Disease? recognize these spots?

[mntlover]

This appeared on the leaves about midsummer. The first summer one plant had it (Cinderella Fairty Tale). The next summer several plants had it.
I thought it may be a disease? Or watering in the sun?
Do you recognize this? I've never seen it before, but was wondering if it was cercospora, which I haven't seen before.
Thanks!
Duane

(working on figuring out more disease resistant parents.)

[John Moe]

Duane - It looks like the damage from a rose slug. The eat away the top surface of the leaf thus reducing its ability to contribute to the photosynthesis process.
John

[mntlover]

Interesting! I haven't seen any slugs. Do they come in at night and prey on my babies while I sleep?
Duane

[jbergeson]

I agree with the slug diagnosis. Yes, they come out at night. The product called Sluggo does seem to work, and is non-toxic.

[mntlover]

Excellent! Thanks for the help!
Duane

[MidAtlas]

"Rose slugs" aren't actually slugs, mind you, despite the name--they're actually sawfly larvae, and as far as I know are not attracted to nor affected by Sluggo (which is a specific killer bait for actual slugs, and has no effect on insects like these). You can see them as mostly green, curled up caterpillar-like critters on the undersides of the leaves during the day, and they start out as eggs laid by the adults inside of small "bubbles" in each leaf. The trick is to catch them early, and it also seems to me that they seem to target certain rose bushes for unknown reasons while leaving some others completely alone. It's not consistent from season to season, though, so one year it might be one rose that's attacked a lot but an adjacent rose is unaffected, and then the plants might well exchange fates the next season. Any insecticide labeled for them will work, which is probably most general insecticidal products (I usually kill mine by hand, because they're not usually too dangerous to roses here.)

Stefan

[mntlover]

Thank you. I will be sure to keep a wary eye out for them. Glad to know it isn't a disease of some kind, as it started on some of my most disease resistant plants I'm breeding with.
Duane

[roseseek]

Yup, sawfly larvae, "rose slugs".

[david zlesak]

They are sure small and blend in well. They scrape the lower sides of the leaves leaving a "window paning" effect. There are 3 species around here in the Twin Cities area. Two have just one cycle per year and after June the new growth is okay. The bristly rose sawfly/slug has multiple cycles per year unfortunately and the damage continues on throughout the summer without treatment.

[mntlover]

This must be one of the two June varieties because I notice it in mid summer on the growth to that point, but not after that for the next cycle of flowering branches. Also, I notice it on only certain varieties: there are more the second year than the first, but not each of the plants.
Interesting little green grubbie thing (thanks for the picture!). We have worms on our currant bushes each year, so I was wondering if they might be the culprit, but clearly a different worm (slug, grub, or whatever...).
Thanks again guys!
Duane

[roseseek]

Their presence is completely weather dependent. Along the California coast, when we have "green house conditions", they will flourish and remain active as long as those conditions continue. Once the humidity decreases and the heat increases, they disappear. In my yard, nine miles from the Pacific, where the topography is fairly level so the marine influence remains fairly constant, I observe their activity when the fogs are fairly heavy and continuous. Once they subside and the sun remains less filtered, they move to the more protected spots in the yard until "summer" arrives and the conditions become less to their liking and none of their damage is apparent. Down in coastal Los Angeles, where I worked for years, we would have sawfly damage on many plants most of the year except late August through October when the real "heat" arrived there. It was during that eight-plus month period the once-flowering plants would "repeat", because "spring" conditions were fairly constant. O'Neal blueberry would flower and fruit most of that period, also and R. Banksiae would deliver flush after flush of blooms, leading quite a few to believe they had discovered a repeat flowering Lady Banks.

[mntlover]

That might explain so much more on plants last year. June's weather was not normal here: it was more like May's weather, much more cloudiness and rain, without the sun heating things up like normal. Well, I guess I know when to really look out for them. Thanks!

Duane