Weeds and weeding

Weed management is a key part of restoration on Gang Gang as it needs to be pretty much everywhere.

Worry-wort  –  the years when St John’s Wort bothers everyone
Annual, perennial or vegetable?
–  Confessions of a micro-weeder
Con-eyes-are (Conyza)
–  weeds can seem to come from nowhere, but it is not always mysterious.
Every season is different – the downside of a wet season.
A weedy reprise – revisiting the results of past weeding.

Worry-wort  –  February 2019

Plant names that end in “wort” indicate a history of use in Europe as medicinal or food plants. For example, the well-known weed St John’s Wort (Hypericum perforatum) has been used for thousands of years as an antidepressant, antiseptic, anti-inflammatory, expectorant and tonic for the immune system. It has recently had a revival in modern human medicine as an anti-depressant, although not without some controversy.

Since its introduction to Australia, St John’s Wort has been such a problematic weed that scientists started biological control trials in the 1920’s. Of twelve agents introduced, six have established: three beetles, an aphid, a midge fly and a mite. This long scientific journey has demonstrated that while biological controls can be important agents of control, they are not magic bullets. The early work in controlling Prickly Pear with beetles was a huge success that is now permanently imprinted on the nation’s psyche. This is unfortunate as it was a complete fluke whose success has never been repeated.

In the case of St John’s Wort, all those predatory invertebrates have had only a modest impact, and in our district, it seems that they are having no effect this year. The amount of St John’s Wort growing could be viewed as something to get depressed about, which is somewhat ironic given its medicinal properties.

The plant is palatable to livestock, but poisonous when eaten in large quantities. Oddly, the effects of eating St John’s Wort include sensitivity to sunlight and … depression! The photo-sensitization results in serious skin damage, which in turn leads to weight loss, reduced productivity and, in extreme cases, death. Hence the early and prolonged search for biological control agents.

Its yellow-flowering presence has been conspicuous in December and January in paddocks, along roadsides, seemingly everywhere. I am guessing the combination of winter drought and warm season rainfall has played a role here. From February, the yellow will gradually turn to green then dark brown as the flowers finish and the seeds start developing.

At Gang Gang we were certainly caught out this season. Over the last 15 years we have been pulling out any plants that we have encountered, which seemed to be in just a couple of small patches. This year is different. It has appeared in many new spots. Possibly, powerline inspection vehicles have bought in seed. Not that our vehicles are squeaky clean, we just try hard to avoid driving over the place for this exact reason. Alternatively, the new patches could be small plants, previously unnoticed. Who knows.

The only practical response is to be less haphazard with our weeding, and be more vigilant and systematic. To this end, we have tagged the nine sites we know of with a GPS and put reminders in electronic diaries to go and check them next December. Because the worst part of this story is that the weed puts up suckers in a circle around the larger flowering plants. If you do not want to use herbicides you have to dig up a tracery of surface roots the radiate out from the established plants, or you will have many more new shoots coming up.

Competition from perennial pastures is considered essential for long-term control. This makes the use of herbicides tricky if the surrounding non-target pasture species are damaged by spraying.   Grazing can also be used to manage St John’s Wort and may be the only practical measure on steep slopes. Don’t graze when it is flowering however, as it is most toxic at this stage of growth. Also, provide shade trees to reduce the effects of photosensitization.

If you are a long-term reader of this column, you may remember the near-panic over Fleabane (Conyza) which had a good season in 2012 (see below), at which time many people thought it was taking over the landscape. I soothingly suggested that this was not the case, and indeed, no one has mentioned Fleabane since that time. Hopefully, St John’s Wort is going to do a similar thing, and gradually subside in dominance in coming less-favourable seasons.

Do not confuse St John’s Wort with the innocuous native Hypericum gramineum. The native is smaller, the flowers are more orange than yellow, and it does not sucker aggressively. Unlike the European wort, the native wort is a responsible grassland citizen of modest demeanour.

Annual, perennial or vegetable?  –  November 2013

After nearly two years contributing to the gazette, it is time to get something off my chest. I am publicly owning up to an obsession and this is the right time of year to be dwelling on it.  I am a micro-weeder, and spring is peak micro-weeding season.

Late October and early November is when most species of exotic annual grasses and forb make their final sprint towards reproductive success, after a quiet autumn and winter, harvesting water and nutrients. It is now or never.

In our part of the world, the main targets of the micro-weeder are the shivery grasses : Briza maxima, Briza minor (and yes, there is a Briza media in Europe that has yet to be introduced to Australia).  There is also Vulpia, whose seeds can penetrate a sheep’s hide, and Aira whose wispy flower heads give the impression of a ground mist.  The forbs that I chase include Trifolium (the clovers – we have nine species) and Hypochoeris glabra (the annual version of flat weed) plus more than can be described here.

