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Thursday, April 21, 2011

Magnolias Dont Last Long in Our Desert Environment

Q. We purchased a home two years ago with two existing magnolia trees in our front yard. The trees are about 8 feet tall, have some leaves on them but they don't look overly healthy. I've treated both trees with soil acidifier and a product that contains an insecticide and fertilizer each year. We also have an automatic fertilizer injector for the yard. Do you have any other recommendations for them?

Two magnolia planted on the east side of Las Vegas showing some signs of stress with dieback on the tops and sides. Old magnolias for Las Vegas

A. I have said this before but it probably doesn’t hurt to say it again. When we plant trees, shrubs or any other plant for that matter that is out-of-place in our desert environment then it will cost us more time, energy and money to take good care of it. Magnolia is clearly out of its element here in the desert. So it will require more from you to make it healthy and keep it in good shape.

The acidifier might be of some help but you can get excellent acidification from compost and decaying organic matter such as wood mulches.

I hope they are not planted in rock mulch. That will be their doom if they are. Try adding compost around the tree and watering it in if you can. The fertilizer you’re using is fine but I would also recommend an iron chelate as a fertilizer applied now which contains EDDHA in the ingredients.
Magnolias planted near a west facing wall on a building in rock (boulder) mulch in Las Vegas. OMG.
You can skip the insecticide treatment. Magnolias are not a good choice for this climate and I will not give you a lot of hope in getting these to large trees. Enjoy them while you can. We don’t see many large ones here for a good reason.

Wind Damage to Leaves Can Look Like Insects Eating Them

Wind Damage on Plum Leaves
Q. Something is eating the leaves of my small grapefruit tree. I have checked it often to see if I could see the pest that was the culprit, even at night, and cannot find anything. What do you recommend?

A. Without seeing it I am not sure anything is eating your grapefruit leaves. Wind damage to the leaves is the most common reason for damage to citrus leaves that resembles feeding damage by insects. We did have some pretty good winds recently. Wind damage most resembles tearing, shredding or ripping of leaves. I would not apply an insecticide if you are not convinced it is insect damage and then only if the damage is not recoverable by the tree without your assistance or interferes with fruit production.

Wind damage to persimmon leaves.

April Todo at the orchard

Unthinned peaches might look like the bottom picture but after thinning it should look like the top picture, fruits about four inches apart.

Thinning is at the top of our list of things to do. We have been thinning peaches for the past three weeks. Thinning is now to include plums and plum relatives like pluots and the Keifer pears.
Delta type pheremone trap

With these warm temperatures we need to check to see if peach twig borer is flying (pheromone traps) and replace the sticky surfaces and the pheromone capsule. Tomorrow is not an irrigation day but if the plots need irrigation then irrigate the plots. It is important right now to make sure the garlic and onions are not stressed or the garlic may not size up properly and the onions may not get to a good size as well.

Dieback of new peach growth due to peach twig borer. Later it can get in soft fruit.

The orchard phone on the computer now seems to be working well. The number for the orchard is 702-257-5532.

Asparagus will need to be harvested. When harvesting please remember the next harvest day isn’t for three days so we need to harvest the spears accordingly. At 90F the spears may grow an inch a day if there is enough water.

• Thinning peaches, nectarines, plums and Keifer pears
• Harvest asparagus
• Add drip for hops and plant hops
• Irrigate vegetable plots where needed
• Spray nectarines with insecticidal soap/spinosad for thrips control
• Weed vegetable plots
• Remove suckers from trees

Shade is Important for Vegetable Growing in the Desert

 Hoophouse with 30% shade at The Orchard

Q. I have to build a small raised bed for vegetables and herbs. I want to provide protection from the wind and cold and, later, the summer heat. The sun screening in the stores are the 25-30% type. What is the best sun screening level for sun screen?

A. We generally use about a 30% shade cloth for most vegetables. Even at 30% this is too much shade for some vegetables such as okra which does much better in full sun. Okra originated out of the area of northern Africa we now call Ethiopia and Eritrea. This probably explains why they don’t like much shade and enjoy our full sun.
I would not go above 30% shade for those vegetables which we value for their flowers and subsequent fruit that develop from flowers. Decreasing light will affect flower production. For leafy vegetables you can go higher in percent shade, perhaps in the 40% shade category.

Sap Can Ooze From the Trunk of Fruit Trees in the Desert

Sap coming from apricot limb.

Q. Our mature apricot tree has been a good producer of sweet apricots during the 7 years we have owned the house. This year the apricots were not sweet and there is sap coming out of one of the limbs. Now, after harvest, several limbs are dying. I am attaching a photo of the damage. Is there anything we can do to save our tree?

A. Sap coming from the limbs of apricots is usually an indication of stress or damage of some sort. Apricots are not as notorious as peach or nectarine for getting borers or boring insects in their limbs. Damage from borers is typically on the upper surface of limbs because of sunlight intensity or sun damage and it’s very thin bark. Damage from sunburn borers can cause sap to flow near the damaged area.
Your picture seems to indicate sun damage but that can also be from damage from boring insects. By late June or July if this damage were from boring insects or borers you would see a limb which has leaves which have totally turned brown and perhaps limb death. Branch death would be a clear indication of borers and of course the limb should be cut out and removed.

Diluted white latex paint for controlling sunburn and consequently borer damage.

There is no chemical spray that you can safely up like to apricots for controlling borers. We usually rely on whitewashing limbs and the trunk with a dilute white latex paint and remove limbs that are heavily damaged. This white latex paint is diluted with an equal amount of water, mixed and applied with a brush or sprayer on the upper surfaces of limbs, western and southern exposed areas of the limbs and trunk. This white wash helps to decrease damage to the limbs from sunburn and subsequent infestation by boring insects.

