Tomato farming: biology and origin of Tuta absoluta

Tomato damaged by Tuta absoluta

Tuta absoluta’s threat to Solanaceous crops originated from South America before spreading to other parts of the world. The common name for Tuta absoluta is the tomato leaf miner, named so because of the pest’s preference for tomato.

This dangerous pest favours tomato (Solanum lycopersicum) and sometimes potato (S. tuberosum).

Tomato leaf moth has a life cycle of 29 to 38 days depending on the temperature.

The pest prefers higher temperatures meaning the higher the temperature, the faster it will reproduce and the more damage it will inflict on the plants. This is not to imply that it is not there during the cold season, in my experience, this is an ever present enemy of progress.

Female leaf moths can lay up to 260 eggs for their entire lifetime, a hell lot of eggs right? The life cycle is such that when fertilized eggs are laid, they hatch into Larva (caterpillar form) which transforms into a pupa which later becomes an adult insect (moth).

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 unmistakable marks all over the plant.

Tuta absoluta Life Cycle

The worst part of this dreaded pest is that the adults are very active only during the night! They hide out of the field or under the leaves during the night. This makes it difficult for you to detect them early enough so that by the time you see moths flying around or plants that have been damaged, about 30% of your fruits have already been damaged.

How does Tuta absoluta look like?

It’s important for you to fully understand what you’re up against when dealing with crop pest or diseases. In this case, you need to understand what the tomato leaf miner looks like.

The adult moth has a grey-brown colour and approximately 6mm in size. You can comfortably see them with your naked eye.

The only downside like I’ve mentioned before, the adults aren’t active during the day.

The newly hatched caterpillars are 0.5mm and develop a black band behind the head when maturing. Their backs are pinkish in appearance. A fully grown caterpillar is about 9mm in size.

Now, after exploring what is Tuta absoluta and how to easily identify them, it’s time to understand exactly how they get introduced to your tomato field.

Sources of infestation

The most common source of infestation so far is buying seedlings that have been infected by the moth’s larva. Therefore, it’s essential to only buy seedlings from certified plant nurseries.

You can further tell a health seedling by looking at the colour. Healthy seedlings are strong, vigorous and dark green as opposed to yellowish.

So, do your homework and buy or grow healthy seedlings. This will give your tomato crop a good head start.

Tomato damaged by Tuta absoluta

Other sources of infestation are wild hosts in the same family as the tomatoes and buying infected fruits at the market. The former is more common than the latter. Therefore, you need to ensure that the surrounding crops are either non-solanaceous or free from the pest altogether.

Economic impact:

There are reports of Tuta absoluta wiping out the entire tomato crop causing 100% losses! If you don’t take the necessary precaution measures, you’ll just be part of the Statistics

If there’s anything you need to remember is not to underestimate these ferocious bugs.

Second, pesticides won’t help you much because these very bugs have their own way of dealing with the chemicals. It’s called resistance!

How to control Tuta absoluta:

I get several questions, mostly from start-up farmers. The biggest and most common is, what chemicals should I use to control Tuta, my answer has been simple: prevention is better than cure. When you already have an attack, chemicals alone will not work, you need a combination of several strategies.

There are several approaches that are cost-effective in dealing with these tomato leaf miners.

The first one is to prevent their infestation as much as possible and second, deal with them before they exceed the economic threshold level. And the best way to deal with them is by using natural ways as much as possible.

But first, you need to identify their initial effects or their presence through regular scouting and monitoring.

Scouting entails looking for any abnormal signs on your crop. You should do these as regular as possible to detect any changes earlier enough.

When scouting and monitoring your crop for Tuta absoluta, check for the following symptoms.

Blotch-shape mines and under worst cases leaves dying off completely, Malformation of the plant caused by the mining of the stem since the caterpillars prefer stems and leaves but also under the crown of the fruit, deformation or curling of leaves and necrotic areas, the fruit developing an abnormal shape, obvious exit holes on the fruit, premature flower and fruit dropping or reducing in size, lesions and distortion on growing points, stems either forms witches, broom distorts, die back or wilts altogether, damage and fruit developing wounds which in turn serves as avenues to other disease-causing pathogens.

One other big problem is that fruits with Tuta holes on them become a port of entry for many other diseases especially fungal ones, talk about disaster!

Control:

Once you realize that your crop might be or is at risk, act fast by taking any of the following control measures.

Remember that some of them are aimed at preventing while others aimed at eliminating the pests.

Preventive measures:

1. The most common and effective way of prevention so far is the use pheromone based Tuta traps. These attract and trap all-male adult moths especially when they are active at night. In turn, the females follow the males in the trap and they die together. When a lot of males die, no mating and without mating, their reproduction will be hindered and that is what you definitely want. 20 traps are needed per hectare for monitoring whereas 40 traps per ha are needed in cases of high infestation levels. The number of moths trapped serve as a guide for your next course of action. We have two different types of traps in stock, some are buckets of container based while others Use yellow sticky traps to attract and trap the adults. (Refer to my previous article on Tuta traps).
2. Use of pest exclusion nets – grow your tomatoes inside the insect nets while growing outdoor or within the greenhouse. If growing in the greenhouse, make sure the nets aren’t damaged.
3. Control human and animal traffic to the fields – both humans and animals are vectors for spreading the bugs. So it’s important to control how they enter and leave your farm.
4. Sterilize the soil – before you plant, ensure to properly sterilize the soil to kill all the eggs that might be present in the soil.
5. Quality planting materials – buy quality seeds and seedlings from credible sources to ensure that they have not been infected by the larvae.
6. Practice crop rotation with non-solanaceous crops and completely remove any post-harvest plant debris.
7. Feed and irrigate your crop properly and ensure the field is free from weeds.
8. Only when the above listed strategies fail should you resort to spraying of anti-tuta chemicals (kindly consult your chemical dealers on which chemicals are effective). One caution though is that you should avoid a consistent use of the so called “Powerful anti-tuta chemicals". An over use of these will in the long run result into resistance development, which means more trouble for you. Unfortunately, this is the most common strategy around Zambia, which perhaps partly explains the incessant Tuta problems we are facing.

Conclusion:

Tuta absoluta can and will bring you down to your knees. They will wipe out all your crop at a snap of a finger when they strike. But the benefits of growing tomatoes and reaping great rewards outweighs the threat of this merciless bug.

Tuta trap

We at Ebenezer Farm believe Tuta traps are effective prevention and control tools. We supply two types of traps:

1. Bucket based trap at k85 each
2. Yellow sticky trap k70 each.

Alternatively, you can buy only Tuta Lures (rubbery stuff containing a chemical that attracts Tuta insects to the trap) at k55 each and we will teach you how to set the traps up at your farm.

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by Polepole Pascal,

Call or WhatsApp us on +260-968-081817.