DEAR JOAN: Can you please identify these green and white caterpillars that have invaded my tomato garden this year?

They are light green with like a lime green strip running along their backs, white stripes and black spots on the sides. They are about 2½ to 3 inches long.

We have only lived in California for three years, but we have had a garden each summer and this is the first time that we have had a problem with these guys. I found four of them in my tomatoes yesterday and I am sure there are more but didn't really want to play hide-and-seek.

I was going to start throwing out my plants for the year, but then I saw these guys and didn't know what to do with them.

The dreaded tomato hornworm.
The dreaded tomato hornworm. (Courtesy of Beth Harris)

Any advice on how to keep them out of my tomatoes for next year? I haven't really noticed that they are eating the tomatoes themselves so I guess they are leaf eaters?

Beth and Mike

East Bay Area

DEAR BETH and MIKE: Congratulations. You aren't a real gardener until you've done battle with tomato hornworms, the scourge of many a tomato patch and, in my case this year, the pepper crop.

If they haven't gotten to your tomatoes yet, it's only because they haven't gotten around to it. They eat leaves, but they also go after both green and ripe tomatoes. If you find a tomato that looks like it's been rubbed with a piece of sand paper, that's the work of a hornworm.

During the season, it's best to handpick them. Don't squish them -- it makes a horrible mess. Just take your garden shears and snip them in half. My friend is kinder and drops them in the green waste bin. Another friend lets the hornworms have one plant for their very own.

Hornworms are very hard to find as they are expert at camouflage. When at rest, they look exactly like a tomato leaf. The surest way to find them is with a black light in the dead of night. The hornworms will fluoresce under the light.

Wasps kill the younger hornworms and the small braconid wasp (Cotesia congregatus) lays eggs along their backs. The offspring will eventually consume the hornworm from the inside out.

The life cycle of the hornworm starts with a moth, which lays eggs on the leaves of the tomato plant. The eggs are yellow and are laid singly instead of in clusters. The eggs hatch and the tiny larvae (hornworm) begins to eat. The larvae will go through several stages, becoming up to 4 inches long. They then drop to the soil, burrow in and pupate. After about two weeks, a moth emerges, breeds and starts the cycle over.

Thoroughly digging up your beds after harvest will destroy the pupae in the soil. If you are pulling out your tomatoes anyway, just put them in the compost or green waste. Next spring, keep an eye out for them and pick them off when you see them. You also can use Bacillus thuringiensis or spinosad.

DEAR JOAN: Our back yard has some oak galls on the ground. Something has been chewing on them. Could it be a squirrel, rat or maybe a waskelly wabbit?

Shirley

Concord

DEAR SHIRLEY: It's probably squirrels, but a number of creatures might give the galls a bite or two.

Galls are those strange-looking balls you see on oak trees. A tiny wasp grows inside and then chews its way out.

They are created when a cynipid wasp bores a hole into a branch and lays an egg. The tree produces the gall to protect itself, but at the same time it provides a safe chamber for the next wasp generation.

Contact Joan Morris at jmorris@bayareanewsgroup.com.