The Daily Southerner, Tarboro, NC

September 14, 2012

Ask A Master Gardener

Tight Lines
Rick Goines

TARBORO — “Ask A Master Gardener,” published weekly, helps our readers to solve common problems concerning horticulture, gardening, and pest management through a trained and supervised staff of Extension Master Gardener volunteers.  The Extension Master Gardener program is an educational program designed to enhance public education in consumer horticulture.

Submit your questions by email to askemgv@gmail.com.  Or, you can call the local Extension Center at 252-641-7815 and tell them you have a question for a master gardener. You ask the questions and a local Master Gardener will return your call with a solution to your problem and share it with our readers.

Answers reflect research collected from land grant universities (NCSU or NCA&T) and through a national extension website, www.extension.org.  



Q. Noel C. (Tarboro) asks – I think my roses have some kind of blight.  Blooms are smaller and the leaves have brown/black spots and turn brown and fall off. Stems seem to be drying up.

A. These symptoms could be the result of an infection by a virus. A virus is a submicroscopic disease-causing entity that can only be viewed with an electron microscope. Some symptoms typically associated with viral infections include: distorted and malformed leaves or growing points; stunted growth; a mosaic pattern of light and dark green or yellow on leaves; yellow spotting on leaves; other spots or line patterns on leaves; and cup-shaped leaves. However, virus diseases cannot be diagnosed on the basis of symptoms alone. Some of these symptoms can also be caused by high temperatures, insect-feeding, growth regulators, herbicides, and nutrient deficiencies and excesses. The best way to tell if a virus is infecting a rose is if the same symptoms occur year after year. If the deformed or abnormal growth never disappears, dig out the entire infected plant and replace it. The reason it is necessary to remove the plant is that a virus is systemic - found in all parts of the plant. So, pruning away the afflicted parts will not remove the virus from your rose. There are no chemicals that cure a virus-infected plant or any that protect plants from becoming infected. Your only course of action is to rogue-out the infected plant and discard it.

To guard against virus diseases, consider the following measures:

1. Purchase certified virus-tested or virus-free plants.

2. Maintain strict insect and mite control.

3. Control weeds because they may harbor viruses, mites, nematodes, and insects.

4. Destroy virus-infected plants.

5. Disinfect pruning tools by cleaning them with rubbing alcohol, drying, and spraying with a light coat of oil to prevent rusting.



Q. Ruby A. (Tarboro) asks - What is the black film on the leaves of my crape myrtle trees?

A. The black film you are seeing may be sooty mold, a fungus that grows on the honeydew secreted by plant-sucking insects such as aphids, mealybugs, or scales that feed on the sap inside leaves. The water and sugars ingested by the insects are excreted as honeydew, which adheres to the leaves and also drops to the objects below. Sooty molds are not plant parasitic, but they can be unsightly and even decrease the vigor of the plant by blocking the sunlight required for photosynthesis. Since the presence of sooty mold indicates a pest problem, the first step in control is to identify and suppress the insects. Horticultural oils provide good control of such sucking insect pests and also help to loosen the sooty mold.



Q. Nancy H. (Tarboro) Asks – I’ve noticed that town crews are pruning and trimming trees along some of the streets this week.  Should I be pruning the trees in my yard now?  



A. Although the town’s pruning is more directly related to protecting the power lines that the limbs are encroaching, late summer is not a bad time to prune, but not really the best time.  Let's turn that question around - when is the "worst" time to prune a tree? From the trees point of view the months of April, May and into June may be the worst time to prune.



Why?  First, this is the time of year when trees deplete their energy reserves and put most of it into new leaves. Pruning at this time places the energy that has been moved into branches, twigs and leaves onto the burn pile or into a landfill. This practice places the tree in a stressed state, with an energy deficit that may not be completely recovered in that season.



Secondly, this is an active time of year for many disease and fungal pathogens (Oak wilt for example). The warm spring months of April, May, and June typically bring high humidity from spring rains, these factors provide an ideal environment for many pathogens to flourish. So, you have the environment for a pathogen, you have a pathogen - now, to complete the "disease triangle" there has to be a host! How about that tree in your front yard that was just pruned, it is probably a good host for some pathogen. So, yes, spring can be a bad time to prune.



Another "bad" time to prune is late autumn into early winter.



Why? Pruning in late autumn and early winter can lead to winter injury. The pruning wounds may not have time to "harden off" or prepare for winter. This can lead to deeper freezing in the tissues around the wound and in essence a larger wound can be created that the tree will have difficulty dealing with.



So that leaves us with the summer months and late winter (dormant season pruning). Typically late winter or dormant season pruning is the "best" time to prune.



Why?  During the late winter months (February and March), harmful pathogens are at a minimum, mostly inactive; therefore, this is a safe pruning environment from that standpoint. During this season, deciduous trees have hardened off and when the growing season begins the wounds will be sealed and the callusing process will begin.

Pruning trees correctly not only enhances the trees visual appearance, but it can also ensure a tree will become structurally strong making it more resistant to stress brought about from disease, insects, or environmental extremes. If you’re not sure how to properly prune, just ask a master gardener.

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“Ask A Master Gardener” also wants to include your “tried and true” gardening tips and techniques and snapshots from your garden; please share in an email to askemgv@gmail.com or by writing to “Ask A Master Gardener”, c/o The Daily Southerner, P.O. Box 1199, Tarboro, NC 27886.