Why do I focus on all this small stuff (including clovers!) when most of landholders are wrestling with perennial weeds – briar rose, St Johns wort and the dreaded serrated tussock? Well it is a question of scale mostly – the big things compete with the large perennial grasses – they look intrusive  and  they are easy to point a sprayer at.  The small annuals are more insidious, they suck up all the nutrients when most of the natives are dormant, and come spring, there is little room or resources for the native seedlings and re-sprouting perennial forbs.  In this way, the annuals have a much greater impact on more plant species, even though they look small and innocuous.  When you are weeding and can see things up close, the intense competitive effects of the exotic winter annuals are very clear.

There is a sweet spot in the development of the winter weeds in late October – early November, when it is ideal to hand weed.  It is the time the buds are forming and the grasses start heading up, just before the flowers emerge.  Some people think that grasses don’t have flowers, but like all higher plants they do, it is just that their flowers are very small and they don’t have petals to catch the attention of insects.

This sweet spot is when weeding is easiest and most effective. Earlier, the plants are still sucking what they can from the soil and it is difficult and fiddly to pull out the tiny plants which nonetheless have well attached, dense mats of roots.  Any later, and the flowers are developing and seeds can be dropped before you know it.  The sweet spot is when the plants have transported most of their energy to the developing flowers and have a lesser hold on the soil.  The bulging inflorescence, still sheathed by leaves, is easy to grasp and the roots come away with little soil on them.  It is a most rewarding time in terms of weeding efficiency.

I do know that I am not completely alone in my madness. My friend Jeff is equally keen on maintaining a totally native grassland.  He even sets tapes in parallel across the area to be weeded and works systematically in strips.  I prefer a more meandering style of work.  Some people who are ostensibly sane can also be micro-weeders.  Some keep their vegetable gardens immaculate when it comes to non-vegetables.  And I have certainly seen individuals on their hands and knees weeding clover out of their front lawns – more than once.  But why groom a commonplace lawn when you could have an native grassland sparkling with wildflowers?

Luckily for the micro-weeder, the season is short, leaving ten months or so for your fingers and knees to recover and to enjoy the fruits of one’s labour.   Until those ominous little green hairs re-appear between the dormant  tussocks next winter.

Con-eyes-are (Conyza)
  –  February 2012

With the extraordinary run of wet seasons in 2010-12, many people are commenting on a plant that ‘appears to have come from nowhere’. Of course they have been skulking around the landscape during the drought in the form of heavily chewed plants, on ungrazed roadsides, in gardens, and stored as seed in the soil.  One conspicuous plant that many people have commented on this year is Conyza.  It is bright green, stiffly erect, usually with a single stem, with fuzzy leaves alternately arranged all the way up the stem, which can exceed two metres (but more often  around one metre high).  They have a somewhat unexciting inflorescence – a branch of creamy-brownish flower heads with no apparent petals and tiny fluffy seeds, which are dispersed by wind.

Livestock are quite partial to Conyza and when the tops are chewed off, the plants regrow from the broken stem into a branched form although repeated grazing (or mowing) kills them.  Having  a lot of energy invested in leaves all the way up the stem means that they compete well with tall grasses, but can’t afford to have their tops knocked off too often.

When our property Gang Gang was de-stocked seven years ago, there was less than a handful of well-chewed Conyza plants.  Last summer (2010-11) we noted too late that a few of plants had seeded and this year, there are concentrations of new plants where the seeding had taken place, and a lighter sprinkling of plants all over the open areas of the property where seeds have been dispersed more thinly and widely by wind.  Having discovered then well before flowering, we decided to have a serious attempt at control this spring/summer.

But why try to control this plant when we have around 90 other exotic species growing on the place?  For a start, as it increased under low grazing pressure, we figure that it is only going to become a worse problem in a de-stocked situation.  Second, it looks out of place in a native grassy woodland – it is quite visually intrusive, looks unlike most native grassland plants and gives an impression of neglect.  Third, as it only grows from seed, it is unlikely to have much of a soil seed bank; wind dispersed daisies such as Conyza generally rely on good dispersal over soil-stored seed for persistence.  Fourth, it is easy to pull out.

So the campaign started in November. It is now late January, serious flowering has not started yet and we have broken the back of it, although it was more work than we bargained for.  The repeated storms have meant successive waves of seed germination, and we have resorted to using herbicide on some of the larger concentrations of plants when our bodies started complaining about all the bending and pulling.  However, we are now down to hand pulling the last of the scattered plants.  The next months will still require repeated combing of the landscape, but this is a much more pleasant task than spraying.

