Weed control on the farm

Whether a plant is a weed depends on your point of view. Because our property was a working farm until we moved here, about three-quarters of it has been cleared of native vegetation and replaced with a variety of pasture grasses and leguminous plants. The remnant natural vegetation was not fenced when sheep were introduced, so a lot of the more palatable indigenous plants were eaten out and the pasture species invaded.

For now, however, we are not classing these introduced pasture plants as weeds. However, there are a number of plants which are universally recognised as weeds in this part of the world because of their ability to invade native vegetation and pastures and which can rapidly take over large areas. On a working farm many of them are kept in check by grazing, so we lost one of the most efficient control methods when we removed the sheep from the property.

We are lucky not to have all of the weeds which are considered major problems in our area. Taylorina and arum lily can be found in large numbers around Albany and Denmark, but they do not occur in our immediate vicinity.

While most important weeds are easy to identify and commonly recognised by local people, others can be difficult to name. A very good resource is Weeds Australia which has a practical key with pictures and seems to include a wide range of problem plants. The following list covers all the important weeds which we are actively trying to control:

Thistle

thistle
The floral emblem of Scotland, which we would have preferred that they kept to themselves. A spiky plant which grows up to two metres high, it has purple flowers which set large numbers of very light seeds which are spread by the wind. Stock generally will not eat them, certainly not as they grow larger, so they often stand out on grazed pasture.

The thistles were the first weeds that we attacked. Our tenants had ignored them so when we moved in there were infestations on many areas of the farm. We just dug them out with a hoe, making sure that we found them before they flowered, and left the bodies on the ground or hung them over a fence to dry out. They have a limited ability to regrow from the base after this treatment, but the resulting plants are weak, so a second hoeing usually finished them off. With dilligent work, we had the thistles well under control after three years; now we just occassionally find a plant which presumably comes from seed blown onto the farm.

(?) Blackberry nightshade

blackberry nightshade
This compact bush might not really be blackberry nightshade (we are not sure, but it does belong to the potato family). A large specimen can be a metre high and a metre across, and will produce very large numbers of green berries which turn black when mature. The ripe berries drop to the ground or are eaten by birds.

We commenced control of these plants soon after we started on the thistles, again hoeing them or pulling them out by hand, preferably before they flowered. This was not too successful because we did not put in enough effort at first, and there were large numbers of plants, mostly in patches in the pasture. A change in tactic decreased the work required and resulted in almost immediate control - we just mowed them with the brushcutter (or the lawn mower if the ground was smooth enough) when they were about 15 centimetres high. As soon as they re-grew (as with the thistles with much reduced vigour) we mowed them again, and then with their natural growing and flowering season over, and with no seed set, the remnants died off.

For several years we saw very few of these plants, but then they came back in large numbers, and in many different places around the farm. We are not sure, but the density of the plants suggests that they came largely from seed stored in the soil rather than carried in by birds. The paddock across the road, from which stock had been removed, suffered a very dense and extensive infestation at the same time. So again we removed plants by hand and mowed the areas with thousands of plants in a few square metres, and now we are waiting to see what the longer-term result will be.

Update 2010: Although we still get a few of these plants, they are generally isolated and easily controlled if we manage to remove them before they set lots of seed.

Bridal creeper

bridal creeper
This wiry plant grows from a bulb composed of many finger-like segments. It has small white flowers which develop into green berries which are often eaten by birds and thereby transported to new areas - we seem to get new plants appearing all the time under our mulberry tree. They are considered a problem because they can grow over and smother native vegetation, but on our property they never seem to get more than ten or twenty centimetres high, and although they are all through the native vegetation, they do not make a big impact and only occur as more-or-less isolated plants.

We have made no serious attempt to control bridal creeper. Trying to pull the plant up almost always results in the stem breaking, leaving the bulb in the ground to produce a new plant. On the advice of a friend we did a test poisoning on a few plants with glyphosate, and it certainly killed the whole plant including the bulb. However, the local authorities have in the last few years released several biological control agents aimed at bridal creeper, so we are waiting to see how they work - the best candidate is a rust (fungus) but we have not noticed any effect so far on our plants.

