Tuesday, July 3, 2012

Time to check for hungry redheads


Redheaded pine sawfly caterpillars
eating mugo pine


Have you checked your mugo pines for hungry redheads this week?

When I checked our one mugo pine last week, all was well.  When I checked it again this morning, I found three colonies of redheaded pine sawfly caterpillars (Neodiprion lecontei) munching away on needles.  There must have been 40 or 60 or 100.  I didn’t count.

Sawflies are related to wasps and bees, but the adults are small and do not sting.  The “saw” part of their name comes from the saw-like ovipositor of the female.  The larvae, or caterpillars, are plant feeders and look like hairless caterpillars.  They chow down on a variety of pines and can damage, even defoliate, a small tree.

For several years I’ve tried to mechanically control the redheaded caterpillars by handpicking them and dropping them into a bottle of soapy water.  But I wasn’t a perfect caterpillar picker, so some always dropped down into the thick pine to return as future generations later in the year or the next spring.

This year I put away the bottle of soapy water and researched on the Internet for a more terminal solution.  I began with a search for “Killing redheaded sawfly caterpillars” and from the long list of entries chose “Sawflies of Trees and Shrubs” by the University of Minnesota Extension.  I read only the “redheaded” (there are many kinds of sawflies) and “Management” parts.

At the end, the publication gave a thoughtful list of factors to consider and then three ways to control them:  mechanical (such as hand-picking), biorational insecticides (insecticidal soap if the caterpillars are very young), and conventional insecticides.

Dead & dying caterpillars after
dusting with carbaryl
Since my hand-picking skills had failed to control them, and since I didn’t have insecticidal soap, I used one of the recommended conventional insecticides, acephate (brand Orthenex). I sprayed mid-morning Tuesday.  While I was spraying, I received a sad reminder why I try to avoid pesticides: They kill all insects, not just the bad guys.  Too late did I see the young, inch-long, bright-green praying mantis.

When I checked on the redheads five hours later, they were busy eating mugo pine needles and singing, “Who’s afraid of the pesticide spray….”  I revisited the Minnesota website and chose another weapon, carbaryl, which I had in powder form (brand Sevin).  I lightly dusted the colony areas.  Two hours later: All visible caterpillars were dead.

During future, regular walkabouts of my garden, I’ll check the mugo pine for new infestations because redheads seem to have spring and autumn generations here in central Maryland.  Walking periodically through your garden to observe what’s happening is a good way to keep pests and other problems under control.

4 comments:

  1. Must put in a plug for Sevin. It is a good product. Used to use it on my tomatoes when I had a garden. Glad you licked those 'redheads'!

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  2. Sevin (carbaryl) is very deadly to beneficial pollinators. For that reason this is not the best insecticide to use in a vegetable garden.

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  3. Anybody try spraying diatomaceous earth? That stuff works on so many things it would be great if it would stop those redheads. It might slow down the preying mantis if you don't see it in time but at least it leaves nothing toxic behind. I'd like to hear what you think.

    David L

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    1. Yes, has anyone tried D.E. on chewing critters such as sawfly caterpillars? I've seen lots of recommendations for using it as a barrier against slugs. I suspect it wouldn't be too effective against the caterpillars at the end of the mugo pine branches, but how would it affect them on the ground underneath the plant? Good Q, David.

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