Help with what brand fungicide to buy?

Longlocks(z6 PA)May 16, 2005


Have many large mature (15+ year) rhodies (average of 9 feet tall) that are suffering badly.

Problem does not appear to be insects..think it is a fungal leaf spot disease? Not really sure, but reading this article published online by Clemson University and looking at the accompanying picture of Septoria leaf spot this looks like what I've got.

Recommended treatment is a I'm wondering what brand to use? Article mentions specific fungicide sprays like triadimefon, propiconazole, thiophanate-methyl, chlorothalonil or mancozeb but not which BRAND contains these ingredients.

I have never used a fungicide before so felt rather helpless the other day when confronted by the many many products out there! Can anyone recommend a brand that would contain one or more of these mentioned fungicides that they've used successfully? Any brands to stay away from????

Thanks in advance for your help!


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morz8(Washington Coast Z8b)

Funginex, Daconil....Bayleton is a product easy to use as it is systemic and awkward lower leaf surfaces don't necessarily have to be covered. Whichever you buy, be sure to understand and follow the container directions very carefully.

But, I wonder if you wouldn't like to get a visual ID of your plants problem before treating. There are lots of leaf spot diseases, and insects and cultural problems that might lead you to think you have a fungus of leaves. Could you post a photo, or take an example leaf to your nearest county extension agent or full service nursery.

Most foliage spots are cosmetic only and not particularly harmful to the plants. Not all varieties of rhododendron are susceptible to leaf spot disease. And often fungicides work best as a preventative against new foliage being infected, they are not always successful as a sounds like with the size of your plants, spraying would be a major task and I'd like you to be sure what you are spraying for before investing the time and expense of such a large project.

    Bookmark   May 16, 2005 at 3:25PM
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Longlocks(z6 PA)

Okay, some pictures.

If you saw this leaf, wouldn't you think some garden critter was chomping on your leaves?

I did too, but there are NO INCECTS bothering these plants. I've looked and looked and looked (and yes, I went out at night with flashlights and searched for slugs, zilch nada on the insects.

Well, here's how these holes in the leaves get started:

As you can see they are brown spots (these can be like leaf on left where they are sort of "freckled and small" and all over or like on the leaf on right where they are bigger and fewer).

Eventually the brown spots decay away leaving a hole...making it look as though your leaf has been eaten by some critter. Entire leaves can disappear! In the following picture you can see a leaf with a brown spot AND with the holes left where other brown spots have now decayed away:

We've always had a few leaves do this over the years; but I didn't think it was anything to be terribly concerned about; I simply pulled the 'icky' leaves off.

However, now practically every leaf on every rhodie (and native mountain laurel I've got) is like this. (Only difference with the mountain laurels is that they tend to become yellow with the brown spots and they fall off of their own accord without being cut or plucked off).

I know if it is a fungus that I need to remove the leaves and discard them...BUT and this is a big BUT...if I do that, I'll kill the plants because I'll practically have to denude them of all of their leaves! Also realize that spraying a fungicide will not "cure" the already sick leaves...but perhaps I can get rid of enough of the fungus to allow plants to regenerate and come back healthier next season?

These rhodies are simply huge (like trees) really -- they tower over me! They are growing on a slope and large portions of them lie directly on the ground (making getting under them down there to spray almost an impossibility) and removal of leaf litter underneath them was really hard, but I finally got almost all the old leaves out from under them. (They've been accumulating leaves for 15+ years and they are under a vast canopy of hardwoods (oak and ash trees) so there were a LOTTA LEAVES!)

Since rhodies need to be well muched and like acid, I figured the leaves (red oak espcially since it is particularly acid) were good for the plants and that's why I left the leaves under there. I'd noticed that when I raked the oak leaves out from under my native mountain laurels (virtually have a whole forrest of these) that they tended to I figured they needed those huge leaf piles under there; likewise my rhodies....but now with this problem that I'm having I'm wondering if I did wrong to leave the leaves so long?

At any rate, if someone can confirm that what I've got is leaf spots (a fungal disease) and suggest a course of action that will save these plants I'm all ears!

The amount of fungicide I'll need to spray will be vast (and it isn't cheap!) and reading all the warning labels makes me VERY leary about using them...there's no way I'll be able to spray undersides of leaves thoroughly, etc., without getting this stuff all over me! Is there any alternative to get rid of fungus problems that don't involve nasty chemicals?

(oh and by the way, I never water these plants by spraying water on the leaves; they are always watered by hand down at the roots and this is done early in the day as I understand watering at night can often promote fungal diseases of this type).

Thought I was doing everything right as these shrubs have flourished for quite some time! Are rhodies more suseptible to fungal disease when stressed? We had jillions of the Brood X Cicadas last year!

