A highveld grassland, one of the many areas of Gauteng that has become infested with pompom weed
As custodians of a five-hectare plot of indigenous grassland, we are always looking at ways to protect the biodiversity on our property, and one of these ways is to remove alien invasive species. Like many properties, ours originally had a number of invasives that are potentially damaging to the environment; plants with few native enemies, that proliferate freely, and that out-compete the natural vegetation, thereby reducing biodiversity.
One of these species is pompom weed (Eupatorium macrocephalum = Campuloclinium macrocephalum), a particularly aggressive perennial invader that can look quite 'pretty' in full bloom, but is damaging to South Africa's grasslands. It is a summer-growing perennial that can reach a height of up to 1.3m. The plant reproduces by seed that is dispersed on the wind, and a single plant can soon become hundreds if not removed.
Pompom weed has become a common sight on Gauteng's road verges
Various methods have been proposed to control pompom weed, including herbicides and biological control, and for land where Pompom has completely taken over - think a 'sea of pink' where once there was only an indigenous grassland - these might be the preferred solutions. But for properties where there is still a manageable population - a few plants here, a patch over there - mechanical control is simple and effective, albeit labour intensive.
Properties such as this still a have manageable population of pompom weed and are candidates for mechanical removal
It's important to mention that when using mechanical control (manual removal) one needs to avoid disturbing the soil as much as possible. Aggressive measures such as large-scale tilling are not only ineffective, but can also harm native species growing on that land. Disturbing the soil also provides space for other weeds to grow, especially if you have annuals such as Bidens spp. (blackjacks), Tagetes minuta (khakibos) or Conyza bonariensis (hairy fleabane). This is why it is recommended to cut back such species at their base, rather than pulling them out. In the case of pompom weed however, cutting it at the base does not kill the plant, and usually encourages new growth, often with more flower heads - which can leave land owners with a bigger problem than they initially had. To remove pompom in its entirety one needs to remove the root crown from below the ground, as this is where the roots, leaves, and flower stalks develop from.
Successful mechanical (manual) removal of pompom weed requires removing the root crown, circled above in red
Removing the stalk (highlighted in green) is useful as a temporary measure to delay flowering of pompom weed, but it does not kill the plant. As with the previous image, successful mechanical removal requires removing the root crown, again circled here in red
Here follows a description of our preferred method of mechanical removal of pompom weed, using the flat side of a blunt pick, which we find easier and less intrusive than using a hoe, mattock, fork or spade:
1) Aim the pick about 5-10cm away from the plant (depending on its size), and dig it into the soil at an angle, so that the blade of the pick is below the root crown of the plant. How deep depends on the size of the plant - larger plants require a lower depth, whilst smaller plants usually only require a few centimetres.
2) With the pick head still in the ground, gently loosen the soil by leveraging the pick until you can easily pull the plant out. If the plant 'resists' then loosen the soil a bit more.
3) If the stalk breaks off without the root crown attached, then repeat the process to see if you can find the root crown and remove it, otherwise the plant will regrow.
4) Once you have removed the root crown, gently stamp the ground back down into place
5) If the plant has buds or is in flower or has seeds, then cut off all flowerheads, bag and destroy them. If the plant has yet to flower, then you can leave it lying on top of the ground, where it will soon wither and die.
Some points to keep in mind:
- If you accidently break off the stem without the root crown attached, try searching for the root crown and remove it. Failing this you will need to wait for it to grow back, which may be in a few weeks or the following season.
- Small pieces of the root crown can easily grow back. If you see roots still in the ground then check them to see if there are any pieces of root crown still attached - a small knobbly bit at the top of the root.
- In heavily disturbed areas - such as man-made mounds - the root crown may be many centimetres below the surface. In this case you will need to carefully dig the soil to find the root crown and remove it.
- If the pompom weed bears dry flowerheads carefully remove them, bag and destroy them before removing the plant. Attempting to remove the plant with dry flowerheads bearing seeds may cause those seeds to disperse.
- Very small pompom weed seedlings can be removed using a hand-weeding tool.
- If the pompom weed is growing beside or 'inside' another indigenous plant, such as a bulb or grass, try to remove the pompom without disturbing the other plant. If you do have to lift both plants then remove the pompom and replace the desired plant back in the excavated ground, gently firming it into place. Water lightly around this plant if the ground is particularly dry.
- Take care to identify pompom weed correctly - especially if the plants are small - as there are a number of indigenous grassland species that look similar when they are young (see images below).
- If you have time, sow seeds from surrounding plants - such as grasses or bulbs - into the spaces left by the removed plants. A healthy grassland is likely to already have a large soil seed bank of such species, but areas that may be heavily infested with pompom weed will benefit from additional seed to help speed up the recovery process of the area. Locally indigenous pioneer, sub-climax and climax grasses can be used, along with seed from native non-grass species.
- Removing pompom mechanically requires consistent effort during the active growing season, (October-March). Plants are easily overlooked, so walk your property at least once a week to search for and remove plants.
- It is easier to detect emerging plants early in the growing season in areas burnt as part of a veld management strategy.
- Lastly, it is worth supporting your neighbours in their pompom weed removal efforts. As the seeds are dispersed by wind there is a possibility that unmanaged populations can spread from surrounding properties. If you have time and resources, offer assistance to your neighbours to help them remove it from their land.
Below are more images to assist you.
A young pompom weed (circled in red) can look similar to native species such as Coleus pentherii (circled in green)
Another pompom weed circled in red
Scan the ground carefully for pompom weed seedlings
Pompom weed seeds are easily dispersed. If plants already have flowers or seed try to cut off, bag and destroy the flowers and seed heads before removing the plant
A beautiful five-hectare plot of indigenous grassland from which thousands of pompom weed plants were removed. This was achieved by two people walking the property for a few hours each day, 3-4 times a week, over two growing seasons (Oct-Mar), and manually removing plants as and when they were found. Regular monitoring and removal (if new plants are discovered) is ongoing.
