St John’s Wort is by far the most prevalent weed on Highfield. Introduced from Europe, Asia and North Africa, it was brought to Australia in 1875 as a garden plant and for use in herbal medicine. St John’s Wort has become a severe weed in parts of NSW.

A perennial pest growing in most paddocks

When we came to Highfield 11 years ago, St John’s Wort was growing in most paddocks; in some, it grew very thickly. It was also present in parts of our conservation area – particularly those places that had been grazed before the covenant had been established.

As a perennial weed, it regrows each year from the roots of last year’s plant. It has weighty roots – two types, a deep tap root and long spreading roots that creep under the top layer of the soil, helping to spread the plant.

Over the years, we have had several suggestions on controlling the St John’s Wort on Highfield. Here they are.

“Spray it with herbicide”, they said.

Early in our time at Highfield, we took that advice. We got a spray team out to spray the heaviest infestations. It didn’t work, and frankly, we didn’t want to use herbicide at all. We felt compelled to do so as novice farmers, wanting to be seen to do what was ‘acceptable’. We never did this again. We’ve stopped doing most ‘acceptable’ things.

“Apply loads of superphosphate and then graze it heavily”, they said.

Well, we didn’t want to do this either. Most of our grasses are native grasses perfectly adapted to low phosphate conditions. We were concerned that if we used this approach, the heavy application of superphosphate would damage our native grasses. And if the superphosphate didn’t hurt the native grasses, then heavy grazing would. Anyway, superphosphate is a non-renewable resource, and we also didn’t want to use it for that reason. So, this method didn’t fly for many reasons.

“Harvest it and sell it to the herbal medicine industry”, they said.

St John’s Wort is a commonly used herbal treatment for mild depression. You see it in the herbal medicine section of the chemist all the time. But, well, our aim was to reduce the amount of St John’s Wort, not turn it into a commercial venture. Besides that, I was sure that growing anything for the pharmaceutical or herbal medicine industry would have required strict regulations and licenses. No, that suggestion wasn’t going to fly either. Cute idea but ill-informed.

St John’s Wort and grazing

St John’s Wort can be highly toxic to livestock. It contains hypericin – a chemical which, when ingested by sheep exposed to sunlight in high quantities, can cause photosensitivity and acute sunburn. It can also cause liver damage and loss of lambs. However, if sheep graze St John’s Wort when the hypericin levels in the plant are low, which is the case at certain times in its yearly cycle, it is less likely to harm the sheep, and grazing can be an effective way to control the plant.

St Johns Wort in flower

St Johns Wort in flower

This then was going to be our approach. Combined with making our paddocks smaller with the use of fencing so we could better control the grazing and, by taking an approach to grazing for full ground cover at all times of the year and by grazing to foster our native perennial grasses, we would attempt to control the wort by careful grazing management. But would it work? Many raised their eyebrows.

After years of careful grazing and seeing the St John’s Wort regrow from its roots each winter, prosper, flower and then set seed, we thought we would never make any progress. Last year, we put considerable thought into the process. We would attempt to graze the paddocks with wort with loads of livestock in short duration pulses. We rotated the sheep through the most heavily infested paddocks regularly, always attempting to graze the wort when it was short and vulnerable while maintaining full ground cover and the health of our native grasses.

Importantly, we removed the sheep when the wort began to flower – when the hypericin was at its peak so that our sheep wouldn’t suffer the negative consequences of the chemical combined with sunlight.

However, when the wort began to flower, we felt like we had made no progress. The yellow flowers stared at us as if to mock our approach. And, of course, flowers mean the seed is set, continuing the whole process of its reproduction.

The beautiful Chrysolina Beetle

The beautiful Chrysolina Beetle

Last year, we noticed a lovely, shiny black and iridescent beetle was attracted to the wort. We looked it up. Chrysolina was its name, and it clustered at the top of the plant. Turns out Chrysolina is a biocontrol for St John’s Wort, but it was only in a tiny area of one paddock. It wasn’t going to make a difference in one year.

As usual this winter and spring, we spent time looking at the paddocks to see when the wort would emerge. In anticipation of it sprouting from its roots, we sent the sheep in to do their usual control work. However, very few of the plants from last year sprouted any new growth at all. We pulled up some of the red-brown stems from last year to inspect the roots – nothing was sprouting!

Again, we waited to see if we were checking for the wort too early in the year, but something was very different as winter went into late spring. This year, there was hardly any wort at all.

Our sheep quickly ate the small amount of wort that was emerging. And something else had changed, too. In some parts of the paddocks, what wort there were bore loads of black iridescent Chrysolina bugs. In some instances, they had completely defoliated the plants. No leaves mean no photosynthesis and no photosynthesis means – well, death is pretty close by.

But what was happening in the conservation area? We hadn’t used grazing to control the wort there at all. Was the wort going to re-sprout in the conservation area? Our hunch was yes. However, on inspection, we found that the wort in the conservation area was much reduced.

So, what has caused such a dramatic reduction in St John’s Wort this year? Well, in agriculture, you are dealing with living systems. There are so many factors to consider, and, no doubt, many factors have led to progress. Here is what we think is happening.

Better grazing – stronger grasses

Fencing to better control grazing and regular grazing by the sheep when it is safe for them to eat it over several years has been a factor. But grazing to maintain full ground cover has probably also strengthened our native grasses and meant they could better compete with the wort for space in the paddock.


The beautiful Chrysolina Beetle and its larvae have also had an effect. However, this is the first year we have seen them in good numbers. No biocontrol works in one or two years, but gosh, it’s good to have them. They will undoubtedly help us more each year as their numbers develop.

But what about in the conservation area where we hadn’t grazed?

Well, our hunch is that the gradual recovery of the conservation from overgrazing in the years before the covenant was applied has meant that the native grasses have recovered and are now out competing the wort. So, we are getting a result there even though we are not grazing in that area.

Seasons come, seasons go

It is also possible that the three wet La Nina years may have had some sort of impact. Maybe?

Results against advice

Whatever the reason for this year’s success in controlling the wort, we are so glad to be finally making progress. And we are making progress without using herbicide and non-renewable resources like superphosphate and fossil fuels to apply herbicide or spread super.

Slow and small solutions

We’ve seen this before.By observing and making small changes (‘nudges’ we call them), you can allow nature to heal slowly and over time. We’ve seen this sort of approach work several times now. As another example, read our blog post on Revegetating Sheep Camp Hill.

Next winter and spring, we will observe our wort once again – let’s see if we can get a long-term result out of these minimal actions, all based on helping nature do the work for us.


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