Creepy caterpillars will morph into beautiful butterflies

The orange dog caterpillar munches on a citrus leaf.

Garden columnist Dan Gill answers readers' questions each week. To send a question, email Gill at [email protected].

I have found some bizarre caterpillars on my satsuma tree. They are mottled brown and white. When I poked one, two red prongs shot out and produced a bad odor. The caterpillars are eating the leaves of my tree, and I was wondering what to spray to control them. — Tim Gleason

This is the orange dog caterpillar, the immature form of the giant swallowtail butterfly. The large caterpillar, mottled brown and white and larger at one end, is disguised to look like bird droppings. If it is poked or disturbed, an orange dog caterpillar will extrude a two-pronged red or orange scent gland (called the osmeterium) from its head. This defense mechanism is common to all the swallowtail (papilionid) butterfly caterpillars.

What a transformation: A swallowtail butterfly stops by a milkweed plant.

The osmeterium is harmless. The foul odor produced is meant to discourage predators like birds from eating them. And the forked shape of the osmeterium looks like a snake’s tongue sticking out, also meant to scare birds.

Because the orange dog caterpillar grows up to be one of our most beautiful native butterflies, whenever possible, it is nice to leave the caterpillars alone and let them develop into butterflies.

On larger, older trees, the damage done by these caterpillars is generally minor and will not affect the overall health of the tree or the crop. Orange dog caterpillars typically occur in small numbers, and it’s worth tolerating some damage to have more of the butterflies that delight so many people.

On young trees with fewer leaves to spare, damage must be monitored carefully. If an unacceptable amount of damage occurs (one-third of the leaves or more), pick off the caterpillars and destroy them. Spraying an insecticide is rarely needed, but you may spray your tree with BT (Dipel, Thuricide, Biological Worm Control) or spinosad if you feel the situation warrants it.

Better yet, collect the orange dog caterpillars. Put them on a larger tree or give them to friends with larger citrus trees so they can complete their lifecycle. They would be especially welcomed by friends with butterfly gardens.

Cold damage from a 2018 freeze likely cause the decay on this queen palm tree.

I have found a large rotten cavity in one of my shade trees. Should I fill this cavity with concrete? — Peter

The old practice of putting concrete or other fillers in cavities was discontinued a long time ago. It did not help the trees deal with the decay and possibly made matters worse. There’s really nothing you can do that will help the tree deal with this decay. You may gently clean any decayed wood out of the cavity and monitor the progress of the decay, but that's about it.

Unfortunately, the decay will continue to eat away at the trunk. Over time, it will structurally weaken the trunk and make the tree more likely to go over in high winds. Now that hurricane season is kicking into high gear, it is important for homeowners to check out their trees for signs of decay in the trunks. Dead trees should be removed immediately.

A tree that is sickly, low in vigor and shows significant signs of rotten or decayed areas in the trunk or termite damage should be considered for removal if it poses a threat to buildings on your or neighboring property. Also, look for any large dead branches in the tree. These should be removed, especially if they pose a threat to structures such as homes or garages.

You may want to have a licensed arborist come out and evaluate your tree. Having your trees evaluated by a professional arborist and getting problems corrected takes time. That’s why it is so important to take care of trees well before a hurricane threatens.

A list of licensed arborists by parish is available from the Louisiana Department of Agriculture and Forestry. Do an internet search using — LDAF licensed arborists — and click on the link. All practicing arborists must be licensed by the agriculture department. Be sure to ask to see a copy of their license.

Kale is a nutritious green as well as a colorful plant in the landscape.

VEGGIES NOW: Vegetables to plant in September include transplants or seeds of broccoli, cabbage, cauliflower, Chinese cabbage, collards, English and snow peas, Irish potatoes (plant small, whole potatoes saved from the spring crop), kale, kohlrabi, leek, lettuce, mustard, onion, shallots (plant small bulbs) and Swiss chard. Plant seeds of snap beans, beets, carrots, radish, rutabagas and turnips. It’s getting late, but plant tomato and bell pepper transplants this weekend if you haven’t already.

HERBS NOW: Herbs to plant in September include transplants of basil, sage, rosemary, thyme, oregano, chives, lavender, Mexican tarragon and mints. Plant seeds or transplants of dill, parsley, fennel, cilantro, arugula, borage, chamomile and chervil.

ROSE TALK: Rose expert Allen Owings will present a program Tuesday, Sept. 5, on projects at the LSU AgCenter Botanic Gardens rose display garden. It's part of a meeting of the New Orleans Old Garden Rose Society at 6:30 p.m. at the East Bank Regional Library, 4747 W. Napoleon Ave., Metairie. The session is open to the public.

TRIM ROSES: Repeat-flowering roses should be cut back by about one-third in early September.

MAKE THEM KID-SIZED: If you want your kids to work in the garden, it’s a good idea to purchase gardening tools specially made for them and properly sized for them to use. This gives kids a chance to identify with gardening more closely because they have their own tools. It’s safer, too.

Dan Gill is a retired consumer horticulture specialist with the LSU AgCenter. He hosts the “Garden Show” on WWL-AM Saturdays at 9 a.m. Email gardening questions to [email protected].

“Now ‘tis spring and the weeds are shallow rooted. Suffer them now and they’ll o’ergrow the garden.”

— William Shakespeare