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Wednesday, October 2, 2013

Sap Oozing from Apricot May or May Not Be Borers

Q. Can you tell me what happened to the apricot tree?

A. Boy that does not look good. The first assumption people make is borers. This can be true but there are other things that can cause sap to ooze for limbs and the trunk. Stress is one of them particularly in plum. Another is overwatering or rotting of the trunk. So the first thing I would do is pull that mulch away from the trunk and inspect it.

Sap oozing from limb
You may have to take a sharp, sterilized knife and cut into the area just an inch below the level of the mulch or soil directly below the sappy area. The wood should be cream colored. The cut does not have to be big, just a knick is enough. Just enough to see the color of the wood or actually just below the bark, the cambium layer.

If the wood has good color then remove a couple of globs of sap and cut the same way just below the sap. This will be a bigger cut, enough to see the wood. Look for any signs of sawdust or sappy sawdust just under the sap. If you see traces of tunneling just below the bark and in this cambium layer then you can conclude it is borer damage.

During winter, cut into the limb and reveal the borer, removing all loose bark or remove the limb if it is bad enough.
Lastly watering too often, keeping the soil moist without letting it dry out can also cause sap to bubble to the surface which is really due to stress again most likely.

Pull the mulch away and let it dry out if you think that might be the problem. If borers are the problem, dig them out with a sterile knife and let the tree heal afterwards.

Wait Until Very Early Spring to Prune Grapes

Q. Should I cut my grape vines back?  They're on a trellis, and are 1 year old.  During the summer they spread out very well, and produced several large groups of table grapes.  I've attached a photo.

A. Regarding your grape vines, I would wait until late February or early March to prune them. We still have some potentially difficult times to go through this winter for grapes. Cutting them early may result in a loss of bud wood and fruit production.

            When pruning, you will cut back this past years growth (it will be a different color) so that only one or two buds remain. I prefer two. Also I usually prune it back so that ten or twelve buds remain if I do it early. Then just before bud swelling in the spring (like about early March) I cut then spurs back to two buds. This way if there is dieback during the winter I won't lose the fruit producing spur.

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.

Be Careful How Close You Plant Figs to Walls

Q. We planted a very small fig tree next to our wall 11 years ago and now it is taking over the whole backyard, I heard the roots can do considerable damage to our plumbing and wall.

20 year old Fig in winter showing form to keep it small and productive

A. If the trunk is closer than about several feet I might worry but otherwise I would not unless it is getting its water from your neighbor’s yard. If it is getting a lot of water from your neighbor, then this will pose a problem to your wall in the future.

            Always water on the side of a plant away from a wall or foundation. It will not be a problem to water on one side of the plant while not watering on the other. Plant roots will grow where there is water and not grow or grow poorly where there is none or it is limited.

            Whenever possible, try to keep soil within 3 feet of a wall or foundation as dry as possible. This helps to reduce problems with roots and corrosion of cement by soil salts.

            As a safety precaution you can cut the tree roots on the side toward the wall. Leave the roots exposed to heal a few days and then you can bury them again. Figs in particular can handle severe pruning.

Tricks to Desert Container Gardening: Expanded Edition

Q. I was wondering if there is a trick to container gardening. I have been using potting soil, along with plant food, and my plants keep wilting. What am I doing wrong?

A. There are two things you should be aware of regarding watering and containers in our climate. Don't use small containers and never let the soil get too dry before you irrigate again.

            Small containers do not work well in the desert. They just don't hold enough water and their soil volume is small so it heats up rapidly. Plants use a lot of water in a desert environment. This means they have to draw upon a large reservoir of water in the soil. Large plants in small containers use the water in the soil quickly.

            When the soil dries, it shrinks. In containers the soil dries from the outside, inward. The outer surface of this container soil can be very dry or hydrophobic, meaning it will repel water. When the soil shrinks in the container, it pulls from the sides of the container leaving a large crack. The combination of this large crack between a very dry soil and the inside of the container wall makes a nice channel where water can flow. Water applied to dry container soil flows down the inside of the container wall without wetting the soil. Of course you see it run out the bottom and think you have wetted the soil when in fact the hydrophobic soil surface is still dry.

            Plant water use can be 25 to 40% higher in our hot, desert climate than in more moderate climates. You have to use larger containers to compensate for this higher water use or water more often.

            Another problem. If containers are left exposed to the sun, the soil in the container dries rapidly and can get very hot, sometimes reaching temperatures around 160°F (70°C).

            Most plant roots are not as tolerant to heat as aboveground parts. Why should they be? Soil can be a great temperature buffer. Large soil volumes provide a better cushion against high soil temperatures than smaller ones. Also, wet soils are slower to get hot than drier soils so set your irrigations clock to irrigate containers just prior to the heat of the day.

            Here are some other suggestions about growing plants in containers in our desert environment.

