I'll try. First, all fungicides are preventatives and to best work, need to be applied from the first day the plant could be exposed - which is usually plant out date. Once the fungus disease is on the plant all any of them can do is slow it down, not cure it.

As to brand you choose to use - your choice. Research shows that Daconil is the most effective but some don't think it is safe. Copper-based is supposedly safer in some respects and apparently more effective on bacterial diseases but not as effective with fungal diseases. You choose.

Any spray can damage the plant if improperly applied - too much, too often, in the heat or direct sun, etc. Follow label directions carefully.

Dave

There is much confusion about fungicides because many people want the best product for a host if ailments and it just don't work that way in many instances. The 2 products mentioned are readily available to home gardeners and while chlorothalonil has both oral and dermal LD50 of 10,000 mg/ kg, fixed copper typically has an oral LD50 of only 1000 mg/Kg making it far more toxic. You should see the label word "CAUTION" with such products having an LD50 range 500- 5000.

Various fungicides available to licenced pesticide applicators are in many respects safer than either of those, but because of their specified mode of action the target disease may develop resistance to the materials if they are not used properly.

There are different fungicides that have curative action. Again, not available to the home gardener.Sadly, many gardeners repeatedly apply chlorothalonil to prevent Early Blight in tomatoes even while researchers agree that it is a poor choice for that use. It is a better preventative fungicide for Late Blight.

So back to the original post. Under your weather circumstances you are well advised to spray---- but what is the predominant disease you are trying to prevent? What are your circumstances? If Cooper runoff into streams occurs it is very toxic to fish. Labels with the products are your best guidelines.

Most of the pros on here are strongly for fungicides. I try not to use them, IMHO I do not think it is good for the soil, and I find the best defense for fungal diseases is a healthy plant, and I do not agree that it is necessary. Most average home gardeners do not use fungicide. My grandfather never used fungicide and gave away tomatoes to the whole neighborhood. I harvested upwards of 300 pounds last year without fungicide. Though by October the fruit was rotting, I had already harvested way more than I could eat all winter long.

The strongest argument for fungicides is for the prevention of late blight, which can completely ruin a crop in a few days, but they are far from 100% effective, especially if you are not extremely dilligent and thorough. They can also increase yield by keeping the plants alive with blemish free fruit longer... but at what cost? Copper is organic but is not completely benign to people or the soil or the environment.

Peter,

I don't think anyone wants to use fungicides and it certainly should be avoided if at all possible. It all depends on weather and climate and what varieties you are trying to grow. Like your grandfather I grew tomatoes for around 20+ years without using fungicide. I too had way too many for my own use and gave away bushels of them. I only grew a couple if varieties and these did very well for me. My main variety was discontinued so I started experimenting with different ones to replace it. Anyway to make a long story short whether it was a change in climate or just lesser resistance I started having a lot of problems such that I no longer was getting enough for even my own use, even with 3 or 4 dozen plants. This was not from late blight but early blight, septoria, ect. It would completely defoliate a plant in a month or so such that you might get a couple if tomatoes from each plant. The principle problem is wet conditions such that the rain and or dew stays on the plant for most of the day. My advice would be to assess your climate and weather conditions and decide for yourself if you need it or not.

hoosier,

Yes I do agree, if the climate and conditions are heavy long-term rain, it may be time to consider some fungicide. There is no one-size-fits-all approach. It also all depends on what you want. Are you ok with some tomatoes, you get what mother nature gives you, or do you want to pull out all stops for the best harvest possible? Since I still have tons of cans and frozen tomatoes from last year that no one is eating because they upset my wife's stomach, I am ok to get what I get. Other people (such as Dave for instance) will not be satisfied unless they are fully stocked for the entire winter (which is fine, of course.) It is a personal thing.

It is interesting that no one talks about fungiciding potatoes, when they suffer from all the same ailments.

Agree with hoosier. Late blight is definitely not our focus in our commercial fields as we have never experienced it here. Early Blight, Septoria, and the bacterial diseases are our issues and regular application of Daconil have proven to be quite effective at preventing the crop losses we used to experienced. Had to admit to my sons that they were right about insisting on that change and that's hard for the old man to do.

But in the home gardens, where I garden organically as much as physically possible, I limit myself to organic fungicides and prefer liquid copper Soap Shield in conjunction with compost tea foliar applications, infected foliage removal as needed, no overhead watering, etc.

Do I have more disease issues than the sons do in the commercial fields? Definitely. But my production numbers and overall plant health is still substantially better than if I used nothing at all.

Dave

PS: and no I don't treat my potatoes because they are first, more resistant/tolerant, and second, the food parts aren't directly affected as with tomatoes.

Thank you for all the responses....So far I have no problems with my plants and am just trying to avoid them. Unfortunately I only have room for 7 plants, I have 5 in the ground and 2 bush varieties in buckets on my deck. Last years crop was disastrous, one big problem was blossom end rot and read that can be caused by not enough calcium in the soil, poor draining soil or planting too early... which is what I suspect.....