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Wednesday - May 12, 2010

From: Austin, TX
Region: Southwest
Topic: Diseases and Disorders
Title: Red-backed bugs on mountain laurel (Sophoro secundiflora)
Answered by: Nan Hampton


I found red-backed bugs (in fact two end-to-end like the east Texas love bugs) on my mountain laurel which has been losing leaves. Are these bugs the culprit?


Sophora secundiflora (Texas mountain-laurel), according to the US Forest Service "...are primarily pest-free, except for infestations by caterpillars of a moth in the family Pyralidae."  The moth is Uresiphita reversalis (Pyralid moth or Genista broom moth).  You would see the caterpillar and its damage from chewing on the leaves if they were infesting the plant.  Obviously the bugs aren't the caterpillars and since there don't seem to be any other serious insect pests I don't think the bugs are the culprit.  The Forest Service site does mention that the mountain laurels are especially susceptible to phenoxy herbicides.  One of the commonest of these phenoxy herbicides is 2,4-D.  These particular herbicides are used against broadleaf weeds on grass lawns, pastures or in grain fields.  The problem is that they are very volatile and can drift for miles with the wind and effect plants far from their application. They have been especially detrimental to grapevines.  If you or your neighbors have been using any of these on your lawns, it is possible that some has landed on your mountain laurel and is causing the problem. 

Another possibility is that you have had some environmental change where the plant is growing.  Mountain laurels like well-drained soil to grow in.  They don't like having 'wet feet'.  Has the drainage in its vicinity changed?  Is there the possibility that the soil has become compacted by a lot of traffic—foot or vehicle?  If you think that this has happened, you need to remedy this by stopping the traffic and adding a hardwood mulch over the soil surrounding the tree.  It will help protect the roots and eventually work its way into the soil and relieve the compaction. Better yet, you could carefully work some of the mulch into the soil so that when the tree does get water (from rain or supplemental watering) the water gets to the roots and doesn't stand on top of them.  Whatever you do, don't fertilize the tree. In the first place, native plants don't need fertilizing and a plant under stress (as yours seems to be) should never be fertilized.


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