does fungicide kill on contact?

I have peach trees that I spray with fungicide a few times a year. I've always wondered how long it is necessary for the fungicide to stay on the trees before it is effective. I live in the pacific northwest, which is why they need to be sprayed (cold and wet winters), which also makes it hard to time the sprayings. I was told to apply the treatment in december, january, and early march. Following that schedule has kept the peach leaf curl pretty much under control, though I still see a mild amount. I'd like to know if I can just get the stuff on the trees and not worry if its going to rain later that day, or if it makes a difference if the stuff sits for a few days before it starts to get washed off. Or is it more important to time the sprayings early or later in each month according to current amounts of rain, and/or temperature? For my own records, I can track when I spray, and how long it stays before the first rain, and then whether I see lots or little peach leaf curl the next spring. But there are too many other variables involved for me to know what has the most impact. Anyone know of any more definitive data on this subject? Thanks.
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As always start by carefully reading the label. Then follow it.
The deal with fungicides is that they prevent the infection they don't cure it. Spraying it after the fact is like putting the bullet proof vest on top of the gunshot wound.
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Beecrofter wrote:

This is not just a recommendation. The label is the law.

Depends on the fungicide and the extent of the infection. All the fungicides I can think of will kill spores on contact, and if the spores have germinated and invaded the plant, some fungicides will kill them too. However, if the fungus has really gotten a hold on the plant you need a systemic fungicide to cure it. Systemic fungicides are not recommended on plants which produce food (or more precisely, eating the plant products from a plant on which systemic pesticides have been used is not recommended).
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Yes, of course I read the label and follow its guidelines. But the labels on any fungicides I've read don't answer my specific questions, such as how long the product must remain on the tree in order to be effective. And if the fungicide only prevents the infection, it seems like there needs to be a continuous presence of the fungicide to provide protection during all of the vulnerable times. Again, there is nothing that states that in specific terms, only vague and general (like: 'during late fall/early winter'.) I understand that labels can't be any more specific, as each site differs. But it would be nice to have info, such as how many inches of rainfall should be allowed to fall on the trees between applications (so I could measure the rainfall, and know when to reapply.)
But given the two answers I've seen, it is helful for me to see the clarification that the fungicide is just killing the spores. And I know what once infected, there's nothing I can do (and I certainly don't want to put anything systemic on the trees, I like to eat the peaches too!)
Thanks.

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You might want to consider replacing the peach with one that doesn't need spraying. 'Frost Peach' is one that was developed for the PNW climate and is quite resistant to leaf curl as well as not requiring the same number of heat days as other peaches in order to ripen fruit. It bears at a very early age, also.
pam - gardengal
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