TALK REPORT FOR NOVEMBER 2016

10 November 2016:  Dr Candice-Lee Lyons on “Biological control of weeds – history, principles, and examples”

This most informative talk by Candice-Lee Lyons (who was supported by her husband and young son) gave us all a broader perspective on how invasive alien plants are being controlled.

There are three methods used to control invasive plants. The Betty’s Bay Hack Group, which has been working in the area for over 40 years, uses mainly the mechanical method. This includes chain saws for the large, mainly acacia, species (e.g. rooikrans), and poppers and snickers for the smaller plants (e.g. tea bush and young acacias). The stumps are then poisoned, i.e. the chemical method.

The third method is biological control. Biological control is introducing an agent to suppress a weed and often the agent and the weed come from the same country. The agent could be an insect, e.g. wasp, or a fungus.

The main route of invasion is  through garden plants, accidentally or deliberately. The tea bush and myrtle and pittospermum are examples now causing big problems in Bettys Bay. They are Category 1b Invasive plants which need to be removed and destroyed. Many years ago myrtle was introduced for hedging. A moth and a midge which were introduced as biocontrol are not  proving to be very effective. These plants now all need to be removed mechanically.

Independent research into biocontrol of invasive species began in South Africa in 1960. Now 23% of species under biocontrol require no other control method. Thirty-eight per cent require intermittent control using other methods. Biocontrol is popular and well funded in South Africa. The research field is growing because of the huge positive gains in clearing invasive aliens plants.

Candice’s presentation focused on the 10 most invasive species of acacia which have biocontrol agents. Several are growing in private gardens here. They are all in Category 1a or 1b – to be removed, or Category 2 – for which a permit is required.

Biocontrol agents also require permits. The average process takes 4/5 years, varying between species, but is getting faster. Two strategies are used: (a) complete density reduction when the weed has no beneficial properties, and (b) containment preventing further spread where the weed has beneficial properties, and here the agent attacks the flowers/seeds.

Biocontrol on certain plants has limited effect, e.g. lantana as it has become very hybridised since it was introduced into South Africa in the 1800s. Two water plants  – Hyacinth and Parrots feather – are also now targeted by biocontrol agents.

There are a few pros and cons of biocontrol. It is enviro-friendly with no adverse effects on non-targeted species, and it is permanent. But success is unpredictable, and the slow process needs to be integrated with other control methods.

 If you are keen to rescue our Betty’s Bay fynbos from the numerous invasive aliens causing problems here in our Biosphere Reserve, please come and join our Hack Group.  (Phone Frik on 028 272 9891/084 600 9891).