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Leaf scorch has varied causes

: I have a Fan-tex ash which is dropping a considerable amount of leaves. This has been going on for several years and I’m trying to get a handle on it. The leaves have brown spots on them and are curling up before dropping. I have seen another ash tree near my house that has the same problems. I have been told that it could be overwatering.

A: The leaves in the pictures you sent seem to have fairly good color and size except for the brown scorching in the interior of the leaves. (Those of you who get my newsletter will see the pictures.) If this were from water, I would expect the scorching to be all along the edges. But let’s keep that option open.

From the pictures, I would have assumed it was ash whitefly but you told me that you found no insects. Ash whitefly is fairly easy to see as waxy or cotton-like substances on the leaf surface. Plus, you would see some white insects flying around the leaves, along with the leaf curling and stickiness.

From what I could see, tree is either growing in a lawn or near a lawn. Ash trees do not do well in rock landscapes over time so hopefully it is not growing there. It is possible for trees in lawns to be underwatered; this can happen because we water the lawn in shallow frequent irrigations while trees need deeper irrigations.

Lawns can compete with trees for water very effectively causing the tree to be underwatered. Trees living in lawns need to have the lawn removed from around the trunk to a distance of a least 2 feet. This area should then be mulched with an organic mulch.

Removing the grass from around the tree helps keep lawnmowers from damaging the trunk. Repeat damage to the tree trunk by mowers or line trimmers can cause the tree to not get enough water and leaf scorch. I don’t know if this is the case with your tree, but if the trunk has been damaged at the base, this could cause the scorching on the leaves.

The burning or scorching on the leaves also looks a little bit like leafhopper damage, but it is a bit early in the year for this to happen. You would be seeing insects on the leaves and, like the name suggests, they would hop.

The leaves also appear like they might have been scorched by some sort of foliar spray.

Q: I have a row of Italian cypresses that are about eight years old and planted 2 feet apart along my pool. They are being watered twice a week for an hour. I have lost a few of them and I’ve noticed that the bark around the dying ones seem to be dry, cracked and peeling away from the stems, exposing the trunk. I’ve also noticed sap oozing from the bark. Can you give me some insight into the problem and a solution because I seem to be losing them every year.

A: You should not have to water Italian cypress that often. Watering deeply once a week should be plenty.

I have never seen borers in Italian cypress so it makes me think that this is perhaps cyprus canker instigated by overwatering. Once these trees get cyprus canker, they usually die. Cyprus canker is very common on Leyland cypress but not as common on Italian cypress.

Pull back on your watering; begin watering once a week at the most and water deeply. I am afraid, though, that if this is canker, the trees are gone.

Q: We recently planted eight queen palms. The center fronds have started to yellow. I get different answers on watering schedules and so forth. I think the yellowing is due to overwatering.

Recently, I put two fertilizer stakes in the ground per palm. Can you help me understand how to better care for them or provide me with other information that might be helpful?

A: You are right that it could be overwatering. It also might be nutritional or from high levels of salts in the soil if you have unamended raw desert soil.

I do not know how your trees were planted but sometimes they are planted in sand with no amendments in the backfill. These trees need to have good drainage, lots of compost in the backfill around them and, if the soil was a raw desert soil to begin with, the soil needs to be leached of salts before planting.

To try to get a handle on what the problem might be, I would make some foliar applications of a complete fertilizer plus iron. Add a small amount of wetting agent or surfactant to this mix before spraying it on the foliage; it will help the fertilizer and iron to be taken up by the leaves.

When mixing the fertilizer and iron in the spray tank, you might want to consider using distilled or reverse osmosis water. Our tap water can be quite alkaline, which can cause some of the fertilizer elements not to work.

I would spray this on the foliage in weekly intervals for four or five applications, as needed. It is very important to use a freshly made solution each time you spray. After a couple of applications, you should see the foliage change in color to a darker green if you have a fertilizer problem.

In the meantime, you might want to consider applying an iron chelate to the soil near where the water is being applied. The water will help carry the iron chelate to the plant roots. You would need to do this in addition to the foliar sprays.

If these trees are surrounded by rock mulch, they will not do well over time. Well, queen palms don’t do well here anyway unless they are very protected, and they will do even worse if they are surrounded by rock mulch. These palms should be surrounded by organic mulches several inches deep.

Bob Morris is an associate professor with the University of Nevada Cooperative Extension. Direct gardening questions to the master gardener hot line at 257-5555 or contact Morris by e-mail at extremehort@aol.com.

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