Sap Coming from Small Fruit Trees Usually Borers

Q. I have some newly planted peach and nectarine trees with sap coming from them. They don’t look healthy.

Sap oozing from newly planted fruit trees nearly always borers.

A. Borers are most likely the problem. On small, newly planted fruit trees it doesn’t take many borers to kill the trees. They usually “attack” the south or west sides of a trunk or the limb of a tree. That’s where there is sun damage. Painting these trunks and limbs with white latex paint lowers the surface temperature about 4 or 5 degrees. It may be enough in some cases. But shade is better.

Borers will usually start to damage the hot side of a tree, either west or south.

            The sun plays a role also. Direct sunlight on the trunk of a thin barked fruit tree can be a problem. The “smell” of sunburned and dying or dead limbs and trunks attracts female borers that are looking to lay their eggs, scientists believe. When limbs and trunks of newly planted fruit trees have sun damage, then borers are more likely to be found.

This is a locust tree. Borers "smell" or find their way to the sun damaged areas of any tree. Here the top of the branches have been damaged by the sun. The bottom of branches out of sunlight are undamaged.

            What to do? 

Shade the young tree from Western and Southerly direct sunlight. Paint the trunk with diluted white latex paint. As a last ditch effort, drench the soil around the tree after it flowers (if possible) with a borer systemic insecticide and don’t eat the fruit for at least 12 months after the application.

Which came first? Here sun damage eventually led to borer damage.

Sick Oak Tree and Its Spring Recovery

Q. I have a sick oak tree in our backyard. It is an older tree and but not growing well. Our gardener suggested hiring an arborist to treat the tree and help it recover. Can we purchase something to correct this? Would an arborist be able to save it? Your thoughts.

Sick Oak tree trunk in the backyard. 'Heritage' live oak is a good tree choice for two-story homes in Las Vegas.

A. From the picture you sent it looks like a southern live oak such as 'Heritage'. It looks like the trunk of the tree is slow to recover and has some pretty old wounds. Getting it to recover depends on how far “gone” it is. You will not know that until the summer hits. Even though it's a 30 to 40 foot tree (size-wise think of it as a bit larger than European olive). This particular oak is classified in between xeric and mesic and a native to southern Texas and into the Chihuahuan desert. It does well where there is a bit more water and also into the drier locations. The "cons" of this tree

       All oaks like amended soil and don’t like the soil “mineralized” by rock mulch over time. Rake the rock back three feet from the trunk. Change this area over to a layer of organics that can rot on top of the soil. Add a thin layer of finely screened compost to the soil. Water the tree two feet deep once a week right now. This can be done with a sprinkler on the end of a hose. This may be increased to twice a week if it gets hot and windy.

            Oaks in general dont like rock up to the trunk but prefer growing in soils getting organics periodically. Rocks cause the soil to become “mineralized” over time (organics in the soil are lost to decomposition). This is the reason for adding compost and wood chips to the top of the soil.

Tree roots require deeper irrigation. The bigger the plant, the deeper the roots. Use a length of rebar to judge how to deep to water. To get water deeper with the same amount of time, add more drip emitters!

            Secondly, this tree needs additional water each time its irrigated; 15 to 20 gallons during the first few years but now may be 30 to 40 gallons each time. Instead of increasing or decreasing the minutes, add more and larger drip emitters to the area under the tree. Put sprinkler hose water into a 6 to 8 foot wide area under the tree for about one hour and encourage the roots to “chase” the water into this newly wetted area. This will increase the trees vigor and cause it to heal fast. No need for additional fertilizer if the compost is rich with nutrients.

            If you see evidence of borer activity from previous years, it probably was reinfested each year since that time. Soil drench the area under the tree with a borer systemic insecticide. Apply it as a soil drench after the tree finishes flowering.

Ash Trees With Bark Lifting

Q. Our ash trees have “bark drop” as they got older. Should I worry that the light tan areas of bark are peeling in long sheets four feet long, and this bark seems to be coming away from the tree in small chunks?

Bark coming off or lifting from readers tree.

A. Worry only if your ash trees had the bottom branches recently removed and they were planted on the south or west sides of a building or wall. Try to leave the bottom limbs attached to the trunk as long as possible so the trunk is shaded by the limbs. Once the tree has gained some height and age, some of the lower branches can slowly be removed.

