All mine pretty much look like that, specially the ones closest to the house. The heat will radiate off the stucco or afternoon sun side. The roses are crispy critters and will crumble in my hand. From now until Sept I lay off fert and just water, water water. It has been un-usually hot and has not been lower than 111 for the past week and a half. .....Arizona

That's heat/light stress. It happens even in my colder climate to my roses. Some varieties have more delicate new growth than others do. Even well watered roses can show the damage shown in your pictures. Nothing much can be done. Shading the roses when the sun is most intense, a daily event, is not practical in most cases.

Moses

He suspected that, Moses. As I said I thought it would be sun effect.

However, the cultivation of rose bushes never ceases to amaze me. Surely you, especially the gardeners who live in climatic zones with very hot summers, will have seen the effect of sunburn on the leaves of their rose bushes.

Not always that an excess of sun acts on the leaves does it of the same form. This way of "burning" is very curious.

Why only burn the final triangle of each leaf and does not occur on the rest of its surface?

What is that orange line that divides burned area / area without damage?

Oh!! I always wonder and wonder about all the things !! Hahahaha In the end, curiosity is what incites us to learn. True?

CampV, in my case it is two roses that do not grow near any wall. They only have air around them. Both are in garden areas that receive sunshine absolutely all day. From it leaves until it gets. And that in Spain is a lot of sun !!!

Oldrosarian, In fact, applying fertilizer at high temperatures can cause damage to the leaves.

However, in this case it is not the cause. I only use organic fertilizers in my rose bushes. It is difficult to end up damaging the roses with these fertilizers. I fertilized long before the leaves were damaged in this way that is seen in the images. In addition, we always water before and after the application of any fertilizer.

Yes, I think the cause should be sunburn. What happens is that it is singular how the sun burns these leaves only in half of them and not in the whole leaf.

I think it is caused by hot temperatures, not necessarily sun. The roses I have in full sun do not get burned like that normally, even though we have temps in the 90sF a lot in the summer. However, about two weeks ago it was 105 degrees F, and a few of my roses have burned leaves like yours. I have an old old rhododendron in FULL shade. However, I noticed yesterday that it also go burned leaves just like your roses when we had that heat wave.

Regarding the pattern, I have NO actual information - just a guess. I guess that the plant is trying to save itself, and as much leaf surface as it can. So, it stops sending water (fluid) out to the tips of the leaves, so it can save the rest of the leaf.

Jackie

I agree with Jackie as we just had two hot days out of nowhere and even bushes in shade were crispy because they aren't hardened off properly if the temperatures fluctuate too drastically or dramatically. Usually the heat gradually rises here in the summer, and the plants get used to the heat slowly; but if it goes from say 60 degrees for weeks and then 100 degrees one day, the plants suffer. Also I believe there exists more heat tolerant roses and ones that aren't so heat tolerant. Not sure if that's the case here but the heat dries out the leaves in my garden just as much as the direct sun can.

Jaqueline, it is interesting his explanation for the fact that only the tips of the leaves are burnt.

I would like to look for information on this fact. Is it possible that the rose bush stops sending sap to some parts to preserve others from death?

I mean if that botanically is possible? I will imagine the explanation of the process. Maybe it's a crazy idea but I'll expose it:

It occurs to me to think now what happens in autumn. As temperatures drop, the rosary is ready for winter. Before dropping the leaves the rose bush "recovers" the nutrients from the leaves and accumulates them in the roots. Then, since it is not going to specify the leaves for photosynthesis, the amount of abscisic acid and ethylene increases, and this increase causes that in the zone of abscission (leaf-to-stem bonding) the leaf detachment finally occurs .

In this case it is not a matter of recovering the nutrients from the leaves nor does the rosal need to be detached from them because it will continue to specify them for photosynthesis and transpiration. Ethylene and abscisic acid do not increase and so leaf detachment does not occur (leaf senescence). It only allows the tips of the leaves to die, leaving the part that is possible to them alive. This part of the saved leaf of death will continue to be useful for photosynthesis.

Hahahaha Sorry It was just an idea of what could happen. Should be an amateur with botanical knowledge who could tell us if this is really the process or we are in error.

Leaf size and "vein" size and number determines the water carrying capacity at a fairly constant rate, coming from the leaf and leaflet base outward to the tip. When that capacity is reached, that's it. If there's more demand due to higher temperatures, the leaves can't keep up. Since all the water comes from a central place and flows at the same rate, one will see the "line" when flow stops. On smaller leaves and leaflets, I see total crisping as water can barely get to them. It doesn't seem to matter how much I water them over a certain amount as they can't absorb any more, although a small, but constant flow may avoid it.

Vaporvac, great explanation !! It seems to make sense. Yes!

It is curious because this process is not happening now, when temperatures are the highest of the year. It occurred in spring, in the month of April ... I remember perfectly that in two variety especially, Rosa 'A. Shropshire Lad 'and Rosa' Munstead Wood 'without too high temperatures, some of its leaves have this process.

It does not occur throughout the rose bush. Not all tips become this aspect. Only some of them.

Last year it happened the same in the two roses that I comment. At this moment I also see in other rose bushes some stems that at their end have some loose leaf with that aspect.

I'm not very worried about the issue because I see that it does not affect the whole rose bush. It only ever occurs and few leaves are affected.

But I was curious to know why.

Many thanks to all for your participation.

Maria.