Update 2010: We have noticed a few bridal creeper plants with yellow leaves which might be fungus attack, but we have not studied them closely.

Wavy gladiolus

wavy gladiolus
This particularly pernicious weed has strappy leaves which spring from a simple bulb. Small bulbs produce small plants, but over several seasons the bulb can grow larger and eventually will support a plant up to half a metre high. These large plants can produce a cream coloured flower in spring, but the most important method of reproduction is by the enormous number of bulblets which are produced by each mature bulb each season. We unfortunately help these small bulbs to spread by ploughing our (compulsory) fire breaks each spring, and kangaroos and rabbits also seem to scratch up the bulbs, spreading them further. We are not sure to what extent the seeds contribute to the plant's movement into new areas.

These are particularly difficult plants to control. Pulling them up by hand leaves many small bulbs (each just a couple of millimetres in diameter) which are usually spread out at the same time, and their hard waxy leaves are resistant to herbicides. We are not sure of the effect of mowing, but it is possible that if they are cut off at or below ground level, at the right stage in their growth, that they can be killed in this way. In the past we have tried to remove them by hand, but this was not very successful despite a considerable effort, so we will keep looking for more efficient methods of control. In the meantime this is the one weed which is probably increasing rather than decreasing on the farm.

Watsonia

watsonia

watsonia

Watsonia is another gladiolus-type plant which grows from a bulb. It favours wet areas so is at home on the low-lying land around Youngs Siding, especially along the roadside drains. In paddocks sheep and cattle will eat it which means that it is not such a problem under grazing conditions. In other areas, however, it forms dense clumps with plants up to a metre and a half high which shade and crowd out any smaller plants. Each spring mature plants produce a flowering stalk which carries around ten groups of 3 to 4 bulblets along its length. When the above-ground parts of the plant die off in summer, this stalk dries out and falls to the ground. Given the slightest opportunity, each bulblet will sprout in the following winter, creating a line of thirty to forty new watsonias. These plants will take several seasons to become large enough to produce a flowering stalk, but the original plant will have created a new bulb before the rest of the plant died off, and this bulb will sprout a new large plant in the next season. Bulbs can also divide to produce two new plants; we are not sure if Watsonia sets viable seed and if so how well it disperses.

For several years after moving to the farm we ignored the watsonia. Controlled in the past by the sheep, they were largely restricted to the line of the drain immediately outside one boundary of the property and to sections of the drain which goes through the farm, and looked like they would only spread slowly. This turned out to be a false assumption, and they are now well established for several metres inside the western boundary, which is almost 500 metres long.

Some years ago the local authority used a digging machine to re-make the drain along our boundary, and in the process dug out a significant amount of watsonia along the road. We took advantage of this unexpected helping hand, and the next year used the brushcutter to mow all the plants down before the flower stalks had formed. This was quite a bit of work with the collapsing boundary fence and its rusting wire, and small trees and other desirable plants getting in the way. We also removed some of the more isolated plants by hand. The effect was quite rewarding. There were no flowers or bulblets to create new small plants in the next season and the disruption to the watsonia's growth reduced their vigour in the next season; in some cases it might even have actually killed the bulb. So in subsequent years we repeated the mowing (after first removing the remains of the fence) to prevent propagation from bulblets, although the bulbs left in the ground still produced a minor forest of watsonia. We removed the remaining plants from along all but the end of the main drain by hand, and some plants along the road. We even collected a couple of trays of native seedlings, courtesy of the state government, and did a bit of revegetating along the road in patches where the watsonias had been totally removed.

We were told that watsonia is susceptible to glyphosate herbicide although it is not the product which is officially recomended for its control. But glyphosate is what we have, so we tried it on selected patches in addition to slashing and removal, and the results were encouraging - it killed all the plants which we sprayed. We have to use it carefully, since (due apparently to the detergent used with it) the herbicide is not very frog-friendly, and watsonia loves water. We minimise the detergent but include a bit of liquid fertilizer to encourage the pores in the leaves to open up and take in the glyphosate, and since we spray by hand we should be able to control where most of it goes. We plan to spray larger areas in future while manually removing isolated plants and patches and those near water.