The advantage of patrolling your patch regularly is that you get to see new things, enjoy the birds and locate the rogue Black Thistle, Sweet Briar, St John’s Wort and Blackberry plants that are establishing everywhere.  A small seedling Blackberry is a very different challenge to a ten metre wide patch of grasping thorns.

If you run livestock, it would seem that Conyza is of only benefit to you.  Marwan Omar at Au-Najah National University in Nablus, Palestine, found Conyza bonariensis to be as good as commercial rations for fattening Awassi lambs.  It’s good to have some good news coming out of Palestine for a change.   Given that it is nutritious to livestock and not very grazing tolerant, it is unlikely that this year’s surge in Conyza populations will be permanent.

Conzya is also reputed to have an unbelievable array of medicinal properties viz.  leaves can be used as a wound poultice and disinfectant, it has diuretic properties, controls fever (a febrifuge), controls worms, is insecticidal, anti-rheumatic, anti- diarrhoeal, a liver tonic, treats gastric ulcers, gonorrhoea, haemorrhoids and urinary tract infections.  So I don’t know why we would need a doctor with a few Conyza in the paddock.

Notes for the botanically inclined
Family: Asteraceae (daisies)
Genus: Conyza
Species around the district:
Conyza sumatrensis – seems to be the most common one, green shallowly lobed leaves.
Conyza bonariensis – narrower leaves, smaller greyish plant which flowers earlier than C. sumatrensis.
There are other species recorded in the Southern Tablelands, they require some botanical skills to key out.

Origin: exotic species, native to North (C. bonariensis)  and South America (C. sumatrensis).
Common name: Fleabane
Life history: Annual (grows and flowers within one year), active growth in spring and summer.
Indumentum: leaves are hispid (bristly) with spreading sepate (segmented) hairs.

Every season is different  –  December 2014

Australia’s climate is notorious for its variability, and it is little wonder we have trouble detecting climate change trends from our personal year-to-year experiences. This year the season was distinctive in the enormous amount of winter-growing grasses and forbs[1] that flowered abundantly in October-November. Hand-weeding the native grassland around the house was a nightmare this spring due to the mass germination of the annual exotic species of Vulpia, Trifolium, Briza, Petrorrhagia and Linaria [2].

Rather than creating a 20 metre belt of beautiful weeded grassland around the house as in other years, this season I was scratching to keep the inner few metres clean. It was most disheartening, and almost had me becoming nostalgic for the droughty years.

How could all that seed still be in the ground after four years of conscientious removal of the plants before they could set seed? Apparently weeds can be like dirty dishes, they never entirely go away, however persistently you might work on it.

Looking back at my rainfall records for the previous eight years, it is evident that while the cumulative rainfall in 2014 has been lower than in some other years, the March and April totals this year were particularly high – each recording 95 mm. In addition to that, the rain fell quite evenly. In the six weeks from the first of March, there were 19 rain days – that’s rain on almost half the days. This is the time when the season is mild, and soil is still warm. This is the time when all the cool-season annual grasses and forbs germinate.

It must have been perfect conditions for establishment of seedlings; and perfect conditions for weed growth.

Annual plants do not have the same form of insurance as perennial plants. Perennials typically store energy in roots or stems, ready for re-sprouting when growing conditions are good.

Winter-growing annuals rely entirely on the production of seeds to carry on between growing seasons. Their key to success is to invest all their energy in producing numerous seeds. It seems like a risky strategy, but the evidence is that it can work, even in Australia’s variable environment.

Their seeds drop in November-December and lie in, and on, the ground throughout summer. Their persistence is ensured by the numerous seeds produced, and the fact that some of them remain dormant in the soil for years. This means that there are seeds available for a number of seasons ahead, regardless of the growing conditions.

There really is something behind the gardeners’ adage – one year’s seeding, seven year’s weeding. It is critical to identify any new types of weed promptly and remove them before they go to seed on your land. One advantage of all my apparently futile weeding, is that the close observation it requires has enabled me to prevent invasions by African Love Grass (Eragrostis curvula) and Fireweed (Senecio madagascarensis) through early detection.

Putting my whinging aside for a moment, there has been a definite up side to 2014. Conditions also happened to be great for a number of winter-growing native grassland plants, most notably the Yam Daisy (Microseris lanceolata). I have not seen such extended flowering and seed production, a big boost for this grazing-sensitive species that is struggling to regain its previous abundance. The sun orchids (Thelymitra spp.) and the tall brown and yellow Tiger Orchids (Diuris sulphurea) were also growing in their hundreds on Gang Gang, and in places that they had not been seen before.

