Striga can be found in most
sub-Saharan African countries
Striga, also known as witchweed, attacks cereal crops as a parasitic weed. This weed affects 300 million people and 40 million farms. Because of the lack of witchweed solutions, countries that did not have any infestation 25 years ago are now facing large amounts of crop losses.
There are various varieties of Striga, but the most common is S. hermonthica. S. hermonthica has had a severe impact on the agricultural industry. It is estimated that $7-10 billion of loss occurs every year because of Striga.
In Western Kenya, where our pilot project is currently operating, Striga has infected 217,000 ha of crop land. Roughly 30% of all land in Western Kenya is infested with Striga, causing $60 million of crop damage.
A map from Evans Atera showing the persistence of striga in Western Kenya
THE PERSISTENCE OF STRIGA
Striga is able survive drought and thrive in poor soil conditions. Persistent cereal mono-cropping, or growing the same staple crops for every season, depletes the soil of nutrients. As climate change is demonstrated in intensified heats and longer droughts that challenge maize production, Striga survives. Each Striga plant can drop 50,000-500,000 tiny seeds into the soil each season - and these can stay dormant for decades, only germinating when triggered by hormones put off by the target crop.
OTHER SOLUTIONS TO STRIGA
Striga attaches to the root of the staple crop. Damage to the staple crop occurs before it breaks the soil, so weeding is ineffective.
PUSH AND PULL CROPS
Specific crops that are known to attract or repel weeds can be planted strategically around a field. The adoption rate of this practice by farmers is low as it requires extra labor and expensive seeds.
Rotating different crops through different seasons can help add nutrients to the soil that helps maize grow. Unfortunately, Striga seeds will still sit in the soil for up to 50 years, therefore when cereal crops are planted again, the Striga will return.
STRIGA RESISTANT SEEDS
Maize and sorghum seeds have been bred for Striga resistance. However, they don't appear to be fully restoring crop yield (around 20% increase in their published trials) . Aditionally, these seeds do not address the bank of Striga seeds in the soil and will have to be used every season. We recommend farmers invest in the best seeds they can afford. But, we also acknowledge that price and access are critical limiting factors for farmers already burdened with severe crop loss.
IR Maize: CHEMICAL HERBICIDE
Imazapyr-resistant Striga was an important development in Striga management. However, the chemical application hasn't adapted well for small acreage farming. Due to toxicity, the chemically-coated seeds are sold with gloves. Additionally, while the maize may do well, the imazapyr will kill other non-weeds. We conducted trials in 2019 and had a very low germination rate with our IR Maize rows...potentially because the seeds were six months old and had aa limited shelf life. Like other methods, IR Maize does not deplete the Striga seed bank in the soil and therefore, the product will have to be used every season. In general, while IR Maize trials have showed good results, there are low adoption rates with farmers because of the costs and environmental concerns.