Beginning of ash sunburn after it was recently planted. The orangish-red color of the trunk or limbs is not normal for this tree and it was facing the sun. 

            Your job will be to discover if the trunk has been damaged either by the sun or by borers or both. Before you begin, establish which side of a wall or building the tree was planted on and make a mental note. South and west sides of walls and buildings are the hottest and most damaging.

Ash borers in the trunk of a young ash tree. Removing the loose bark will reveal their nasty work.

            Next remove any loose bark including those strips you mentioned. Use your hands first two pull off any loose bark. It won’t hurt the tree. Finally use a sharp and sterilized knife blade about 5 inches long to make the trimming cuts to undamaged wood just below the bark. The undamaged wood should be white or light green. The purpose is to hasten the healing either of the trunk or limbs and discover what did the damage.

Even though this is fruit tree it still demonstrates how to correct borer damage with a knife.

             It’s always a good idea to leave the lower living limbs for shading the trunk as long as possible. This shade helps protect trunk and limbs sunburn. Once these areas are sunburned, they will attract boring insects because these insects are attracted to damaged trees and shrubs. The sun burned areas are in the trunks and limbs where there is the most intense sunlight. This is usually the West or South facing sides or the tops of limbs and branches.

Reasons for Palo Verde Limb Dieback

Q. The palo verde tree in our daughter’s yard looks like it has damage. The top has some dead branches in it. We have had to remove some limbs because of this problem. Can it be saved?

A. There are several different kinds of Palo Verde used primarily in desert landscaping. All have tender new growth that can be severely damaged when exposed to intense sunlight. It is important these trees are pruned throughout their lives so that the tree’s canopy shades the trunk and limbs.

If desert adapted trees have limbs removed that expose the trunk or large limbs to direct sunlight and sunburn, borers can be a problem in these trees such as Palo Verde and acacia

            Pruning them in a fashion that exposes limbs and the trunk to intense sunlight causes damage that causes limb death that becomes visible a few years later. It’s a progression that usually starts with bad pruning practices. This progression begins when too much is removed from these trees. When too much is removed, the limbs and trunk are exposed to high intensity desert sunlight.

Exposing the trunk and lower limbs to direct sunlight and sunburn can create future problems to trees like the Palo Verde.

            Intense, direct sunlight on young limbs first causes a discoloration due to intense sunlight. As this direct sunlight repeats day after day, exposed areas of limbs and trunk facing the sun die. Water can’t through dead areas of the trunk and limbs.

            Unless this sunburn causes severe damage, the top of the tree probably looks fine. The tree can still move water around the damaged area from roots to tree branches. The damage could be as much is 50% of the limb and trunk area and the tree looks fine.

This is not Palo Verde but when the trunk and limbs are exposed to intense sunlight for a long period of time, year after year, the intense sunlight can damage or even kill the living part of the tree under the sunburned area. The beginning of this damage can be very attractive to some wood boring insects which can make the damage worse.

            This damage from sunburn attracts insects such as borers that feed on living parts of the tree close to the damaged area. This feeding by borers causes even more damage that reduces water movement to the limbs. Perhaps the first year or two, trunk and limb damage goes unnoticed because the canopy looks fine.

The first sign of sunburn is a discoloration or off-color to the trunk, limbs or even fruit on fruit trees.

            But at some point, damage becomes severe enough that water movement from roots to the canopy is reduced.  Limbs start dying back because the tree can’t get enough water past the damage. This usually happens during the heat of the summer when demand for water is highest.

            The homeowner now notices the limb death in the canopy. The homeowner removes dead limbs. This exposes the tree to more intense sunlight and further damage. Tree damage is so severe and unsightly the homeowner considers removing it. This is the tree “death spiral”.

            What to do? Damage to the tree may be already extensive. Decide whether you can live with this damage or not. If not, have the tree removed. If you decide to keep the tree, then encourage it to heal as quickly as possible. Contribute to this healing by giving it enough water on a regular basis and apply fertilizer in early spring.

Acacia Dropping Its Leaves

Q. My young acacia tree has abundant growth but only on the top half of the branches. Each of these branches are losing many leaves half way up the branch. There is a lot of growth at the top of the tree but not much below. Am I watering too much, too little? I water every five days during the summer.

