or even three when they are locked together in an amorous embrace. Coffee ground mulch is also very helpful. In addition to masking the odour of beetles, it makes my sandy, slightly alkaline soil a more acidic, which the lilies like, and the beetles don’t seem to like coffee grounds much, so are less likely to live in the soil around the plants. I’ve also found a spray of neem oil works wonders, as long as the rain doesn’t wash it all off. My experience is that Asiatic lilies (Lilium asiatic) are the most susceptible to the beetle, while my Japanese lilies (Lilium auratum) hardly even get nibbled.
Of some concern are comments on this site from folks brewing up their own sprays of cigarettes or rhubarb leaves. Both produce highly toxic, broad-spectrum pesticides that will kill just about everything, and neither should be used in home gardens. Seriously, folks, you might as well use Round-Up as either of these home-brewed poisons!"
The phytochemicals in tobacco, rhubarb, dog-strangling vine, etc., have evolved as broad-spectrum insecticides, and are indeed toxic to all but a few insects that have evolved the ability to metabolize the toxins. So even though these are "natural" compounds, you need to use them with caution. Be especially careful to avoid spraying flowers, so as not to poison pollinators. These compounds are toxic to mammals as well, so avoid spraying any vegetation that pets are likely to chew on.
Has anybody else had any luck with coffee grounds?
Tracey submitted the following:
"I had been informed at a Master Gardener meeting last year that the application of coffee grounds around the base of the lilies helped to deter these little pests, as they are attracted to the odour left by previous infestations. The coffee supposedly masks the smell. I have been visiting my local Starbucks regularly and obtaining used coffee grounds. I have been sprinkling them about once a week around my lillies and with a fair amount of success. To date I have counted five of them only, and when I find them, I kill them and then apply horticultural oil to the plants to kill the eggs and larvae. I haven't seen any in over a week and I check daily for infestations. My garden is in Oshawa, Ontario."
And Bonita had a great idea for those of you finding it hard to get down on your knees to search for eggs and larvae (and we know how easily lilies can snap if you bend them too much to look under the leaves):
"A 'stick mirror' makes it much easier to see eggs under the leaves, than getting down on your hands and knees."
Last week, one reader observed that his martagon lilies (Lilium martagon) seemed somewhat less affected by the beetle than his Asiatic hybrids. It’s not surprising that certain Lilium species and hybrids are less preferred by the lily leaf beetle—all herbivore species show some degree of variability in their host preference. A study from the University of Rhode Island found that the hybrid Black Beauty was a less suitable host for the larvae than Oriental Pink. A British study showed that Lilium regale and the hybrid Golden Joy suffered less damage than the hybrids Tiber, Brindisi, Conca d’Or and Eliganzer.
Have any of you had better luck with certain hybrids or species? Please share your observations with us!
I can't seem to get the comments to stay open, so I thought I'd reproduce Bonnie's comment here:
I also hand pick & drop them in boiling water, I use rubber gloves to remove the larva & do the same. I have tried boiling off rhubarb leaves and use the cooled juice to spray on plants. After boiling off, drain & disgard leaves, keep juice in spray bottle to use as needed. The plants I tried it on did not get attacked, but must be sprayed often, especially after a rain.
Although biological control of an introduced pest such as the lily leaf beetle can provide an effective, long-term solution, it is not an overnight fix. Although they are inflicting massive mortality on lily beetles in their New England release sites, it will be years before the parasitic wasps Tetrastichus setifer and Lemophagus errabundus show up in most gardens. In the meantime, most gardeners will resort to squashing eggs and picking the adults and larvae off the plants.
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!