🌿 Weed
ANX-WEED-0000260
Purple Witchweed
Striga hermonthica
Purple Witchweed (Striga hermonthica), an annual parasitic broadleaf weed of the Orobanchaceae family.
- Family
- Orobanchaceae
- Growth habit
- Parasitic broadleaf
- Life cycle
- Annual
- Invasive status
- Native parasitic weed, but a devastating agricultural pest across its range
- Native region
- Sub-Saharan Africa.
- Reproduction
- Seed - produces enormous numbers of dust-like seeds that can remain viable in soil for over a decade, germinating only in response to a host root's chemical signal.
Environment
Habitat & Growing Conditions
- Habitat
- Cereal fields, particularly in nitrogen-poor soils across the savanna zones of sub-Saharan Africa.
- Climate requirements
- Semi-arid to sub-humid tropics.
- Soil types
- Thrives especially in poor, nitrogen-depleted soils, where host crops are already stressed.
Impact
Crops Affected & Economic Impact
- Affected crops
- Sorghum, maize, pearl millet, rice, sugarcane - attaches to host roots underground before emerging
- Competition impact
- Most of the damage happens underground before the parasite even emerges - it can destroy 30-100% of a cereal crop, and is considered one of the biggest biological constraints on African food security.
- Economic impact
- Estimated to cause billions of dollars in cereal losses annually across Africa and affects the livelihoods of over 100 million people.
Management
Control Methods
- Control methods
- Resistant/tolerant crop varieties, delayed planting, intercropping with trap or catch crops (e.g. the 'push-pull' system using Desmodium), and improving soil fertility (Striga is worse in poor soils).
- Organic control
- Hand-pulling before the parasite flowers and sets seed (it must be pulled before flowering, since damage is already done by the time it emerges), soil fertility improvement, and push-pull intercropping.
- Chemical control
- Herbicide seed-coating on resistant maize varieties (imazapyr-resistant maize) is used in parts of East Africa; conventional post-emergent herbicides act too late since most damage is already done underground.