THE COASTAL GARDENER:

Unbeknownst to you, a month ago there was quite a party in your garden. You weren’t invited, but now, a month later, you’ll have to do the cleanup.

A brief inspection of the garden this week reveals holes and tattered margins on the leaves of many plants. Sometimes little chewers avoid the veins of the leaves; sometimes they don’t. Some leaves look like they were hit with a shotgun. In the worse cases, entire leaves are gone; chewed to a stub. The culprits are caterpillars.

Caterpillars are the larval stage of moths and butterflies. However, it is moths that cause the majority of the damage in our gardens. A quick lesson on the life history of moths will help explain why it seems like caterpillars are overwhelming our gardens in Orange County both coastal and inland right now.

Moths fly at night, primarily when the temperatures are warm. Take an evening walk with a flashlight through your garden in winter or spring and you may have a hard time finding a moth. Turn your porch light on in March or even April and see how many moths are attracted. Not many.

Adult moths are active when night temperatures are high. For a moth, the warmer the better. Also, moths navigate by the light of the moon. A night with no moon means fewer moths than a night with a full moon.

Warm nights and full moons result in lots of moths. Now, jump back in time to about a month ago, specifically to the night of July 11. It was a Tuesday, and we were in the midst of our first big heat wave. On July 11 the mercury soared in central Costa Mesa and Newport Beach. If you were out in your garden at 10 p.m. that night it was 71 degrees Fahrenheit. Even at the coldest moment, at precisely 1:30 in the morning, the thermometer was still sitting at 65, three degrees warmer than the historical average for the day.

Just as important, the moon was full on the night of July 11. A warm and balmy July night and a full moon. Party time for a moth, and the party was happening in your own backyard. It was a garden party of epic proportions, and the attendees were coming from far and wide.

Of course, the moths in your garden that night had a purpose. The reason for their big party was to mate and lay eggs. Moths are incredible egg-laying factories. An adult moth can deposit hundreds of eggs on your plants in a night. About 10 days later these eggs hatched and out came hungry larvae, or caterpillars. For the first week or two, these little guys were so small a gardener either doesn’t notice the damage or doesn’t give it much attention.

But now, 30 days later, the caterpillars have grown to become leaf-eating machines.

Sometimes gardeners refer to these pests as worms, but a worm could apply to many slithering, crawling creatures like earthworms and flatworms, beetle grubs, nematodes, sawfly larvae and more. “Worm” is a bit confusing. What we’re really dealing with are moth larvae, but since that will never catch on, the term “caterpillar” will work nearly as well.

Birds and diseases claim a few of the caterpillar bounty. Braconid and other wasps, Tachinid flies, and some other beneficial insects will cull a few more. For the rest of the caterpillars, a gardener has a few options. If you’ve one of the lucky ones you may be able to do nothing. A few chewed leaves, in the larger scheme of your garden, may not be a big deal. You can live with it.

If the infestation isn’t too heavy or is isolated to only a few plants, you may be able to hunt for them and dispose of them manually. They can be difficult to see, so a keen eye is an asset.

Bacillus thuringiensis var. kurstaki, Bt for short, is the best pesticide control. Bt is a naturally occurring microbial pathogen that is specific only to the larval stages of moths and butterflies. It has no effect upon other insects, including other chewing pests like sawfly larvae, grasshoppers, snails and slugs. Likewise, it has no effect on reptiles, amphibians, birds, natural predators, pets or mammals. It can be used on vegetables, herbs and fruits with no contamination issues.

Bt mixed with water and applied as a spray it’s odorless, tasteless and invisible. Once a young caterpillar eats a small amount of foliage and ingests Bt, it stops feeding. In about 24 to 48 hours, the caterpillar dies.

Something appears to be eating my dichondra. It is turning brown rapidly. Help. Hurry!

Ashleigh Costa Mesa

You almost certainly have an infestation of flea beetles, Chaetocnema repens.

Flea beetles are serious pests to dichondra, causing many dichondra lawns to be replaced with grass turf. Larvae feed on small roots and cause dichondra to wilt and die, often in large patches. Adults feed on dichondra leaves, producing distinctive crescent marks on the upper surface. The dichondra appears to be suffering from a lack of water or from fertilizer burn.

Quick action is required before the entire area turns brown. The Bayer Company makes a very effective granular product with the active ingredient cyfluthrin. It works well, is safe to use and has a minimal effect on groundwater pollution or runoff.

your toughest gardening questions, and the expert nursery staff at Roger’s Gardens will come up with an answer and publish it. Please include your name, phone number and city, and limit queries to 30 words or fewer. E-mail stumpthegardener@ rogersgardens.com, or send to Plant Talk at Roger’s Gardens, 2301 San Joaquin Hills Road, Corona del Mar, CA 92625.

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