During intense rainy periods, yes. The Midwest spray guide recommends weekly up through shuck split, then 7-10 days for first cover, then 10 days for second cover, then 10-14 days for additional covers.
https://ag.purdue.edu/hla/Hort/Documents/ID-465.pdf
I would say that’s pretty much a max schedule, under the worst conditions. For example, I’ve not found it necessary to spray before shuck split, although we do get some catfacing on peaches, as a result. But we can generally thin those off.
Once the fruit is out of the protective shuck, then it’s game on. Insects want to destroy it, the rain wants to rot it, not to mention scab. We will spray weekly, if persistent heavy rains occur (we got 13" of rain in May). It’s impossible to grow peaches with this kind of rain, unless a protectant fungicide remains on the fruit. The rain is constantly washing it off. Even so the protectant will do it’s job in the process.
Once rain lets up, we back off to the 10 to 14 day spray intervals (again depending on how much/frequent rain occurs.
Once a peach shows brown rot, it’s done for. Some people have mentioned they have arrested brown rot on peaches with Indar, but for us, we can’t sell those.
In terms of products to control rot, cost is a consideration for us. So we typically don’t use the more expensive/acre products because we haven’t had to. In the beginning, when I started as a backyard grower, I used the more expensive stuff (Pristine, Elevate, etc.) because cost didn’t really matter. But when you start spraying acres, cost matters.
I mostly use Captan, Indar, propiconazole, and Topsin.
You’ll notice in the Midwest Fruit Pest Management guide (linked above) that the compounds rated excellent are generally azoles, or strobys. The problem with them is that they are at high risk for resistance buildup, from a commercial standpoint. The nice thing about captan is because of it’s multi site activity, fungi can’t develop resistance to it (at least not so far). Many times I use captan at the 1/2 rate along with an azole, which tends to provide excellent control.
If you are seeing some rot on peaches, you should be able to rescue the rest with a powerful azole, like Indar. Or use one of the powerful pre-mixes. That should save the rest of your peaches. As mroot mentions, strobys and azoles have systemic activity, which is why they can save your peaches, even if other peaches on the tree are showing symptoms. I don’t use the newer pre-mixes because they are very expensive, and up to this point, haven’t had to. Most of the pre-mixes also have systemic activity.
The systemic activity does prevent washoff. The problem is that the compound is either broken down quickly inside the fruit, or doesn’t stay in the skin long enough to give long term protection. So those really can’t help much more than a week, under heavy rain conditions.
Most fungicides we are discussing have a 0 PHI on peaches. There is an REI on captan.
With my captan and azole mix, I can generally keep rot on peaches to a bare minimum, even in the worst of weather. If it rains continually for a week before peaches ripen, sometimes they will look OK during picking, but they will start to rot very quickly once they counter ripen. There’s nothing to be done about that. I just explain to customers the extreme rainy circumstances, and reimburse them for any peaches for which this occurs.
TangOs is a particularly hard peach to protect from rot, even with an intense spray program. Other than that, other donut peaches I’ve grown have done fine with our spray program.
I once tried washing blackberries in a chlorine solution to try to extend their self life for a trip we took. The problem was they took on the flavor of the bleach and weren’t very good.
People have always tried home remedies for pest control, but the results are almost always significantly inferior to compounds manufactured specifically to treat the pest (I would say “always” except that someone may be able to offer an example to prove me wrong, so I’ll stick with “almost always”.)
I’ve heard of milk, hydrogen peroxide, vinegar, etc. While some of these may offer some benefit, they are going to be found wanting under serious pest pressure.
I don’t want to discourage anyone from trying home remedies, but for home growers, I would recommending testing on a small scale (i.e. one tree) vs. betting a whole year’s peach harvest on the experiment.
