Article prepared by Ms Bridget O’Connor of the Kasisi Agricultural Training Centre, a member of ZAAB
There has been debate among scientists, extension staff and farmers about the invasive worm that is attacking Zambian maize this year. It is not like anything seen before in Zambia. Stalk borer? African armyworm? Bollworm?
It is now confirmed by many scientific quarters that it is the Fall Armyworm (Spodoptera frugiperda), an alien invasive moth native to tropical and subtropical regions of the Americas. According to Dr Georg Goergen of IITA in Benin, it was detected for the first time on the African continent last year in January 2016 and caused devastation in several West African countries. This year S. frugiperda is also in Burundi, Zambia, Zimbabwe and Malawi. Its name “Fall” comes from the fact that it cannot survive the cold winters in North America and the moths return to tropical habitat on storm winds in the “autumn”, which Americans call “fall”.
The S. frugiperda is known to have a remarkable dispersal capacity and is observed to migrate every year from its endemic area in the warmer parts of Central and South America over more than 2000km crossing the USA up to Canada in the North and reaching Argentina and Chile in the South. How it came to West Africa last year is not yet known. Amongst speculation is that the introduction is accidental, that easy air travel has increased phytosanitary risk, that climate change variations in high-altitude wind streams may have favoured the shift from one continent to another.
The Fall Armyworm prefers to feed on graminaceous plants (including maize, millet, sorghum, rice, wheat and sugar cane) but can also attack crops like cowpea, groundnuts, potato, soyabean and cotton. More than 80 host plants have been recorded and there can be host specific variations of S. frugiperda. However the larva (caterpillar) always has a distinctive upside-down Y marked on its face.
In climatic regions allowing constant generations such as Brazil, the third largest maize producer in the world, S. frugiperda is considered the most important pest on this crop and causes damage estimated at more than $600m annually. The economic consequences may not be limited to its direct effects on agricultural production but also has the potential to adversely affect access to foreign markets. In recent years, quarantine interceptions have significantly increased at European entry points and, in 2015, S. frugiperda was reassessed and ranked as A1 quarantine pest on the European and Mediterranean list.
Dr Georgen warns that S. frugiperda is likely to become more damaging to maize than other species of the same genus occurring in Africa because: a) S. frugiperda also actively feeds during the daytime, b) adult female moths lay their eggs directly on the maize plants, c) older larvae become cannibalistic tolerating only few congeners on the same host plant, d) the mandibles have serrated cutting edges easing feeding on plants with high silica content. Damage on maize may be observed on all plant parts depending on development stage of the larvae. On grown maize plants larvae also attack reproductive organs feeding on tassels or boring into the cobs. Following hatching the neonates usually bore into the host plant and develop under protected conditions. Hence control with contact insecticides is often ineffective although is still the most widely practiced management measure.
According to Dr Goergen of IITA, long use of synthetic pesticides and the use of the Cry1F GM (genetically modified) maize in the Americas has led to the emergence of resistant populations of this pest. According to Dr Gilson Chipabika of ZARI, in Zambia it seems that this population is not responding to most insecticides especially the fourth and fifth instars. Some crops in Zambia have been scorched by the chemicals and many farmers do not have the correct protective clothing to apply strong chemicals. Some farmer families complain of the strong smell and have experienced respiration problems. Many farmers grow maize close to the homestead. Apart from the health problems that chemicals can cause, they also negatively impact on non-target organisms such as beneficial insects (both pest predators and pollinators), birds, livestock and other wildlife. A number of predators can be observed on affected plants here in Chongwe where chemicals have not been used.
Farmers who practice agroecological/organic methods with a lot of diversity and legume intercrops have had less attack than conventional farmers. Some have had no attack at all, some only had a small amount of attack on the early planted maize. On these farms there has already been build-up of a wide diversity of predators which are able to control the armyworm. When African armyworm attacked 4 years ago one of these farmers found that whereas his neighbours on all sides had huge problems, he only had a bit of damage on his boundaries when the armyworms had finished all the grass on the other side. Some farmers are putting sandy soil into the maize funnels which is abrasive to the skin of the fall armyworm and can kill it. It is recommended by these farmers that there be regular scouting and application of sand at first sight of damage. Even better would be to put sand in every funnel of maize at knee height as is recommended at KATC against the bollworm and now it will be even more important against the Fall Armyworm. Some farmers find applying ash or detergent powder is successful. Bt (Bacillus thuringiensis) is a microbial pesticide permitted in organic farming and effective against the Fall Armyworm. Liquid Bt Looper Kill is available in the country as well as a powder Bt Halt. Neem oil or crushed Neem seed extract is also effective.
