Trees have troubles! And from the calls to USU Extension offices, two highly desirable and widely planted landscape trees have more than their share.
The cutleaf weeping birch used to generate the most owner concern. Enough of them have died that quaking aspen now holds the top spot.The conditions for birches in general, but particularly for the weeping forms, contribute to poor performance. They're adversely affected by hot, dry weather and would be more at home given some protection by larger trees.
Roots are greedy, and normal lawn care doesn't supply enough water and fertilizer. They're often under stress, which encourages bronze birch borer attack. Tops of trees, single limbs, part of a clump or even entire trees are dead nearly everywhere they're planted because of this destructive insect.
If your birches still look good, now is the time to spray with dursban to prevent borer attack. Do some deep watering every two to four weeks and apply extra nitrogen fertilizer by July 1 to be sure it reaches the root zone. A soil application of iron sul, Sequestrene Iron 138, or Miller's FerriPlus will head off iron deficiency.
The quaking aspen displays numerous maladies. Dozens of organisms attack them in their native habitat, but vast expanses on a hillside usually aren't examined closely. Not until we have a few in the yard do we focus attention and notice disfiguring symptoms on this widely planted specimen.
-Marble-size galls: These are conspicuous but not particularly damaging to twigs. They're caused by a tiny fly, and there's no practical control recommendations unless you want to prune the twigs off.
-Sprouts in the lawn: These are not abnormal - just the way quakies grow! It's a clonal tree, meaning that if you plant a quakie, expect a forest. Just mow the sprouts off. A lawn weed spray could affect the parent tree, depending on sprout distance, size and number treated.
-Large knobs in grass: Quakies have shallow roots, and the traffic to which they're subjected promotes abnormal growth. Chop off that section of root.
-Borers: Several beetles attack trees, especially when weak and under stress. Sap oozes from holes. A dursban spray about now may reduce larvae invasion. Inject or otherwise work ethylene dichloride into open holes (you may have a sawdust plug). This spray is sold as Boresol or Ferti-lome borer killer.
-Leaf spots: These are caused by a fungus that attacks just as leaves emerge from the bud and enlarge. Early spring sprays of benomyl, daconil or copper containing fungicides will help. Leaf spots are very difficult to control when springs are wet and cold.
Use similar cultural techniques as given for birches. Don't overwater, especially in poorly drained soils, but shallow, frequent lawn irrigation may not supply the needs of large trees.
Unless you're a glutton for punishment, plan future tree planting to avoid troublesome birches and quaking aspen. There are many trees with fewer problems and weaknesses that do well in the Mountain West.
-ENJOY IRIS BLOOMS: The extensive iris collection at the Farmington Utah State University Botanical Garden will be on display May 27 from 1-4 p.m. The garden is just north of Lagoon off U.S. 89.
-LAWN WATER: Apply 1 1/2 inches of water this week.