This post is written by Sara Hendery, Communications Coordinator for the Feed the Future Innovation Lab for Integrated Pest Management

From afar, an expansive field of Parthenium hysterophorus appears as a lush and billowy sea of white and green. Up close, however, the noxious weed reduces crop yields, increases agricultural labor burdens, causes human health issues, and significantly threatens livestock well-being.

When livestock graze on parthenium, invasive in Africa, Asia, and Australia, both milk and meat are tainted. The weed leads animals to contract a number of conditions such as lesions, mouth ulcers, and contact dermatitis. In extreme cases, if livestock consume an excessive amount of parthenium, reduced fertility or even death may result, and cattle from parthenium-invaded areas have lower market value.

Parthenium’s adverse impact on livestock is one of several reasons why the Feed the Future Innovation Lab for Integrated Pest Management at Virginia Tech aids management of the weed in East Africa. Utilizing classical biological control, the team releases two host-specific natural enemies native to Central and South America—the leaf-feeding beetle Zygogramma bicolorata and the stem-boring weevil Listronotus setosipennis—approved for release to manage the weed in several East African countries and South Africa, following their earlier successful use in Australia.

“In Ethiopian local markets, milk tainted by consumption of parthenium is sold at a lower price than untainted milk,” said Wondi Mersie, leader of the parthenium project in East Africa. “In parthenium-infested areas, people taste the milk before they purchase it. If the milk comes from a cow that grazed on parthenium it will have a bitter taste and either its price is reduced or it may not get a buyer. This primarily affects women because they are the sellers of milk in the market or buy it for their infants. Parthenium leaves and flowers contain many compounds that persist in the body. At present, the impact of these compounds on the overall health of children including their immune system is not known.”

In a study conducted by the Women and Gender in International Development team at Virginia Tech, Ethiopian participants reported that cattle feeding in parthenium-invaded lands lowered the price of milk by 50 percent and market value of cattle by 40 percent. Farmers spent half or more of the money from milk sales on feed for their cows to curtail them from eating parthenium, often gaining zero profit from milk production.

Study participants also confirmed that the unpalatable taste and smell of milk produced by cows that feed on parthenium is a major detriment to sales to larger customers outside of the market. If selling milk to a hotel or major company, parthenium-tainted milk would not be accepted or would not be bought a second time. Additionally, children often reject parthenium-tainted milk due to its bitter taste.

But for many small-holder farmers, parthenium-tainted milk is the only available option.

Lorraine Strathie, a South African researcher on the parthenium project, said that the introduction, successful establishment, and widespread distribution of host-specific natural enemies against this weed, known as one of the most destructive invasive weeds in the world, can ultimately bring about significant long-term, sustainable control, and help restore livestock health in invaded areas. This weed was successfully controlled over time in the rangelands of Queensland, Australia, using eleven introduced natural enemies, resulting in considerable, cumulative economic benefits.

“Parthenium is a serious economic concern for agricultural production, conservation of biodiversity, and human and animal health,” Strathie said. “The use of natural enemies against parthenium is self-perpetuating, cost effective, and can be integrated with other control methods. It is a critical management option for farmers burdened by high labor rates and food insecurity.”   

In September of this year, both Zygogramma bicolorata and Listronotus setosipennis had caused dramatic, localized extensive defoliation and stem damage to parthenium infestations where they had been released in southern Ethiopia, resulting in more suitable vegetation replacing the weed. Continued, concerted efforts to mass-rear and distribute these biocontrol agents to as many suitable sites in the country and East African region are needed and require national government support, so that benefits can be more fully realized for the millions of farmers affected in the entire invaded distribution.