Read Up on Ash Decline and Decide What to Do

 Does Ash Decline Exist? 

'Modesto' ash in a lawn and its dieback.

Read up on the tree disease here, here, and here and decide for yourself.

What is known?

In Las Vegas:

The "condition" was reported by landscaper Nanu Tomiyasu to Yours Truly in late 1980's on mature, 30 foot tall mature Modesto ash trees growing in a lawn near Cashman Field. The trees were given supplemental water and fertilizer but removed when they failed to respond. Yours truly took the State Pathologist, Dr. Wally Sheta, to the site where he thought it might be Ash Yellows and a sample was prepared and sent to the University of Florida for confirmation. The report came back negative for Ash Yellows and this "condition" was not pursued after the trees were removed. It has since been seen in Las Vegas on varieties of Modesto, Raywood, Fax-Tex and Rio Grande ash trees.

In Arizona:

This "condition" has been reported in Arizona by Jeff Shalau in 2018 after an investigation begun by Extension plant pathologist Dr. Mary Olsen started in 2009.

This condition has been reported in the Journal of Arboriculture by Bricker and Stutz in 2005 as a tree disease and MLOs are suspected to be the cause.

All trees infected by this condition die a slow death regardless of irrigation and fertilizer applied. 100% mortality. To my knowledge no pesticides were applied.

What is suspected?

The condition is a disease called Ash Decline in Arizona and caused by an MLO, a Mycoplasma like organism.

Because it is an MLO, it is thought to be spread by insects.

Infects ash trees with Arizona ash (Fraxinus velutina) genetics. Shamel ash (F. uhedi) is thought to be resistant. No trees other than those with F. velutina genetics has been infested.

What to do?

My recommendations are:

1. Remove ash trees showing symptoms after the dieback has been confirmed it is due to Ash Decline to prevent the spread of this condition.

2. Stop the planting of ash trees in the Las Vegas valley.

Bob Morris

To Remove or Not Remove Ash Trees with Dead Branches?

Q. I have been following your comments on ash tree decline. You believe those trees should be promptly removed.  Is this to contain the disease?

Does Ash Decline Exist? Something is causing the limbs to die and water and fertilizer dont change anything.

A. This disease is called Ash Tree Decline in Arizona and Ash Dieback in California. In California, ‘Raywood’ ash has been the hardest hit. In Arizona and Nevada ash trees like ‘Modesto’, ‘Raywood’, ‘Fan-Tex’, ‘Rio Grande’ and other ash trees having Arizona ash genetics have shown branch dieback and “failure to thrive” symptoms.

 We suspect it is an MLO and the "disease" is spread by "something" from tree to tree. Insects? Pruners? Cicada feeds on plant roots like this tree, climbs out of the ground onto the trunk and pupates (leaves its "skin" behind, cuts into trees with its ovipositor and lays its eggs. A possible culprit in its spread?

The disease itself is thought to be an MLO (Mycoplasma Like Organism). What we do know is that it’s probably transferred to new trees by insects, just like other MLO’s. So, my recommendation has been to contain the disease by removing potentially infected trees, so they don’t become a source of inoculum to other trees. If suspected trees receive more water and fertilizer but fail to grow, then we should assume it has Ash Decline until we know differently. I have not seen it on any other trees but relatives of Arizona ash.

Was Your Ocotillo Alive When You Bought It?

Q. I have tried to grow an ocotillo several times with little to no success. Please give me your input on watering and other care.

From the Sonoran Desert and very low water use (xeric), can easily handle rock mulch, but can take up to two years to see any results.

A. Buy and plant in the spring from February through April or in the fall from late September through mid-November. Make sure the Ocotillo is alive when you buy it from the nursery. The wood just below the surface should be green when scratched with your thumbnail even though there may be no leaves. The smaller canes should not snap when bent but be pliable.

Normally I dont care for information from vendors but this aint bad on Ocotillo from Miracle Gro!

            Contrary to some popular ideas, mix about 10% compost in the planting hole about 2 feet wide. The whole doesn’t have to be dug deep just deep enough to accommodate the roots. The compost mixed in the soil keeps the soil open, adds plant nutrients and beneficial microorganisms.

            Plant it the same depth it was growing in the container or in the wild. Use lots of water to settle the soil around the roots. The soil around it should be muddy when you’re finished. Construct a basin 2 to 3 inches deep around the plant. Immediately stake the plant to keep it from moving while the roots are growing. Staking may take one to two growing seasons.

            Water no more than once a week during the heat of the summer during its establishment by filling the basin with water. Water once a month in the winter. After it has been established for two or three growing seasons use four drip emitters placed about 12 inches from the plant. Fertilize it once a year in the early spring just before growth.

Spring Bouquet Viburnum is NOT a Desert Plant but You Can Grow It

Q. What’s happening to my Spring Bouquet (Viburnum tinus)?  It has bloomed beautifully in the Spring for several years (including this past Spring), but many of the leaves are turning brown, and appear to be burnt.  I didn’t see any evidence of spider mites or other pests.  I checked the drippers, and it is getting sufficient water.

