Fungicide: Over- and Undersides of Leaves?

[GaryStPaul]

Some, including Carolyn, have noted that when using Daconil only the upper surfaces of the leaves need to be sprayed. I'm also using (alternating with) Bonide Copper Fungicide, the directions for which say to spray both top and bottom surfaces. What is the difference, does anyone know?

TIA,
Gary

[gorbelly]

Daconil is systemic, whereas copper works on contact.

Contact vs systemic: Contact fungicides (protectants) are not absorbed by the plant and stick to plant surfaces. They provide a protective barrier that prevents the fungus from entering and damaging plant tissues. Systemic products (also known as penetrants), are absorbed by the plant and are able to move from the site of application to other parts of the plant.
http://www.ipm.iastate.edu/ipm/hortn...ungicides.html

[amideutch]

When we are talking fungicides there mode of action can be contact, systemic or protectant. They eradicate the disease from within the plant (Systemic) or from the outside of the plant (Contact) or put up a barrier or coating on the outside of the plant (Protectant) not allowing the disease to infect the plant and Daconil is a protectant and this pertains to airborne disease.

As far as Daconil applications are concerned it should be applied to all plant surfaces.

Ami

[ginger2778]

So far I love this thread. Thank you, Gary for asking this question. I just learned.

[gorbelly]

There is some conflicting information about Daconil (chlorathonil) out there. My current understanding is that it is locally systemic to some degree for a limited time, i.e., the plant does take it up/absorb it, where it remains active in the plant tissues for a time, and that it is a protectant, i.e., it does not cure, but prevents infection. Although systemic and protectant are often thought of as mutually exclusive, they don't have to be. Nor does either category have to be totally binary.

However, Daconil's manufacturer, Syngenta, calls it a contact protectant and recommends covering all surfaces of the plant.

I've read sources that claim that, because it has limited systemic activity, it's longer lasting than something that is is more easily removed by weather, but is not truly systemic and therefore does still need frequent re-application--but not as frequent as something of which the mechanism is purely contact.

I don't use it, but if someone as experienced as Carolyn says it doesn't need to be sprayed with as thorough coverage as, say, copper, I would think there's merit to that.

[carolyn137]

Originally Posted by amideutch

When we are talking fungicides there mode of action can be contact, systemic or protectant. They eradicate the disease from within the plant (Systemic) or from the outside of the plant (Contact) or put up a barrier or coating on the outside of the plant (Protectant) not allowing the disease to infect the plant and Daconil is a protectant and this pertains to airborne disease.

As far as Daconil applications are concerned it should be applied to all plant surfaces.

Ami

Thank you Ami,you beat me to it when you said Daconil is a protectant, not systemic,and here's how I found out about Daconil and what it does.

I was spraying my plants with Daconil and alternating with liquid fertilizer and wanted to know if I could do a twofer and combine the two to save time. So I called Ortho,whose Dacolnil I was using at the time and they connected me with a wonderful man who told me the following.

He said that Daconil covered up the receptor sites on the leaf surface for the most common foliage fungal pathogens,that would be Alternaria solani,aka Early Blight and Septoria Leaf Spot and prevented those pathogens from attaching and initiating infection.
Ortho had titrated how many molecules of chlorothalinol,aka Daconil, was needed and to mix it with anything else was a no no since it would dilute the Daconil molecules.

There are no attachment sites for those fungal pathogens on the undersides of the leaves.So what they protect from is new airborne infection,but there's also splashback infection to consider and that's been discussed here at Tville many times.

Hope that helps, and also noting that other companies sell Daconil,here at home,Bonide is being used, but with all the storms and rain it needs to be reapplied frequently.

Carolyn

[GaryStPaul]

Yes, very informative. Thank you all.
Gary

[Yak54]

Interesting. One of the brands of chlorothalonil that I sometimes use is the Bonide brand called Fung-onil. In the directions for use it says that it may be combined in the spray tank with products that contain copper for control of bacterial diseases of tomatoes. I have done this a few times with no ill effects. However I personally have gotten better results using copper mixed with Mancozeb.

