What's Happening...
Frequently Updated Horticultural News for the Southeastern Pennsylvania Area
September 11, 2007

  • Bacterial Leaf Scorch (BLS) is probably the single most important shade tree disease currently facing many areas of the country today. Some have stated that it may become the major shade tree disease for the new millennium. The disease is caused by a bacterial pathogen named Xylella fastidiosa. The primary hosts include the Red Oak and Pin Oak. Other Oaks that are confirmed hosts include Scarlet, Shingle, Bur, Laurel and Water. The chronic effects on infected tree crowns are similar to that seen from severe soil compaction. The slow and gradual decline of an infected tree is caused by the limited uptake of water to the crown. During early stages of infection, brown leaf scorched symptoms typically affect a small area of the crown (e.g. a single branch). Usually the scorch symptoms initially show up late in the season (late July or August). As the years go by, other areas of the crown are often progressively affected. Often it takes only 3-5 years for the entire crown to show symptoms. It typically requires about 10 years for a diseased tree to lose most of its aesthetic value. Early defoliation in September on affected Oaks is another good indication for the possible presence of this disease, since Oaks typically hold their leaves well into November/December. During the early years of infection this symptom does not necessarily indicate the branches are dead, since they often leaf-out again the following year.
     

  • Treat your Hollies now!  Many Hollies have been affected this year with Scale problems including Cottony Taxus and Cottony Camelia and have had their leaves yellowing and dropping because of Holly Leafminer.  MERIT (a systemic, injectable insecticide), applied this fall, will control these Holly pests adequately for the next season.  Also, treat Hollies in November or December with anti-desiccant to prevent leaves from being burned and blackened by the harsh winter winds.  A second application is recommended in January or February.
     

  • MERIT is a systemic insecticide that is very effective against some of the most difficult to control pests.  Soil applications will be taken up by the roots and moved upward into stems, twigs and foliage.  A single soil application, this Fall or early next Spring, controls pests such as aphids, soft scale insects, adelgids and lace bugs.  It is also en effective repellant of Japanese Beetles.  Merit is ideal in situations involving a small amount of plants which would normally require 2 or more sprays to control insect problems.  Now is the time to treat these plants to provide protection.
     

  • Procera Root Disease of White Pine, a soil borne fungus disease, has affected numerous White Pines in our area during the last few years. This disease is normally fatal and appears to only affect White Pines, our most common evergreen tree. Typically, the affected tree is fifteen to twenty feet tall and has died "suddenly". In most cases, the ultimate death of the tree is the result of a Pine Bark Beetle infestation. However, the initial weakening that led to the eventual demise of the tree, was probably brought on by Procera Root Disease. Treatment consists of removing the dead tree as soon as possible plus spraying and fertilizing the adjacent White Pines to control the Pine Bark Beetles.
     

  • Elongate Hemlock Scale is a very serious pest of Hemlocks in Southeastern Pennsylvania. Look for Hemlocks with a "yellowish" cast, especially on the lower branches. The damage will resemble Spider Mite damage. This insect can be controlled with a properly applied spray.

  • Be on the lookout for Botryosphaeria Canker, a fungus disease, on drought damaged trees and shrubs. Scattered dead branches on Azaleas, Rhododendrons, Dogwoods, and many other trees and shrubs can be seen at this time of the year. It has been particularly troublesome on Rhododendrons. Infection occurs through wounds, pruning cuts, and leaf scars. If pruning cuts or wounds near the soil line are invaded, large portions of the shrub can be killed. The best management practice is to water during dry periods, prune out the cankered area, and disinfect pruning tools between cuts with rubbing alcohol, spray disinfectant, or 10% bleach solution. Fertilization may be helpful.
     

  • Have the trunks of your recently planted Red Maples (Acer rubrum) developed cankers (dead areas)? If so, the problem is probably being caused by Cryptosporiopsis Canker, a fungus disease. Small and/or weak Maples may be girdled by these cankers and die. However, most trees will overcome this damage with proper care - fertilization and possibly pruning. There is no specific treatment for the disease.