Scale Insect Management - E Letter

This week-end I removed most or all of the old foliage from some Lenten rose, Helleborus orientalis, at home.  I had noticed an infestation of scale insects.  This is not a routine problem on Hellebores, and I don’t encourage you to do it unless you have a problem.  But it illustrates an easy and effective control strategy. 

While treatment with a relatively benign insecticide such as horticultural oil may have reduced the numbers associated with the infestation, removal of the old foliage was much easier and probably more effective.  While most people don’t want to use some toxic product, we still tend to look for some product to solve our problems.  Often the solution lies not in some product but in some strategy. 

Scales are microscopic insects that secrete a protective coating, the scale, which makes treatment with insecticides difficult.  Insecticides don’t penetrate the protective coating.  Horticultural oils may be able to ooze up under the coating where they may kill the insect within.  But since most of the scales in this case were under the leaves of a plant that grows low to the ground, spraying them would have been difficult at best and of questionable value. 

On larger trees and shrubs scales may be found on stems as well as under leaves.  In these cases treatment with horticultural oils is often justifiable.  It is easiest to apply the oil effectively during the dormant season.  We can literally coat the stems with it.  And there is less chance of injury to the plant while it is dormant; some plants can be damaged with oils on the new growth. 

Pruning is often an easy and effective means of dealing with pest problems.  Fruit trees may have fungal pathogens spending the winter in small stem cankers or in mummy fruit that didn’t fall last summer.  Insects such as scales or whitefly may be overwintering beneath foliage of many plants.  Even if pruning doesn’t eliminate 100% of the problem, it can often reduce the numbers to tolerable levels.  We seldom eliminate a pest problem; we learn to manage it.

So this week-end I removed most of the old leaves from our Hellebores.  They look better now.  And I suspect about 99% of the scale problem is now in a black plastic bag.

You can see pictures of the scale infestation at

http://www.ces.ncsu.edu/chatham/ag/Helleborus%20Scale.html

alcooke

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Al Cooke

Extension Agent, Horticulture

Chatham County Center, North Carolina Cooperative Extension Service

N C State University

PO Box 279, 45 South Street, Pittsboro, NC  27312

Phone: 919.542.8202; Fax: 919.542.8246

email: al_cooke@ncsu.edu  

http://www.ces.ncsu.edu/chatham/staff/acooke/home.html