Cold temperatures, lack of iron can bronze leaves

Free wood mulch is available at the University of Nevada Cooperative Extension Master Gardeners Orchard in North Las Vegas. It is located outside of the fence and is accessible seven days a week. The mulch is from trees that have been removed by Las Vegas arborists and chipped. Instead of being taken to the landfill, the mulch is offered free to the public; it is the same type of mulch that has been used in the orchard for the past three years. For more information, call the master gardener help line at 257-5555.

Q: I have a ruby grapefruit tree that looks anemic this year. The leaves are yellow-green, not dark green like my orange tree. Last year, we had several small grapefruit that were nice and juicy but nothing took for this year. Any ideas?

A: Since I cannot see the leaves I am not sure why they look anemic, but here are a couple of guesses for you.

First, there is a bronzing or yellowing color that can occur on evergreen leaves during cold weather. Freezing temperatures and high light intensities in our climate can cause evergreen leaves to take on a bronze or yellow appearance due to cold damage.

Bronzing from winter damage is easy to diagnose since the new growth in the spring is a normal, dark-green color while the older growth that survived the winter cold continues to be discolored yellow or bronze. You may see this in citrus and many other evergreen plants including palms.

The second possibility would be a micronutrient problem such as iron deficiency. In this case, new growth in the spring will show a yellowing color while the veins will remain a darker, green color. This discoloration gets worse on emerging leaves as the season progresses.

To get these iron-deficient yellow leaves to green up at this time of the year, you will have to spray liquid iron on the foliage. I would use distilled or reverse osmosis water when mixing up the spray, and add a small amount of general purpose foliar fertilizer containing nitrogen and one-half teaspoon of liquid dishwashing detergent to each gallon of the mix. You also can buy a commercial spreader to add to the mix instead of the liquid detergent.

Spray the mixture immediately after making it and apply it in the early morning hours before it gets hot. Use all of the mixture; do not leave any in your sprayer.

There can be several reasons why the tree did not produce fruit this year, including the tree going into alternate bearing (heavy one year and very light the next year, which means a regular crop next year), irregular watering and high winds.

Q: I have attached four photos of our apple tree. The photos show extensive bark separation and some white material accumulating under the bark and around the stem of a young shoot. We would like to know what this is and whether, and with what, it can be treated.

A: The pictures you sent are probably enough for me to make a reasonable stab at the cause. I believe the white material is incidental and not significant.

The primary problem you have with the tree is sunburn. This means that the sun was shining directly onto the thin-barked tree for too long during the day. I also believe that the sunburn may have led to borer damage. Even though I can only see sunburn on the trunk and limbs, borer damage is a natural secondary problem that develops after sunburn.

The trees seem to be planted in rock mulch or bare soil in a garden area, and they seem to be limbed up fairly high exposing the limbs and trunk to direct sunlight. Both of these are problems for the tree. The tree also may be in a very exposed part of the yard, with direct sunlight from the south, west or southwest.

You hear me talk about this all the time, but in our climate it is very important to mulch the soil beneath fruit trees with organic mulch for good growth. You would want several inches of coarse mulch surrounding the tree.

When pruning fruit trees that have thin bark like your immature apple tree, you should leave lower branches attached to help shade the limbs and trunk.

At the orchard we paint the trunk and lower limbs with whitewash that we make from diluted white latex paint. This is probably fine in an orchard but might not be so desirable in a home landscape. If you cannot whitewash, then you should at least make sure the trunk and limbs are shaded by leaves and branches.

The darkened area shown in the picture is sunburned and dead. If you take a sharp knife and cut there and in the living area surrounding it, you will see the difference just beneath the bark.

There is a chance the tree can recover. My general rule of thumb is that if the damage is not more than halfway around the trunk or limb, I would give it a chance to recover and protect it. If the damage is more than that, it is removed, either by removing the branch or the entire tree depending on where the damage is located.

Keeping the tree healthy by fertilizing regularly also helps. From the dark green color in the pictures, it looks like the tree has been well fertilized, but I would like to see a fuller canopy for sunburn protection.

Bob Morris is an associate professor with the University of Nevada Cooperative Extension. Direct gardening questions to the master gardener hot line at 257-5555 or contact Morris by e-mail at extremehort@aol.com.