Green grasslands suddenly are pink because of pom pom weed, confusing poets.
The Hartebeespoort dam is suddenly green with water hyacinth. Hartbeespoort Dam, affectionately known as Harties, is a popular recreational destination for residents of Johannesburg and Pretoria.
But alien invasive plant species (AIPs) are threatening the aesthetic beauty and more seriously, the livelihoods of indigenous plants, dams, farms and entire ecosystems.
The biocontrol news and information bulletin has reported a threat to food production posed by the larger grain borer invader in East and West Africa, as well as cocoa diseases in Central Africa.
AIPs are stubborn, bullish and literally take over the neighborhood.
Professor Julie Coetzee of the Center for Biological Control reports efforts to reduce water hyacinth at Harties went haywire because of pollution, so when biocontrol agent, Magamelus, a type of water hyacinth hopper, was introduced to throttle invaders in the dam, which had taken over 50% cover, pollution supported the enemy. This resulted in another invader unleashed, Salvinia.
“When plant species grow outside of their natural distribution range they are called non-native or exotic. One reason why these non-native plants can become invasive is the lack of natural enemies that limit their vigour, density and spread” according to the Botanical Society of South Africa.
There are several ways to reduce populations and numbers of alien invasive plants. A popular method is mechanical control, which is the labour-intensive, physical clearance of infestations of alien invasive plants by chopping, ringbarking and or uprooting alien invasive plants.
This method is often combined with chemical control, for example treating stumps after felling with herbicide, to ensure they die.
Biological control is a more effective and efficient ally to biodiversity because it uses living organisms such as insects, mites or fungal pathogens to control pest populations. “It levels the playing-field by reintroducing some of the specialist natural enemies that help control the invasive species in its native range. The aim is not to eradicate the invasive plant, but to bring its density below an appropriate ecological or economic threshold.”
It’s a booming business because it’s expensive. Biological pest control in Europe, has a 30% market share, followed by North America with about 24%. The global biological pest control market size is projected at about USD 1440 million by 2027, up from USD 692.4 million in 2020.
Biocontrol is actually tested before use to ensure that it does not present a threat to indigenous flora or fauna itself, or crops grown in South Africa or neighbouring countries.
These tests ensure that any potential biocontrol is sufficiently host specific to only target the intended species.
We will bring you more news on the progress at Harties in Spring.
Both pictures: Supplied