However, secretions from the trees' roots stimulate the germination of the witchweed seeds before crop planting.

ECONOMIST: A new twist on an old idea is improving farm yields in Africa

With nothing to feed on, the witchweed then dies, leaving the field clear for the next sowing season.

ECONOMIST: A new twist on an old idea is improving farm yields in Africa

Crops are often damaged by witchweed, a widespread crop parasite that usually germinates after a cereal crop is planted.

ECONOMIST: A new twist on an old idea is improving farm yields in Africa