·       When wetting a very dry container soil, use a couple of teaspoons of liquid detergent in a gallon of irrigation water to help the water penetrate the dry soil. Add the detergent after the bucket is full of water.

·       Always make sure water can drain from the container directly out of the bottom to keep salts moving through the soil profile. Our tap water coming from Lake Mead has lots of salt in it, about 1 ton of salt for every 320,000 gallons (1.28 million liters).

·       When watering, let about 20% of your applied water (1/5 of the volume applied) run out the bottom. This helps flush salts out of the container. This is called a leaching fraction.

·       Replenish container soil regularly. If container plants are annuals such as vegetables, replenish one fourth to one third of the soil volume each time you plant. If the container plant is a perennial such as a fruit tree, remove and replant the tree every 2 to 3 years. When replanting, prune the roots as well as the top to bring it back into scale with the container.

·       Shade the container from direct sun during the day time. You can do this by placing the container inside a larger container. This is called double-potting.

·       Use an inexpensive soil moisture meter made for houseplants to give you a rough idea if the soil is wet or dry. Otherwise lift or push the container. Containers get much lighter when it is time to water. Lift or push it after you finish watering as well. This helps reassure you that the soil is wet.

·       Fertilize lightly once every one to two months during the growing season.

White Fuzz on Palm Frond Can Be Normal

Q. Today I found this frond on the ground and it looks like a fungus on the back of it. Can our palms be saved with treatment?

A. From my perspective, there are two options. The first is to recognize that white fuzz on leaf fronds of many of palms is normal. It depends on which palm it is.

            My first reaction in seeing the picture you sent was that it was normal and this was one of the palms with fuzz exactly where it is in your picture.

            The second option is that it is a disease or insect problem that I have not seen before. We do have mealybugs and scale insects that cause a similar white fuzzy appearance. This normally occurs on palms growing indoors, not outdoors.

            I still tend to think that this is a palm with normal white fuzzies on the leaves. What is troubling is that you told me one of your palms died. If the palm is well-suited to our desert climate, death would be rare.

            So I went searching for diseases that might give the same appearance as white fuzzies on the leaves. I could not find any.

            Many people assume that palm trees are low in water use. They are not. Palms survive very nicely in the desert near an oasis where they can drink freely from available water. They don't survive in the middle of a desert landscape with a minimum amount of water.

            A telltale sign that they are not getting enough water is poor development of the fronds. They may be smaller than normal and scorched around the margins of the leaves. Eventually the bud in the center of the palm dies thus killing the entire palm.

            Palms can be weakened if they are not receiving enough water, if they go through a very hard winter which stresses the central Bud, if they are severely pruned to look like a feather duster in late fall or if new palms are planted in the fall instead of spring and summer.

            My gut tells me that your palm frond with the white fuzzies is one of the normal palms (you can check this by looking at other fronds on the same plant and see if they are fuzzy as well) and that your one palm which died was weakened and the central bud was killed by bud rot.

Italian Cypress Snapping Off in Wind Might be Borers

Q. Because of the wind the other night the tops of two Italian Cypress trees broke off about 11 feet off the ground. Do you think this was caused by lack of water?

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?

Disease Problem Will Stop With a Change in the Weather

Q. I am sending you a picture of my funky looking tree. I think it has some sort of disease problem.

Bougainvillea with Leaf Damage in Circles

Q. I bought a Bougainvillea ('Barbara Karst') last April and planted it in my front yard. After digging the hole I added a local Rose and Flower food in the bottom of the hole. I then added water and then planted the Bougainvillea.
            This plant receives sunlight more than 6 hours every day and I water it as noted on the label. All went well until something started to carve big divots out of the leaves. I sprayed "Ortho Bug B Gone" as I was told and only sprayed it on the plant at night so it would not burn the leaves.
            Well it did the trick but the edges of the plant started to turn brown and shrivel up. As soon as new fresh, unsprayed tender leaves came out, the bug came back and started to carve out holes in the leaves again. Is there something I am doing wrong?

Spurge Weed Problem in Lawn Controlled with Fertilizer, Irrigation and Mowing Height

Q. We have a weed problem in our back lawn and I think it is called spurge. The leaves are small and it's kind of viney. When I pull it, I see this white sap coming from the broken vines. I can dig it out of the soil where I have gazanias but cannot do the lawn that way. Any advice would be so welcome.

Avocado Not a Good Choice for Las Vegas

Q. I saw an Avocado potted tree at Lowe's hardware and was thinking of planting one in my back yard. My question is: When is the best time to plant this tree? Is fall okay? I'm thinking of the winter freeze that might occur. I hope I hear from you soon, in case they sell them out.

Palm Died and Dont Know Why

Q. We had 3 healthy palms in our yard for many years. Just recently, we had to have one removed, but were not able to determine why it died.