Sunday, August 26, 2012

The Heartbreak of Bagworms

 This has been a somewhat strange summer in the garden; hotter than usual, and it has brought it's share of pests not seen before. Back in July, one of my neighbor's beautiful arborvitae started to decline quite rapidly.  Around the same time, I noticed some very small pinecone-like objects hanging off said arborvitae, seemingly spinning in the wind, almost like little Christmas ornaments, made of the very leaves themselves. Knowing these trees don't generate pinecones, I did some research. Sure enough, a quick search of the internet revealed the problem - bagworms.
The little "bags" that I saw actually contain these caterpillars, hanging from the branches by their own silk threads. This pest can quickly decimate an arborvitae, as it has done here. This is the first time I've seen this pest. It can also affect junipers and pines. Often, it will concentrate on one plant, leaving others in close vicinity somewhat untouched.
In July I applied the organic, biological control BT (Bacillus thuringiensis) which is a bacteruim known to kill the caterpillars, but which is safe for birds, animals and other insects which are not caterpillars (be careful near known butterfly colonies, as it will kill them). It appeared most had died after the application (as the spinning I noticed earlier was not the wind, but their own wriggling - nasty!), but short of hand-picking all of the "ornaments" off the tree, there is still the threat of a new infestation next year. This is because when allowed to mature and drop to the ground, each of the bags can contain literally hundreds of offspring for next year's crop.

Here is a close-up of the bags themselves. The best time to spray BT is before they get larger than a half or three-quarter inches long (even better, in May - June, before they appear). These have matured to a length of almost two inches long. At this point (Aug/Sept), the only control is to hand-pick them off the trees.
The jury's out on whether this arborvitae will survive; the others adjacent to it only had small infestations, so they have a good chance, especially with an application of BT next spring before they are attacked again. So if you're out in your garden, and see these bags, start pulling them off. It's recommended that you burn them, but I'm not a big fan of fires in the garden(!). So I just dropped mine in a bucket of water laced with organic insecticidal soap. Good riddance, bagworms! Hope I don't see you next year!

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