Type your question here!

Sunday, September 23, 2018

Whats Causing Warts on Limbs of My Pine Tree?

Q. I have several Mondale pine trees and recently noticed round bumps on some branches. I love these big trees, so I really hope I don’t have to take them out.  I deep water once a week in summer and once a month in winter and they have done very well so far.
Bumps or warts on limbs of Eldarica pine

A. I don’t recognize the problem to your trees as something serious. These rounded bumps are probably resin pockets in the limb. It could be caused by a nonlethal virus disease. It is also possible it could be a physical reaction to weed killers applied nearby.
            Keep an eye on the tree and its growth. Apply enough water and fertilizer to get eight inches of new growth each year on older trees; 12 – 18 inches on younger trees. If the tree is doing well on your watering schedule, then keep it. Just make sure enough water is applied for it to drain 24 inches into the soil.
New growth on pine are called "candles" and you can see why. This new growth should be strong and vigorous in healthy trees.
            Water should be applied to at least half the area under its canopy. Add an extra irrigation when temperatures are above 110 F and windy.
            One application of fertilizer in the spring of each year should be enough. When it is hot and windy (like over 110F), give it an extra deep watering. If the tree canopy is thinning the tree may need water or fertilizer or both.

Whats Causing Top Dieback in Mulberry?

Q. What is causing the “big hurt” on mulberry trees? There was considerable damage to most trees in recent years. What caused so many dead branches this and last year?
Sooty canker disease 

A. Mulberries are solid performers in the hot desert if they get enough water and are pruned properly. I am not endorsing their planting; they use a lot of water and the male trees release large amounts of allergenic pollen, a huge health problem for many residents.

Battle of the Sexes

            The female trees are not “outlawed” in southern Nevada. The male, or fruitless mulberries, are. Female trees can be planted and will produce fruit without male trees because of large amount of airborne pollen produced every year from existing male trees.
Bowl of purple and white mulberry fruit in Tajikistan. Many countries I visited call the fruit "toots".

Sooty Canker Disease

            We see an increasing number of mulberries with dead branches in the tops of the trees. Most of this is “sooty canker” disease. This fungal disease spreads from tree to tree on poorly sanitized pruning equipment, birds and insects.
Sooty canker disease on ash. Looks the same on mulberry.
            It also infects other trees besides mulberry including ash, poplar, apple and many others. Frequently, the health of infected trees was “compromised” in some way making them susceptible to an otherwise weak pathogen.
            What compromises the immunity of otherwise vigorous trees growing the desert? Usually its water; a lack of it causing them to be stressed. The disease organism is transported to this weakened tree on pruning tools, or perhaps by birds or insects. This pathogen enters the tree through open wounds caused by pruning equipment, fresh openings left by dropping leaves, or through the flowers.

Consider this scenario: 

Sanitize pruning equipment before pruning

a landscape converts from large, established trees and lawns to a desert landscape; the lawn is removed and drip irrigation is installed; large established trees do not get enough water and limbs begin dying; landscapers remove limbs with unsanitary tools; the trees become infected; disease spreads because the tree’s health is compromised due to a lack of water.
            Simple solution? Sanitize pruning equipment.

Considering Growing Tipu in the Eastern Mojave Desert?

Tipu tree growing in Las Vegas. Will we get winter temps below 25F? Plant this tree and you are betting we wont.

Q. I have been wanting to plant a tipuana tree since I saw one in person (those pinnate leaves are gorgeous!) and I love the idea of a wide canopy.  You mentioned in a December 2013 blog that here the potential for damage from the roots would not be as concerning in Las Vegas as in other places as long as it was planted “several feet away from foundations, etc.” The location where I would like to plant is between the pool and the block wall.  The wall and the pool are separated by 19 feet.  Would planting 4 feet from the wall and 15 feet from the pool be reasonably safe? I have citrus, duranta repens, and some other cold sensitive plants that I dress in old school Christmas lights and wrap in frost cloth, so I understand it will take extra work to protect from the cold.  What do you think of my chances for success? I do love the leaves, though. Maybe I can talk myself into a purple robe locust instead. 

A.  Just to be a little more clear than the section you read in my article. I am not a big fan of this tree but it has been pushed for planting in the Las Vegas area by a local nursery. You should read some of the comments from Arizona State University (Mesa, AZ) about its use in Phoenix. 
Winter dieback of tipu in Las Vegas.

Comments about Tipu tree from ASU

I am always seeing the downside of plants because I get hit with problems all the time. The Purple Robe Locust is a good tree. It is also not desert adapted but it can handle the low temperatures with no problems.

But it should be grown with woodchips as a mulch and use compost mixed in the planting soil at planting time. It is a medium water user and it will get about 35 feet tall and oval to round in shape. It is not a fast grower, not slow either but about 12 to 18 inches per year if you fertilize and water it well.

