That nasty white powder on your hedge is from dead insects
HUNTSVILLE, Alabama — I was trimming some hedges on the east side of my house the other week, and noticed a white powdery substance on the main trunk and several of the main branches of one of the plants. When I pointed it out to my wife, she asked if it was a white bush fungus. Any idea what it could be and if there is anything we can do to save the bushes? Thanks. – Glenn W.
White bush fungus is a very descriptive term and a pretty good guess for what ails your hedge. It appears that privet is the shrub in question and it has been used for years in creating hedges throughout the South.
Many fungal diseases have a white powdery substance (powdery mildew and downy mildew are great examples) that can be used as an identifying characteristic. However, in your case you have an insect infestation and not a fungal disease. The insect in question is some type of scale, an insect that is very common in our area and on plants such as your privet hedge.
The white fuzzy appearance is from the discarded bodies of the insects after they molt. The two main culprits are the white peach scale (Pseudaulacaspis pentagona) or euonymus scale (Unaspis euonymi), both of which have similar life cycles and host plants.
Scales are insects that attach to leaves and stems of plants and literally suck the sap of the living tissue. They go through several life cycles in a growing season and this allows them to spread quite rapidly on susceptible plants. They are often found on the underside of leaves or down on the main stems and trunks of the shrub so getting an insecticide to the insect can be difficult. Many scale insects have a waxy, protective coating over their bodies that make contact insecticides almost ineffective.
What to do
To control these insects I would suggest the following. Wait until we have had three good hard freezes to ensure your plants have gone dormant. Prune back your shrubs by half and remove all of your trimmings and discard. Do not mulch or compost these trimmings since they are infested with the scale. Next spray the shrubs with a dormant oil per label directions. You could also use NEEM oil and both of these insecticides are organic. The oil coats the insects and suffocates the scale. This is very effective way to treat the infestation.
I would repeat this in January or February and then follow up with a systemic insecticide application in April as new growth begins. The goal here is to control any scale insects as they are emerging from dormancy and not allowing them to begin their life cycle. A product containing acephate or imidacloprid is a good choice and readily available at local garden centers.
One must be persistent in trying to control scale infestations. The best defense is a good offense – meaning never allowing the insects to gain a foothold. Another good option is to plant shrubs that are not as susceptible to scale as the privet hedge you presently have in your landscape. There are numerous shrubs that could be used to perform the same functions as the privet but not have the problems with insects that you are seeing now. For the long term I would consider replacing these with a more insect- and disease-resistant selection.
Harvey Cotten is the chief horticulturist and vice president at the Huntsville Botanical Garden. Write to email@example.com or c/o The Huntsville Times, P.O. Box 1487, West Station, Huntsville 35807.
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