Issue: August 2, 2008
Winter, spring, and summer can cause problems for globe willow trees
Question:
We have a globe willow tree that we planted in 2006. It was in a 5-gallon bucket when we bought it. It did fine the first year but this year it looks awful. In early spring it looked beautiful when all the leaves appeared. In late April and early May the leaves started turning yellow and falling off. Now new leaves start growing but they do not get very big when they curl up and dry up. We took a clean piece of white paper and shook a branch from the tree over the paper and a lot of small specks fell on the paper. These specks move about on the paper but they are so tiny that you cannot make out as to how they look. What do you think we are dealing with here? Do you think the tree will do better next year if we just leave it alone for this year?
Ray G.
Answer:
You, and many other people, have been observing tree problems this year. In some cases, the problems resulted from the dry winter, from the late freeze in the spring, or from pests. I think your tree is suffering from a combination of these stress factors.
You did not tell where you live but much of New Mexico was dry during the winter and that may be a factor affecting your tree. This can result in problems in the summer because roots that began growth in the late winter may have died in the dry soil. This results in a reduced ability to provide water to the tree in the spring and summer as growth begins. Irrigation later and the summer rains can help, but cannot completely restore the plant.
Another weather factor that influenced much of New Mexico was the late freeze. Such cold weather can damage plants after the leaves have formed and even before the buds open. The result may be the initial development of leaves that then died. This may also result from the winter drought mentioned earlier.
Stress during early growth, especially late freezes, may result in greater susceptibility to insect and other arthropod pests. Your test for this was the right thing to do and gave me good information. The small things you observed on the paper may be aphids (an insect) or mites (an arachnid). Both of these fall into the category of arthropod pests (animals with jointed legs and an exoskeleton). Both feed by sucking the sap from the cells in the leaf and can cause the leaves to fail to form and ultimately drop. Even though these are both arthropods, different chemical control measures may be required. To determine which pest is the problem, take a sample of the pests to your local NMSU Cooperative Extension Service office. Collect some twigs and leaves and also some samples collected on paper. Put them into a tightly sealed jar with alcohol. The Extension Agent may be able to recognize the pest involved, or send them to a specialist at NMSU. With a proper identification, proper treatment can be determined. If you prefer organic control, include that information with the sample. The recommendation will provide organic measures if such treatments are available for your specific pest.
In the meantime, you can minimize the damage by washing the plant with a strong jet of water. This will wash many of the pests from the new growth and twigs, perhaps allowing them to grow with minimal damage. Many of the damaged leaves will also be washed from the tree. While you wait for the results from your sample, be sure the tree is adequately irrigated (moistening the soil to a depth of 2 feet every 10 to 14 days). Apply irrigation water below the dripline (soil below the outer extent of the branches) and outward from the dripline for several feet. Next winter, irrigate once a month to moisten the soil to the same depth in the same region of soil mentioned above. As buds swell in the late winter (initiating root growth) be sure the soil has been moistened. If there has been precipitation, you do not need to irrigate if the soil is moist to a depth of 2 or more feet. (Other trees species may need to be irrigated to a depth of 3 feet.)
Question:
I have noticed a lot of branches in my trees with no leaves on them. We had a hail storm the other day that probably caused this. Can I prune these branches, or should I leave them?
Answer:
If the absence of leaves on the branches is due to the hail and you have no other reason to remove the branches, just wait and let new leaves form. If these are branches that you need to prune anyway, then you can prune them. This will be less harmful than mid-summer pruning branches with many leaves. That is because these defoliated branches will need to draw stored energy from the branches and trunk to produce new leaves. Pruning before production of new leaves reduces this drain on the stored food reserves. However, minimize the amount of pruning you will do at this time. The leaves, once formed, will begin feeding carbohydrates into the food reserve in the branches, trunk, and roots for growth next year.
Any branches that are dead (dry and brittle) can be pruned now without harming the trees.
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.
Please copy your County Extension Agent and indicate your county of residence when you submit your question!