Sunday, June 26, 2011

Hungry, Redheaded Pests

Redheaded pine sawfly larvae dining on our mugo pine




If you have a mugo pine, it’s time to give it a look-over to see if it’s being eaten by groups of redheaded pine sawfly larvae.

We have one mugo pine that anchors a corner where two perennial beds meet in our back yard. A couple of weeks ago I checked it for the signs of the redheaded pine sawfly larvae and found nothing. When I was weeding and mulching on Thursday morning, I found three groups of the larvae busy eating the needles of our mugo.

What do I look for? First, I look for branches where needles seem to have been eaten. Then I look for—surprise here—the red heads of the sawfly larvae. A third sign comes after I shake the pine where I find the larvae and hundreds or thousands of bright-green fecal pellets, called frass, shower to the ground, sort of like a green snowfall in miniature.

Larvae in soapy water
What do I do when I find larvae? Since we have only one mugo pine, I pick them off with my fingers or tweezers, depending on the size of the larvae, and drop them into a bottle of soapy water. I find it easier to pick older, larger larvae with the tweezers and younger larvae with my fingers. Of the three groups I found, one was older, one was younger, and one was in between—so I used tweezers and fingers.

Some of the larvae didn’t appreciate my picking and went into their defensive mode, vomiting a pine-smelling resinous substance that they store to teach predators a lesson. I knew when my tweezers and my fingers suddenly were sticky and smelly.

Larvae frass, locally called 'green snow'
I stopped counting when I passed 100. I think I caught most of the larvae, but I’ll check back the next couple of days to make sure. I’ll also have to check back in August for a second generation. If I can’t control them by picking, I can spray with horticultural oil or a registered pesticide, but with one small Mugo pine, I haven’t had to do that yet

If you want additional information about this native pest and to see a short video of them in action, I recommend you visit Mike Raupp’s “Bug of the Week” website. At the Home page, click on “Archive” in the left column and then look for his posting of July 16, 2007. To access “Bug of the Week,” CLICK HERE.

And if you have a mugo pine—or other pines under 12-feet tall—better check now for this pest.

7 comments:

  1. What a joyful and smelly activity you have, and with one tree, at that! This is a very useful commentary, Bob.

    One has no time to rest with a garden that has such a variety of plants, shrubs and trees. Aren't you happy that there is also a night... to rest!

    ReplyDelete
  2. You deserve the best, Raj--a mugo pine tree and three or four groups of redheaded pine sawfly larvae. Then you will be a happy gardener too!

    ReplyDelete
  3. I picked off the redheads on Thursday. I checked Friday and saw none. Today (Sunday) I checked again and found two small groups--one of nine and one of 32, which I picked and dropped into soapy water. I hope that is the end of the early "crop."

    ReplyDelete
  4. Valeetah MotschiedlerJune 26, 2011 at 9:28 PM

    Thanks for the info. I just planted a new dwarf Mugo pine I bought at a nursery. I was not aware of this pest.

    ReplyDelete
  5. I had the same problem on a mugo pine but it was small enough that I could fill a jar/bucket with soapy water and dip the branches in.

    ReplyDelete
  6. Monday: Again, two small groups, which I've just picked and dunked in the bottle of soapy water. How many more redheads are lurking in the needles and mulch under the mugo pine? How much more time do I want to spend sitting and picking? Is it time to start thinking about the unthinkable--nuking them with a spray?

    ReplyDelete
  7. There are several parasites and native birds that feed on European pine sawfly larvae. Also, rodents often eat the pupae in the soil. However, these biocontrols do not usually provide adequate control of the pest in the landscape and the nursery.

    ReplyDelete