A. Spring Bouquet is the marketing name given to the compact form of a flowering shrub found in the nursery trade in California. Technically this group of shrubs are called Laurustinus so let’s just call it Spring Bouquet viburnum. It’s gotten some tracking in the Mojave Desert mostly from people moving here from California. It’s not a desert plant but it comes from the dry Mediterranean area so think rosemary, oleander, Laurel, junipers, and cypresses like Italian Cypress. Like other Mediterranean plants it’s mesic in its water use so plant it in soil amended with compost and it may not like being surrounded by rock after a few years down the road. It grows best on the east or north side of a home. You will take more chances growing it on the south or west sides in a sunny location, but it may do okay in the shade of a tree during the hot afternoons and surrounded by other plants. It will not like rock on the soil surface as it gets older.

            Like other Mediterranean plants the biggest disease problems are root rots from watering too often or poor water drainage. Viburnum like yours gets aphids and thrips in the spring. In the heat of the summer, it may get spider mites and thrips damage may continue. So, you are right for checking or spider mites when summer temperatures arrive. If spider mites are problems the leaves appear dusty and oftentimes light webbing can be seen.

This webbing from spider mites (why do you think they are called spider...mites...?) on tomato but if they are spider...mites...then you will see webbing on your plant as well.

            However, the usual problem is planting them in hot bright locations and then surrounding them with rock on the soil surface. The soil amendments last for a couple of years but they slowly dissolve into desert soil over the next 3 to 5 years and the plants start getting burnt edges around the leaves.

            Before buying an insecticide look at it at about 2 PM. Is the location where it’s planted hot and very sunny? Is the plant surrounded by rock on the soil surface? If the answer is yes to both of those questions, then it’s probably a location problem combined with a soil problem and not spider mites. Nurse it through the summer and in the fall rake back the rock, amend the soil with compost and cover as much of the area with woodchips as you can.

Try the paper test for detecting mites because they are so small

Rosemary for Oils and Cooking are Different

Q. I use rosemary in my cooking, which I purchase from the store.  It is expensive and it does not last very long if I don't use it all. I would like to plant a rosemary bush in our yard so that I can use it in my cooking as I please.  Is there a difference between rosemary bush used for "cooking" and regular rosemary used in landscaping?

Honeybees like Rosemary flowers and these plants flower all season long and particularly profuse in the winter. So put them where people are not afraid of bees.

A. Landscape rosemary works if you want a balance between visual appeal and cooking. Use the new growth that has the flowers if you want it for cooking. If you are serious about a type of rosemary used for cooking, then pick a variety recognized for its oil content.

Landscape rosemary focuses more on looks, green foliage and flower color, rather than oil content About as sophisticated as you can get with landscape rosemary is the difference between an “upright” and a spreading or “prostrate” form. If the new growth is pointing upward, it’s an “upright” form. If the new growth is growing more horizontally then it’s a spreading or “prostrate” form. The prostrate form is a good choice if you want it to cascade down or over a wall but not considered a strong form for cooking.

            Rosemary is a Mediterranean plant which means it likes dry and rocky soils found in southern Italy, Greece and Turkey, rock gardens, non-desert parts of California, but it’s not a cactus so it doesn’t like an unamended desert soil contrary to what the University of Florida tells you. When in doubt it’s always safe to amend desert soil a little bit when planting anything you are not sure about, even cactus.

The oil content in rosemary is what gives it the flavor you want for cooking. The most aromatic portion of the plant with the highest and best quality oil is the new growth containing new flowers. So, if your primary focus in having arosemary plant is cooking then focus on varieties of rosemary with high oil content such as ‘Benenden Blue’, ‘Flora Rosa’, ‘Tuscan Blue’, ‘Majorca Pink’, ‘Arp’, ‘Albiflorus’, ‘Huntington Carpet’, ‘McConnell's Blue’, ‘Irene’, ‘Holly Hyde’, and ‘Hill Hardy’ to name a few.

Rose of Sharon a Popular Las Vegas Plant 40 Years Ago

Q. I just saw Rose of Sharon (Hibiscus syriacus) for sale at a local nursery. It reminded me of a yard I saw over 40 years ago in the Huntridge area that had a row of these plants which were spectacular. I was wondering what your thoughts were on this plant in our climate.

I think this is a Rose of Sharon, aka shrub althaea. I only identified as a hibiscus and many of you know I have a farm in the Philippines and we have tropical hibiscus there. And now, the crazies are planting tropical hibiscus in LV?

A. Rose of Sharon is a hardy and fun deciduous shrub for our climate that grows about 10 feet tall and 4 to 6 feet wide and covered in large Hibiscus-like flowers all summer long. Keep in mind it should go into the mesic part of your yard because it is MESIC and not XERIC!!!!. It will not like rock much or unamended soil. But Rose of Sharon is hard to find from local nurseries. The flowers range in color from white to blue to purple to red depending on the variety. These shrubs are underappreciated in our climate. There is some great breeding work done on it at Texas A and M at the Vernon Center.

Plant this shrub in a bright north or east area in the Mojave Desert with compost amending the soil and wood chips as a surface mulch. It’s not meant to be planted in isolated areas all by itself or surrounded by rock. It likes companionship in areas with lots of light and wood chip mulch. It’s considered mesic in its water use and not meant for desert landscapes.

            It’s easy to propagate from no bigger than pencil-diameter sized cuttings about 8 to 12 inches long with the leaves removed and dipped in rooting hormone. Use potting soil in small containers as the propagation medium. Plant no later than early summer. If grown as a flowering hedge, put them 4 to 6 feet apart and irrigate the row with drip tubing instead of emitters. Propagating Rose of Sharon and other hibiscus.