A. Acacia trees are desert plants. Most desert plants are opportunists when it comes to using water. In other words, when water is present they grow like crazy. When water is absent, their growth slows and they then try to use as little water as possible. Desert plants may even stop their growth and drop their leaves when water is not available!

This is not Acacia but Palo Verde. Boring insects, or borers, may feed on a variety of trees and shrubs or very specific ones. Borers, like the flat headed apple tree borer, has a variety of trees they attack including the desert trees. Sometimes they attack trees with sun damage and other times they seem to attack trees without any cause at all.

            All plants are tremendous competitors for water, nutrients and light. They want to be “top dog” in their plant community by taking as much water, nutrients and light as possible when it’s available. By doing this, they take away these building blocks of growth from other plants.

            When water is present, trees try to get as tall as possible as rapidly as they can before they start to fill out. They grow upward first and then put energy into horizontal growth once they’ve established some height. This growth in height takes away light and shades competitors. This early growth in height, when there is a plenty of water and nutrients, oftentimes is at the expense of putting on lower growth .

We commonly see borers attack fruit trees and many different landscape plants. This flat headed Appletree borer infested a young Apple tree recently after was planted. The tree was so young that extensive damage was done by a single borer found feeding in the tree.

            Watering schedules take two different forms; how much water is applied and how often water is applied. It’s difficult to say with certainty without seeing the tree, but it sounds like it is receiving water too often.

            Watering every five days means nothing to me. I can take a sip of water hourly and someone might think I am drinking plenty of water. But another person might ask, how big are your “sips”? One teaspoon or 1 pint?

            How much water to apply? When watering trees, give them enough. Apply enough water to wet the soil at least 24 inches deep. Apply this water to at least half the area under the canopy of the tree. Once it enters the soil, the water spreads horizontally further than this.

Use 3 eighths inch rebar to estimate how deeply water has penetrated into the soil after an irrigation. Check the soil in 3 or 4 locations.

            Use 3/8-inch diameter rebar that is three feet long. After irrigating, push this rebar in the soil in three or four locations to check the watering depth. Wet soil allows the rebar to slip in easily to the same depth as the wet soil. Dry soil makes it hard to push further.

            It should slip into the soil at least 24 inches deep. Once you know how many minutes this takes, the amount of time you water won’t change. Each irrigation will be 24 inches deep.

            If using drip irrigation, space emitters about 2 feet apart. If using a basin or moat under the tree, the basin should be as wide as half the area under the canopy. Trees grow. This means the basin must expanded every three years. If using drip emitters, add more emitters every three years.

Basin under a tree used to capture the water for irrigation. If using a hose or some other delivery method that releases a large quantity of water rapidly, a basin is required to keep the water from going everywhere else but around the tree.

            How often to apply water? Look at the tree canopy. It will tell you. When the canopy of the tree starts to thin out, it’s time to irrigate! Desert trees tell you when to water when their canopies begin to thin out.

Random Thoughts Regarding the Desert and Our Hot Summer

Perhaps this summer has been brutal but plants like palo verde can handle “brutal” weather. 

 "Native" palo verde in Arizona in bloom

Be careful how these plants are pruned. The tendency is to prune them too high and this removes the shade that the tree naturally provides the trunk and limbs. Watering also helps. Plants like palo verde respond very nicely to increases in applied water very quickly..in just a few days. Water these plants with a hose to give them a shot of water and improve shading of the limbs and trunk. 

 

Sap coming from Palo Verde. Removing too many branches and exposing too many large limbs and the trunk can lead to sun damage of this thin barked tree.

Hopefully plants like palo verde were not pruned to allow excessive sunlight to shine on the trunks and limbs. Also, water in the soil helps keep limbs and the trunk from burning because these areas release water to the air and help cool the limbs and trunk through evaporation of water from microscopic holes that can open and close called stoma or sometimes called stomates. If water is restricted it cannot cool itself properly and they will burn. OR water loss can be faster than the plant can replace…as in the case of apple fruit…and burning occurs.

That is a wide variety of plants to have sunburn on. Sunburn on trees is usually restricted to trees with a think bark (palo verde fits this) and a lack of shade covering the limbs and trunk. Sunburn is on the sides of the trunk and limbs that face the sun and not on the other sides in the shade. If this damage extend into the side in the shade then it is something other than sunburn that is going on. 

