Tomato Fungal Diseases

So far two fungal diseases have hit my tomatoes. Powdery mildew and tomato leaf spot. Powdery mildew is a common visitor to my farm. But this is the first year I've seen leaf spot. Wow, it's always something new when gardening in the tropics. I find it strange that it isn't the same diseases and pests year after year. Instead, the problems seem to cycle through, then reappear again years later. Well......except for the common things like aphids and stink bugs and powdery mildew. These last three also are cyclic, but not a year goes by that I don't see them on the farm one place or other, one time or another.

Powdery mildew has always been a headache. So I try growing veggie varieties that claim to have some resistance. That helps. I've tried a number of sprays that people suggest. I never had much luck until I learned that prevention was the key. Once powdery mildew is there, you can't cure it. But prevention works fairly well. 

Both powdery mildew and leaf spot. 

I've tried a number of different "natural" sprays. This year I've been using sulfur spray and it's worked best of all the sprays I've tried. But to be fair, this is also the first year I've been spraying as a preventative, not a cure. So I'll need to experiment with the other sprays to see if they work as well as sulfur for prevention. Once a week I've been looking over the plants, removing any infected leaves. Then I spray. The tomatoes are growing in a greenhouse, so rain is not an interfering factor. This factor may be the main reason the sulfur is working. It simply isn't getting washed away. 

Tomato leaf spot is a new one for me. It too is a fungal disease. I noticed that some tomato varieties are more resistant to it than others. Indigo Cherry Drops is super susceptible. Since I haven't been overly wow'd by this variety, I opted to simply remove the plants. Less plants for me to deal with. Of the remaining plants, I removed any leaves that had leaf spot and then sprayed sulfur. 

A bad case of tomato leaf spot. 

Whenever I see diseases stressing the plants, I'll add more fertilizer to boost the plant growth. In this case I've been using extra urine or compost tea in the irrigation water and applying fresh grass clippings as mulch. I can't say for certain that this helps, but I have a feeling that it does. 

Powdery Mildew

Powdery mildew is a given here in Hawaii. The air carries a lot of moisture. Plus a lot of various fungus and mold spores. So rusts and various mold diseases regularly cycle through. Some years are worse than others. And I actually saw one year where there were no fungal diseases, but it was our worst drought year too since we moved here. That's no longer the situation. Things are back to "normal" and we see bouts of various fungal diseases routinely. 

I've tried battling powdery mildew in the past, usually with zero luck. I've learned a few things since then. 

1- When possible, grow varieties that have some resistance to powdery mildew. 

2- You can't cure powdery mildew once it's there. 

3- Start treating early to prevent powdery mildew. 

I still haven't settled upon my preferred line of attack. I tried the milk trick, but it failed. But then, I didn't start early enough.  I tried the urine trick and also failed. But again, powdery mildew had already infected the plants. Eventually the light bulb went on and I realized that I need to prevent powdery mildew, not try to cure it. 

I plan to try experimenting with various treatment methods, but for now I have resorted to sulfur spray when I first saw a few early dots of mildew on the greenhouse plants. Spraying once a week has kept the powdery mildew in check for most of the plants.....at least well enough for them to produce their fruits (cucumbers, squash, and now tomatoes). I plan to continue with the sulfur for now, but later this year I'll purposely plant susceptible plants out in the main garden just so I can conduct an experiment. 

What to use? I've seen suggestions for...

...diluted milk

...diluted urine

...compost tea

...sulfur 

...neem oil 

...baking soda (I added this after "P" emailed me)

...various commercial chemical fungicides 

Ideally I'd like to come up with a spray that this farm can produce for itself, as opposed to buying.

What poor victim will I use in this experiment? I'm thinking of summer squash. I've seen them succumb before the poor plant even gets its first female flower. Most open pollinated cucumbers are almost as bad.