Remove oleander caterpillars while young

By Audrey Post
MS. GROW-IT-ALL®

Q: Big hairy worms have been giving me fits for the past seven years, eating the leaves on my mandevillas. I use the white powder and maybe it cuts the population, but I hate the way it makes my plants look. What else can I use that will kill the worms but not kill the plant? I am attaching a photo so you can see what a charmer this is.

A: Yes, indeed, that is one charming pest you have there. It’s a Syntomeida epilais, commonly known as an oleander caterpillar. Supposedly it feeds only on oleanders, but it obviously has developed a taste for mandevillas – as your photo illustrates. Through a little research I learned that its original host was a pineland vine that is now rare, so it has been known to try new foods.

A mature oleander caterpillar is orange with tufts of black hair and is about 2 inches long. The adult moths are purplish-black with white dots on their wings and are sometimes called polka-dot wasps. They reproduce three generations a year, and sometimes the process overlaps and you can see larvae and moths at the same time. They’re really rather exotic looking, but they can be devastating. While they usually don’t kill the plant, they can defoliate it and leave it vulnerable to diseases that can kill it.

This is one caterpillar that birds and small mammals have learned to avoid because its primary diet, oleander, is so toxic. There are beneficial insects that will eat oleander caterpillars -- predatory stinkbugs, parasitic flies and wasps, even imported red fire ants eat the clusters of eggs – but the best way to control them is to pick them off by hand. The spines generally pose no threat to humans. [Ms Grow-It-All® update: A subsequent column, post date Dec. 17, 2008, discussed one person's allergic reaction to the oleander caterpillar, so use gloves to pick them off just to be safe.]

The egg clusters can be found on the undersides of leaves, and you can scrape them off into a plastic bag – a newspaper bag works well for this – and throw them in the trash. Young larvae, which are more yellow than orange, eat the tissue between the veins on the leaves. Snip off the infested leaves, but them in a plastic bag and then place the bag in the freezer for 24 hours to kill the caterpillars. Larger larvae can be picked off, placed in a plastic bag and frozen the same way, or dropped into a can of soapy water.

Obviously, it’s hard to pick larvae from large oleanders because of the height, but a mandevilla vine should be easier to manage. Horticulturists recommend your friendly white powder, Bacillus thuringiensis, for large plants.

The key appears to be catching them while they’re young.

Q: What should I do to try to save a hanging spider plant that was left outside when we had frost? The leaves have turned black and slimy.

A: Those cold nights sometimes sneak up on us, and different microclimates in our yards and gardens sometimes get colder or warmer than the “official” temperature recorded. It could have been 37 at the airport but 32 on your porch.

If it wasn’t too cold for too long, the plant might survive. Cut off all the slimy, damaged foliage and clean up any debris on the soil surface. You can bring it inside, give it some water and see if it starts to grow again, or you can skip the water, move it to a protected location such as an unheated shed and let it rest until spring.

However, unless it’s a variegated variety or a sentimental favorite, I’d pitch it and start over next spring with something else. Solid green spider plants have become invasive in the ground here in North Florida, and those airborne babies can make that leap from the hanging basket to the ground very easily.