Q: Is it common for the chitalpa tree to partially defoliate in the summer? What would be the optimum amount of water for 15-foot chitalpa tree growing in Kingman, Arizona?
A: Chitalpa, like some African sumac, is notorious for leaf drop in the middle of summer. According to several authorities from New Mexico and Arizona, this is common with this tree.
According to the plant pathologist from New Mexico State University, this tree has a bacterial issue that causes some of its water tubes to get plugged. That causes the leaves on the tree to get scorched like it’s not getting enough water, and in severe leaf scorching, the leaves drop.
It’s a similar, if not the same, illness we see on grapes called Pierce’s disease. From what I understand, there is no cure for this disease, and each plant has it because of how it’s propagated.
Some scientists think this disease may be transmitted by a small insect similar to a leafhopper. So, get rid of any weeds growing nearby to the tree.
It is possible this disease could be spread from your chitalpa to nearby grapes. The symptoms are similar: leaf scorch and leaf drop, but in grapes, it’s eventual plant death.
You can try giving it more water all under its canopy and see if that helps. If it’s a lack of water, you will see the tree improve. Anyway, apply enough water to wet the soil under the canopy a depth of 2 feet.
Q: About a year ago, you helped us diagnose a spider mite problem on our creosote bush. We took care of that as you directed. The results were encouraging and seemed to get the problem under control. However, we think the mites have come back with a vengeance and are considering a severe pruning to revive it.
A: Creosote bush can be cut back to a few inches above the ground, and it will grow back after a few occasional waterings. Look at the creosote bushes mowed off near desert roads probably by a road grader from the Department of Transportation. Because they were cut down and got some extra water from the road when it rained, they came back like gangbusters — dense and green.
What concerns me more is why the spider mites got out of control in the first place. The creosote bush has its share of spider mites naturally, but they are frequently controlled by predators such as other insects and mites. However, in your case, the balance between “good guys” and “bad guys” got out of hand with the “bad guys” winning.
The problem with spraying a pesticide is killing off the “good guys,” then the “bad guys” get out of control because few or no predators are left. So, we usually avoid spraying pesticides unless we don’t have any choice.
I like your idea of cutting it back and letting it regrow. But I think you also must do something different, or the spider mites will just be back again.
Control weeds in the area. Spider mites like to feed on many kinds of plants including weeds, and these can play host to a growing population of “bad guys.”
Secondly, be careful of watering too often. Creosote bush should never be on an automatic irrigation system because it just doesn’t like to be watered that often. Water it no often than four times a year with three of those irrigations during the hot months.
Q: My Sensation lilac is dropping leaves, and they have a dry burn on them. New buds are coming out in July. Is my lilac going to survive?
A: Sensation is a French lilac (Syringa vulgaris), and it typically doesn’t do well in the hot Mojave Desert at 3,000 feet and below. Above 4,000 feet, where it’s cooler, French lilacs will fare better. It is just too hot for French lilacs at lower elevations.
The better choices are the Chinese lilacs (Syringa x chinensis ), which are more heat tolerant. If you are going to try any lilac, make sure it gets plenty of morning sun but shade in the afternoon. Plant it on the east side of a home so it gets afternoon shade.
Use plenty of compost to amend the soil at planting, and mulch the soil surface with wood chips or anything else organic. It will grow the best surrounded by other plants with a similar need for water and soil improvement. It is not a desert plant, so don’t surround it with rock.
Q: What is the difference between red tip photinia and Fraser photinia?
A: My understanding is that they are the same plant, just different common names. The Latin name has both photinia and Fraser (fraseri) in it. That explains why it is sometimes called Fraser photinia. Because it’s new spring growth is red, it is sometimes called red tip photinia. I prefer the name red tip photinia because it describes the plant.
When in doubt about the plant, go back to the Latin name to see if it’s the same plant. Plants can have several different common names but only one agreed-upon Latin name.
By the way, this plant is considered mesic — needs to be watered more often than xeric plants —and it grows better in amended soil and doesn’t like to grow in hot spots or surrounded by rock.
Q: I have a 30-foot tall Chilean mesquite tree that looks nice and healthy but has a 2-foot long dry black streak on its trunk. What is it and what’s the problem?
A: These dark streaks on the trunk are a common occurrence on mesquite, particularly if it had been pruned in the past. In common vernacular, the tree bled after it was pruned. If your tree otherwise looks healthy, then there is nothing to worry about.
Mesquite gets a minor bacterial disease problem called wetwood, aka slime flux, which causes a similar staining on large limbs and the trunk. But the black stain is constantly wet and smelly.
Slime flux is a bacterial infection deep inside the tree which causes a wet, yeasty oozing to flow from limbs that attracts flies. It’s spread from tree to tree by lots of things including tree trimmers who think they are arborists. It’s not a lethal disease problem for the tree, but it may cause owners some angst.
I have a picture of a mesquite tree with a black streak on its trunk on my blog. I will repost it for you to look at and compare.
Q: My apricot tree has yellowing leaves. What nutrients are missing? The tree is 3 years old and only produced one apricot.
A: Production of apricots and leaf yellowing are probably not closely related. Your tree at 3 years of age is still young for fruit production.
The leaf yellowing looks like the early signs of iron deficiency. The darker green veins are starting to appear, and this yellowing is on newer growth at the tips of branches. The darker green veins and their appearance on the newest leaves give it away as probably iron deficiency.
It is late in the growing season to apply iron to the soil and see much improvement. Soil applications of iron are done just before new growth starts in early spring and in anticipation of an iron problem. This type of yellowing is cleared up with leaf sprays of foliar-applied iron.
Spraying an iron solution on the leaves early in the morning — three or four times a couple of days apart — will make these leaves greener. Improving the overall nutrition of the tree by adding iron to the soil next spring will also improve production and fruit quality.
Q: I have two spiky-looking stick plants, and they basically look dead. Last summer we got one or two flowers on top but nothing this year. They are kind of ugly in their current shape, so was wondering if I can revive them or maybe it’s time to replace them?
A: They look like ocotillo that are native to the Sonoran desert to our south. This is what they look like in the desert when it’s been dry for a while. They grow leaves and put on growth after a rain.
Ocotillo is a desert plant and xeric in its water needs. Xeric plants don’t like to get water often, but when they get it, they take quick advantage of the rain, put on leaves, and grow.
Give this plant a chance. You told me it flowered, so that is a sign it is still alive. Don’t water it too often, or you can kill it. It is better to water it when you remember rather than putting it on an automatic timer. Rely on the “shoot, I forgot to water it” method of watering.
Bob Morris is a horticulture expert and professor emeritus of the University of Nevada, Las Vegas. Visit his blog at xtremehorticulture.blogspot.com. Send questions to Extremehort@aol.com.