Lily Leaf Beetle Battles

The lilies are poking through the soil only an inch, and already these horrible pests are at it!

The dreaded Lily Leaf Beetle has invaded my gardens early this year. Attractive in its red-orange shell,

Lilioceris lilii can destroy a plot of precious lilies overnight! True lilies and fritillaria are most susceptible; oriental, trumpet, rubrum, and tiger lilies are favored fare. Additionally, some oriental trumpets, Turk's cap, and native North American lilies might be affected. Daylilies seem unappetizing to this beetle.

The bad news is that these insects are difficult to control or eradicate. Researchers are working with parasitic wasps released in Rhode Island a few years ago, hoping the wasps will spread through the other affected states. Other than the hope that this will happen, we gardeners have little choice in how we'll deal with these beetles.

The beetles overwinter in the soil around the lily bulbs, emerging at about the same time that lily tips begin to poke through the soil. The beetles are voracious chewers and your tender lily sprouts will be shot through with holes almost overnight, but the most damage comes from the larvae. The emerging females begin laying eggs immediately, as many as 450. These eggs will hatch in just a week or ten days.

Timing is critical for control

First sign of trouble

As soon as your shoots appear, begin monitoring them every morning and evening. The bright beetles are easy to see and, for a small patch of lilies, hand-picking is the most effective method. However, these insects are fast and they can fly. And they are clever: they sense your movement and drop to the ground - upside down so their black underside makes them hard to see. 

Place a few drops of dish detergent in something shallow and wide, such as a whipped topping container. Add some water, but not too much. When you see a beetle on a leaf or stalk, place the container just underneath, taking care not to bump the plant. Then either pick off the beetle, or flick it off into the soapy water. Sometimes, they'll pull their dropping off trick and fall right in without your help. 

Lily Leaf Beetle eggs are easy to see

First step done! Now, set aside the soap solution and check the undersides of the lily leaves for eggs. They are easy to see. Look for irregular lines of bright orange dots. The best way to ensure that all the eggs are destroyed is to remove the leaf and drop it into the soapy water. Some gardeners prefer to crush the eggs in order to preserve the leaf, but this leaves the chance that some eggs will drop to the ground and hatch anyway. If the leaf is badly damaged, it will die anyway and fall off.

Second step complete. Now, the really yucky part of control: the larvae. If you've missed some eggs in your initial efforts, you'll soon see leaf damage that is far worse than the adult eating habit. Turn over the damaged leaf and you'll see brown globs on the underside. These are the larvae, and the brown stuff is...wait for it...excrement. Right! The larvae carry their frass on top of their bodies as protection and camouflage.

You can either remove the entire leaf and drop it into soapy water, or if the damage isn't too great, scrape off the larvae into the soap solution. Wear gloves!!!

If you are diligent about the early hand-picking and egg removal, you should be able to weather the Lily Leaf Beetle storm without too much damage. In the space of a week, at this writing, I've removed over twenty adults from my three small lily beds, and found and destroyed only two egg masses. The leaf damage is minimal and for the last two days, I've only found one or two adults hanging about.

What other alternatives are there?

Researching the best way to control the Lily Leaf Beetle, I found this from University of Maine Cooperative Extension:

• Neem oil. An effective insecticide, but one that does not work immediately, rather takes long enough that the beetles can do a lot of damage and lay a lot of eggs. 
• A systemic synthetic insecticide imidacloprid provides effective control when applied to the soil in early spring. 
• Malathion is an effective chemical spray for adults and larvae.

Get an early start on controlling these nasty critters!