Why an Integrated Approach is Best
These cherry tomatoes were planted long after the other plants in the tunnel and ripened much later. Even so, no Tuta absoluta attacked them, which proved the effectiveness of biological pest control. Photo: Bill Kerr
I once used an organic product to control tuta absoluta (tomato leaf miner) in my own tomato crop. Unfortunately, the manufacturer has stopped production of the product. However, since I was only using my harvest for breeding purposes, I decided to stop spraying against the pest.
In the past year the plants have suffered quite a bit of damage; this year there were significantly fewer. I planted my first tunnel as soon as the frost was over and the last tunnel began to ripen in March. These tomatoes do very little harm, although I have never sprayed them or used traps.
I planted a quarter of the tunnel to a cherry tomato variety much later than the rest of the crop. This one is just beginning to bear fruit, while the rest has been ripe for some time; however, there is no evidence of pests or larvae on this batch.
Looking closely at the plants, I recently saw a number of Macrolophus spp. Nesidiocoris tenuis was found in various stages of development as well as sporadically. Both are microbugs that prey on T. absoluta and other pests. Macrolophus is now taking control of T. absoluta in my tunnel.
Slight plant damage
More than 20 European countries now use macrolophus for pest control, which is sold to tomato growers.
If their prey is not available in sufficient numbers, Macrolophus spp can survive by feeding on the tomato plants, and there is a record of flower loss and other damage when their populations are very high. Even so, they prefer insect eggs and larvae in the first instar.
In general, the small potential harm is worth the protection the bugs provide. They also feed on whitefly, aphids, and thrips.
We still have a lot to learn about the local Macrolophus beetles. For example, they can be better adapted to our conditions than those imported from the Netherlands. Anyway, they seem easy to pull up.
Another group of beneficial insects are Trichogramma spp. Parasitoids. These are tiny wasps that parasitize the tomato leaf miner’s eggs and other pests. There are many in the genus, some of which are more specific about what they control and others have a wider range of prey.
Over time, more natural enemies will become noticeable. It is reported that some of the imported natural enemies are not well adapted to high temperatures. Since the inside of my tunnels can get particularly hot, this could suggest that our local bugs are better adjusted.
Another approach is to set up pheromone traps available from suppliers of local organic products. These are an effective tool in reducing tomato leafminer populations.
A combined approach
Combating this pest is not a one-size-fits-all approach, and there is still a steep learning curve ahead of us. What is certain is that at some point we will have to switch to integrated pest management with a combination of beneficial organisms and insecticides that do no harm to the natural enemies of T. absoluta.
This approach also means tomato growers need to do a lot more exploration and study to truly defeat this extremely destructive pest.
Bill Kerr is a vegetable specialist and breeder of various vegetables.