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 established 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.

“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,” said CABI Chief Scientist, Dr. Matthew Cock.

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 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.

“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,” says Dr. Matthew Cock.

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.

“This invasive species is now a serious pest spreading quickly in tropical Africa and with the potential to spread to Asia,” continues Dr. Matthew Cock. “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.

Photo by: CABI