Are you growing weed trees?
Take responsibility by identifying and controlling these intruders
LAST week’s article listing a few gardening responsibilities hopefully sparked a degree of interest from concerned readers as to whether they were unknowingly harbouring weedy trees in their yards.
As mentioned in the article, Biosecurity Queensland (BQ) has classified a number of trees, amongst many other plants, as environmental weeds, meaning they can have a detrimental impact on our biodiversity by outgrowing native vegetation due to an absence of natural controls such as pests, diseases and insects. Not only do they impact our native flora and fauna, their propensity to easily spread is a concern for all who cultivate for leisure (gardeners) or for profit (commercial producers).
What many gardeners would not know is that all Queensland landowners are bound, through the 2014 Biosecurity Act, by a General Biosecurity Obligation (GBO) to take “all reasonable and practical steps to minimise the risks associated with invasive plants under their control.” Invasive plants usually fall into three categories:
1. Prohibited Invasive – meaning they cannot be allowed to enter Queensland and if they do, must be reported to BQ within 24 hours of sighting,
2. Restricted Invasive – these plants are common in many areas of Queensland, and cause significant damage to the environment. Many can’t be sold or given away as a plant, or be released into the environment. Some of these plants are quite common in our own region, some even planted many years ago as feature plants, hedges or street trees.
3. Invasive – many of the plants on this list are well established around our region, but are still covered by the GBO requirements.
I’d like to highlight some of the trees on the Restricted
Invasive list, and hopefully inspire as many gardeners as possible to recognise weed trees and act on their responsibility to prevent the spread of these unwelcome invaders.
The first of our garden intruders is the infamous privet, both broad-leaved and small-leaved species (Ligustrum lucidum, L. sinense). Our region is a hotspot for both, which are spread by seed usually greedily eaten and distributed by birds such as kurrawongs, rosellas and silver-eyes. Some specimens can reach over 100 years of age, and produce millions of viable seeds over their lifetime.
To add insult to injury, when privet flowers (broad-leaved in summer, small-leaved in spring), it has been known to cause severe allergic reactions for those living nearby.
Common spots in which to find them in gardens, are under large trees, around fence lines and growing up through hedges. Manually remove smaller seedlings, and use a recommended herbicide (see website link in Garden Cuttings) for foliar or cut-stump applications.
Next of our weedy trees has been the subject of controversy in Toowoomba for many years, being planted as far back as the late 1800s as street and parkland trees. Whilst no doubt a beautiful shade tree, the camphor laurel (Cinnamomum camphora) has become one of the worst woody weeds in South-East Queensland and beyond. Bearing black fruit like privet, these plants are easily spread by birds with similar gastronomic tastes.
You’ll find them growing in the same spots as privet, too. Large specimens have extensive, sometimes disruptive root systems, and the camphor released from fallen leaves restricts germination and growth of plants under the canopy. Removal and control methods are similar to privet, but check the factsheet on the website listed in Garden Cuttings.
One of the weed trees listed as a Restricted Invasive plant is less abundant than the previous two, but is more widely spread across Queensland due to its adaptability. The broad-leaved
pepper tree (Schinus terebinthifolius), is an “occasional” weed in our region, but is spreading slowly and insidiously nonetheless.
This is another plant that bears berries, these ones bright red, which are very attractive to fruit-eating birds and mammals. In addition, the sap is quite toxic to humans and can cause rashes, sores, swellings, colic and even eye haemorrhages.
The pollen is also an irritant. Also, of concern to mango and citrus growers is the tree’s ability to host mango black spot and citrus witches broom disease. Small seedlings are difficult to hand-pull due to a stubborn root system, with chemical control recommended in the BQ factsheet link listed in Garden Cuttings.
Last week’s article also highlighted the Chinese celtis (Celtis sinensis), another weed tree quite abundant and widespread in South East Queensland and the South Burnett regions. Eventually growing to 15m tall and wide, the berries of this tree are also spread by birds and mammals (flying foxes).
Many Toowoomba yards have Celtis seedlings or trees slowly crowding out ornamental plants and becoming the dominant species. An accidental introduction of the Asian wooly hackberry aphid has seen many Celtis trees being almost defoliated by these voracious sap-suckers, but an unwelcome side-effect of their honeydew excretions is the copious amount of sooty mould produced on the trees and spreading to all plants in their immediate vicinity. Hand removal of small seedlings and herbicide application as per the BQ factsheet will see this weed kept under control.
Controlling these weedy trees, if found on your property, is not only beneficial for your own garden plants, it’s a great way to reduce the spread of unwanted and damaging plants to your neighbourhood, suburb, town and region.