If your clivia leaves suddenly look hollow, slimy or chewed down to the base, the amaryllis borer is the likely culprit. This striped caterpillar is one of the most destructive clivia pests in South Africa, and a group of them can wreck a mature plant within a few weeks. The good news: it is easy to spot once you know what to look for, and easy to control if you act early.
What is the amaryllis borer?
The amaryllis borer, also called the lily borer or amaryllis caterpillar, is the larva of a night-flying moth, Brithys crini. It feeds only on plants in the amaryllis family, which includes clivias, amaryllis (Hippeastrum), crinums, agapanthus, nerines and Haemanthus.
- The caterpillar: black with bright yellow or cream stripes along its body, growing to about 4 cm long. Young caterpillars are tiny and pale, and hard to see.
- The moth: a dull grey-brown moth with a wingspan of about 4 cm. It flies at night, so you will rarely see it.
- The eggs: laid in clusters on the undersides of the leaves. They are about the size of a pinhead.
How it damages clivias
The young caterpillars hatch together and tunnel inside the leaf, eating the soft tissue between the upper and lower surfaces. From the outside, you see pale, see-through "windows" in the leaf. As they grow, they work their way down the leaves into the base of the plant, where the new leaves and the flower bud form. There they eat the heart of the plant and can reach the roots.
A small attack only spoils the leaves. A heavy one destroys the growing point, and the plant collapses or rots. Young plants and seedlings are most at risk, because they have so little tissue to lose.
Signs to look for
- Pale, transparent patches or tunnels inside the leaves
- Leaves that feel soft or slimy, or break off at the base
- Black, sawdust-like droppings (frass) in the leaf bases
- A sour smell of rotting tissue in the centre of the plant
- Striped caterpillars hiding deep between the leaves during the day. They feed mostly at night.
When it is active
In South Africa the borer is active from about September to March, with several generations each summer. Fully grown caterpillars drop into the soil to pupate, and the next generation of moths emerges a few weeks later. That's why one treatment is rarely enough: new eggs keep arriving all summer. On the Highveld, the warm, wet months from November to February are usually the worst.
Treatment: a systemic plus a contact insecticide
We recommend combining two types of insecticide. Each does a different job.
1. A systemic insecticide for lasting protection, such as Koinor
A systemic insecticide is absorbed by the plant and carried through its tissue, so it reaches caterpillars hidden inside the leaves and deep in the base, where sprays can't. Koinor 350 SC, which contains imidacloprid, is widely available in South African garden centres. The Clivia Society also recommends a systemic such as imidacloprid for this pest.
- Apply it as a soil drench, so the roots take it up. Mix it at the rate given on the label and water it into the potting mix or the soil around the plant.
- Apply it early in the season, in September or October, before the damage starts, and repeat at the interval given on the label.
- It takes a few days to move through the plant, so on its own it is not a quick fix.
2. A contact insecticide for a quick knock-down, such as cypermethrin
A contact insecticide kills the caterpillars it touches. A cypermethrin-based spray works fast and is ideal when you find an active infestation.
- Spray the leaves thoroughly, including the undersides, and direct the spray down into the base of the plant, where the caterpillars hide.
- Spray in the late afternoon or evening, when the caterpillars come out to feed and bees are no longer active.
- Repeat at the interval on the label while you are still finding caterpillars.
Together, the contact spray clears the caterpillars you can reach today, and the systemic protects the plant from the ones hidden inside and from the next generation.
Use them safely
- Always read and follow the label. It sets the mixing rate, how often to apply, the protective clothing to wear, and which plants and pests the product is registered for.
- Protect bees and birds. Clivias are pollinated by bees, butterflies and sunbirds. Never spray open flowers. Where you can, apply the systemic after flowering.
- Keep it out of water. Both products are toxic to fish and other aquatic life. Don't use them near ponds or let them run into drains.
- Wear gloves, keep children and pets away from treated plants, and store products in their original containers, locked away.
Treating a badly damaged plant
- Remove the caterpillars by hand. Gently open the leaves and check deep into the base.
- Cut away leaves that are rotten or hollow, back to healthy green tissue.
- Let the cuts dry, then treat the plant with the contact spray and the systemic drench.
- Keep the plant on the dry side for a while to stop the rot spreading.
Clivias are tough. As long as the base and roots are still firm, a damaged plant usually sends up new leaves and recovers within a season or two.
Prevention: check every week
- From September to March, check your clivias weekly, especially the undersides of the leaves and the leaf bases.
- Rub off any egg clusters you find before they hatch.
- Check your agapanthus, crinums and amaryllis as well. Borers spread from one amaryllis-family plant to the next.
- Inspect new plants before they join your collection.
Caught early, the amaryllis borer is a nuisance rather than a disaster. A few minutes a week is all it takes to keep your clivias healthy and ready to flower next spring.
Have a question about clivia care? Email us at hello@bushlily.co.za, and follow us on Instagram @bushlilyza and Facebook for more growing tips.
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