Tuta absoluta (Lepidoptera gelechiidae), also called Tomato leaf miner, is a highly destructive insect pest to tomato plants. I understand it when you are not sure what to do when tomato leaf miner attacks, but you still feel you have to do something. So, you result in spraying pesticides unsparingly on your crop. Unfortunately the result is poor due to the resistant nature of tuta absoluta to most pesticides. And this results in significant losses of your crop, investment, and money used to buy the chemicals. This also means your reputation as an agribusiness entrepreneur is repudiated for exceeding the Minimum Residue Levels (MRLs)
Tuta absoluta is a threat to the Solanaceous crops. It is also referred to as the Southern American moth since it originated from South America.
Photo courtesy: Adult Tuta absoluta and larvae.
Its common name is Tomato Leaf miner named because of the pest’s preference for tomato.
It has a life cycle of 29-38 days depending on the temperature. The pest prefers high temperatures meaning the higher the temperature, the faster it reproduces. Female moths lay up to 260 eggs during their entire lifetime. The most destructive stage is the larval/caterpillar stage which lives as a miner in the leaf, fruit, or stem. It burrows in and sucks sap from the leaf leaving behind a silvery tunnel on the leaf. Adults are nocturnal- which means they are only active at night. This makes it difficult to detect them early enough before they have done their damage.
Sources of infestation
- a) Buying seedlings that have been infected by the moth’s larvae.
- b) Wild hosts in the same family of solanaceae.
- c) Buying infested fruits from the market.
Silvery tunnels made by Tomato leaf miner and damages on the fruits.
Economic impact
It is reported that tuta absoluta has a devastating effect wiping out entire tomato crop causing 100% losses. Therefore, if you don’t take necessary precautionary measures, you will just be part of the statistics. Pesticides alone won’t help much because most develop a resistant nature to pesticides.
How to control Tuta absoluta.
There are several approaches which are cost effective.
- a) The prevention of the infestation
- b) Dealing with them before they exceed the economic threshold level.
- c) Regular scouting and monitoring to identify their initial presence and effects.
- d) The most effective in preventing them using the natural ways as much as possible.
These are discussed as follows;
Scouting and Monitoring
Scouting entails looking for any abnormal signs on your crop. It should be done regularly and bed to bed to detect any symptoms early enough.
When scouting and monitoring your crop for tomato leaf miner/ tuta absoluta, check for the following symptoms:
- Deformation or curling of leaves and necrotic areas.
- The fruit developing an abnormal shape.
- Exit holes on the fruits.
- Silvery tunnels on the leaves which under severe cases cause leaves dying off completely.
- Collapse or malformation of the stem caused by the mining effect of the caterpillars.
- Lesions and distortion groat the growing points.
- The presence of the excrement/droppings of the larvae on the fruit, stem or leaves.
- Wilting on the infected plant organ.
Photo Courtesy: life cycle of Tuta absoluta and the damage on the leaves & fruits.
- Damage and fruit developing wounds which in turn serves as avenues to other disease causing pathogens.
- Premature fruit dropping or reduction in size of fruits.
Preventive measures using natural or biological ways;
pheromone trap
- Use of pheromone traps; these traps are installed with female pheromones which lure and trap the male adult moths especially when they are active at night since the adult moths are nocturnal. This will leave behind females to produce infertile eggs thus controlling their reproduction. 2-4 traps per hectare can be used. If the
catch is high, more traps should be installed. The traps can be used in both open field or in greenhouses
The pheromone trap
- Growing crops in a protected environment e.g. shade nets and greenhouses. The vents should be covered with the insect nets; ensure that the poly-film is not damaged.
- Use of the light e.g. sport light or bulb and water. Water is put in a container or bucket approximately ¾ full. The water can be poisoned with pesticide or not and then put in a raised place. Then a source of light is hung on top of the water and the light switched on throughout the night. The light will attract the moths and eventually they will get drowned in the water with the poison.
- Control of human and animal traffic to the fields. Both humans and animals are carriers for spreading the pathogens. Therefore it is important to control how they enter and leave your farm.
- Use of Bacillus thuringiensis (BT)- based insecticide formulations. Mirid bugs are the most common predator against T. absoluta.**
**NOTE: The limitation of biological control is that it has a slow mode of action and is not efficient especially when populations are very high.
Cultural Control
Ploughing, manuring, irrigation, crop rotation, solarization and the elimination of symptomatic leaves and destruction of infested tomato plants have all been used to control this pest. The removal of alternative reservoir hosts such as nightshade is strongly recommended before and during the cropping cycle.
Chemical control
This is a last resort remedy to control tuta absoluta as a requirement of the Integrated Pest Management. (IPM). Frequent spray with the same product makes the pest resistance, hence it is required to alternate the products after at least two sprays to confuse their life cycle. The reports from a regular scouting and crop monitoring help the farmer in decision making on what to spray, when to spray, which product to spray and the targeted pest or disease. The following products can be used:
- Voliam Targo 20ml/20ltr
- Ampligo 10ml/20ltr
- Actara 8g/20ltr
- Pegasus 15ml/20ltr
- Karate 8g/20ltr
- Match 15ml
- Escort 10ml/20ltr
Caution: Do not apply when bees are actively foraging especially Pegasus and Actara, since they are a threat to these most important pollinators.
Conclusion
Tuta absoluta is a great menace to farmers. It can bring you to your knees. It has a devastating effect. They can wipe out all your plants if not controlled leading to great losses. However, the rewards of reaping the tomatoes are sweet if you are well armed with the correct information.
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