 

In my opinion too many of the lower limbs were removed on this Palo Verde which can lead toward sunburn

You can apply the same logic to agave and desert spoon. Not enough water can contribute to sunburn. If they are droughty then will burn more easily than if they are getting enough water. 

A lack of soil improvement…poor soils that were not improved by adding compost at the time of planting…YES, this includes cacti!...may sunburn or turn yellow from intense sunlight. Sunburn comes in different degrees of severity…mild sunburn is a yellowing of leaves or fruit but not death of the plant tissues  beneath the damage. Medium damage results in yellowing with some brown or tissue death in or near the center of the yellowing…there is tissue death and this tissue death will attract bugs and other critters that sense the plant is damaged. 

Borers will attack sun damaged areas on the trunk and limbs of trees

These are bugs that are “decomposers” who want to break down these damaged plants and “recycle” them…naturally. The third stage is death of the tissues facing the sun, not only brown but cankered with bark or the skin dead and scaling or peeling back. This makes a pretty ugly plant. But the sides away from the sun are not damaged and the plant will survive unless some “decomposers” get in their and try breaking them down by feeding on them. Borers are in this category. They are goners if they look bad enough you cant live with them any longer. In most cases they will survive.

Prevent Plant Sunburn with Adequate Water and Wood Mulch

Some thin barked trees and shrubs will get sunburned if they don't have enough protection from strong sunlight.

This reddish-brown discoloration is sunburn. In the first stage of sunburn we see the beginning of death onsides exposed to the South and West

Plants that typically get sunburn include many of our fruit trees, mostly peach and apples. Ornamental trees and shrubs also get sunburn. I get a lot of pictures of sunburn sent to me with sunburn and include Japanese blueberry, locust trees, ash trees, Indian Hawthorn, and others. 

This is the trunk of an ash tree on its west side. It first got sunburn. After sunburn the borers attacked it. What you see now is loose bark covering dead wood killed by borers. You can take your fingers and just pull this bark off of the trunk easily. You should do it anyway. You will not hurt anything. That site is already dead. The tree is still alive because the trunk is alive on the other side of the tree.

The natural way to protect these plants from sunburn is to allow these plants to shade their own trunks and stems with leaves. Not providing enough water can thin out the canopy of trees and shrubs and encourages sunburn. 

When you pull this bark away from the trunk you will see oval-shaped holes in the wood. These are exit holes of the bores. Removing the bark also removes hiding places and birds have a better chance picking them off when they emerge.

Having rock mulch around plants that do not like rock mulch also reduces the number of leaves and increases the chance of sunburn. Plants that do not like rock mulch, like the ones I mentioned above, will develop an open canopy, leaf loss, and sunburn. 

This is sunburn on a bottle tree. The leaves drop from the canopy and expose the trunk and limbs. High sunlight intensity causes sunburn once the leaves are gone

What's the problem with sunburn? When we get sunburn we recover. When plants get sunburn, particularly in a desert climate, they frequently decline and die. Attack by boring insects, or borers, is the first phase after sunburn. The borers create more damage and more leaf loss and more sunburn. After that, the plant falls into a death spiral. 

Sunburn caused the top of this Japanese blueberry to die. Then the top had to be removed and it was pretty ugly. Japanese blueberry should not be in rock mulch. They should have wood chips around them.

Use surface mulches particularly wood chips and not bark. Don't water trees and shrubs daily but water them two or three times each week during the heat of the summer. Reduce the number of times per week during the cooler months. When you do water, give them adequate amounts so that the soil is wet to at least 12 inches and preferably 18 inches.

Euonymus Plants Have White Spots and Dying

Q.My euonymus plants are dying. These are all plants that have been in the ground 8-10 years. Now, they are getting a white spot on their leaves and shortly afterwards the plants die. The plants in my backyard did this last year, and now plants in the front have the same symptoms. Some people said they needed more water. That didn't do anything for the white spot. I tried cutting off the spotted leaves. That might help, but I am not sure. Is there anything I can spray or dust the plants with to stop the fungus?

Powdery mildew and leaf death. Powdery mildew is deeper inside the canopy were it is shady.

