Battle with Pom-Pom weed

The control of the pom-pom weed is a difficult task in that the emergence of the aerial parts of the plant from underground rootstock depends on the amount of rain and the temperature. Once these aerial parts emerge a flower is produced very rapidly and the associated seed production starts.
Due to the short time from emergence to seed production it is essential to spray the plants as soon as possible after emergence. However if spraying is done too early plants that emerged and germinated later require a follow up spraying which doubles the cost and effort needed. To get the timing right is relatively easy on small areas but on larger areas you cannot get to spray all of the plants during the ideal “window”. The only way to overcome this is to have more logistic resources and above all manpower. Despite this any plant that is sprayed while it is actively growing is potentially killed which eliminates the rootstock and reduces the strong emergence in the following year.

The second problem is the control of single plants and small stands of plants as these are spread out throughout the reserve and lead to the development of large infestations. A single plant that emerges from rootstock and flowers will have accompanying seedlings for a few meters around it obviously from the previous season’s seeds.

This season the fight started in early December, 2008,  and was tackled on a number of fronts. The Welgevonden conservation team sprayed large infested areas of the southern plains with tractor mounted sprays in the areas that are tractor accessible. The less accessible areas are sprayed using knapsack sprayers. This approach managed to control a large proportion of the plants before their mass flowering and associated seed development.

The second line of attack was with the assistance of the Working for Water Program. This was the first time Working for Water have got involved with controlling pom-pom weed in this area so it was a learning process for all involved. This team concentrated on the infestation in the Sterkstroom Valley and the associated tributaries later moving onto other smaller localized infestations. The scope of this program was a great help especially from the manpower perspective. The manpower displayed a strong dedicated work ethic, where well organized and trained and went about getting the work done as quickly as possible.

The third line of attack was a small control team that constantly moved around the reserve finding and spraying all located plants especially concentrating on the valleys and vlei areas spraying individual plants with a knapsack spray.

Estianne Retief from the Agricultural Research Council (ARC) approached Welgevonden do carry out some trials on a rust fungus (Puccinia eupatorii) to evaluate its impact on the growth and survival of pompom weed. It is expected that it will definitely reduce the growth and reproduction rate of the plants. By attacking the stems and leaves the rust also depletes the nutrients that the rootstock needs for surviving the winter. Hopefully over a couple of seasons an visible impact will be noticed.

The rust was collected in Argentina and tested under quarantine conditions in a laboratory on over 30 plants from the Asteraceae family (pom-pom family), various crops, morphologically similar plants and indigenous plants. It was proved without a doubt that Puccinia eupatorii is 100% specific to pompom weed and will not attack any of the SA indigenous plants.

A rust fungus found on pom-pom weed near Pretoria was also identified as Puccinia eupatorii, until recently there had been no record of this specific rust in South Africa. ARC do not know how this rust came into South Africa, but rust fungi produces so many tiny spores that it can stick to basically anything and survive for a couple of months, without a host, so it could certainly have traveled with somebody from overseas.

Initial results from the trials show that the rust fungus is definitely having an effect on the pom-pom weed. During the chemical control of the pom-pom weed the rust fungus was seen to be present in most areas where the pom-pom weed occurred as long as there was enough moisture present. Attempts to isolate the rust fungus and identify it will be done next year.

All the efforts to control the pom-pom weed over the last few years are definitely paying dividends. The badly infested areas are showing less infestation although more isolated pockets were observed. These should be countered by the multi-pronged approach. The results of this seasons work are difficult to judge as we will have to wait until the next season. With the experience gained this year Working for Water have indicated they would like to increase the number of teams working on Welgevonden in order to complete spraying here sooner so as to be able to assist other landowners around Welgevonden who have requested their assistance.