Nothing in the photo suggests blackspot. Around here, Rosa Glauca is essentially immune to blackspot. Actually, I find it hard to believe that any of the common fungal diseases would be a serious and recurring problem for this rose.

Have you checked for spider mites?

I don't think it's black spot. I've never seen Black Spot (the specific disease Diplocarpon rosae) on glauca here or in Canada even though other roses in the same gardens had it.
What I'd do would be take off the ailing leaves, put them in ziplock bags and refrigerate them until Tuesday and then get them to your County Extension agent to passalong to your state people who know plant diseases. Ask them to look on the undersides of the leaves for the signs of Downy Mildew (which is very different from Powdery Mildew) and which can only be seen with a microscope.
That doesn't look like 'classic' DM, but there are some regional variations.
Be sure to tell the state people about the first occurrence last fall and now this one and point out the temperature ranges in those times.

I do not know what that is, but I do not believe it is black spot, either.

I saw glauca with BS late in summer, but it looks very different. Do you spray or apply otherwise any insecticides? It looks like spider mite infestation to me, as Mike already mentioned.
Olga

I realised I was not clear in my previous post. When insecticides are applied in the garden, especially on a regular basis, it kills beneficial insects that control spider mites population and they explode. Somebody made a joke here some time ago that when you use Sevin or Merit it looks like you spray spider mite eggs :(
Olga

It sounds like the consensus is that it's not black spot, so I"ll stop using the fungicides (the fact that they didn't help is evidence that this was the wrong diagnosis to begin with).

The only insecticide I've used in my garden is Neem, and I did spray the roses a couple of times when I noticed caterpillars on some of the leaves a few weeks ago, but I stopped spraying when I stopped seeing caterpillars. It sounds like I may need something stronger than Neem. I'm headed to the garden store right now so I'll pick up something for spider mites and see if that helps.

mrblandings I have something that looks pretty close to this on my Iceberg (white). It is like when the leaves age. They will drop off eventually if I don't get to them first. In your picture there are healthy leaves next to the effected ones is it the same plant?
(I would post a pic but don't know how Instructions anyone?)

I would have guessed spider mites, BUT the question came from Massachusetts and it's May and it's been a cold May, at that. Unless this plant is growing in a heat island, spider mites aren't a likely culprit.
But, do you see any fine webbing on the underside of the leaves and if you finger one between your thumb and forefinger, do you feel an almost imperceptible grit?

Wait-- first, you don't have a diagnosis yet. If it is spider mites, it begins on the oldest leaves, which develop a pallor, usually grayish-yellowish-green at first. In more advanced cases, leaves dry out and die. Usually you see a fine stippling on the upper leaf surface. The underside looks dusty. Mites and their webs and eggs are visible with a 6x hand lens.

Second, you need advice from the board here rather than from an ignorant box-store clerk.

So check the plants first and come back. If it is not mites, then we need a sharply focused picture of a flat leaf.

If the neem label says "azadirachtin" or "whole neem oil," then it contains a natural chemical insecticide that might (I don't know) encourage spider mites. The Green Light RTU product contains the added insecticide pyrethrins. If it contains only "hydrophobic extract of neem," then it is nothing more than vegetable oil with an odd scent. Oils can kill mites by smothering them, but you have to thoroughly coat all the lower leaf surfaces and stems, and repeat in a week. Oils can also damage foliage in hot weather.

Most rose growers do not apply any insecticide to the whole plant without a pressing need. The most commonly used mite control is a hard spray of water after removing the damaged leaves.

My R. Glauca had this last year and has a little one it now. It is not spider mites. My guess is a form of Cercospora or antracnose or maybe just older leaves getting ready to die. Older leaves on Glauca are not always on the bottom, in fact I have a lot of leaves which come out in the middle and on top of last years branches before the bottom leaves. I have found that blackspot resistant roses are more prone to Cercospora and antracnose. It did not hurt my plant last year and I suppose that is what is the most important to you. Yes it looks bad and it usually gets worse as the year goes on but I don't think there is anything you can do about it especially if its just old leaves dying. Good luck.

