The rapidly growing ”false lemongrass” or Cymbopogon afronardus in Uganda smells of citrus fruit. It is refreshing with a lemony smell you would think, but it is something that cows turn up their noses at. So much so that they actually risk losing weight if their pastures are infected with the fragrant weed.

This is a problem in Uganda that scientists from the Faculty of Agricultural Sciences (DJF) at University of Aarhus are helping to do something about through Danida’s agricultural sector programme.

False lemongrass does not occur naturally in Uganda. The plant was introduced some time in the past but no one knows how it happened. After it reaches a certain size, the cattle will simply not eat it. It contains aromatic oils that give it a very strong smell that is displeasing to cattle.

When the cattle do not graze the plant, it will outcompete the other plants in the pasture and grow to its full size, which is about two metres. That makes it extremely difficult for the cattle to walk about and they actually risk losing weight in their search for food. The plant is very competitive and is the first plant that grows after a field has been burned.

Head of research unit Per Kudsk from the Department of Integrated Pest Management, DJF, is a leading expert on weed management. He says:

- Even in Uganda, where labour is relatively cheap, it is expensive to clear the fields of false lemongrass manually. Clearing one acre manually corresponds in cost to the price of a cow. That means we need to find other ways of doing it. A targeted use of herbicides would be better for controlling the weed and improved knowledge of the plant would make control of it easier and more efficient.

Back in the 1960s quite a bit of research on false lemongrass was carried out in Uganda, but that ended suddenly when Idi Amin threw all foreigners out of the country in the beginning of the 1970s. Now research has been taken up again and this is why DJF makes its appearance on the scene.

Per Kudsk has gathered all available literature on the subject and written a review. This is just one of the initiatives that scientists from the Danish agricultural faculty are taking to help the Ugandan farmers in their struggle against false lemongrass.

- We advise and support the work being done with regard to setting up experiments, optimising and comparing various weed control strategies, acquiring materials, helping prepare project applications, and publishing articles, explains Per Kudsk. He can list several subjects that would be relevant for the scientists in Uganda to address.

- It is possible that the plant’s ability to outcompete other plants is because it secretes compounds that inhibit the growth of other plants. That is one of the things that will be investigated in a new project, which started in 2007. False lemongrass is a tussock grass but its seed biology is also an interesting study since the seeds are supposedly the reason why the plant is so widespread in the area in Uganda called the “cattle corridor”. We know that glyphosate is effective as an herbicide, but we do not know how long the effect lasts and how much the effect depends on what is done afterwards, such as fencing in the areas so that native plants are given time to re-establish, says Per Kudsk.

For more information please contact: Head of research unit Per Kudsk, Department of Integrated Pest Management, Faculty of Agricultural Sciences, University of Aarhus, telephone: +45 8999 3582, e-mail: Per.Kudsk@agrsci.dk

Text: Janne Hansen