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Old 08-11-2008, 01:19 PM
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Dithane M-45 Fungicide

Has anyone used it?

It is a systemic fungicide that I bought for 8 bucks. It comes in powdered form and it seems to be concentrated...man is it strong. I passed by two local nurseries and both told me that they use it. They both produce robust/healthy plants so I took their word for it. It isn't that time of the month to spray so I wanted to consult with the Orchidgeek council.

Right now I am using Physan 20 which I think is more a preventive type of product...so far I am controll the fungus...although I have now included a fan in my setup to dry out the water off the Catt. leaves. Sorry for the run-on sentence. Anyway, does anyone have any good or bad things to say about it?
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Old 08-15-2008, 03:24 AM
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Systemic fungicide..... I think it is not a good idea for orchid. As it rely on some kind of fungus to feed its root. Killing the fungus would eventually kills the orchid. Unless it is proven not harming those orchid (and its specific fungus) that you are growing.
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Old 08-15-2008, 03:29 AM
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My friend have been telling me to peel off all dead leave including those wrapping around the PB. As those dead leaf will get wet easily and provide good base for fungus to grow on.
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Old 08-15-2008, 08:48 AM
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"Systemic" as applied to biocides implies that the material is absorbed by the plant and distributed upwards by one the plant's transport systems. It's Dithane, not Dia...

Dithane M-45 is a formulation of the common (and excellent) fungicide mancozeb. It is not a systemic. It never enters the plant, only exists on the surface. That's not a bad thing, in fact, I'm not a fan of things that invade the plant. Seems to me that they could be more damaging than non-systemics. I've used mancozeb for many plants and it does a great job of killing fungal spores.

The down side is it's a solid powder that disperses in water to make a milky emulsion. You spray it on the plant and when the water evaporates it leaves a noticeable white powder coating on the foliage. Secondly, this white powder is easily washed off so the residual activity is limited to keeping the foliage dry.

It's an excellent, and cheap, fungicide that kills spores in a broad range of ways so it does not generate resistant strains of fungus. It coats leaves with an unattractive white powder. It washes off very easily. It is not seriously dangerous, but I would not spray it in my living quarters because the powder can blow around in air currents and contaminate food and food preparation surfaces. You certainly do not want to breathe the powder.

It's a very good fungicide, but you need to know the limitations before using any product.
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Old 08-15-2008, 11:23 AM
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Several excellent growers in my local Orchid Society mix it with just enough water to make a thick paste which they then smear on those pesky black rot spots that can appear overnight on the leaves (especially on Catts) that all of us outdoor growers are plagued with during Florida's rainy season. It works great if you get to it early enough..it stops the spots from spreading so you won't lose the whole leaf and when mixed this way it forms a pale greenish/yellow paste (the powder is yellow) that is not nearly as noticeable as the black spot was! It doesn't seem to hurt the plant at all, this is the 2nd summer I've done it and plants that might otherwise have suffered significant damage with loss of entire leaves and growths have just a spot on a leaf.
For routine preventative maintenance spraying, in his book Florida Orchid Growing Month by Month, Martin Motes recommends a concoction of Aliette, Manzate and Cleary's 336 which is thiophanate-methyl. These products are available at growers supply and agriculture supply stores and online, you just have to look around for them. I know they are all available at Hicks Orchid Supply, in Winter Park or Winter Haven (Florida), I can't remember which but they do mail order.. only draw back is they are wholesale so you must buy BIG bags that are expensive & unless you have a big collection you don't need that much. On the other hand they'll last you forever but if you look around on the internet you can find outfits that will sell smaller quantities or you can get a few friends together and photocopy the labels and instructions and split it several ways. Hope this helps, Jen

Last edited by Jen; 08-15-2008 at 11:26 AM. Reason: repeated sentence
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Old 08-15-2008, 12:17 PM
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Wow, thank you guys for the information. I thought the fungicide was a lot more serious that what you guys mentioned. I was already thinking,"should I, shouldn't I".

Jen, where can I find that book you mention!?

Now I know what those faded white droplet marks are...I thought they were signs of hard water.

I noticed that as soon as I added fans to my area I have had less problems. Also, I have sprayed PHYSAN 20 every 15 days. I will start a preventive program with Dithane instead...since PHYSAN has been a little "iffy".
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Last edited by FLaCo; 08-15-2008 at 12:20 PM.
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Old 08-15-2008, 01:15 PM
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You are correct to use a prophylactic program for fungicides. You have to prevent infection. After you get it you can only prevent it from spreading. The "droplet marks" might be water drops..it just depends.

Nice post Jen. The yellow must be a feature of M-45. All the mancozebs that I've ever seen are white. Thanks for the paste suggestion.

The most effective fungicides are the strobilurins...Heritage, Compass and others. They are expensive but long lasting and relatively safe for the user. One of their advantages is the ability to "translocate" or move themselves around to cover all the foliage surface. They are somewhat resistant to washing off. Their main disadvantage is that they kill by blocking a single biological pathway so fungi can become immune if you use them continually. The mainstream advice is to mix with a contact killer like mancozeb.
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Old 08-17-2008, 01:58 AM
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FlaCO, the book you asked about by Martin Motes is available at OFE, their web site is [OFE International Web Page[/url], they have all kinds of cool orchid stuff. oops apparently I'm not allowed to post a url until I've made 5 or more posts, so just google OFE orchid supply & you'll find it, the book is $19.99 & worth every penny. The white spots may be just hard water spots, in any case they come right off with lemon juice, which will clean and shine the leaves and is not harmful to them. Alot of growers use lemon juice to clean & shine their plants before a show.

Last edited by Jen; 08-17-2008 at 02:05 AM. Reason: additional info
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Old 08-17-2008, 12:31 PM
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Thanks a lot for the info Jen. I think they are nearby ...and I may just pass by. Thanks again!
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