Intercropping to beat witchweed
Striga, or witchweed, is the most serious weed of maize and sorghum crops in sub-Saharan Africa. Attaching itself to plant roots, harvests are doomed even before farmers realise the weed is in their crop. But intercropping with a forage legume, silver leaf (Desmodium uncinatum) interferes with the weed's capacity to attach itself to the crop, and also repels stem borer pests. The Kilimo Trust, based in Uganda, is now working to make silver leaf seeds available to more farmers.
Pickett We have certainly found the major problems to be in Kenya, Uganda and Tanzania, but it is certainly expanding everywhere. It is the major problem, I think - together with stem borer, as a kind of insect damage - that is responsible for yield loss in sub-Saharan, savannah, cereal agriculture.
Laiser What are the losses?
Pickett The losses can be complete. You can lose an entire crop. But certainly you'll be down to the equivalent of under 1 tonne per hectare, whereas if you control it, you can get up to 2, 3, 4, 5 even 6 tonnes per hectare.
Laiser What does this weed cause?
Pickett What actually happens is the weed attacks the cereal plant before the weed actually breaks the surface of the ground and flowers. So once you see the flowers, the purple flowers, then it is too late. The plant has already attached itself to the cereal plant and it's already started to steal the water and the nutrients from the cereal plant.
Laiser You have found a plant that can stop witchweed, is it?
Pickett That's correct. What we were doing is we were using an intercropping technique, where we grow plants between the maize or the sorghum, to really repel or frighten away the stem borer moths, the larvae of which were boring into the stems and causing damage. The farmers that we work with wanted us to use a legume; what they actually wanted was an edible legume, because that is what they normally intercrop with. We couldn't find an edible legume that would frighten away the stem borer moths, but we did find a forage legume, a cattle forage legume. It is called locally silver leaf. Desmodium uncinatum is the scientific name. And that was very good at frightening away the moths, but by pure chance, we noticed that it was also controlling striga, the witchweed. And we have now found that there is a very clever way that it does that, by interfering with the way that this parasitic plant, the witchweed, attaches itself to the host plant. It interferes with that process so well that you can, within a couple of seasons, see a fantastic increase in yield. And it destroys the seed bank for the parasite, and you start to lose the parasite altogether.
Laiser Wow, that is so great. So what next?
Pickett Well the work is being funded by Kilimo, a charitable organisation based in Kampala, Uganda, and they are hoping to collaborate, or they are collaborating with the national programmes in Tanzania, Kenya and Uganda, to have a very much bigger programme, so that many, many more farmers can come into contact with this approach, so that they can get the seed for the intercrop, so that they can start to do it themselves.
Laiser What advice do you have for farmers with a witchweed problem?
Pickett To get some seed for silver leaf and start to grow it in their field, in between the rows of maize. But in fact the best way is to establish the Desmodium plants from seed, and once they have just got established, then sow the maize between the Desmodium plants, so the maize can grow through the Desmodium, protected from the witchweed.
Laiser Do you think Desmodium is available, can be found in areas where they plant maize?
Pickett It is not normally available. Part of the Kilimo project is to make it more available. The idea is that once farmers can take part in the programme, they can generate seed which can repay the initial cost. Because once it is established, it is a perennial. And so all you have to do is, when the maize is harvested, you let it [the Desmodium] flower, you gather the seed, and then you cut it down, use the cuttings for cattle food or dairy goat food, and make a hoe cutting through the Desmodium for the next season's maize.
Laiser Wow, that's all. What is your last word, anything you would like to say?
Pickett I think what I would like to say to the farmers of East Africa who have a problem with stem borers, and particularly with the witchweed, that there is help coming, and it really does work very well. Providing they look after the Desmodium plants that control the insects and the parasitic plant, then it will work well. I know that the farmers can do intercropping really so well that they must be able to benefit by this technology. End of track.
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