Scientists discover new crop-destroying Armyworm is now “spreading rapidly” in Africa

New research announced today by scientists at CABI confirms that a recently introduced crop-destroying armyworm caterpillar is now spreading rapidly across Mainland Africa and could spread to tropical Asia and the Mediterranean in the next few years, becoming a major threat to agricultural trade worldwide.

Fall armyworm is native to North and South America and can devastate maize production, the staple food crop that is essential for food security in large areas of Africa. It destroys young plants, attacking their growing points and burrowing into the cobs.

An indigenous pest in the Americas, it has not previously been established outside the region. In the past year, it was found in parts of West Africa for the first time and now a CABI-led investigation has confirmed it to be present in Ghana. It can be expected to spread to the limits of suitable African habitat within a few years. 

Plant doctors working in CABI’s Plantwise plant clinics, which work to help farmers lose less of what they grow, have found evidence of two species of fall armyworm in Ghana for the first time. This has been confirmed by DNA analysis undertaken at CABI’s molecular laboratory in Egham, Surrey (UK). In Africa, researchers are working to understand how it got there, how it spreads, and how farmers can control it in an environmentally friendly way.

CABI Chief Scientist, Dr. Matthew Cock said, “We are now able to confirm that the fall armyworm is spreading very rapidly outside the Americas, and it can be expected to spread to the limits of suitable African habitat within just a few years. It likely travelled to Africa as adults or egg masses on direct commercial flights and has since been spread within Africa by its own strong flight ability and carried as a contaminant on crop produce.”

Known as the fall armyworm because it migrates into temperate North America in Autumn (fall), this pest has long been a problem throughout tropical America, damaging vital crops. It mostly affects maize (corn) but it has been recorded eating more than 100 different plant species, causing major damage to economically important cultivated grass crops such as maize, rice, sorghum and sugarcane as well as other crops including cabbage, beet, peanut, soybean, alfalfa, onion, cotton, pasture grasses, millet, tomato, potato and cotton.

Earlier this month, Reuters reported that a plague of suspected armyworms destroyed 2000 hectares of crop fields in Malawi and was spreading at alarming rates. These outbreaks can cause devastating losses and have resulted in a mounting debt crisis amongst many farmers in affected areas.

Following the first signs of a potential problem in Ghana in 2016, noted by plant clinic doctors, the CABI-led Plantwise initiative worked with the Plant Protection and Regulatory Services Directorate of the Ministry of Food and Agriculture, Ghana, to investigate the identity of the organism responsible and to determine if it was the first instance of fall armyworm being present in Ghana.

Damage to maize crops was investigated at three different survey areas within Ghana and the caterpillars associated with the damage were photographed, collected, and sent to the CABI laboratory in Egham, UK for analysis. Once samples are received in the lab, a small portion of each caterpillar is removed for molecular testing. DNA is isolated from the cells, and a specific gene is amplified, sequenced, then compared against authenticated ‘barcode’ sequences for definitive identification.

CABI Chief Scientist, Dr. Matthew Cock said, “The analysis of our collections from three different regions in Ghana has shown that both species or strains of the fall armyworm are widespread attacking maize. This is the first time it has been shown that both species or strains are established on mainland Africa. Following earlier reports from Nigeria, Togo and Benin, this shows they are clearly spreading very rapidly. Fall armyworm can be expected to spread to the limits of suitable African habitat within a few years.” 

Urgent action is now needed to help farmers and researchers working in affected areas to accurately identify and work out the best strategies to control this pest. He continued, “This invasive species is now a serious pest spreading quickly in tropical Africa and with the potential to spread to Asia. Urgent action will be needed to prevent devastating loses to crops and farmers’ livelihoods. CABI will support national extension services to help farmers identify the different species quickly and accurately, and conduct studies to work out the best way to control it – for example biological controls which reduce the need for insecticide.”

Farmers in the Americas have learnt to live with Fall armyworm, but often rely on chemical control to deal with the pest, despite evidence of limited results. CABI will use the lessons to be learned from the American experience and, through the Plantwise programme, work with extension staff to inform and educate African farmers on the best “Integrated Pest Management” strategies – a mix of biological and cultural controls – to produce greater success and reduce environmental impact.

Ag. Director, PPRSD, Ebenezer Aboagye said, “Initially farmers thought it was maize stem borer, Busseola fusca, and therefore did not pay much attention to its control until they realized the damage was unusual. They later resorted to the use of different insecticides without success.”

Dr. Matthew Cock explained, “Biological control for fall armyworm will need to be studied as the potential for Africa is not well understood yet. It may take several years to identify and test a suitable biological control for this pest in Africa so urgent work is needed right now. In the meantime, we will need to support national programmes to encourage the best types of pest control, and not resort to indiscriminate use of insecticides which are harmful to the environment and have limited success.”

“The African maize-growing countries may plan for this by preparing alerts for extension services and researchers, and assessing advice on the best management options for farmers.  In Ghana, Plant Protection and Regulatory Services Directorate (PPRSD) through the Plantwise program is developing photo sheets to facilitate identification and factsheets and pest management decision guides to inform extension staff are being prepared, which can be adapted across Africa.  Such information aids will be disseminated in hard copy and through the Plantwise knowledge bank, and awareness-raising activities to inform farmers are ongoing.”