Bio-controls and Landcare
Published on 17 December 2024
By Acting Landcare Coordinator Simon Lubinski
Landcaring can be rough. Who’d be a Landcarer? You turn up to your site, filled with enthusiasm and energy, with dreams of a beautiful bushland setting, animals scurrying about, birds calling softly to each other, the gentle trickle of water flowing down a creekline… Nup. It’s a whole lot of weeds!
Landcarer’s learn to look at a site with different eyes. Weeds aren’t just weeds. They’re habitat, they’re a food source, they’re structure, they’re a border holding out other weeds. This is all true, but it’s still a tough gig. Sometimes, we’d love to know, isn’t there a better way? Surely something else can do the work? Surely!
Well what about bio-controls? We’ll release some bugs and they’ll do the work. Sounds good. Sounds great! Let’s have a look at some of them.
Cactus Moth
The Cactus Moth Cactoblastis cactorum is the poster child of successful bio-controls. In 1926, the Moth was released to attack Prickly Pear, a nasty Cactus taking over 24 million Ha cropping and grazing lands in NSW and Queensland. The Moth laid it’s eggs on the Cactus with the hatched larvae eating the fleshy leaves from the inside out. The release was so successful that by 1933 most of the Prickly Pear had been eradicated.
Salvinia Weevil
Salvinia is a rampant water weed that left unchecked can choke waterways. The Salvinia Weevil Cyrtobagous salviniae feeds on the invasive weed helping to control infestation. Muddy Lake near Dora Creek is an area where there has been a recent release of the Salvinia Weevil to help treat a significant outbreak. Several releases were carried out in a short amount of time. Weevil numbers eventually grew to a large enough number to begin controlling the infestation. There is still Salvinia in the Lake, however at a much reduced level. The Salvinia Weevils have survived over winter and are keeping the Salvinia to a manageable level.
Bridal Creeper Leaf Hopper
The Bridal Creeper Leaf Hopper Zygina spp was first released in Australia in 1999. The Leaf Hopper damages leaves of the Bridal Creeper plant by piercing plant cells and sucking out all the cell contents. Leaves are left completely white with a good sized population of leaf hoppers. The insect has been shown to be very successful at controlling large infestations.
Trad Smut
One of the most recent releases, the Trad Smut fungus Kordyana brasiliensis has been shown to be very successful at tackling Trad. Some releases have been more successful than others, and winter temperatures seem to slow the spread significantly. The fungal spores spread via wind and water, so more open sites show a quicker spread. The fungus quickly defoliates the runners and the stems die quickly.
Cats Claw Creeper Jewel Beetle
Not all biological controls work well in our climate. Cat’s Claw Creeper is an invasive weed that can smother trees and shrubs. The Cat’s Claw Creeper Jewel Beetle Hedwigiella jureceki attacks the leaves of the Cat’s Claw Creeper vine, reducing the creeper’s vigour. Adults chew holes in the leaves, while larvae mine within them. So far, releases in the Lake Macquarie area have not been very successful, and with release sites showing little sign of damage.
Madeira Vine Beetle
If you have Madeira Vine onsite, you know what a horrible weed it is. When the Madeira Vine Beetle Plectonycha correntina became available for release, hopes were high. However, despite numerous releases at a large number of sites around Lake Macquarie, the results have been disappointing. The beetles have been unable to make a significant impact on the weed, so unfortunately, it’s back manual and chemical controls. Research continues in the area, so we’re hoping for another bio-control in the near future.
When weighing up whether to use bio-controls onsite, there are a number of considerations:
Great things about bio-controls
1. Chemical free!
2. Works outside of normal business hours.
3. Very cheap.
4. Can be very effective.
Not so great things about bio-controls
1. Generally need a large size infestation to support a growing population. Small infestations are often not enough to support a viable bio-control population.
2. Seasonal: Like weed growth, bio-control numbers ebb and flow with the seasons. A lot of our bio-controls (and weeds) come from warmer areas of the world. Cold winters can often impact a population.
3. Bio-controls need weeds to live: well, yeah, obviously. The problem is, once weed density diminishes, many bio-controls will start to die out. Once the weeds start to flourish again, bio-control numbers increase. There’s a time-lag between weed growth and bio-control increase.
4. Too successful: just imagine, a bio-control that works too well! The problem here is a smothering weed, like Trad, prevents other weeds from germinating. Once that weed is killed, it opens up a large area to allow new weeds to germinate. It’s why we ask Landcarers to clear small areas gradually. Sometimes we’re just swapping one weed for a whole host of others.
So, bio-controls are a mixed bag. Some work really well, some not as well as others. It’s important to understand that a bio-control is a tool in a broader strategy. A bio-control can be an important part of an Integrated Pest Management (IPM) solution. When you use a bio-control to help stop the spread of a weed, and then follow up with a combination of manual removal, cultural controls and chemical application, weeds can be successfully controlled. Depending on only one method can often be unsuccessful, or unachievable. Talk to your Landcare Support Officer about options for your site. And we’ll keep you in the loop about what’s coming up in the world of bio-controls.