Trees suffering from ash decline should be removed

Q: My Arizona ash tree is about 20 years old. Six or eight limbs have dried up and died within the last couple of weeks. Can you tell me the cause of this and what I can do to prevent more from drying up?

A: First, my heart goes out to everyone who was impacted by that horrific event near Mandalay Bay. Let’s hope and pray that it does not happen again.

Judging from your description, most likely your tree has a disease called ash decline. It is important to know the scientific or Latin name of this tree, Fraxinus velutina, because it is called by many names in nursery trades including velvet ash, smooth ash and desert ash, among others. I would not select another ash tree as a replacement.

About four or five years ago I stopped recommending the planting of Arizona ash or Modesto ash in the Las Vegas Valley. Arizona ash also includes Raywood and Fan-Tex ash, which are types or cultivars of Arizona ash.

I would be leery of ash trees labeled as “Bonita” and “Fan-West” because they have Arizona ash genetics in them, but they are too new in the landscape industry to make recommendations for or against planting them.

I personally believe if these trees are getting adequate water, not too often and not too little, and you see this problem, then assume it is ash decline and remove them as soon as possible. We don’t know how this disease spreads so get rid of them and not plant another until we can figure out how to stop it. I am concerned it might be spread by insects such as cicada.

Look for suitable replacement trees. If replacement trees are planted in a rock or desert landscape, then replace it with a desert landscape tree that provides the same benefits. To my knowledge, this disease is not present in the soil, so replacement trees should be fine if planted in the same spot.

Q: Can you tell from the pictures what is wrong with my grass? The dead grass removes easily without a tug, and some of the green grass near the dead grass can also be removed easily like there are no roots. Once it got cooler, the problem has not gotten worse.

A: Thank you for sending such good pictures. I will repost them on my blog. It helped me a lot in this particular case.

Your description made me think it was an insect problem because there were no roots attached. However, once grass dies, the stems rot and all dead grass pulls up easily and without roots attached.

There could be more than one problem going on. Include insects as a possible problem when living, green grass growing on the edges of the brown or dead grass has no roots when pulled up.

In your pictures, the dead or dying areas are semicircular or nearly circular around a green grass center. That is very telling. It is easier to spot this circular or semicircular pattern in grasses that are mown below ½ inch. It’s harder to see it in taller grasses.

This problem is most likely a turfgrass disease called “frogeye,” usually associated with the Fusarium complex of diseases. This disease likes warm to hot weather and very moist conditions.

Other grass diseases like cooler weather, and we don’t see them during hot weather. Still other diseases like moisture but not too much of it. Different diseases, different environments. This disease likes it hot and wet

What to do? First, know when to look for this disease. Because it likes hot, humid or moist environments, look for it during the summer months and when the monsoon season is approaching. You won’t see it during cooler times of the year.

Avoid watering at night. Just before sunrise or when the sun is up is fine but not while the lawn is sleeping. The problem is worsened if the turfgrass or lawn is stressed for some reason during hot weather. Avoid drought stress of the lawn during hot, summer months.

This disease likes to attack areas of the lawn growing in swampy soils or soils that drain poorly. Punch holes in the lawn and soil with a core aerifier during the months just before hot weather. A hand device can be bought, or a gasoline-driven machine can be rented for this purpose.

Don’t mow with a dirty mower. Clean and wash the blade and bottom of the deck of the mower after the lawn is mowed. Mow the lawn shorter during the summer months but never below 1½ inches.

Fertilize the lawn three to four times during the year. Apply a fungicide that is labeled for the disease frogeye or Fusarium when damage to the lawn is first seen during hot summer months. Follow label directions.

Q: I have not been able to get the leaf-footed plant bugs under control on my almond, pistachio and pomegranate trees. The nuts turn black inside. When the almonds first formed and were still soft, I could see sap oozing where the bugs pierced the fruit. I have been spraying with pyrethrin until the weather got too warm. Someone recommended using diatomaceous earth on them.

A: If you search the Internet, you will see all sorts of homemade remedies recommended by different people. These include diatomaceous earth, repelling them with garlic or hot pepper sprays, and even oils of mint and rosemary. The problem is they have no documented history of working.

Until we have some definitive answers about what is working and not working and still safe enough for food crops, we are left with either trying products recommended on the Internet in a trial-by-error method or using products with a known history of success.

I frequently look at the University of California integrated pest management recommendations for insect control. It publishes information that works but, unfortunately, many of the so-called organic methods have not been tested adequately.

Pyrethrin sprays come from organic sources, and some sources are manufactured. Read the label. The label makes this distinction.

There are synthetic pyrethrins, some called pyrethroids, labeled for controlling this insect pest on pistachios. They do work if the directions on the label are followed. Synthetic pyrethrins are designed by chemists to mimic natural pyrethrin’s toxicity. But they are synthetic and may or may not be as safe to use as pyrethrins.

I usually do not promote recommendations found on the Internet that have not been shown to have a history of success. If I do mention something without a history of control, I follow it up by mentioning so.

Bob Morris is a horticulture expert and professor emeritus at the University of Nevada, Las Vegas. Visit his blog at Send questions to

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