by Connie Oswald Stofko
Now is the time to start checking your lilies for the red lily leaf beetle, said John Farfaglia, extension educator with Cornell Cooperative Extension in Niagara County.
A reader gave me a heads up a few days ago that she had spotted them on her fritillaria, an earlier springtime plant that the pests also damage.
The red lily leaf beetle, which we first talked about in 2015, is a fairly new invasive species in Western New York. It can cause extensive damage to lilies and fritillaria. The pests aren’t a problem for daylilies, which aren’t true lilies.
Now is the time to get outside to look for the beetle itself, Farfaglia said, or to look for signs that the beetle has been eating the leaves of the lily. If you see signs of the beetle or of damage, treat the plant.
If you had the red lily leaf beetle in a previous year, you have about a 95 percent chance of having them again, he said. Still, he suggests not treating the plant until you actually see signs of the pests.
One way to treat your plant is to use a pesticide. Farfaglia recommends that home gardeners use neem oil because it is less toxic than other pesticides listed on a Cornell factsheet about the red lily leaf beetle. People have had reasonably good luck with neem oil, he added.
Another reason to wait until you see signs of the insect to treat is that the treatment may not work if you do it too early, Farfaglia noted.
However, if you need to treat your plant, do it before the flowers open. Don’t use insecticide on a plant with open flowers.
Pick off the adults, larvae
You can also try picking off the red lily leaf beetles.
It’s difficult to pick off the adults because they’re fast. You can try holding a jar of soapy water underneath a branch that has beetles, according to the Cornell factsheet. When disturbed, the adults tend to drop from the branches. Your goal is to catch them in the soapy water as they drop. Wait a few hours before dumping out the soapy water to make sure they have completely drowned.
The larvae are also difficult to handpick, and they’re gross because they cover themselves in their own feces to fend off predators. See the life cycles of the red lily leaf beetle here.
“As disgusting as it is, handpicking really does help,” Farfaglia said.
Try cedar mulch, coffee grounds
In 2017, Farfaglia told us about a gardener who thought that cedar mulch might stop red lily leaf beetles from damaging plants. The gardener noticed that where she had cedar mulch, the red lily leaf beetles didn’t bother her lilies.
He asked gardeners who tried cedar mulch to let him know whether or not it worked.
“I recall hearing from only one person who tried it, and they still had damage,” he said. “I want to hear from more people.”
Another possible remedy is coffee grounds. Place the coffee grounds around your lilies.
Farfaglia hasn’t heard back from any local gardeners who have found that effective, either.
“But there are soil benefits,” he said. “The coffee grounds can add nutrients and organic matter to the soil. If you have extra coffee grounds, it’s worth a try.”
If you tried cedar mulch or coffee grounds, please let Farfaglia know how it worked for you.
“If you tried it, whether your results were positive or negative, I would like to hear,” he said. You can contact Farfaglia at firstname.lastname@example.org or 716-433-8839, ext. 226.
Bonus tip: If this information is helpful to you, make sure to subscribe to Buffalo-NiagaraGardening.com. You’ll receive great gardening tips emailed directly to you every Tuesday. And it’s free to subscribe!