Patrick

For what it's worth (not much?), I brought some leaves to the garden store (a real garden center / nursery, not a box store) and they repeated the opinion that it was most likely fungal, and that they saw no signs of spider mites. I see no obvious insects on the leaves, but I have no magnifying lens to look more closely. There is no gritty feeling to the leaves, and the problem does not just affect older leaves. In fact some small new leaves seem to come in yellow from the start.

I will takes some more pictures tomorrow and try to get better detail of the leaves.

I've never grown R. glauca but I have been intrigued by it. It is supposed to be very disease resistant so BS is probably not likely at least not this early. Could this be some sort of deficiency caused by all the rain we have had?

More photos:

Front of a leaf:
{{gwi:264333}}

Back of a leaf with a green insect. I've found a few of these on the rose leaves but not very many:

{{gwi:264334}}

A set of leaves with healthier and less healthy leaves together:

{{gwi:264335}}

These red bugs are all over the stone wall next to the roses, but I didn't see any of them on the roses themselves:

{{gwi:264336}}

Those "red bugs" are a species of mite, but they aren't spider mites, which are rather a bit smaller than those and clear except for two small red spots on the upper sides of their bodies. Spider mites are also slower moving than those red mites are. When I was a boy growing up in southeastern Pennsylvania I used to see red mites like that crawling all over our asphalt driveway when the weather was warm. I think they're either scavengers or predators. I don't believe they're plant pests.

Are those green insects slow moving, or fast moving? Do they move in a seemingly deliberate manner, or do they stop and start abruptly? I'm almost certain that green insect is a plant-feeding insect (and one that feeds by sucking the juices out of the plants it feeds upon), but I'm not sure of the insect family yet. I'm also not sure it's your problem. Frankly, at present I'm inclined to suspect a fungus is your problem, although it isn't black spot.

The green insects stay in once place unless I brush them off. I suspect they are feeding on the leaves, but as I said I don't see very many of them, so I don't think they are the main problem.

As I stated in my post above my R. Glauca has the same leaf problem and also I have over 100 R. Glauca seedlings which I polinated with other species roses last year which have the same leaf problem. Although I don't worry about it much since R. Glauca always has this. Anyone else with R. Glauca have this porblem?

Patrick

I had/have a similar drive me nuts problem with a rose. For many years I experimented with different sprays, fertilizers, advice etc. The leaves looked not unlike yours with the yellow islands in amongst the green and usually fell off about mid summer. Finally on this forum someone came up with a possible solution. It was the soil. They had a similar situation, took the leaves to their county ag office and he said it was their heavy clay soil. As water accumulates in a poorly drained soil the rose doesn't get enough oxygen and the leaves start looking funky and then falling off. My rose is going on 20 years old now and repeats the new leaves, falling leaves cycle every year. Perhaps you need to look to your soil.

That is an excellent observation Mary. Surely everything should be checked out, Ph, soil test. But my R. Glauca is in the ground like Mrblandings R. Glauca is but what about my 100 seedlings which are potted in a completely different soil, Bed builder soil 1/3 River sand, 1/3 top soil, 1/3 cottenseed hulls and pine bark. And I mean my leaves look exactly like theirs. I was just wondering if it might be just an R. Glauca thing and if anyone else with an R. Glauca could chime in. None of my other roses have this and they are in the ground next to R. Glauca. I don't know what's up.

Patrick

Possibly Cercospora, Anthracnose, or just too much water in recent days/weeks.

Once in a while, very isolated as a leaf or two and this is experience from a 8 and 10 footer that are 8 years old in zone 3a. Never sweated it as I viewed it as normal attrition - soil alkaline and dry as a bone in both spots

I grow almost all modern roses, so I can't speak to your specific type of rose. I tried to cut down my rose leaf saga to a paragraph or so, but it went on a good 10 years of searching for the answer. One of the things that boggled my mind was that there were 3 roses planted next to each other. 2 of the "funky" leafed variety, the other in the middle was Iceberg. Iceberg's leaves always remained unaffected. Rootstock problems? Different varieties react differently? More questions then answers.