It would be easy to get very discouraged in the face of the almost pure stands of watsonia which occur along our road, and in fact people driving past us as we pull them up have slowed down to suggest (kindly or otherwise) that we are wasting our time. Certainly watsonia control is a long-term project, but we are happy with our efforts after just a few years, and hope that within another five years or so the majority of the infestation will be under control. We might even try to encourage our neighbours all along the road to have a go at their watsonia so that the plants do not reinvade us from bulblets carried along the drains by winter runoff. With less watsonia and a bit of revegetation, the roadside verges could become a significant area of natural vegetation in the neighbourhood.

Update 2010: The watsonia along our drain and boundaries is well on the way to eradication. In some areas they appear to be gone for good, and in most others there are relatively few plants. The ones left are generally more difficult to get to, growing in amongst desired plants or on ant nests, but we decrease their numbers every year and a couple more years should see them largely gone. We have convinced our neighbour, who has a worse infestation than we ever had, to start control measures, and this year he sprayed a large area and was rewarded with a sea of yellowing leaves.

Kikuyu
kikuyu
This African grass was originally planted on the farm as a lawn around the old house, and lots of farmers in the area use it as a pasture grass, so many people do not consider it a weed. However it is causing us a lot of problems. It invaded the garden beds and then the orchard, and patches have appeared in the paddocks and around our new house. These patches all rapidly expand, and grow over and compete with any other plants they encounter. The citrus trees in the orchard suffered more than most, with yellow leaves and very weak growth despite lavish applications of fertilizer and trace elements. Poisoning the kikuyu around the trees had a dramatic effect; within a few months the leaves had changed to green and healthy new growth appeared. This grass is also a major problem to rival watsonia on roadside verges, but we only have a couple of patches (one already killed) along our fence lines.

Kikuyu spreads by seed and runners. The latter can travel underground for up to half a metre before puting up a green shoot, and the rhizomes can form strong dense subterranean mats once they are well established. When mowed or regularly walked on it behaves like a lawn with low, prostrate growth, but when it is undisturbed or it finds a barrier such as a fence or a tree trunk, it grows longer, more vertical stems, eventually creating an aerial mat around 30 centimetres high. In this way it can overwhelm small plants while limiting nutrient availability to larger ones.

Our initial approach to controlling the kikuyu was to dig it out. Given our soils and the toughness of the kikuyu stems, this is generally hard, slow work, and it is very difficult to be sure that every last piece of runner has been removed. We found that in the time that it took to clear one square metre of grass, two square metres had been added to all the other patches yet to be tackled. In addition, if continuous removal was not carried out, within a few months a cleared patch would be reinvaded from the surrounding area, a very depressing situation.

So we bought a 20 litre container of glyphosate (commonly sold as Roundup), and started a spraying campaign. With 15 millilitres of concentrate making up one litre of spray, we have enough to kill most of the vegetation on the farm! The first area to be treated was the orchard, with the gratifying results described above. Other areas have now been sprayed, but it is turning out to be a difficult task. Some rhyzomes survive the herbicide, so several periods of spot spraying are usually required before all the grass in a patch is finally erradicated. Also the spray only has an effect on green leaves, so viable seeds can be released by the dying plants. We did not appreciate the extent to which kikuyu can reinvade by seed, and so are now doing repeated spraying and digging of areas which we thought were cleared. Of course using a broad-spectrum herbicide to try to kill a weed which loves climbing up over any other plant it encounters is very difficult - especially with the xanthoreas (blackboys) which have leaves hanging down to ground level. Significant kikuyu control is obviously not going to be achieved without considerable effort over a long time, but we have considerably reduced its original area, and in some more isolated areas appear to have achieved complete eradication.

Update 2010: Kikuyu has not returned to areas which we thought were free of it, but it persisted for a long time in our orchard. Just in the last month we hopefully killed the last remaining plant in this area, but we will not be sure until next winter. In several other areas it is contained but we are making little headway in removing it because it is growing amongst desirable plants. Kikuyu eradication will really be a long term project.