Quickness of fungicide action

While I don't know much about Mancozeb, anytime I have used fungicides in my garden, I've always thought it is better to make sure the fungicide has time to dry on the plant. If you put it on and then it rains an hour later, well, I don't know how effective it would be. I like to let the stuff dry and let the plant soak up the stuff, so it has the chance to help the plant. With the fungicides I've used, they usually call for repeated applications. Hopefully, someone will recognize and have more specific info for you. Good-luck. Darlene

Thanks Darlene. It looks like the board won't cough up a definitive answer. I'm using your approach, but I'm getting the willies from all the rain, heat, and humidity lately. I think that's perfect weather for black-rot. Ken

You're probably right. We've had tons of rain too, perfect for tomato plant fungus. Even if it sits on the plants for a couple of hours - it should be dry, shouldn't it? Different fungicides may be different though. Sometimes I've had to get stuff on, no matter how rotten the timing, so I wouldn't wait too long. Have you checked Jack & Lum's sites for any info on black-rot? Or your county agricultural agent? Good-luck. Darlene

applications.

Hi Dar V,

(And hello everyone else i'm new!)

Here is a webpage with some info on:

It has data about the substances breakdown in soil & in rain about 1/2 way down.

HTH, Dave

Most fungicides don't kill existing infection and are mainly applied as a preventive. Some specific applications are intended for killing existing spores, but you will have to look around for them. My understanding is that Mancozeb is a preventive and will not kill an existing infection.

If that's true, then the Mancozeb needs to be on the plant when and if a spore lands on it. Once it's washed off, it would have zero effectiveness. Sounds believeable to me. Ken

I believe Mancozeb - Penncozeb will ramain to some extent after a rain. A lot depends on the amount of rain and the length of time it rains. I believe that if the fungicide is on for several hours prior to a rain, some of it will remain after a light rain. You might just look at the leaves after a rain and see if there is any spray residue on them. My understanding also is that Mancozeb - Penncozeb will not kill an existing infection. You will need a systemic fungicide to do this and they are expensive. Prevention is the best route.

Mancozeb is a preventative like previously said. A good rule of thumb is that you will lose 1/2 of the spray for every inch of rain you recieve. Mancozeb also spreads with rain so sometimes rain can help coverage. It needs to be dry before the rain and "usually" that calls for the spray to be on at least 2 hours BEFORE the rain. I also spray it every 10 days whether it rains or not because of dew. Systemic like Nova are soaked in to the plant unlike mancozeb/penncozeb/dithane which lays on top of the leaf. Mancozeb will not kill an infection like a systemic can it just prevents it from spreading.

Hope this helps.

Bob