A. I am not sure what you mean by a white spot, whether this white spot can be rubbed off or whether it is permanent. These plants do get powdery mildew which looks like leaves have been dusted with white flour in some locations.This disease occurs on plants in shady locations.

If it is powdery mildew it usually means they are not getting enough sun or the canopy of the plant is not open enough for air movement. Powdery mildew, unlike other fungal diseases, requires very little humidity to become a problem. It is spread by splashing water from overhead irrigation hitting the leaves and splashing on others carrying the disease to these leaves and so it spreads.

You can buy a dust or spray to control powdery mildew but that just circumvents the problem and it will come back. The long term way to control it is to get more sun on the plants (move or prune them to open the canopy up), improve their health with fertilizers and appropriate watering. If the plant is under watered the canopy will be very open and I doubt you would have powdery mildew unless it is in shade or partial shade.

A white spot can also mean scorching of the leaves due to direct intense sunlight. This type of damage cannot be rubbed off with your fingers. It is permanent damage to the leaf. If this is the case then the plant may be in the wrong spot (intense sunlight or lots of reflected heat and/or light from windows and a west or southwest exposure and planted in rock.

 If this is the case then you need to move it away from this intense location into one that is more cooling with less intense sunlight. This is not a desert plant and cannot handle this kind of exposure. It does not like rock mulch very much so put it in organic mulch on the soil surface.

If it has only one drip emitter, put two or three depending on its size. If you are watering every day then water deeply every other day or every third day now. Make sure you fertilize this plant in the spring with a good tree shrub fertilizer.

If you want to move this plant, you can move it to a new location in October, moving as much of the soil with it as possible, and mulch it. Predig the hole and move it and plant it in less than 30 seconds once the roots are exposed.

Euonymus does much better with a wood surface mulch.Neem oil is a pretty good organic control for powdery mildew.

Sap Coming From Peach Trunk to Top of Limbs

Q. Our peach tree has sap coming out from the ground level to the top of one of the limbs. Not sure if too much water, not enough water, too many bugs or what.

A. This is the time of year we start noticing borer damage in peach trees. Sap comes out from the limbs and possibly all along the trunk.

Branch dieback due to peach borer damage.

A clear indicator of borer damage will be that the bark around the sappy areas will peel off, leaving bare wood under it with clear feeding damage (looks like someone took a miniature sander to the wood with no clear pattern) and if you pull enough bark away you will see flattened, oval exit holes from the adult beetles.

Bark peeling away from dying branch due to borers.

You may even see some sawdust under the bark in these "sanded" areas from their feeding. Remove all loose bark all the way into good wood. You may even find a flattened, ugly larva of a borer just under the bark still feeding. Keep it for a pet if you want to.

Borer in removed dead branch

If damage is more than 50% around the limb, cut it off. Do not paint with black tree wound paint. Paint the trunk and remaining limbs with diluted white latex paint (50/50 with water) on the upper surface of all branches down to one inch in diameter and the trunk.

Borers like limbs and trunks exposed to the hot and intense sunlight. White paint keeps limbs and trunks several degrees cooler than brown limbs and trunks and helps to reduce damage to these parts by intense sunlight. 

Cutting Back a Recently Planted Peach Tree or Not?

Q. Last week I purchased a semi-dwarf Elberta peach from a local nursery to replace the nectarine I took out. Tree is approximately 65" tall. When I mentioned to one of the salesmen that I was planning to prune it back to the 4/5 branches that begin about 20" from the ground, up to about 26", he was pretty adament that this was not as good idea as the hormones that promote root growth are located at the tips of branches that I would prune off?

I remember that when I purchased my last tree from the orchard the gardener there recommended that I cut it back to about 24" tall. So, the only thing I can think of for conflicting instructions is the nursery tree had leafed out and the Orchard one was dormant? Anyway, any advice would be greatly appreciated. Also, if you recommend pruning, should I do it now or wait until the tree goes dormant?

A. You can do that to this tree but I would wait until winter. Taking the center out of a Peach tree and leaving the lower scaffold limbs is quite common. This is how we train a fruit tree into open center form. One of the major dangers that can occur when we take the center out of a tree, is sunburn to the top surface of the remaining limbs. We can discourage sunburn to these limbs by leaving some smaller branches above this area that might produce some shade to the upper surface of the lower limbs.

