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Weeds and Travellers

Saturday, Jun 21, 2014 at 19:00

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Weeds are everywhere. From the city to the bush, desert to rainforest, coast to outback, wherever you go you won’t be far from a weed. Each year weeds cost the country several billion dollars. Many of them are agricultural weeds infesting crops and pastures, but there are also heaps that are environmental weeds infesting bushland, waterways, even deserts. And then there are the weeds in your garden….

That’s not so good, I hear you say, but what does that have to do with me as I travel around the country?

And just what is a weed anyway? Let’s get that sorted out first.

The best definition of a weed is that it’s a plant in the wrong place, where it’s not wanted. Usually a weed is not wanted because it grows faster than the “desirable” plants, be they crops, pastures or native bush or scrub. Thus weeds reduce the ability of “good” plants to grow and be productive. By growing faster than their neighbours weeds compete with other plants for water and nutrients, for space and light. So they tend to take over an area, dominating and even killing other vegetation.

Weeds may have other nasty habits as well, like being unpalatable, even poisonous to grazing animals (eg Patterson’s Curse is poisonous to horses), seeds contaminate fleeces (Noogoora Burr) or causing humans to get sick (Parthenium Weed), harbouring animal pests like rabbits (boxthorn), increasing bushfire risk (blackberries, lantana) - there is a long list of bad habits, but that’s another story.

Most weeds share some common characteristics, the traits that make them “weedy”. Ironically if we describe someone or something as weedy we usually mean weak, spindly, even sickly.

Masses of dried off Noogoora Bur beside a western river

A weedy plant though is the exact opposite, being vigorous, tough and robust. Most weeds can grow very fast and under a wide range of conditions. Eg Water Hyacinth can grow so rapidly that an infestation may double in size every week under ideal conditions. Weeds flower and set large amounts of seed very quickly eg Boneseed, Capeweed. Their seeds are easily spread, often being equipped with hooks, spines, wings or other devices that help them hitch a ride on animal coats, in the gut of birds and animals, or on the wind eg thistles or the aptly named Velcro weed.

Seed pods of Noogoora Burr easily hitch a ride on animal fur, wool, clothes.

Weed seeds stay viable for a long time, often years or decades – Serrated Tussock seeds stay viable for 20 or 30 years. Many can reproduce vegetatively (when a detached bit of plant just takes root and grows), without having to produce seeds – broken off bits of willows and prickly pear will grow almost anywhere.

Most weeds are plants that have come from another country where their growth is usually held in check by other plants, diseases, grazing pressure or some other factor that limits growth. Once here though, without their natural constraints some lose all their inhibition and can grow out of control. A few weeds are native species (eg Cootamundra wattle) that have responded to changed conditions and behave as if they were in a new country.

Weeds got to Australia by a variety of ways. Many were deliberately introduced as garden plants (Sweet Briar and Pattersons Curse), as potential crops or pasture plants

Buffel Grass in Northern Simpson Desert

(Buffel Grass, African Love Grass), or for shade, landscaping and land rehabilitation purposes (Prickly Acacia and many Willow species). Others took a more devious route. Prickly Pear was introduced to feed the lava of cochineal insects that were the source of red dye used for the coats of the redcoats (soldiers) that came with the First Fleet. Blackberry seeds were introduced on purpose. In 1858, Ferdinand von Mueller began cultivating blackberries at the Melbourne Botanic Gardens, and scattered their seeds in the bush, so that others would have food to eat if they got lost.

Only recently declared a weed, willows have a huge impact on waterways

He had no idea how wildly they would grow. Serrated Tussock, a grass weed, was used to stuff pack saddles imported from Argentina – as the saddles were discarded the very long lived seeds grew and thrived. Whisky Grass was probably used as packing in crates of whisky brought in from America. And so on.

It is this unsuspected capacity of weeds to hitch a ride that brings us to realise that, as travellers, we can (and probably do) contribute to the spread of weeds. And once we have given weeds a free ride they really take advantage with their capacity to grow and reproduce in a wide variety of places and conditions.

Mud on vehicles will probably contain weed seed

It is no accident that most of our road verges are full of weeds. Vehicles spread weeds, especially their seeds. And once established along roads it’s an easy step for weeds to invade adjoining crops, pastures or bushland.

So what can we travellers do to avoid spreading weeds?

The first thing is to learn to recognise some of the most common weeds in areas you will be visiting. That requires a bit of effort but there is a wealth of information online. There are a number of weed links at the end of this blog. Build weed awareness into your trip planning.

Stay on the track; avoid driving off-track into or across weed infested areas. Wet soil and mud inevitably contains seeds that, once lodged on our vehicles can be transported thousands of kilometres.

Stay out of weed exclusion areas eg Noogoorra Burr exclusion areas along the lower reaches of the Fitzroy River.

Use wash down facilities where they are available.

Washdown facilies - not common but a good idea

If washing at home, do so on an area that you mow, so that any seeds that do germinate can be knocked down.

Firewood collected from weedy areas like roadsides will probably harbour weed seed. Carry and use clean firewood. Observe warnings against carrying bush-collected firewood into particular areas eg Fraser island.

Camping gear, footwear and even clothes can carry seed. Clean off as much seed as you can before moving camp.

Don’t break off bits of weeds or move them to a new location. If you are fishing along creeks or rivers lined with willows don’t cut branches to prop up rods.

Footwear and clothing carries seed around

Willow branches stuck in sand will soon grow.

And a note about personal safety and weeds. Watch out for signs advising of weed spraying. Don’t eat blackberries that have been sprayed. Weeds can also cause human health problems. Many common weeds such as Parthenium Weed, Ragweed, Rye Grass and Privet cause asthma and other respiratory problems, especially in children. Some weeds can also cause skin irritation and some like Lantana are poisonous. There are no common characteristics of a poisonous or harmful weed that would help distinguish them. But as a general rule, plants with a bitter taste, unusual smell, milky sap or red berries may be poisonous.

Finally a point for wildflower photographers - here are a couple of photos of weeds (purple Patersons Curse and yellow Capeweed) that put on a colourful display in spring. While both can provide useful stockfeed in difficult times neither are wildflowers - but they trip up even professional photographers, often turning up in wildflower calendars.