Podocarpus Leaf Scorch Update from Previous Question

Q. Thank you so much for responding to my letter. I did want some clarity on these trees because I was surprised you determined this was a watering and not sunscald. First off, these trees are in a courtyard about 5 ft apart and they are on the same run station.  The trees on the south wall are actually shaded by the wall.  The trees on the north wall are getting more direct sun, so I figured the leaves had sunscald.

If you don't mind my asking, why do you think it's a watering issue? I clearly diagnosed it incorrectly so I'd like to learn how to better diagnosis this issue if I come across this again.

Readers Podocarpus with leaf scorch on the north side.



Podocarpus showing no signs of leaf scorch and with rock mulch, a potential problem in the future.

A. I recently started a Yahoo group discussion page because I felt my blog did not give enough opportunities for discussion. It can be found in Yahoo Groups as desert_horticulture@yahoo.groups.com As long as you become a member (which is free but you have to be admitted by the Administrator) you can ask questions, post your thoughts about someone else's comments or add with your own experiences. It is meant for sharing information. To send a question for my blog you have to send it to me in an e-mail which is Extremehort@aol.com

            It is always difficult to assess a situation remotely. I have to rely on what I know about a particular plant, our climate and soils and my personal experience. I have these plants myself and they are located next to my home on the east side. They get a very small amount of water but it is regularly applied.

            First of all, we know they are not true desert plants so we have to add a lot of extra things to get them to grow well here. Soil improvement at planting times is one of them. They will do better with wood surface mulches as well as long as you keep them away from the trunk during the first five years. Besides that, the microclimate or their exposure to the elements can make a difference.

            I also know that these plants can suffer if they get watered too often or if they don't get enough water. The problem is, they look similar if they get watered too often or not enough. When they get watered too often, the roots begin to die. Once the roots begin to die they can't take up enough water and they look like they are drought stressed. Drought stress will be leaf tip burn like yours or even branch dieback if it is extreme. If it is a chronic lack of water in summer months they usually have leaf tip burn.

            I know that plants growing on the north side of the building, or the east side as in my case, are in a cooler location than they are on the South or West sides. High temperatures, wind and lots of sunlight drive plant water use up tremendously. So, plants on the north side and East side will not use as much water as they would on the South and West sides.

(As a side note, ideally, we should be irrigating plants on the south and west sides differently than the plants on the north and east sides. This means they should be on different valves.)

            You called it sunscald and in a way you are right. Usually the term sunscald has to do with burning of the limbs and trunk of a tree, not the leaves. But that is a technical issue and you would not necessarily know that as a layperson but I got what you meant. We would actually call this leaf scorch or tip burn.

Leaf scorch on mockorange

            Leaf scorch typically occurs around the margin of the leaf. Leaf scorch occurs because not enough water is being pulled by the roots of the plant and transported to the leaves. The margins of the leaves, or edges, are furthest from the veins and they are the first to show a lack of water, resulting in scorch.

            A lack of water can occur because not enough water is applied, or there is root damage so it can't take up enough water, or the plant is just is not suitable for a very hot and dry climate and it can't take up enough water in enough volume. We see leaf scorch in plants here like the really big sycamores (that always get cut down when they are about 15 years old because they look so bad) and a few others.

Sycamore with leaf scorch due to reflected heat from south facing wall

We will also see leaf scorch from plants that are stressed in other ways. For instance, if a plant is suffering in a lack of a nutrient, like iron in iron chlorosis, it will scorch when the same plant which is healthy will not. An unhealthy plant just cannot handle the extremes like a healthy one can.

Leaf scorch resulting from iron chlorosis in apricot

 

            Your plants have leaf scorch or the leaves are dying back on the north side but they are doing well on the south side, as you said. I am assuming that the plants on the north and south sides are getting similar amounts of water. If they are good on the south side, then it appears like they can handle that very hot and bright exposure okay (at least for now).

            These same plants should have no problem handling a north (less stressful) exposure ... but they ARE having trouble. So I ask myself, why do they look poorly on the north side when that should be where they look the best? The reason they look bad on the north side is because of leaf scorch, judging from your picture.

