Question
Last spring and summer (2009) in Ridgefield, CT, from about May to July, insects badly chewed many of my newly planted myrtle/periwinkle/vinca minor groundcover plants.  I saw many gnat-like insects flying around the myrtle patches at the time of the devastation, but I'm not certain the gnats were actually doing the chewing.  I tried spraying with organic, non-toxic spray, but that just seemed to chase them away for a short while, and we had a very rainy summer, so the spray was repeatedly washed away.  The rainy summer may have increased the gnat population, because I had transplanted a first round of these myrtle plants in 2008, and the early round had thrived without incident.  I transplanted all the plants (both years# from my family home in Westport, CT, where they had thrived without any care whatsoever for something like 40 years #so I feel guilty about moving them on top of everything else#.  The problem ended only when the gnats appeared to reach the end of their life cycle in July.

Do you have any idea what could have been eating these myrtles?

Also, does the kind of salt used to melt snow and ice when one's driveway is ploughed, or the sand used for traction, harm myrtle plants?  I have them lining the driveway, and the first year #2008#, a number of the leaves wound up with brown leaves in the spring, and I had a feeling it was due to the salt or sand.  I trimmed away the brown leaves, and the new growth put out in the spring was prodigious #unfortunately only to be decimated later by the bugs).  I've instructed my snow plow guy not to use salt or sand this year, but I was still wondering.

Finally, in the interest of directing energy at root growth and new sprouts in the spring, should I prune away the stalks left by the insects after they ate the leaves?  All the patches have at least some leaves left, so I wouldn't be leaving anything leafless.

Answer
Jay,

Any of the salts used for ice removal can be very hard on plants. The salts can accumulate in the soil so if you are having trouble getting plants to grow in these areas this could be the reason. There are no gnats (primitive flies) that do what you are describing so I'm at a loss to explain the damage you are seeing. It could be slug or snail damage (was the leaf damage ragged and torn?). I doubt that pruning at this point will make any difference. If the cause was slugs then putting out slug bait this spring may help (see http://www.livingwithbugs.com/slugs.html for information about slug and snail control). Also, you should dig a few up and look at the roots. Often root injury or disease is the main problem when a plant dies. Sorry I can't be more specific but post a follow up if you have questions.

Jack DeAngelis
http://www.livingwithbugs.com