The season may also been kind to those with intensive sown pastures. Some of the winter -growing perennial grasses will have had a great chance to build up. Fescues, rye grasses and Phalaris come to mind. Though with my severe allergic reaction to Rye Grass and Phalaris pollen, I will not be cheering on your behalf!

Sue McIntyre
December 2014

[1] Forbs are all herbaceous plants other than grasses

[2] For plant descriptions see: http://plantnet.rbgsyd.nsw.gov.au

A weedy reprise  –  February 2013
Avid readers of the Gundaroo Gazette may recall my first contribution twelve months ago. I wrote about that weed Conyza (pronounced “con-eyes-are”). Remember? Bright green, sternly upright and simply everywhere? Many people were wondering where it appeared from.

Last summer I was obsessively combing the slopes to control the Conyza before it went to seed, balancing repetitive strain injury against a possible victory against this plant that I had taken a set against.

Wading through the thickly-grassed hills of Gang Gang a year later, I note how differently one can perceive a familiar place from year to year. Instead of striding over the landscape, my progress this year is limited by the dense compacted grass litter, renewing my already over-developed sense of fire hazard, and I resolve to do even more burning this autumn.

But at least in the Conyza department I can happily report that our efforts last summer were not in vain. Conyza numbers are right down and the desiccated days of December and January this season have reduced germination and delayed flowering. The plants are wilting and many of them have been grazed by kangaroos.

But don’t be fooled. These are tough hombres. They now have multiple stems sprouting from the point where they were chewed off, and while wilted, a few points of rain will be enough to initiate some flowering and seeding. So I keep on chipping them out from the hard soil, grudgingly admiring the ones on rocky outcrops that seem to have tapped into groundwater and which are still bright green. Others seem to have put out a horizontal rubbery root close to the soil surface, presumably in response to the light rainfall we got on Christmas Eve. While I’m out there, I find a number of black thistles, their prickly purple buds ready to go, completely unfazed by the heat and dryness. Like serrated tussock, you have to keep going back and back to control that last armful of persistent plants. I also spot the odd blackberry seedling. Far from retreating, these plants are colonizing, their fruit dispersed by animals from large plants elsewhere. Vigilance is essential.

Unlike Gang Gang where the weeds are lovingly hand-pulled and the problem is more a question of aesthetics than economics, the folk on the slopes and plains of NSW have been most concerned about Conyza becoming an ‘emerging’ weed of broad acre crops. One species in particular (Conyza bonariensis) has been doing extremely well in situations where crops are grown repeatedly using the popular no-tillage approach. This involves sowing the crop into paddocks without cultivation, instead using herbicides to kill any potentially competing plants – Conyza amongst them. Conyza is becoming resistant to the herbicide treatment, enjoying the conditions, and causing a great deal of worry.

More research is being called for to find improved control methods for Conyza – more effective herbicide treatments and exploration of biological control possibilities.

Reading this takes me back 30 years to the time when I worked in the rice fields of the Murrumbidgee Irrigation Area – studying the weeds from an ecologist’s perspective.
There were three ways of growing rice at the time, each method favouring different kinds of weed. The no-tillage method encouraged perennial weeds, while broadcasting rice seed directly into flooded fields encouraged aquatic weeds. The third type, traditional cultivation with delayed flooding, encouraged semi-aquatic annual grasses. If any particular weed species got out of hand, there was an option to try a different sowing method or to rotate the rice crop with winter wheat or with pasture. This could prevent the continuing build-up of the problem species. Rice growing in Australia is full-on high-input industrial agriculture, but growers and researchers managed to develop alternative, viable cultivation options that maintained some diversity in the system and reduced chronic weed problems.

Before the development of herbicides and artificial fertilizers, the rotation of different crops was a standard and necessary practice. There is now a tendency to discard rotation, as fertilizers and herbicides can provide rapid, satisfying results and thus prop up the most profitable crop year after year. In the case of no-tillage, this is the currently preferred growing method for broad-acre crops as it reduces the risk of soil erosion. But like passengers rushing from one side of the boat to another, complete uptake of the no-tillage method can cause the system to list like an unbalanced boat. The rise of Conyza in the cropping zone is not really a crisis; there are not that many super weeds in the world. The boat needs to be trimmed.

At Gang Gang, the variable seasons create an approximation of crop rotation. The growing conditions that result from varying temperature, wind and rainfall will favour different plants over time. By sticking to only one crop and cultivation type, farmers are providing roughly similar growing conditions year after year – the conditions most suitable for that crop. It is just unfortunate that there will be a number of weeds that also like those conditions. Most plants have an Achilles heel, and knowledge of their ecology can help identify their weaknesses and keep ahead of the game.

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