Dan

[carolyn137]

Originally Posted by Yak54

Interesting. One of the brands of chlorothalonil that I sometimes use is the Bonide brand called Fung-onil. In the directions for use it says that it may be combined in the spray tank with products that contain copper for control of bacterial diseases of tomatoes. I have done this a few times with no ill effects. However I personally have gotten better results using copper mixed with Mancozeb.

Dan

Yes,that's the name of the Bonide product Freda is using for me,I couldn't remember the name.

Could it be that copper is much smaller than the fertilizer I wanted to combine it with and that's the reason that that combo was OK?

And yes,I always suggest Mancozeb as a protectant for bacterial foliage diseases rather than copper,just from reports back and several places for a few decades.

Carolyn

[Yak54]

I never thought about the copper being smaller than the fertilizer you wanted to use. Good thinking for sure. I also have a bottle of Daconil which is the Garden Tech brand of chlorothalonil and there is no mention of compatibility with anything else.

Dan

[carolyn137]

Originally Posted by Yak54

I never thought about the copper being smaller than the fertilizer you wanted to use. Good thinking for sure. I also have a bottle of Daconil which is the Garden Tech brand of chlorothalonil and there is no mention of compatibility with anything else.

Dan

I now remember something else that the man from Ortho told me and that was that if Daconil was mixed with certain ingredients that it could block the Daconil.Roughly what he said was that if two molecules have the same charge,they repel each other but if one is positively charged and the other negatively charged that they attract, and I do know that is a fact,that the Daconil would be bound to an oppositely charged molecule,thus diluting the effective concentration of Daconil.

But I can't remember if he ever gave any specific examples, but I can't see why that couldn't happen.

I'm pretty sure he was someone in the lab where testing for effective concentrations were titrated and once he knew I had some background,scientifically, he just kept going, and I thought that was great.

Carolyn

[Yak54]

I guess I'll have to go back to my previous method of using Daconil alone cause I sure don't want to spend all day trying to make all my molecules line up to be positive or negative, LOL.

[ScottinAtlanta]

Originally Posted by carolyn137

There are no attachment sites for those fungal pathogens on the undersides of the leaves.

Carolyn

Not sure I understand that sentence. Does that mean we don't need to spray Daconil on the undersides? That would save ALOT of time.

[carolyn137]

Originally Posted by ScottinAtlanta

Not sure I understand that sentence. Does that mean we don't need to spray Daconil on the undersides? That would save ALOT of time.

This is a twofer answer,take your choice.

What I said,no receptors on the undersides of the leaves and yes,it saves a lot of time.

BUT, many say to spray the whole plant and that's b'c Alternaria solani, Early Blight,can also cause stem lesions.

They start out small and then become elliptical as noted below.

https://www.google.com/#q=tomato+ste...a+solani&hl=en

I think perhaps the best of the link list

https://pubs.ext.vt.edu/450/450-708/450-708_pdf.pdf

However,stem lesions are not that common,leaf lesions are,and given the choice, IMO I'd be more concerned with leaf lesions than I would stem lesions.

And your next question might be,well, if receptors are only found for Early Blight on the upper leaf surface than how do the spores attach to the stem?

Very good question say I,and I don't know the answer.

There are some scholarly links at the top of the general Google link search and perhaps an answer might be there.

Carolyn

[Yak54]

Originally Posted by carolyn137

Yes,that's the name of the Bonide product Freda is using for me,I couldn't remember the name.

Could it be that copper is much smaller than the fertilizer I wanted to combine it with and that's the reason that that combo was OK?

And yes,I always suggest Mancozeb as a protectant for bacterial foliage diseases rather than copper,just from reports back and several places for a few decades.



Carolyn

Mancozeb works better for me on early blight than chlorothalonil