According to Dr. Goergen, in its native range numerous parasitic wasps, flies and other predators have been recorded as natural enemies of the fall armyworm. And that some species, in particular egg and larval parasitoids, are frequently introduced, resulting in noticeable levels of control. We would like to know how the ZARI programme to breed up such pest predators for release is faring.
Dr Goergen also reports in the IAPPS newsletter of October 2016 that there has been detection of promising isolates of nucleopolyhedroviruses (NPV) for the Fall armyworm. These are natural viral diseases specific to the pest and one has already been produced for the African armyworm, SpexNPV. However, according to Professor Ken Wilson, the process of registration for use in Zambia of these biological pesticides has unfortunately not yet started. According to Dr Goergen the development of biopesticides including the use of endophytic entomopathogenic fungi is in its infancy and needs increasing attention for providing viable alternatives to conventional insecticides. He says there is an urgent need for developing ecologically sustainable, economically profitable and socially acceptable IPM programs to fight the fall armyworm in Africa.
According to a University of Florida publication, the most important cultural practice, employed widely in southern states of USA, is early planting and/or early maturing varieties. Early harvest allows many maize ears to escape the higher armyworm densities that develop later in the season (Mitchell 1978). Reduced tillage seems to have little effect on fall armyworm populations (All 1988), although delayed invasion by moths of fields with extensive crop residue has been observed, thus delaying and reducing the need for chemical suppression (Roberts and All 1993).
Prof Wilson suggests that to effectively and sustainably assure food security in the midst of African armyworm migrations, a robust, country-wide surveillance and early warning system using pheromone traps that attract male armyworm moths by using the artificial scent of mating female armyworms is needed so that farmers are alerted in good time about impending outbreaks. These are used in combination with local weather reports to forecast armyworm outbreaks at a local level – so called ‘community based armyworm forecasting’. The same traps that are used to check for African armyworm could also be used for Fall armyworm – you just need to change the pheromone septum. Investment in an extensive network of pheromone traps in Zambia could pay dividends and be cost-effective. Knowing if there will be an invasion of a pest will allow the country to be prepared for controlling the pest. Also correct identification of the moth caught in these pheromone traps is crucial.
There is a regional organization ‘Red Locust’ that has the mandate for monitoring African armyworm and giving early warning but the warnings have not been forthcoming.
- Setting up effective early warning system
- Correct identification of the moths caught in the pheromone traps
- Start the process now for entry approval of viral controls specific for the African and Fall armyworms
- Research biological control methods of Fall Armyworm, e.g. sand in funnel of maize, greater cropping diversity, sunhemp and other legume intercropping, push-pull technologies.
Information for this article has been collected from:
Professor Ken Wilson, Lancaster University (working on African armyworm for the past 25 years) <firstname.lastname@example.org>
Donald Zulu, researcher/lecturer at Copperbelt University (currently pursuing his PhD at the University of Reading, UK) email@example.com
Dr Gilson Chipabika, ZARI firstname.lastname@example.org
Sebastian Scott, Agricultural Advisor, Grassroots Trust email@example.com
Dr. Georg Goergen, International Institute of Tropical Agriculture (IITA), Biodiversity Resource Center, Cotonou, Benin firstname.lastname@example.org. (IAPPS newsletter October 2016.)
Mrs Gloria Musowa Mwanza, Chongwe Organic Producers & Processors Association (CHOPPA)
Mr Vincent Choongo and Mr Deadricks Hadunka, Kasisi Agricultural Training Centre email@example.com
Sand technology – Mr Moses Mulenga and Mr Kelly Kalolo, Farmers in Chinkuli, Chongwe
University of Florida http://entnemdept.ufl.edu/creatures/field/fall_armyworm.htm