XVI. Vegetables and Pest Management

29 October 2009

The primary purpose for this trip is to learn about citrus. However, when faculty at the Institute heard that I also work with vegetables, they decided I should also learn about vegetable production in Morocco. It has been very enlightening, so..let's talk about vegetables...

I’ve mentioned before that tomato production in Morocco has been very difficult this year due to a recently arrived invasive pest called Tuta absoluta…sometimes called “absolute disaster”. It’s a small brown moth, not more than ¼” long. The larvae mine the leaves and then start eating on the fruit.

Here's an example of a couple of mines...this is minor damage...because the pest is excluded, but in an open field, the entire leaf can be covered in mines.Tuta absoluta has destroyed thousands of hectares of open field tomato production.

T. absoluta originated in South America and moved into Morocco late last year from Spain. It has moved into all the vegetable growing regions very quickly. Interestingly, one of the things I’ve heard from some students and others is that they think that it came from Israel…intentionally! Israel is a real sore point and some media people choose to fan the flames with nonsense like this, which then spreads among the population rapidly.

Over the past couple of weeks I've visited a number of vegetable production operations and packing houses (not just citrus!), and Tuta absoluta is a major issue. However, in this area, most vegetable production is not open field, but protected cultivation. A different kind…high tunnels, but not covered with plastic, but with a very, very fine mesh to exclude pests.

The use of mesh may have started with banana production, and now it seems most of the tomatoes, peppers, and summer squash/zucchini in this area are produced in the tunnels. They call them serres, which in French means glasshouse or greenhouse, even though they are more like “nethouses”.

It is high quality vegetable production, and, like the citrus, mainly for export. The farms I’ve visited use IPM techniques, and some of them are “biologique” the European version of certified organic.

They use bumblebees for pollination and pheromones for monitoring and mass trapping, as well as releasing natural enemies within the houses. They also use Bt for the larvae and sulfur for Tomato russet mite.

I’ve been told that they grow tomatoes in the same place for 4-5 years, then change to a different crop. I asked about soil diseases and nematodes, and was told it wasn’t that big a problem(!!). But…I have seen some pretty heavy duty soil sterilants stockpiled in the fertigation stations of several of the operations, so they must have some really different regulations for “biologique” than we do!

As a result of Tuta absoluta, the net houses are carefully managed. They repair any tears immediately, painting over them with a kind of glue, and keep them as closed as possible.

Getting into most of the houses is quite an effort. It’s like trying to get into an envelope…three times, with the flap going in different directions each time. There is a with a rubber band along the edge of the curtain to snap it back in place, and a very narrow space to get through. It’s very awkward; you have to be very skinny or very agile to move quickly through them.

I don’t think the system is very convenient for workers, but they seem to be doing pretty well at excluding the moth. It apparently rides in on worker clothing, boxes, etc., so it takes vigilance.

They use the pheromones religiously…both for monitoring and mass trapping. It costs about $5.50 per ampoule, and it has to be changed every 3 weeks. They have water traps about every 50 m (165 feet) in the houses - with the pheromone, sometimes with an insecticide in the water to kill them if they don't drown first.

A couple days ago I visited a farm called Ourika with an entomology professor from the Institute, and they had a much better system. They had three self-contained rooms with traps for the moth in each one. You enter one, close the doors and then enter the next, etc. They were big enough that a small delivery truck could drive in, the vegetable lugs could be loaded and then it could drive out. The whole house was also covered with not just one layer of netting, but two. When we arrived, I wondered why I couldn’t see into them very well, and that was the reason.

With two layers, tears in the netting are not as critical. If the tomato foliage touches the inner layer, it is unlikely that the moth would be able to lay its eggs through both layers. Apparently with just one layer, they have to be very careful to keep foliage away from the netting or the moth lays its eggs through the net.

They are growing mostly “grape” type tomatoes, i.e. 4-5 salad size or 8-10 cherry/grape size on a cluster. The large ones are picked mostly red, packed in the cluster and sold that way. Ones which become detached from the cluster or do not have a calyx are sold on local markets. The fruit look very nice, but I’ve bought them in the market…they don’t come close to field grown for flavor. They are okay, but I wouldn’t want them in season!

They are grown in soil, and the net houses have more air movement than plastic, but they are pretty hot and muggy. I think it’s the whole fertigation regime and probably the varieties selected for shipping that mean little flavor.

The pepper varieties I’ve seen include California Wonder, a poblano-type, and a Serrano type pepper. The squash is mostly just ordinary zucchini, and boy does it grow fast…they said the squash grows 3 cm (about 1¼”) per day. They harvest it between 18 and 24 cm (7 to 9 ½”)…but some of them were very fat for the length…again, not my choice for top quality, but they said the buyer sets the standards.

I think we’ve infected the world with a desire for bigger fruits and vegetables…everything, probably…but the quality is not necessarily better! The last farm with the better nethouse system exports primarily to England, the others to France and other European countries. I don’t think any of the vegetables went to the States. They would certainly meet our supermarket standards, though. And with so much of the open field tomato crop destroyed this year; these guys will probably be supplying most of Morocco as well. They really jumped on the bandwagon to deal with the pest immediately, before it caused damage and have succeeded.

This pest issue demonstrates that growers who keep abreast of emerging pest issues and plan for them can succeed where others have failed dismally. Not that we can (or want to) grow any significant acreage of citrus in net houses, but certainly nurseries could produce planting stock that way. And growers need to make use of any available tools to fight. I think the whole pheromone deal was brand new to many of these growers, but they figured it out in a hurry.
Lesson for growers (and pretty much everybody in today’s world): Know what’s on the horizon, be prepared and take every measure possible to exclude it, and then deal with it when it comes!