The African sugar cane borer, Eldana saccharina, can cause significant losses in yield and RV, wiping out entire crops if left unchecked. An integrated pest management approach is required to ensure long term control is effective.
The Eldana moth has been a persistent pest in Africa for several decades and during its larva stage, one insect can cause losses of 0,5 tons per hectare. It is a resilient pest and it can survive crop burnings, leading to continuous infestation year after year.
However, tried and tested methods coupled with new chemicals are resulting in increased efficiency of Eldana control. This not only ensures a higher yield, but farmers can also leave their cane to mature, resulting in higher RV percentages instead of harvesting immature cane with higher non-sucrose sugars.
The eggs of the African sugar cane stalk borer are yellow and oval and laid in batches under leaves. The larvae are a dark brown colour and if infested, will be found inside the cane. Tell-tale signs of infestation include feeding marks on funnel leaves and holes in tunnelled stems, as the larvae seek out the soft tissue on the inside of the stalks on which to feed.
The adult borers are small, with a wingspan of 35mm. The forewings are pale brown with two dark spots in the centre. The hind wings are whitish, with a short fringe and brown veins.
Both growing cane and harvested fields should be inspected by selecting random pieces of cane and breaking it open. Infested stalks will also have red rot fungus.
Breeding of moths takes place continuously and it is not a seasonal pest. Farmers should therefore be continuously on the lookout.
Adding to the significance of the pest is that no single control method is effective on its own. Unlike Brazil, which has approved the commercial use of genetically modified (GM) sugar cane that is resistant to that country’s cane borer, South Africa is far from approving a GM crop for the industry. The pest therefore requires an integrated approach to management.
The South African Sugarcane Research Institute (SASRI) advocates the simultaneous application of different control measures. These include:
- Correct choice of variety: varieties not ideally suited to your area will be under more stress than those that are better suited, resulting in cane that is more susceptible to pests and disease. Furthermore, varieties like N12, N21, N29, N33, N39, N41 and N42 are more resistant to Eldana. Also ensure that you use high quality, healthy seed cane.
- Good soil and crop management practices: as stated above, stressed crops are more prone to infestations, and ensuring the correct moisture levels in the soil will reduce stress. Managing silicone and nitrogen to maintain optimum levels is crucial, as insufficient levels of the former and excessive levels of the latter increase chances of infestation.
- Good field hygiene: when harvesting, cane should be cut as low as possible to reduce the amount of stubble left on the ground. This also means that fields and loading areas should be cleared of any stalks so that a habitat is not created for Eldana to flourish.
The chemical route
Insecticides like alpha-cypermethrin pyrethroids can be used in carry over cane to allow the crop to mature without excessive damage. A 120-day withholding period applies if the cane is cut green. If burnt, the withholding period is one day.
Alpha-cypermethrin is not a complete solution and can only be used in carry over cane. It should be applied to fields where there is excessive damage or the threat of infestation is high, rather than as a blanket application to all fields.
The natural route
One of the most effective control methods for Eldana is the push-pull method, whereby the habitat is manipulated to provide an alternative habitat for the Eldana moths, while planting crops between the sugar cane that repel the moths. In one trial at SASRI, push-pull (when used in conjunction with the other measures listed above) reduced damage from Eldana by more than 50%.
Sugar cane land does not have to be sacrificed for the additional crops as they can be planted in areas not suited to cane or in wetlands and waterways.
When Eldana eggs are laid in indigenous ‘pull’ plants in wetlands, they are more accessible to their natural enemies and the population can be controlled naturally. GM maize is a good option to use as a pull plant and is referred to as a dead-end trap crop as it is toxic to moth caterpillars and kills them within the first two days of feeding. It can be planted along the borders of the fields.
To repel the moths from the cane and push them towards the GM maize, Molasses grass is used as a ‘push’ plant.
Species of sedges like Cyperus dives and Cyperus papyrus can also be used as pull plants and are planted in wetlands adjacent to cane fields.
SASRI states that for push-pull to be effective it is important that farmers work actively to keep their wetlands healthy and to promote the growth of natural pull plants for Eldana, such as these sedges.
The push and pull plants also have additional uses over and above controlling Eldana. Molasses grass can be cut and used as a good cattle fodder. GM maize, which is resistant to damage by stemborers such as Eldana, can be used for human consumption or as cattle feed. The sedges, if managed well, can be used for weaving and basketry and also have medicinal properties.