As long as the spray had time to dry--which should only take a couple hours--, there is no problem. It would not take 16 hours to dry the leaves.

Kate

Propiconazole label states for ornamental use "Allow spray to dry before overhead irrigation is applied". (presumably, this applies to rain as well). Turf managers consider that three hours drying time is the rule of thumb for systemics.

Contact fungicides (like Mancozeb) are always more sensitive to wash-off by rainfall or irrigation than systemics, because their mode of action relies on drying and remaining on the plant surfaces. The rule of thumb used by turf managers is no rainfall or irrigation within the day of application (turf managers almost always apply their fungicides first thing in the morning). Of course, a heavy rainfall is going to wash off at least some of the remaining contact fungicide no matter what

Turf generally takes longer to dry out than other plants do, but I would still use those as general guidelines.

So you are OK insofar as the systemic is concerned, but you probably lost some of the effectiveness of the Mancozeb simply due to the volume of rain. I wouldn't re spray the Mancozeb. but I would consider applying it again at a shorter recommended interval.

This post was edited by nickl on Tue, Jul 16, 13 at 10:12

Propiconazole is fully effective by itself, so the mancozeb isn't really needed except maybe as insurance against resistance developing to propiconazole. Such resistance is unlikely to develop in the home garden.

Ok thanks for all the advice! The Mancozeb/Propiconazole combo must be an "old wive's tale" as Rosemania is a proponent and also Mr. James Mills from K&M Roses in Buckatunna recommended this combo to me. I already have some tebuconazole, so I may just go with the Pro- and every now and then switch to the Tebuc- just to switch it up.

In my area it has been overcast and raining nearly every day and the humidity has been 100% for over a week and my leaves are still staying clean.

My other question is, so with the "azoles", since they are systemic, is it necessary to spray the bottom and top of the leaves? I always found it kind of difficult to do that in reality and it seems to waste so much spray trying to get the bottom of the leaves. Trying to get the bottoms is also when I run the greatest risk of accidentally getting some on myself, which I obviously want to avoid.

Curious about Mancozeb/Propiconazole myself.

Skipping the point about whether Mancozeb is necessary, can you mix them in the same tank?

Back to the question of Mancozeb's usefulness. My scheme is that Propiconazole is preventive whereas Mancozeb is curative. I use Mancozeb only when I see (significant) BS. No idea where I read this.

I'll try to answer.

The "azole" systemics do penetrate into the plant surfaces, and do travel within the leaves. Nevertheless, if you can, it's a good idea to cover the top and bottom surfaces of the leaves. But you don't have to be compulsive about it.

Mancozeb has been observed to be somewhat curative. of black spot. 'Curative' is a synonym for what the farmers call 'kick-back effect' in fungicides. .However, "officially" Mancozeb is a multi-site preventative. contact fungicide, not a curative. When used in a tank mix, its role is mostly to act in synergy with another preventative fungicide, usually a systemic. AFAIK, it is compatible with all the azoles.

Mancozeb has a negative impact on predatory mites, so current thinking for fruits and veggies IPM is that it should be applied no more than four times in a single season. I think that limiting it on roses would also be prudent.

This post was edited by nickl on Thu, Jul 18, 13 at 9:26

I still use the combo of Mancozeb (surface)/Propiconazole (systemic), as they have different actions.

I mix them in the same tank, with the addition of a liquid seaweed product (Response or Neptune's Harvest).

Propiconaole and tebuconazole are so similar, there is no point in rotating them, except to use up the chemicals that you have.

Tebuconzaole (Bayer) is proven curative on blackspot. That is, it kills the fungal body inside the leaf. It will save the leaf if sprayed within 10 days or so after germination. Otherwise the fungus has already damaged the leaf beyond saving. But the fungus is disabled and, I presume, incapable of sporulating. Propiconazole (Banner) probably has the same effect, but I am not aware of any research to support that assumption. Tebuconazole is also preventative although not 100% effective in that role. But if you spray every two weeks, the combination of prevention and cure is almost 100% effective.

So how does mancozeb make it any better? It's added expense, added health hazard, a risk of encouraging spider mites. It is insurance against BS developing resistance to -azoles, but I've never heard of that happening in a home garden.

Mancozeb alone will provide adequate control if it is used every week with an acid pH buffer. However, it leaves a heavy visible residue.

Of course mancozeb + -azole will work, but so does tebuconazole alone. I don't have much experience with propiconazole, since I observed it to cause stunting of shoots.

Regarding spraying both surfaces, this is the traditional advice. However, it is quite rare for BS to attack through the lower surface, with or without fungicide. When I started using tebuconazole, I stopped spraying the lower surface with no loss of control. In spraying the reverses, you are just using chemicals unnecessarily.

