White birches are one of the most beautiful trees used in landscaping. Unfortunately, many of these trees are living on borrowed time due to several factors.
Birches prefer acidic soils that are common in the eastern United States and the Pacific Northwest. Utah soils are alkaline, and this predisposes the trees to iron chlorosis and makes them grow more slowly. Birches are the climax species of the forest. In a natural growth sequence, the first plants established are grasses, then shrubs, then evergreens and other short-lived trees, and finally, the hardwood trees. As a climax species, they are surrounded and protected by other trees. The shallow root system requires cool temperatures and does best with adequate water. In addition, the trees do not like the hot, dry winds of our desert environment.Two pests cause severe problems for birches. Neither is fatal to healthy trees, but both are life threatening when trees are under stress. The bronze birch borer is a metallic wood-boring beetle. In the Salt Lake area the adult beetles lay their eggs on the bark about mid-May. Larvae tunnel into the trees and cannot be controlled after they are under the bark. They live under the bark and make extensive tunnels that eventually girdle the branches or trunks and cause serious dieback. They live in the tree for an entire season and emerge the following spring. Borers are prevented from entering the trees by sprays of Dursban or Lindane. Thorough coverage of the trunks and main branch areas is essential.
One spray is usually sufficient, but a second is needed if coverage is not good or the borers are numerous, or weather patterns abnormal. Dursban is the preferred choice of most pest-control operators.
Cytospora is a fungal disease that attacks trees under stress. Cytospora organisms are most active in the early spring and cause much of the characteristic dieback in the top of the birch trees. The disease causes sunken dead areas and tiny black cones on the bark. These cones are different than the normal black markings on birches. There are no suitable chemical controls for cytospora. The disease can be controlled by keeping the tree healthy and by pruning to remove dead or dying branches.
Those who have lost their birches often ask, "Is the borer killing my tree, or is the cytospora killing my tree?" In reality, either one invades weakened or stressed trees and the other usually follows within a short period of time.
Birches are only successful when planted in suitable locations. These trees simply are not adapted to high-Ph, heavy clays, soils found in many growing areas. They soon develop yellow leaves and iron chlorosis. If yellow leaves are observed, treat the tree with iron chelates. Even in those areas with higher quality soils, there is a risk. Plant the trees where there is adequate water and where the roots stay cool. In general, the trees do much better with shrubs or ground covers around the base. Soil temperatures under turfgrass are considered higher than those under shrubbery. The worst place to use these trees is in areas surrounded by asphalt or pavement.
Birches are the exception to the rule that trees like deep, frequent irrigations. Since these trees develop fairly shallow root systems, they require regular irrigation. Avoid other stresses on the trees, including damage from lawn mowers, weed eaters, herbicides or other interfering yard maintenance operations. Control pests, such as the bronze birch borer and cytospora, by timely sprays and pruning and protecting the trees from stress.
Another related pest is the birch stink bug. It does no damage to the tree or leaves but feeds on the seed pods. These pests have a disagreeable odor when crushed. They put a real damper on outdoor activities near the trees. Controlling the stink bug is difficult, but they may be reduced by timely applications of Orthene when the they appear.
Ash trees also require spraying about mid-May. The ash borer in Utah is in reality the lilac borer. This pest attacks all true ash trees (not mountain ash), lilac and privet. The pencil-size emergence holes are formed as the insects exit the tree. This borer has killed thousands of trees in our area. Dursbane, Lindane or Thiodan are effective against this pest. Spray the trunks and the main branch areas. Severely infested areas need a second spray if the insects continue to emerge.
- TWELFTH ANNUAL PLANT SALE, plants of every description. Saturday, May 18, 9 a.m. to 3 p.m., south of University of Utah's Huntsman Center. Prices range from $1 to $100. Bring questions, our sales people are horticulturists!
- AFRICAN VIOLET SOCIETY OF UTAH annual show and sale, Saturday, May 4, 1 p.m. to 6 p.m. and Sunday, May 5, 10 a.m. to 5 p.m. at the Garden Center Activity Building, 1602 E. 2100 South, Salt Lake City. Admission is free.