GOODIE OR BADDIE?

QUESTION I planted ice plants in my garden near the beach and now some have these strange white growths on them. Can you tell what they are?

J. Carlson, Waiheke Island

ANSWER What you have here is an interesting scale insect known as ice plant scale (Pulvinaria mesembryanthemi), whose presence in New Zealand was first recorded in 1987. Originally from South Africa, it was found in California in the early 1970s and has since spread wherever its favoured host plants, species of Carpobrotus, also from South Africa, are found growing. Your ice plant, which is host to this scale, looks like C. edulis, known by several common names, including sour fig as it can produce fig-like fruits after flowering. Carpobrotus comes from Greek: karpos for fruit, and brotus being edible.

Although found growing extensively on sand dunes in some coastal parts of New Zealand, and often thought of as native plants, carpobrotus were introduced and are recorded as becoming naturalised here as long ago as

1883. They’re often considered weeds as they’re vigorous growing and compete for habitat with the native ice plant, horokaka, Disphyma australe, which has smaller leaves and more compact growth.

Ice plant scale has been reported here on the native horokaka, as well as other exotic ice plants, including

Carpobrotus, Lampranthus and

Mesembryanthemum species.

It’s generally considered that ice plant scale reproduces parthenogenetically – mature females give birth to live young without mating taking place.

If your carpobrotus plants produce fruit, I suggest you remove them and dispose of them in the rubbish to reduce the risk of seed spread. It’s worth noting that any pieces of your carpobrotus plants that break off can readily root and spread.

It’s unlikely these scale insects will cause severe damage to your plants, but if they do I’d consider a form of biological control of this potentially invasive ice plant. Interestingly, there are reports of naturally occurring hybrid ice plants being found in the wild, apparently crosses between horokaka and

Carpobrotus.