When talking about stubborn garden pests, the lily leaf beetle often comes up in conversation. This small bright red beetle wreaks havoc on lilies and causes many sighs… and discoveries! Several gardeners have shared their techniques for trying to control it.
Here are a few methods suggested by gardening enthusiasts, along with my comments based on current horticultural knowledge. Some approaches are worth trying, others less so… but all demonstrate the ingenuity of gardeners when it comes to protecting their plants!
Coffee Grounds
Apply coffee grounds to the base of the lily at least once a week. In addition, you must of course hunt for bugs at the end of May and remove them by hand. They won’t have time to reproduce, I promise!
Answer
Okay, a strong-smelling product may have a slight deterrent effect on leaf beetles in a new planting, as they search for their prey (lilies) by smell. Once the leaf beetles have found the planting, however, coffee grounds have absolutely no effect.
No studies have shown that coffee grounds have a lasting repellent effect on insects. I believe that the success of this method is due more to the fact that the owner picks up and kills the insects by hand than to the presence of coffee grounds.
In fact, the prestigious Royal Horticultural Society claims that the effectiveness of coffee grounds as an insecticide or repellent is an “urban legend.”
Thuja Trimmings
My sister noticed that her lilies weren’t being attacked by leaf beetles when they were planted near her thuja hedge. So, I simply cut some thuja branches and placed them around the base of my lily plants… MIRACLE! One to two days later, there were no more leaf beetles. So, the smell keeps them away. This improvised “cedar mulch” needs to be replaced after a week, otherwise the leaf beetles come back quickly.
Answer
This is the first time I’ve heard of this technique, so I can’t contradict you. However, thuja releases allelopathic compounds such as thujones, which are known to inhibit the growth of other plants, and I would be concerned that by regularly placing thuja clippings at the base of your lilies, you would end up, if not killing them, at least negatively impacting their growth.
Sulfur Lime
I have been able to control this pest very well with sulfur paste for three years now. I apply it in the spring and again if necessary. But be careful not to spray the buds or flowers.
Answer
Sulfur lime is a fungicide, not an insecticide. So I find it hard to understand why this product would be effective against leaf beetles, unless, as with coffee grounds, it works temporarily because of its smell. However, it can act as an acaricide, but not as an insecticide against beetles such as leaf beetles.
And your opinion is very relevant: sulfur-based fungicide can damage buds, flowers, and even foliage if the instructions are not followed to the letter. It is also not recommended to apply it in direct sunlight or in hot weather.
Careful Manual Harvesting
After trying several recommended products against leaf beetles without success for several years, I got to work as soon as the plants emerged and literally crushed the insects, repeating the process two or even three times a day. I believe this is the only solution for leaf beetles on lilies.
Answer
Indeed, if you eliminate all leaf beetles from your lilies without exception and repeat this task regularly, you will have good control over the insects.
Personally, I tried it, but after three years of hard work, I decided it was too much effort.
As far as I’m concerned, the only real solution to lily beetles, at least for a laidback gardener who doesn’t want to spend their summers treating plants, is to get rid of the lilies. Problem solved!
Larry Hodgson has published thousands of articles and 65 books in French and English over the course of his career. His son, Mathieu, has made it his mission to make his father’s writings accessible to the public. This text was originally published in Le Soleil.
Do you think garlic spray on the leaves might repel them? It seems to work with Japanese beetles on my bean plants. But the beetles continue to munch on my roses no matter how much garlic spray I apply.
Here in Calgary, this is called the Cadinal Beetle. I love the way it will fall, turn over when it hits the ground, hoping you will not see it. I have found only picking/squishing the critter controls it. I check every time I pass my lilies. Oh, don’t miss those black blobs (pupas) under the leaves- works best. Have not seen any in two years! A gardener must be vigilant……
If Thuja works, it would be interesting to know what else might be as effective. Lilies could grow up through trailing rosemary, trailing lantana or mint if such vegetation would be as effective as Thuja.
What about a ground cover – thyme? or lemon balm?? Might be interesting to try different herbs.. get some live beetles- Like 2, and put small pies of herbs out with a piece of lily in middle of eack stack of herbs… Release those beautiful bugs and sit back , have a cuppa and see who’s on first! If gardeners can find the magic herb..You’ll be a star!