Brown, Translucent Areas On Rose Bush Leaves

[PGB1]

Hi All!

We have a Proven Winners brand OSO Easy Double Red Landscape rose bush. I planted it 11 years ago. It grows very well and has many flowers. The plant is about 5 feet wide, 3 feet deep and about 5-1/2 feet tall.

This year, something I've never seen appeared. I just noticed it today and wonder if it is a problem.
Some groups of leaves scattered about the plant have brown areas that are quite translucent.

The only causes I can suspect include:
A) In spring, I pruned it down quite a bit, removing about a foot & a half to 2 feet of height and width.

B) For the last week, it has been hotter than I ever remember it consistently being. The high temps have been in the 90's-F during the day and 80's at night. (Unusual for southeast Michigan, U.S.A.)

C) It has rained in storms repeatedly, perhaps 3 times a day, sometimes at night. Lots and lots of water comes down each time. This is more rain than I remember ever having in the past. Before the first time it rained, while it was hot, I watered the plant very deeply.


For daily care, I snip off the spent flowers. The tool is a bypass shear that is sharp and only used for this rose bush. I wash it after each use and use 70% isopropyl alcohol on the blades before use. Hopefully my cutting didn't cause this problem.

I looked on line and saw all kinds of conflicting causes. Do you know from my description and photos what the problem could be?

Thanks for helping me care for my favorite plant!
Paul

 

[Anniekay]

As you said, it could be a number of things causing this I would guess the most likely culprit would be sunscald . Where the leaf is holding water in spots the suns magnification on the water droplets will burn the leaves. Nothing to stress over, just remove them; the plant will grow more.

 

[cpp gardener]

You have sawflies. A systemic insecticide or spinosad will control them. Their larvae look like very small slugs or bird droppings.

 

[PGB1]

Thank You Anniekay for the information about sunscald. That's interesting & sure sounds reasonable considering the repeating Storm-Sun-Storm-Sun weather this week. Violent storms & hot temps.

Several times this week, the plant did get hit with hours of full sun immediately after a heavy storm. The leaves & flowers were very wet & pooling water when the sun came out. (On the driveway near the plant, I actually saw light steam coming up from the puddles when the sun returned after a storm yesterday.)

Thank You CPP Gardener for the information about sawflies & how to control them. This is a pest which I'd never heard of before your post. They're interesting little insects.

I appreciate the information and will study the plant, looking for the larvae.

I've always had good luck with neem oil on vegetable plants that were being eaten. Do you think it'll help with sawfiles?

Thanks Again Anniekay and CppGardener!
Paul

 

[cpp gardener]

Water droplets evaporate too fast to cause sun scald (see gardenproffessors.com).
Neem might work on the sawflies if it smothers them. Remember it goes bad fairly fast so use fresh. Spinosad is a naturally occurring toxin caused by soil-dwelling bacteria.

 

[Mystic Moon Tree]

Looks like sun damage to me, but like something dripped onto the leaves & caused those areas to burn more heavily. I have seen something similar when applying a foliers spray on a too hot day. If the spots were in the middle of the leaf I might say pest damage, but it looks like sunburn/sunscald.

 

[PGB1]

Thanks Again Everyone for helping me figure this out.
It's been cloudy and less hot with short rains, so the conditions changed dramatically from when the brown leaves were discovered.

Two days ago, I removed the rest of the brown, translucent leaves. I studied the other leaves and found just three with holes. They were green. One tiny insect was on each, but they were too small for me to identify with a magnifying glass.

Today, there aren't any brown leaves or more with holes.

I think I'll be optimistic and go with what Anniekay and Mystic Moon Tree said about sun damage. But, I certainly appreciate the information about sawflies & neem that cppgardener supplied and be on the lookout for them.

Thank You All Again!
Paul