1. Cultural practices
• Intercropping with legumes:
According to research, FAW infestations have been reduced by 20-30 per cent on maize intercropped with beans compared to maize alone.
• Early planting:
Avoidance of offseason agriculture (moths are said to be attracted to extremely late planted/late maturing maize).
Early detection through scouting crops every two days starting
from the current wind direction, checking borders and centres of crop fields.
Restrict movement of infested plant materials from areas where the pest has not been reported.
• Using habitat manipulation techniques:
Use trap crops, landscaping and companion plantings to enhance activity of biological control agents
Of caterpillars and egg masses. Killing one caterpillar prevents more than 1,500 and 2,000 new caterpillars after a period of less than four weeks. Tools should be designed to allow farmers to pluck the larvae out of plants and destroy eggs and larvae of the pest.
Adding sand to maize whorls where armyworms are feeding can help control them
2. Mechanical Control
Deep ploughing exposes the pupae to predators and solar heat.
• Pheromone traps:
These are used to monitor the presence of insect pests and to lure male moths to disrupt mating and to have them destroyed in designed devices, forest margins and shrub land. The chemicals in the leaves are called rotenone and classified by the World Health Organisation as a moderately hazardous or Class II pesticide.
The extracts of Tephrosia leaves can be used for the control of pests in the field, in storage or on domestic animals. Unlike most synthetic pesticides, it leaves no residues on crops because rotenone breaks down within 3-5 days after application.
3. Biological control
The first natural line of defence for the fall armyworm is biological control. This is because they have a lot of exotic predators that include wasps, flies, beetles, birds and rodents. Parasites and pathogenic fungi, bacteria or viruses that would kill or weaken the pest and seed treatment with beneficial soil microbes, which increase the ability of plants to fight off pests, are other measures against the worms that also help plants to adapt to other climate change stressors, including drought.
These are non-chemical, biological pesticides that can also be effective in the eradication of the fall armyworm. These are pesticides derived from natural diseases of insects, such as viruses, fungi and bacteria. In Tanzania, for example, an effective bio-pesticide has been developed against the African armyworm but it needs to go through several registration and commercialisation processes that are costly and time consuming.
Bio-pesticides tend to be effective against a much narrower range of species than chemicals, which is good for the environment.
But it means that they can only be used for a limited number of pests, often making them more expensive than chemicals.
A similar bio-pesticide has also been developed against the fall armyworm, but again this is not yet registered for use in Africa.
5. Transgenic materials:
In parts of their native range in the Americas, genetically-modified Bt maize has been grown to combat the fall armyworm. This may also be an option for South Africa and some other countries where GM crops are already grown. But many parts of Africa do not allow or welcome GM varieties. Interestingly, fall armyworm has also evolved resistance to some Bt toxins, with some evidence for crops resistance.
6. Chemical control
- Chemical pesticides can be effective against armyworms. However, resistance to many chemicals is an issue. Synthetic pyrethroids have been effective at controlling infestations, but according to CIMMYT; extensive use of synthetic insecticides in South America to control the pest has led to the development of resistance.
- Most of the insecticides used are Insect Growth Regulators (IGR). It is not known whether there is pesticide resistance in the fall armyworms blighting southern Africa.
But the variable efficacy may be due to genetic resistance, or it might be as a result of the way in which the spray is applied.
- The application of an insecticide is also usually not economical for control of the fall armyworm but may be necessary if the infestation is extremely severe and/or the plants are under stress. Extensive research, however, is needed to work out which chemical is the best to control the pest in southern Africa.
Insecticides must be applied during the early development stages of larvae because adult larvae may prove to be very difficult to control. They are often inaccessible to insecticides because of their tendency to hide in the whorls and reproductive parts of the host plant. Their excrement also becomes so heavy that it can prevent penetration of the insecticide into the whorls.
- Farmers should start their spraying early and ensure good coverage.