Zimbabwe is currently facing a devastating outbreak of Chilo worm, a species of moth, which is threatening the 2016/17 summer cropping season. The exact species is yet to be confirmed and is also being referred to as the fall army worm.
According to the Zimbabwe Broadcasting Corporation, the pest was first reported by farmers in the Matabeleland provinces and has spread to other provinces and areas such as Glendale, Shamva, Chegutu and Banket.
Zimbabwe has already had to cope with two consecutive years of below average harvests which last year was largely due to drought cause by El Niño. According to the FAO, total cereal production is already estimated to be 27% down from the drought-reduced 2015 harvest. This recent outbreak could make the country’s maize production target of the Government’s Command Agriculture Programme (two million tonnes of maize) very hard to achieve.
Chilo worm grows to about 2.5 cm long, is brown or yellow with stripes and spots along the body. It is a destructive pest which attacks cereal plants such as maize, sorghum, sugarcane. It tends to affect crops which have passed the three-leaf stage.
In its larval form, it feeds on the growing points of young shoots and tunnels into stems and maize cobs, significantly reducing crop yield. Dead central leaves form a characteristic ‘dead-heart’ and leaves display irregular scars, holes and windows. Powdery brown frass can also be seen on the leaves, particularly on the central whorl.
Controlling the pest using pesticides has proven difficult so far, since the worm appears to be resistant to some usual chemicals used for stem borers. Non-chemical control options include rotations with non-grass crops such as legumes, in order to break the life-cycle of the pest, and the removal of hosts such as grassy weeds.
Global warming is possibly contributing towards the high Chilo worm population. Warmer winters lead to reduced winter-killing of pests, so populations can grow quickly in the summer months. Warming temperatures also allow pests to emerge earlier, often when predators have not yet reached high enough population levels to limit pest populations. Furthermore, early emergence can coincide with young, vulnerable crop growth and pest growth rates can be faster.
CABI, 2016. Chilo partellus (spotted stem borer). In: Invasive Species Compendium. Wallingford, UK: CAB International. http://www.cabi.org/isc/datasheet/12859
Chronical, 2016. Chilo worm threatens crop yields. Zimbabwe: Chronical. http://www.chronicle.co.zw/chilo-worm-threatens-crop-yields/
FAO, 2016. GIEWS – Global Information and Early Warning System. Italy: FAO. http://www.fao.org/giews/countrybrief/country.jsp?code=ZWE
The Herald, 2016. The year of the Chilo worm. Zimbabwe: The Herald. http://www.herald.co.zw/the-year-of-the-chilo-worm/
The Sunday News, 2016. Govt on high alert against further worm outbreaks. Zimbabwe: Zimpapers. http://www.sundaynews.co.zw/govt-on-high-alert-against-further-worm-outbreaks/
Zimbabwe Broadcasting Corporation, 2016. Chilo worm outbreak threatens agric season. Zimbabwe: Zimbabwe Broadcasting Corporation. http://www.zbc.co.zw/index.php/news-categories/top-stories/71670-chilo-worm-outbreak-threatens-agric-season