I'm located in Colombia, near Medellin. I went to the local nursery and it turns out due to the humidity, its basically impossible to grow tomatoes outside of a greenhouse or structure that protects it from the rain. Unfortunately, I had to uproot it :(

Medellin has perfect temperatures year round for growing tomatoes. But I don't know much about local conditions and diseases, though. Do you have a dry season and a rainy season where you are? I know that Colombia has many different kinds of climates.

If you have a dry season, it's probably possible to grow tomatoes during that window. You will probably need to spray fungicides regularly, but that is the case everywhere people grow tomatoes. I live in a region of the US known for producing good tomatoes, but fungal diseases are quite common here, so I spray regularly to prevent/delay fungal disease.

Yes, we have great weather and its possible to grow year round, even in the rainy season. The issue is that generally the humidity is higher here and these days with the crazy climates, the rainy/dry seasons are much less defined. For some reason though, it doesn't affect so much the other plants... just tomatoes are more complicated.

I might consider it though, is there an organic fungicide you recommend?

There are many very humid areas of the USA where people successfully grow tomatoes.

The real issue IMO is how often it rains. If it rains almost every day, it's hard to keep fungicide on the plants.

Maybe look into disease-resistant hybrids like Iron Lady, Defiant, Mountain Magic, etc., spray them regularly, and time planting for the driest part of the year?

Organic copper is a standby for many organic tomato growers. I find that alternating with Serenade (Bacillus subtilis) works well for me in my garden, but I don't know how it will do in yours. I know a lot of gardeners in humid areas here will also use a very dilute bleach spray to control mold as well. The important thing is to spray before disease arrives. Organic fungicides can do a lot to prevent disease and delay its progress, but they are not systemic so cannot cure anything once the plants are affected.

I don't want to encourage you to waste your time and garden space if it really is impossible to grow without cover, though, since I obviously have no first hand experience with growing in your conditions. Perhaps setting up a kind of high tunnel or something or a greenhouse if you can is the best--but even then, you will probably need to use fungicide. Growing under cover eliminates the issue of rain, but disease spores still get into these environments. And no matter where you grow, tomatoes are just a really disease prone crop. It's just that excluding the rain means you don't have to spray as much or as often.

I appreciate the advice, but the issue is that its very hard to predict the weather here; in a tropical climate you never really know when its going to rain. Also, I prefer to plant heirloom varietals when possible... especially when there are some inherent risks that can't be avoided. It probably is possible, but its probably extremely difficult in my environment... Actually two people separately said its difficult in this environment. I'll just grow less tomatoes and more of the other stuff that grows well :) Your advice is still very helpful, going to look into those organic fungicides even for when I grow on my balcony.