This post was edited by michaelg on Thu, Jul 18, 13 at 10:52

It's not an old wives-tale and I think calling Mancozeb a health risk is really stretching it. It's no more of a health risk than Daconil or Funginex.

Because of the different action on fungus, rotating the Mancozeb by mixing it in with tebu- or propi- conazole has the same effect as rotating different fungicides. The reason you do this is because the Mancozeb has very limited staying power, as many have referenced above. However, including the -azole at the same time keeps the preventative regimen in play.

Mancozeb is extremely good at knocking back a BS outbreak, whereas you may have to suffer for a week or two with an -azole alone (or longer). You can spray Mancozeb (I use Pentathlon) and reliably be assured that all BS is dead at that point forward. I've seen it work in my own experience. One might get the same results with Daconil, but I'm not sure if it can be mixed with an -azole and you can't spray Daconil in the middle of summer without burning anyway. Mancozeb leaves a residue and it may be hard on the flowers, but it's very kind to the leaves - even in peak summer heat.

diane_nj, what's the intended purpose of the addition of the liquid seaweed product?

This post was edited by ratdogheads on Thu, Jul 18, 13 at 14:46

Tom, as far as I know, all synthetic fungicides, and some "natural" ones, and of course many other substances that we handle routinely around the house and yard, pose some degree of health risk. For example, a metabolic product of mancozeb is a known human carcinogen. There is also evidence that mancozeb exposure increases risk of Parkinson's disease. It appears to be more hazardous than propiconazole. So why double your lifetime exposure by using both when one will do the job?

Nicki referred to evidence that mancozeb can be curative. I never heard of any actual evidence (as opposed to unsubstantiated claims by a vendor) and would like to know more. Mancozeb is a preventative, surface-acting fungicide. It coats the surface of the leaf and kills the germinating spore as it tries to penetrate the leaf with a foot called the appressorium. Can anyone produce any science-based source that says mancozeb kills the fungal body after it has infected the leaf? I suspect the belief that mancozeb is curative comes from a misunderstanding of the (misleading) term "contact fungicide," sometimes used for surface-acting, non-systemic, protectant fungicides like mancozeb. As far as I know, only systemic fungicides are curative, meaning they have the power to kill the fungus after infection. Tebuconazole is both preventative and curative of blackspot.

This post was edited by michaelg on Thu, Jul 18, 13 at 15:41

ratdogheads, I find that the liquid seaweed promotes better substance on my leaves, they are thicker and larger than before I started using the products.

Diane, I've had the same experience. Seaweed contains a growth stimulant that makes the leaves bigger if it is applied as a foliar spray.

Michael,

I would agree that Mancozeb is not "curative." However, in the ever-constant battle against BS, the ability to spray something and know for certain that every spore at that particular instant is DEAD, well, that's a great luxury for this rose grower. ;-)

As for the health-accusations, I agree that many chemicals pose a health risk. So does gasoline and hair spray, but many people handle it every day. With the proper protection - I suit up with eye protection, gloves and respirator every time I spray, plus shower immediately afterward - I think the risk is significantly minimized.

My concern is that everyone gets into hysterics about the safety of a modern product when the old stand-by stuff like Daconil, Funginex, or even sulfur spray has been out there for decades and pose perhaps just as much risk or more. If you take proper precautions, some of the modern stuff - like the -azoles - are a Godsend for rose growers.

Just imagine if Bayer or someone similar comes out with an RRD eradicating chemical (or mite killer). I'm not going to try to ban it from the market if it comes with a bit of manageable risk.

"Nicki referred to evidence that mancozeb can be curative. I never heard of any actual evidence (as opposed to unsubstantiated claims by a vendor) and would like to know more."
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Careful please. I never said that there was "evidence" - I said it "has been observed".. There is a difference. which is why I said it that way. I also know of no actual evidence of a kick-back effect of mancozeb with respect to black spot or any other fungus, but it has been widely observed by rose growers.

In any case, we have personally limited our use of mancozeb around the whole garden specifically because of its negative effect on predatory mites. Damaging mites have been a serious problem with us on our roses and on other plants. We need a healthy population of predatory mites to help keep them under control

Always take precautions when using ANY biocide and follow the label

Here is a link that might be useful: Pesticide Health and Safety Information

Nicki, my apologies for misstating your position. What is it, exactly, that gardeners have observed or thought they observed upon using mancozeb? I am not trying to be quarrelsome, but trying to understand what is being claimed.

a. Existing black spots disappear (surely not).

b. Green leaves with black spots do not all yellow and die but some live on (curative effect as with tebuconazole and, probably, propiconazole).

c. Infected leaves yellow and die but no new infections develop (preventative or surface-protectant action as with Daconil).