TUTA ABSOLUTA

This year, an infestation in my young tomato plants totally stumped me. Because I could find nothing in my gardening books that looked anything like it, I visited my local organic association to see if they had any ideas. “Oh you won’t find any information about it in your books” Juan told me, “you would have to search for references to an outbreak in South America.” “What?? I asked. “How did it end up in my tomatoes?” “It’s the plague” he informed me. “The tomato moth, tuta absoluta, arrived from Chile three years ago imported into Valencia with, of all things, tomatoes!”

I was shocked! Isn’t Spain the tomato growing capital of the world? Isn’t that what all those plastic greenhouses in Almeria are for? You know, the ones that, collectively, are, apparently, the largest man made structure visible from space? How did this happen? Why did this happen? How did this destructive and tiny little moth end up in my garden? I raised all my tomatoes from seed and I live in an area where there is no large scale commercial agriculture; just a few neighbours gardening organically on a small scale, similar to although rather larger than, myself. This throws up all sorts of questions in my mind. To start with, why is Spain importing “tomato products?” Why from South America, thousands of miles away? I thought those plastic greenhouses provided a year round supply for the whole of Europe. Oh yeah, and what I can I do about my infestation? I felt it was time to do some serious geo-politico-bio research.
So what did I find out? Tuta absoluta belongs to the family Gelechidae Lepidoptera, species meyrick. It has a biological cycle of 29-38 days and has the potential to reproduce 10-12 generations a year. The life cycle speeds up as temperatures rise. It is mainly found on tomatoes but also affects aubergines and potatoes and to a much lesser degree, tobacco, tomatillo and peppers.
The nocturnal adult moth is 10mm long and hides among leaves during the day and displays a short erratic flight when disturbed. Eggs are creamy white, sometimes yellow, and measure 0.4mm long (tiny). The female can lay up to 260 eggs in her lifetime.
The larvae are much easier to spot than either the eggs or the moth. They are yellow to bright green and vary from 1mm-7.5mm in length. They are often found inside a lovely looking tomato when you are just about to eat it! The larvae first dines on leaves and then on the growing tips. They also mine leaves and bury into stems. They penetrate immature fruits and the resultant holes provide access for other pathogens. Pupation takes place on a leaf surface, in a curled up leaf or mine or in the soil.
Previously absent from Europe, Tuta absoluta was first reported in Spain in 2006. In 2007 it was found in several places along the Mediterranean coast, including Ibiza. Up to 100% losses have been reported in infested crops. By this year, 2009, the moth has been detected in France, Italy, Malta, Morocco, Algeria, Tunisia, Greece and in a packing station in the Netherlands.
So what to do? There are biological controls available. The larvae of dineulophus phthorimaeae eats the larvae of tuta absoluta. On my own crop, I used a spray application of very dilute neem every two weeks, as recommended by Juan. Although I’m still finding the odd little green worm, now in late October the neem seems to have brought the plague under control. The plants that were attacked when very young never recovered, as their growing tips were eaten out. I continued to raise more plants from seed until June and replaced all that were lost but this has been my worst year for tomatoes in the seven years I have been growing here. I removed all the mined and eaten leaves which generally had the effect of making the plants look weedy and sickly. We did have plenty tomatoes to eat. I just had to get used to cutting out the worm damage and my kids soon learned to reject any tomatoes with holes in them. Luckily, my tomatoes are only for domestic consumption. For commercial growers, the plague of tuta absoluta is a disaster.