Issue: April17, 2001

• Fertilizing oaks
• Fungus on globe willow

Fertilizing oaks

What should I feed my oak trees, live oak, red oak, and burr oak? They are all young trees between 6 & 8 feet tall. TK Odom Hobbs, NM

Trees should receive little fertilization the first two years after transplanting. Fertilizer, especially nitrogen, encourages growth of stems and leaves. During the first few years, development of roots is critical to the young tree.

If your tree has been planted at this site for a couple of years, you can begin light fertilization with a balanced fertilizer (containing nitrogen, phosphorus, and potassium in roughly equal amounts). If the nitrogen is high as in lawn fertilizer, that is okay.

Be certain that the fertilizer does not contain weed killer in addition to the nutrients. Many lawn fertilizers have weed killers in addition to the fertilizer. Avoid these when applying fertilizer near trees and shrubs.

Some fertilizers will also contain additional nutrients such as sulfur, zinc, and iron. These are good for the trees but may not be necessary if they are available in adequate amounts in your soil.

Remember to apply the fertilizer to soil which is already moist, then to irrigate following application of the fertilizer.

Fungus on globe willow

My Globe Willow has some sort of fungus growing only on the north side of it. It seems to be affecting the health of the branches above it. What can I do about it?

You didn't describe the fungus, so let me guess - it is a reddish or orangish threadlike growth. If I am correct, it is probably cytospora fungus that is common on willow or poplar in New Mexico. It is usually found growing on bark damaged by cold weather or some other environmental stress. It is an indicator of previous problems but not the cause of the problems. The injury to branches above it is probably due to cold injury suffered by the xylem and phloem in the stem showing the fungus. These damaged stems are not able to supply adequate water to the growth above causing the reduced health of the branches above the injury.

Your options are (1) to remove the damaged branch if that will not destroy the appearance of the tree, or (2) to care for the tree and hope that the damage was limited and the tree will recover. If you choose option 2, you should still remove all dead or dying branches. However, if this severely disfigures the tree, you may want to consider replacing the Globe Willow with another species of tree.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook.

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