Striga hermonthica or the Purple Witchweed is the single most important cause of poor maize yields, particularly in western Kenya, eliminating 60 to 100 per cent of cereal crops.
This is because the parasitic plant germinates quickly, and is easily dispersed. Its seeds also withstand extreme conditions and lie dormant in the soil until a farmer grows cereals such as maize or sorghum. It’s seeds can also remain dormant and retain viability for years.
“It is a pernicious broad-leaf weed because even burning it doesn’t eradicate it. Its growth pattern also makes it difficult to arrest as it often emerges at the third week right after weeding,” said Nickson Wafula, a government extension officer.
The cost of controlling it, he explained, compounds with time as every plant can produce up to 50,000 seeds.
Controlling Striga
Most non-selective herbicides are not suited for use against striga as it attarches itself to the cereal plant which can scorch the crop.
Glyphosates were an option for its control but their use is being increasingly discouraged and restricted due to fears of carcinogenicity.
“In recent times, I have seen success in the use of atrazine-based pesticides sprayed on crops slightly early post-emergence at the two to three-leaf stage,” informed Wafula.
Alternatives
An emergent bioherbicide, Kichawi Kill, introduced by Toothpick Company, has been shown to increase yields over 50 per cent in previously affected crops.
Its adoption remains limited though as it is still at a concept stage.
“Though effective, I am not seeing as many farmers as we’d like adopting the push-pull method of weed and pesticide control at scale,” the extension workers who traverses 12 counties in Kenya informed. This is partly attributable to most farmers not deriving any immidiate monetary value from desmodium– a key crop for the strategy’s success.