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Parasitic Striga weed invading East African crops



February 13, 2013
Striga invading maize crop

Photo courtesy icipe – African Insect Science for Food & Health

A grim warning of global warming. African maize crops in cooler, upland regions are now being invaded by Striga, a parasitic weed. It usually thrives in the warm, humid tropics of sub-Saharan Africa but is now spreading into elevated regions over 1500m as their soils become warmer, affecting 4 million hectares of maize crops which sustain 100 million people.

Striga or witchweed, attaches itself at the root base, starving the host plant for nutrients. Affected maize crops reach barely 50-90cm high and have negligible yield. Many East African farmers are having to abandon their maize and cow pea crops for cassava, or use ‘break cropping’ where cassava is grown one year so there’s no host plant. But Striga gas a huge seed output with long viability so these control methods are only partly effective.

Mel Oluoch, head of the Integrated Striga Management in Africa program says Striga is a stubborn weed that can only be contained by a combination of technologies and control measures over a period of no less than ten years.

Although maize seed can be coated with chemicals which kill off the weed at germination, the coated seed remains far too expensive for most farmers.

ICEPE promotes a very interesting farming system called ‘Push-Pull‘ which advocates a form of cultural control. It combines crops which ‘pull’ insect pests towards them, but then prevent them reproducing, with ‘push’ crops that actively repel invasive species. Surrounding the crops with pull plants attract insects away from the valuable plants, and interspersing crop rows with push plants repels insects from using crop plants as hosts. Their trials found that using silverleaf, Desmodium uncinatum, between maize rows, smothers the striga and also repels stem borer. As it’s a legume, it also improves soil fertility.

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