The Sunday Mail
Agriculture
Peter Gambara
Fall Armyworm (FAW), which has devastated large maize crops in recent years, can be a real menace and may cause major yield losses if farmers fail to properly scout and control the pest. In this article, I will discuss important aspects of the fall armyworm’s life cycle, how to scout it and measures that can be used to control the pest.
Also called Spodoptera frugiperda, FAW was first spotted in Zimbabwe during the 2016/17 summer season. It can attack over 80 plant species, but has a preference for plants in the grass family, including maize, sorghum, millet, rice, wheat and sugarcane. It can attack cowpeas, groundnuts, potatoes, soyabeans and cotton.
Fall armyworm life cycle
In order to be able to properly scout and identify the pest, it is best for farmers to understand the fall armyworm life cycle. The FAW can have several generations per year and its moth can fly up to 100km per night, and that explains why the pest can spread so fast locally.
The lifecycle of the FAW includes the egg, six growth stages of caterpillar, pupa and moth. The eggs are usually laid on the underside of the leaves. The female moth can lay six to 20 egg masses in her life cycle, with each mass having 100-300 eggs. These eggs can hatch in three to-five days.
As farmers prepare to go on a Christmas break, they should realise that in the seven days between Christmas Day and New Year’s Day, an armyworm, which has already invaded the field, can lay thousands of eggs that can hatch and cause extensive damage to the crop. The eggs hatch into caterpillars, which last for 14-28 days, feeding on the undersides of the leaves. This feeding normally results in windows on the leaves. These caterpillars mostly feed at night and hide during the day. The activity of the caterpillars is evident from the frass (poo) that is seen from the whorl.
It is important to mention that the caterpillars’ favourite feeding spot is the whorl or funnel of the maize, where they feed on fresh and tender maize leaves. The curled leaves provide protection to the caterpillars.
The caterpillar will go through six developmental in star stages, where it feeds and sheds its outer case six times in order to accommodate the larger size as it grows bigger, just like a snake shades its outer skin. A full-grown caterpillar will drop to the ground, where it burrows some two to eight centimetres into the ground before pupating into an oval shape, 20-30cm long. In eight to nine days, the adult moth will emerge from the cocoon to restart the life cycle.
Recovery of a damaged crop
The damage caused to maize by the caterpillars can be as high as 58 percent of crop yield. The damage can be in the form of leaf damage, tassel damage, silk damage or grain damage. It is common to see widely spaced grain or rotten grain on maize cobs at harvest. By damaging the silk, which receives the pollen from the tassels, grain development is inhibited. Crop management should therefore be targeted at ensuring that pollination is not affected by the caterpillars, through regular scouting and spraying where necessary. Spraying should commence once scouting indicates that at least 20 to 25 percent of the plants show signs of damage or infestation.
The Plant Protection Research Institute under the Department of Research and Specialist Services in the Ministry of Lands, Agriculture, Water and Rural Resettlement can provide training to farmers’ groups wishing to be trained on: how to identify the FAW; differentiate the FAW from the African Armyworm and stalk borer; recognise the different stages of the pest; and provide the different chemicals that can be used to control FAW.
A crop with damaged leaves and a lot of holes can actually recover significantly from FAW damage. However, it is important to stress that the nutrition of the crop is essential; as a well-fertilised, healthy-looking crop is more able to compensate for foliar damage than a yellowish and stunted crop. Heavy rains tend to wash the caterpillars off the leaves and drown those in the whorl as the water accumulates in the funnel of the maize. Some farmers have also tried flooding the whorls with all kinds of solutions to drown the caterpillars, including Surf or Omo solutions.
Managing a damaged crop
When farmers see evidence of fall armyworm attack, most will rush to the chemical shop to ask for the most effective/deadliest chemical that can kill the caterpillars. Some of the chemicals that have been tested and approved by the Plant Protection Institute in Zimbabwe include Blast Super, Super Dash, Nemesis, Emamectin Benzoate, Lambda (Karate), Ecoterex 0.5GR, Belt 480SC, Belt Expert, Ampligo, Coragen 20SC, Steward 150EC, Missile 150SC, Blanket 150SC, Indoxacarb 150SC, Vantex 60CS and Carbaryl 85 percent WP.
During spraying, farmers should make sure that the chemical gets into the whorl or maize funnel. Use of a boom sprayer when the crop has reached or passed knee height might not be very useful. It is better to use knapsack sprayers, where workers will direct the chemical into the funnel so that the chemical gets to the caterpillars.
A daily task (Mugwazo) for a worker is to spray 2 x 200 litre drums or two hectares, hence a farmer with 100 hectares can still spray his crop in five days using 10 workers with knapsack sprayers. While chemical control is the most logical thing to do, it should be emphasised that the use of chemicals can have adverse effects on other insects and pests that are beneficial to agriculture like bees, spiders and fish in the lakes.
Bees facilitate pollination on most crops. Most farmers do not provide enough protective clothing to their workers, and this tends to expose them to the chemical drift during spraying and through contact from sprayed plants. Other measures that farmers can incorporate in their management styles to reduce FAW attack include shunning late planting. The late-planted crop (December and January) tends to get attacked more than the November or October planted crop. Farmers should avoid staggering their crops if planting in the same area. A staggered crop tends to continue providing the favoured food for the FAW and one crop breeds the FAW for the next crop. The pest will be very grateful for the continued environment on the farm.
Push and pull strategies
In a push strategy, farmers can use a combination of legumes to intercrop with maize. Crops like beans, cowpeas or cassava will make it difficult for the FAW to locate the maize, making it more likely to skip that field. However, this is only possible with small scale farmers and will be difficult to implement in large tracks of maize.
In a pull strategy, farmers can grow weeds that produce a lot of flowers around the maize fields or in-between maize fields. The nectar produced by the flowers will attract predators of the FAW. Farmers can also grow Napier grass around the maize fields. The Napier grass, will attract the FAW to lay its eggs on it. However, it does not allow the caterpillars to develop on it due to its poor nutrition, therefore very few caterpillars will survive.
Scouting and mechanical control
Farmers can scout their fields on a regular basis to identify and crush egg masses and young caterpillars. Fall armyworm eggs are very small and difficult to see with the naked eye. It is therefore essential that workers are trained on what to look for and what the eggs look like. Some farmers also put large grained sand particles, ash, sawdust or dirt into the whorls of plants in order to suffocate or cause damage to the caterpillars as they get cut by the sharp edges of the grains. Other farmers have used lime, salt, oil and soaps to control FAW. Lime, soap and ash are alkaline and likely to drain the caterpillars of any juice they have.
Biological control
Ants (Masvosve) are natural predators of the FAW caterpillars and pouring some sugary liquids into the maize funnel will attract the ants and wasps to the whorls to feed on the caterpillars. Farmers in some African countries have collected the caterpillars as relish-so those daring among us can also try this.
Many farmers only realise when it is too late that they have lost a substantial part of their crop to FAW. Once a maize crop has germinated, it immediately becomes susceptible to FAW and farmers should commence scouting on a regular basis. While you celebrate Christmas and New Year holidays, please make sure you still have someone who will scout and give you a regular report on possible FAW infestation in your maize crop.
Wish you all a Merry Christmas and prosperous New Year.