            Leaf scorch is a lack of water and my reasoning tells me that perhaps water is applied to often or the soil cannot drain adequately and roots of the plants are dying on the north side. This would result in leaf scorch in the areas where the plants are receiving watered too often or the soil cannot drain adequately. Whereas the plants on the south side are not. So I reasoned that the soil was staying too wet on the north side. On the south side, where it is hotter and water is lost more quickly, the roots are not dying and they are surviving.

            That is in a nutshell my reasoning for what I said. I could be very wrong but with that particular plant I would've guessed the opposite would've normally occurred; you would have seen leaf scorch on the plants on the south side, not the north side. I will be happy to talk with you further about this if you think I am wrong.

Plant Podocarpus With Leaf Scorch May Be Too Much Water

Q. I planted six Podocarpus (Fern Pine) in March, three by the north wall and three by the south wall. Now the three on the north wall have leaves that are turning brown. The three on the south wall are fine. I just didn't realize that the trees would get this much sunscald.  Any suggestions on what I can do, besides give them macronutrients and hope for the sun to change course?

Bottle Tree With Dying Branches

Q. Our bottle tree branches are getting dried and  one side of the branches died 2 years ago. I am enclosing photos of the tree. Can you tell what is wrong with this tree? We love this tree very much. Is there any way to keep the tree from dying?

Bottle tree with dying branches.

 

A. There are two main problems that can develop on bottle tree; those are sunscald on the smooth branches and trunk if put into very intense sunlight and root death due to too much or too frequent watering.

Trunk of bottle tree

            We must also remember that their smooth green trunk and limbs get brown and furrowed with age so there is a natural progression from green and smooth to brown and furrowed. This must not be confused with brown and dead or dying.

            Some of the pictures you sent seems to show much of the dead parts of the limbs are on the upper surfaces of the limbs which kind of points to sunburning. This can lead to limb dieback.

Upper canopy of bottle tree.

            It is important for this tree to maintain a full canopy to shade the limbs. Most of this type of damage might be on the side facing the most intense sunlight which is on the upper sides of limbs particularly on the south and west sides of the tree. If someone got in there and pruned them improperly this could cause a lack of shading and sunburn with limb dieback.

            The other possibility is root rots due to frequent irrigations and not letting the soil dry out between irrigations. This plant comes from semi-arid (but not necessarily desert) regions of Australia. They will tolerate lawns but the soil must drain quickly.

            All you can do now is to remove dead limbs, keep it watered adequately but not excessively and fertilize once a year in the early spring. Surface wood mulches will help as well.

Palo Verde Dont Like Butch Hair Cuts

Q. Attached are pics of a Palo Verde which has some unusual black growths on the upper sides of the limbs. I'm wondering if it has something to do with pruning, since it appears to be only in areas that have been pruned, although other pruned areas are unaffected.

Damage to upper surface of palo verde limbs from reader

Palo verde pruned too high, in my opinio, allowing for
potential sunburn on upper surface of limbs

Palo verde with sunburn damage, borer damage and
limb and trunk damage

A. My first reaction to the pictures was sunburn damage. But I would have to see if this damage was sunken like a canker.
Next I would take a sterilized knife and cut around the edge of the damage and through the damage to see if the wood below the damage was dead or not. If it was dead below the damage and the damage was sunken then it is most likely sunburn damage to the limbs.

The pics you sent had damage all on the upper side of the limbs which is consistent with sunburn damage. You wondered if it might be associated with pruning which it is. The big mistake people make on Palo Verde with the photosynthetic green bark like is pruning so much that too much light gets inside the canopy and burns these photosynthetic limbs. Even though the are designed to absorb light there is such a thing as too much light.

These trees don’t make a lot of shade and when we remove too much canopy we will get sunburn on the limbs. Once we get these limbs sunburned then we have to look for possible borer damage. They go hand in hand and several borers are general feeders and are not really particular what they lay their eggs on.

The adults focus on damaged trees for egg laying. So cut into the damage and look for football shaped exit holes about 3/8 to ½ inch long and ¼ inch wide under the damaged, sunburned bark. If this is the case, don’t prune so heavily next time and leave enough cover to prevent sunburn.