Avoid putting it in very hot locations with lots of direct sunlight beating down on its trunk and limbs. Keep it full and keep the lower limbs shading the trunk as long as possible. Surround it with lots of other plants that like a similar irrigation.
Texas Mountain Laurel in Las Vegas. Can have a spring insect problem but easily controlled.

Consider Texas Mountain Laurel, Texas Olive, Desert Museum palo verde, Red Push Pistache, etc. Even ornamental pear aka Callery pear. A better fit for our climate. All trees have problems but these would have fewer tree life threatening problems.

Use Houseplant Moisture Meter to Know When to Irrigate

Q. I am using an inexpensive soil meter to help me judge went to water again. I redid my landscape to include cacti, ocotillo, agaves and other types of desert plants. Do I let my meter peg to 1 before watering again or is 2 to 3 okay?

A. I have promoted the use of moisture meters for helping gardeners “get a handle” on when to water plants. For non-desert plants, like many of our trees and shrubs, let the soil moisture drop to about 50 -60 % before watering again. If the meter is divided into 10 equal units, this would be about “6” on the meter’s scale.

The scales are relatively accurate

            Desert plants that are not cacti, like Mesquite, Palo Verde, Acacia and leafy succulents, the meter can drop a little bit lower than this before watering; about 40-50% or about “5” on the same scale.
Another example of reading soil moisture with an inexpensive moisture meter..
            Cacti is in a category by itself. I think you are about right. Let the soil moisture drop to between “2-3” before watering again. Because cacti store water inside their modified stems and leaves, they give a visual indicator when their water is running out; the outside shrivels. That is a dead giveaway it’s time to water.
A third example of using a soil moisture meter for gauging when to water again.
            When I am irrigating non-desert plants like fruit trees in a soil that is new to me, I take three readings in different locations around the tree and use the average. I don’t let any readings drop below “5” and I will water if the average is about “6”. After I get the “rhythm” of seasonal water use, I seldom need it after that.

Soil moisture meters I use alot for approximating soil moisture for irrigation
Reotemp Soil Moisture Meter Link
Lincoln soil moisture meter but the price has jumped up too high for me recently

Probes that are longer are more versatile

            The other thing I do is push the probe of the meter into the soil slowly. I want to measure soil moisture near the surface of the soil and watch how it increases with depth. This technique helps me understand how fast water is leaving the soil.

When to Water

            There are two questions you need to answer when watering: when to water and how much to apply. Soil moisture meters help mostly with the “when” to water.
            I judge how much water to apply by pushing a thin metal rod, like 3/8 inch rebar, into the soil. It slips into the soil easily when it’s wet. For trees and shrubs, apply enough water to penetrate 18 to 24 inches deep. For lawns, flowerbeds and vegetable gardens, 12 inches deep. Two foot tall shrubs, vines and groundcovers, 12 to 18 inches deep.
            These are inexpensive meters andnot meant to last forever when pushed into our soils. Once you get the “feel” for when, you won’t need it often. Just occasionally when you aren’t sure.


1.         Insert it in the soil slowly. Get moisture readings as you slowly insert it into the soil. This gives you an idea how the soil is drying out with depth. Newly planted seeds, trees, shrubs, need water frequently but only a little. As they grow they need water less often (deeper) but more of it.
2.         Take three soil measurements in different locations. Insert it between emitters (if that is what you have). Otherwise insert it anywhere, randomly, above the roots.
3.         Observe your moisture meter readings as you slowly insert it and at the depth of the roots. For flowers and grass, this will be about (slowly) 6 inches deep. Remember that plant roots use water using the 40-30-20-10 rule…40% of the water they use is in the upper quarter of their rooting depth, 30% from the second quarter, 20% from the third quarter and 10% from the bottom quarter. If the plants are grass, flowers or vegetables the roots are divided into upper quarter (zero to three inches deep), second quarter (3-6 inches deep) third quarter (6-nine inches deep) and bottom quarter (9-12 inches deep). Tree roots are 18 to 24 inches deep so adjust your “quarters” to this depth. This is why it is important to push it into the soil slowly.
4.         Take three readings like this. Average them. Use this value to determine when to water.

9-10    =   Wet. Don’t water.
7-8    =   Moist. Don't water.
5-6    =  Water.
3-4    =  Water desert plants
1-3    =  Dry. Your plant is dead unless it’s a cactus. Buy a new plant.

How much to water? 

Look at the size of the plant. Can you plant it in a 1 gallon container? Water it ½ gallon. Can you plant it in a two gallon container? Water it with one gallon of water. Can you plant it in a 5 gallon bucket? Water it with 2 ½ gallons (round it to 3 gallons). Got the idea?

3/8 inch diameter rebar used for measuring irrigation depth inexpensively
Trees and large shrubs are more difficult to judge the container. Space emitters every 18 to 24 inches apart under AT LEAST half of its canopy. Water long enough for the water to drain 18 in deep. The easiest way to judge this is using a 3/8 in rebar, pointed or sharpened (flat if you cant sharpen it) and push it into the soil after you water. It will push easily to the same depth of the water.