Tuesday, June 8, 2010

Lethal Beauty

Toby and I had just started on our walk yesterday evening and were not too far from the house. We were at a standstill while he checked out the roadside grafitti, so I was playing with the tree leaves. There on the leaves of a mountain ash was a beautiful beetle.

I dragged the dog back to the house to get the camera, then back again to get the camera battery. When I got back to the approximate location, it took a bit of searching, but the insect was still there. I snapped a few frames and we finished our walk.

This morning I looked it up. It's a beetle, I knew that much. Turns out, its a round-headed appletree borer, Saperda candida. This didn't sound good, so I did a little research.

As attractive as this striped, blue-legged beetle is, its presence does not bode well for my apple trees. The striking adults are nocturnal, feeding on leaves and sometimes fruit. That's not a problem. It's when they set about reproducing that they become "dangerous," for they seek out apple trees (crab and regular) in which to lay their eggs. They make a slit in the bark at the base of the trunk and lay the eggs there (June is peak egg laying time). Soon the eggs hatch and for about a year the young larvae feed just under the bark.

When winter comes, the larvae go dormant. Summer #2 rolls around, and the larvae start to bore into the tree. Here they will tunnel and feed for the next 1-3 years, each winter going dormant. Afterwards they emerge as adults, mate, and the cycle begins again.

Trees that are weak are usually the target. While apples are preferred, mountain ash, hawthorn, service berry, cottoneaster, Saskatoon are also hosts.

What is an apple grower to do?!? The base of trees can be painted with a schmezz made from white latex paint and water. This apparently discourages the adults from laying eggs, and makes the sawdust-like frass from the larvae more apparent if they are present. Shallow larvae can be cut out with a knife, while those that are already tunnelling can be chased with a stiff whire shoved up their tunnels.

An important factor in avoiding these insects is to keep your trees healthy. When they are newly planted, be sure to keep them well-watered to promote good root growth. This means for 2-3 years, not just a week or so after planting.

Because I have an apple tree that is in poor health, I'm going to have to do an inspection when I get home. Check out the base of all my trees for suspicious activity. If I see anything, steps will have to be taken.


  1. Ellen - I saw the same beetle on some shrubs at my house this weekend as well! It is so distinctive - that I'm sure that is it. thanks for figuring out what it is though - I hadn't looked it up yet. and it doesn't sound like good new for my northern spy - it was just a few feet away from it - and it is old and not in the best shape - so I will have to go out too and take a look around the base. thanks!

  2. HI, Emily/Chris - aren't Northern Spies the BEST?!? I planted one not long after I moved here and had five apples last year. Unfortunately, our growing season is so short here that they didn't really ripen (made tarts - they were awful). Hard to find spies these days, though, although Jackie put me on to an orchard in Schuylerville that has them. Good luck.