Campulodinium macrocephalum.png 

​Management should aim to maintain the natural vegetation in a healthy, productive state as this will help to limit pompom invasion. This may require a combination of control methods together with agro-pastoral practices such as mowing, burning and minimum tillage with grass overseeding. 

Herbicidal control

Three herbicides are currently registered for use on pompom weed:

1. Brush-Off (metsulfuron methyl 600 g/kg) made by DuPont. Brush-Off is a water dispensable granular herbicide for broadleaf weed control. For pompom weed mix 25 g of Brush-Off granules in 100 litres of water, or 2.5 g in 10 litres. BP Crop Oil is recommended as the wetting agent at 50 ml per 10 litre water.

2. Access 240 (picloram 240 g/litre), by Dow AgroSciences, registered as a foliar treatment. It is recommended that 350 ml of Access be mixed with 100 litres of water, or 35 ml in 10 litres. The wetter Actipron Super must be added at a rate of 50 ml per 10 litres of spray mix.

3. Climax, metsulfuron methyl (sulfonyl urea) 600 g/kg, by Volcano Agroscience, also registered as a foliar treatment. The recommended dosage is 20g-30g / 100l water plus a surfactant, which could be either Volcano 90 at 100ml / 100l water, or BP Crop Oil at 500ml / 100l water. It should be applied either early summer, at the lower rate, or mid to late summer, using the higher rate.

More details regarding the application of these herbicides appears on the brochure included in the herbicide packet. Herbicides should be applied onto actively growing plants that are starting to produce inflorescences, i.e. from December onwards. Pompom weed dies back naturally in winter so spraying should stop when plants begin to turn yellow in early April.

Mr Jeremy Goodall from ARC-PPRI (e-mail: GoodallJ@arc.agric.za) is testing more herbicides with the view of registration. Pompom weed is very sensitive to a range of cheap selective herbicides that provide over 80% control. All selective broadleaf herbicides will damage any broad-leaved plants exposed to the spray, but they do not affect grasses.

Spot-spraying in light pompom infestations should cause minimal damage to non-target plants. To minimize damage to desirable plants, the herbicide should be sprayed only onto the leaves of pompom weed, to the point at which they are shiny but not dripping. Do NOT spray in windy conditions, when the temperature exceeds 28ºC, when there is dew on the leaves or when rain is likely within the next two hours.

Physical control methods

In general, physical methods of control, such as uprooting or hoeing, are ineffective and make the problem worse through disturbance. It is not advisable to plough lands with pompom weed as this will damage the rootstock, stimulating further vegetative growth and denser stands.

Spread of the plant can be limited by preventing seed production. Aerial stems can be cut right back before the flowers produce seed.

However, be warned that the plants will be stimulated to produce more stems and in order for this method to work the plants will have to be cut back several times until the end of the growing season.

Repeated cutting back of aerial growth should deplete nutrients stored in the roots, weaken the plant and limit seed production. This method however is only practical on a small scale. It is advisable to remove all flower heads from the site, being careful not to spread the weed further, and dispose by burning.

In the case of single or very few pompom plants in an area, each plant can be dug up, taking care to remove at least the root crown (the area where the stem is attached to the swollen, finger-like roots) from the soil. Once the root crown has been removed, the roots will apparently not regrow.

It is important to cause as little soil disturbance as possible, in order to prevent the mass-germination of pompom seeds. Regular follow-up visits to the site for the next three growing seasons are essential to ensure that all seedlings have been removed.

Removing inflorescences.gif
Removing inflorescences to prevent seed dispersal - but heed the warning in bold! (left)

Biological control

Biological control research (introducing, testing and releasing host-specific natural enemies of pompom weed) is underway at ARC-PPRI's weed laboratories at Cedara (near Pietermaritzburg, KZN). The project leader is Dr Andrew McConnachie (e-mail: McConnachieA@arc.agric.za).

PPRI researchers have undertaken three exploration trips to Argentina and one to Brazil to survey for potential biological control agents of pompom weed in its natural habitat. One rust fungus and nine insect species have been brought back to South Africa where they have been submitted for taxanomic identification. Only three of the insect species and the rust fungus (Puccinia eupatorii) are currently being reared and tested in quarantine. The insects include a stem-galling thrips (Liothrips sp.) and two flower-feeding lepidopterans (Cochylis campuloclinium and Adaina prob. simplicius). A document can be downloaded summarising the biology and showing pictures of these natural enemies.

As soon as researchers have satisfied themselves that these candidate biocontrol agents are host-specific and therefore safe for release, as well as significantly damaging to pompom weed, applications for permission to release the agents will be lodged with two government departments (Department of Agriculture and Department of Environment Affairs and Tourism). All of these stages are time consuming, and it will probably be several years before any agents can be released.

Meanwhile a damaging rust fungus – a different strain to the one imported by PPRI – was found on pompom weed in Gauteng. Nothing is known yet about its entry into the country, but laboratory studies on this accidentally introduced pathogen are in progress.