The other thing we can do is to whitewash the upper surfaces of the remaining limbs with dilute white latex paint. White latex paint is diluted with water in a 1:1 mixture. You can use more water than this as long as the remaining wood is white. This lighter color will help to reduce sunburn to the limbs. Apply it with a brush.

Taking the center out of peach tree to make an open center form.

Most of the nursery workers do not know how to prune fruit trees. In fact, few do. Looking at your pictures you could take the top out this next winter.

There is a precaution on peaches I should mention. If the diameter of the wood you are cutting on the main trunk is more than about ¾ inch with no side branches below the cut you may have trouble getting more branches to “sprout” from below the cut. But if you cut the trunk out to just above at least a couple of good side branches you will have no trouble. Don’t forget to paint the tree with diluted white latex paint to prevent sunburn after you make your cuts this next winter.

Another thing. You are going to have problems with that Peach tree if it remains in rock mulch in our desert soils.

Tops Dying Back in Japanese Blueberry

Q. I’m having a problem with my Japanese blueberry trees. Some are fine but the two on the end appear to be drying out from the top down.  Do you have any idea what’s causing this? The soil is not dry and they all get the same amount of irrigation.

A. The usual problem in damage or death to the top of a tree can be found on the main trunk just below the damaged area. I am guessing something has damaged the tree at that point.

            The reason for the damage could be several. Borers cause mechanical damage to the trunk and shut off the water going to the top. Diseases in this same location can do exactly the same thing.

            Because Japanese blueberry is relatively thin barked, sunburn from our intense sunlight can kill the trunk in that location and shut off water to the top. Humans can cause damage to the trunk and shut off its water supply as well.

Top of dead stem on readers Japanese blueberry

            I think we can rule out pathological diseases in our climate. The two most likely culprits are mechanical damage to the trunk by borers or the same type of damage caused by sunburn.

            Inspect the trunk at the location just above the healthy area of the canopy. Use your fingers and see if you can pull away any loose bark. Borers tunnel just under the bark usually on the side towards the most sunlight. This kills that part of the trunk and the bark peels away easily.

            If you don't see bark peeling from the trunk at this location, look for discoloration of the trunk on this side facing the sun. Sunburn to the trunk can happen in one hour of intense sunlight during the midday or late afternoon.

            If it is borers there is nothing you can do to raise the dead area back to life but you can protect the tree from extensive borer damage with an insecticide soil drench once a year.

            In any case, you'll be forced to remove the dead top from the tree with a pruning shears or saw this winter. Once you do this, it may open remaining branches for sunburn as well. Give them as much protection as you can.

            I would not do it now because the sunlight is too intense and will probably cause even more damage to the lower, healthier part of the tree.

Pepper Brown Spots Could Be Irrigation or Sun

Q. I have a brown area on the bottom of my bell peppers. Any ideas?

A. Brown spots on bell peppers are normally from either of two things; a disorder we frequently see on tomatoes called blossom end rot or sunburn.

            If it is on the bottom of the fruit and not in a spot exposed to direct sunlight it is most likely blossom end rot of pepper. Blossom end rot, just like in tomatoes, is normally associated with irregular watering even though it is a nutrient deficiency.

            An inch of mulch in the vegetable bed helps to maintain more even soil moisture and less fluctuating of the water content in the plant. A more even soil moisture content has been reported to reduce the incidence of blossom end rot.

Blossom end rot bell pepper

            The other possibility is sunburn. If the brown spot is on the shoulder of the fruit toward the sun and not the blossom end, then it is most likely sunburn. This is because there is not enough shade covering the fruit. You will see less sunburn on peppers that are buried deeper inside the canopy of the plant.

            With bell peppers in particular we want as much leaf cover over the fruit as possible. Light shade, about 30%, over the plants, also reduces sunburn. Mulching the vegetable garden also helps.

            Having the garden in a location where it is exposed to morning and early afternoon sun, with shade during the late afternoon, will also reduce the problem.

Why Are The Leaves of My Locust Tree Turning Yellow?

Q. Do you have idea why some many of the leaves on this Locust tree are turning yellow?

Poor Canopy Development in Newly Planted Large Tree Could Be Lack of Water

Q. I think I this might be a pink locust tree. I'm seeing a lot of dead branches. The tree was planted last Fall. Should I give it some fertilizer to help it push out new growth?

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.