Oh my gosh, it just dawned on don't think these spots are where the cicadas tried to lay eggs do you? It was my understanding that they laid their eggs in the branches of trees! (Indeed many of the small branches where they injected their eggs are now falling to the ground whenever we have a little wind). These spots on my leaves do not look anything like the branches they laid their eggs in though....perhaps they tried to lay eggs and were unsuccessful but the action of their piercing the leaves is what damaged my rhodies???? When I say we had "jillions" of these things I'm not kidding--there were so many that when they died (and dropped to the ground after mating/laying eggs) there were enough of them that they "smelled" as they decayed! Walking around the garden was a nighmare...crunch, crunch, splat, oops....slipping on a pile of dead decaying cicadas was NO fun!


    Bookmark   May 17, 2005 at 9:44AM
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morz8(Washington Coast Z8b)

Longlocks, photos one and three are showing adult weevil feeding damage. A light infestation of well established plants is mostly cosmetic, heavier and you need to be concerned about root damage from larvae and general stress to your shrubs. There may even be a possibility the openings in leaves caused by the adults could be offering a foothold for secondary fungal or bacterial leaf spot.

The leaf litter under your rhododendrons is beneficial like you thought. Your site sounds much like the ideal conditions they would have in their natural native environments - sloping which implies good drainage, and a constant accumulation of plant debris and remains creating an acidic, moist, loose 'soil' over their roots. It is recommended when dealing with a leaf spot problem to pick up and discard any fallen infected leaves....that sounds like a hands and knees operation in your garden and possibly not feasible.

You definitely have a leaf spot problem, I don't have the experience to tell you which one. Bayleton may be the easiest product for application to the large plants you describe because of the systemic properties, it's expensive. And, it won't do anything to resolve the weevils (beneficial nematodes can be helpful there for reducing numbers of larvae). Orthenex is orthene with funginex so insectidice with a fungicide, but I would truly hesitate to suggest you use that in a large area if you are unused to dealing with garden chemicals. I've used it for smaller problems on a totally wind free evening, wearing hat, gloves, long sleeves and pant legs, then undressed in front of my washer and deposited all clothing there before heading for the shower.

I really would suggest again that you take samples to your county extension agent, describe the size of the plants in question, and ask from the best recommendation safest for a home gardener.

Here is a link that might be useful: fungal and insect problems

    Bookmark   May 17, 2005 at 2:41PM
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morz8(Washington Coast Z8b)

Sorry, I didn't address the cicadas, we don't have those here. The notched outer edges of leaves, though, is weevil.

    Bookmark   May 17, 2005 at 2:44PM
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was wondering if baking soda'water& oil will stop leaf blight on moutain larual or i've being told of nofat milk&water will this help thanks, tony petillo

    Bookmark   January 8, 2012 at 11:40PM
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rhodyman(SE PA, USDA Z6)

There are two major fungi that attack Kalmi, leaf spot and leaf blight. They look similar:

1) Leaf spot, caused by the fungus Mycosphaerella colorata (Phyllosticta kalmicola), is characterized by round to irregular, greyish white to silvery spots, 1/8 to1/2 inch in diameter, with reddish to purple borders. Black specks, the fruiting bodies (pycnidia) of the fungus, form in the centers of older spots. Leaf spot is most severe under crowded, shaded, and excessively moist conditions.

2) Leaf blight, caused by the fungus Diaporthe kalmiae (Phomopsis kalmiae), can be distinguished from leaf spot by the larger, circular, brown lesions that often develop a zonate pattern. The lesions frequently first appear near the margin or tip of the leaf, gradually enlarge, merge with other lesions, and result in the death of the entire leaf blade. The fungus may also spread from the leaf through the petiole into the twig, causing twig blight.


Leaf spot disease is severe on laurels grown in dense shade and with sprinkler irrigation which frequently wets the foliage. Removal of diseased leaves help control this fungus on laurel and other members of the Heath family. Several other leafspotting fungi may be found on laurel, but control is the same.

They are rarely serious enough to warrant chemical control and are often effectively managed by following good sanitary and cultural practices. In fall, it is important to rake and remove fallen leaves from the vicinity of the shrub since many of the leaf- spotting fungi overwinter on fallen leaves and plant debris. This practice reduces the number of spores available to infect emerging leaves in spring.

It is also important to follow sound cultural methods that promote plant vigor. These include proper watering, fertilizing, and mulching, and appropriately timed pruning, and managing insects, particularly the black vine weevil. Leaf spots and blights are most severe under crowded and shaded conditions.

It is much better to prevent leaf blight than try treating an infection.

    Bookmark   January 11, 2012 at 3:35PM
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rhizo_1 (North AL) zone 7

I'll suggest that the cicada shown in the image are simply adults resting and/or getting ready to die. Their habit is to deposit the eggs into slits that they cut into twigs and stems, not leaves. After that act (for the females...and after mating for the males) they die.

    Bookmark   January 12, 2012 at 12:05PM
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rhodyman(SE PA, USDA Z6)

Interesting. However, that picture was posted 7 years ago. Someone hopped on an old thread asking about leaf spot on Kalmia in the azalea group.

    Bookmark   January 13, 2012 at 11:01AM
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