Yellowing of Indian Hawthorne Growing in Rock Mulch Probably Iron Shortage

Iron chlorosis in Indian hawthorne due to poor soil development from lack of organic decomposition of rock mulch.

Q. Following your advice, I am planning to replace all of the stone mulch under and around the existing shrubs in my yard and replace with bark mulch from the orchard stock pile. I have been told that bark mulch attracts cock roaches. Is this your experience?

A. Wood mulch will attract quite a number of animals and foster plants that contribute to the breakdown of the mulch and roaches do contribute to that. These include mushrooms, earthworms, larvae of beetles such as grubs, gnats, and others. Mulches that decompose will attract decomposers.
Roaches tend to congregate in irrigation boxes in the landscape and these should be treated periodically for control if this is a problem. I normally tell people to keep the wood mulch a couple of feet from the foundation of the house.
Rock mulch will give you a more “sterile” environment and if that is what you prefer then stick with rock mulch. There is nothing wrong with rock mulch if it is used with plants that can tolerate rock mulch such as most desert dwelling plants. However, decomposing wood mulch has many, many advantages for plants compared to rock mulch which adds nothing back to the soil and most plants will perform better with wood mulches. If you would like a copy of the benefits I can forward this information to you or any of my readers.

You Can Grow Anything in Las Vegas

Mexican papaya in container

Q. I saved some papaya seeds last year and planted three of them in the spring. To my surprise all three began to grow. It’s hard to tell but the three plants are different sizes. I’d like to transplant them into individual 15 gallon pots. I read where they do not like to be disturbed once they start growing. What might be the right time to attempt that? Meanwhile I need to keep them somewhere once it gets cold outside. What would be the best way to keep them through the winter? And what are the chances they would ever bear fruit some day?

A. Master Gardeners who attend my classes are very familiar with me saying, “You can grow any plant in the world in Las Vegas. It depends on how much time, energy and money you want to use to make it happen.” Rare fruit growers in Phoenix grow papayas outside with some freeze protection applied during the coldest part of the winter. We are not Phoenix but we do have some similarities.
This is what you need to know about papayas to be successful. Papayas prefer rich, tropical, acidic soils. They will not withstand temperatures much below 32F or freezing. Papayas do not like direct sunlight from the late afternoon sun and would prefer about 30% shade if in full sun. Papayas will die growing in soils that do not drain easily but also do not tolerate dry soils.
They are heavy feeders and so require continual applications of small amounts of fertilizer. They need both male and female flowers to set fruit. Sometimes this happens on a single plant and other times it requires a male and female plant. So plant several so that your chances of getting male flowers is increased.
They are normally started from seed and, as you found out, the seed germinates easily. Most of our papayas come from Mexico due to costs of production. They should transplant fairly easily into 15 gallon containers if you are careful and stake it in the new container to keep it upright and wind resistant.
Keep them lightly shaded until the roots have reestablished in the container, maybe one month. They should be able to handle more sunlight after this. Some varieties of these plants may become damaged anytime the temperature reaches about 45° F, others are more resistant to this type of chilling injury. They will not handle any freezing temperatures at all and they become stunted at temperatures even slightly above this.

I have no experience growing them here but it’s reasonable to assume that they would handle morning to mid afternoon sunlight but not late afternoon. They will handle some light shade but will probably not do well in fruiting if the shade is too much.
These trees produce at a very young age, some produce at a younger age than others but they are also very short lived. Of course it would be best if they were in a greenhouse here and handled as a tropical plant.
No one is certain how the fruit is set; whether it is by wind or by pollinators. If you’re lucky enough to keep it long enough to get flowers you may have to do some hand pollination if you do not get fruit set. Your biggest challenge will be to keep it from getting hurt during the winter and still provide enough light during the summer to encourage flowering and fruit set.

Wine Grapes Love Compost in Poor Desert Soils

Q. I have a nice little compost pile that is about ready to spread. I read where fall is the best time to spread compost around fruit trees. Is that true?

Composting wine grapes at the Orchard

A. We do use compost around some of our fruit trees at the orchard. The fruit trees I like for applying compost are persimmon, Asian pear, and other fruit trees that have not originated in arid or desert climates.
All of the fruit trees will benefit from an application of compost, even grapes. If you grow any blackberries or other cane fruit they will benefit as well. I usually spread compost around the fruit trees just prior to spring growth in mid January for the earliest. I will still supplement it with iron chelate. It needs two or three weeks of irrigation to begin moving the nutrients from the compost into the root zone and into the tree.

April is the Time to Treat for Agave Weevil

Agave weevil in agave crown

Q. I have a question regarding 'grubs'. We lived in Texas where we had grass and were accustomed to grubs, but we are experiencing them here. We were dumbfounded and unprepared for grubs in the desert. We have lost several very mature cacti to grubs. I purchased grub control chemicals and have followed instructions but still seem to have them. Is it normal to have grubs here? Are there specific plants they zero in on? Can you recommend what we should use?

A. There are many different types of grubs so when we speak of grubs we have to be certain about which grubs we are referring to. Commonly we find grubs in lawns (white grubs, aetenuis beetles), in compost or decaying organic matter (June bugs), grubs in some cacti such as agave (agave weevils), and others.

Green June beetle life cycle

In cacti it is usually the agave weevil which prefers agaves to other types of cacti or succulents. This frequently requires a pesticide drench over the top of the plant and drenching the rosette about three times; once each in April, May and June according to some growers in Arizona. The liquid is preferred for drenching.
Granular pesticides can be used but must be watered in around the plant and should be a systemic approved for grub control and applied about the same time as the liquid drench. The liquid drench has the advantage of killing newly hatched grubs from eggs laid in the bottom of the leaves in the rosette.