Caterpillars eating my river birch

Moccasin(z9aMobileAL)August 21, 2010

Can you tell me, anyone, what this is? I've cut off the limbs of my young river birch which these worms are eating from the tip inward.

Are they army worms or what? And how do I get rid of them?

Thanks for any help.

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rhizo_1 (North AL) zone 7

They are the Yellownecked caterpillar, often found on birch and other deciduous trees. Always found in hoards, unfortunately, which can be kind of disconcerting.

These caterpillars are prey to just about every predatory insect, bird, reptile, amphibian, and animal out there so I wouldn't worry too awfully much about what you need to do. Maybe strong streams of water from the hose or at the most, some insecticidal soap sprays. I don't even like to see Bacillus thuringiensis-kurstaki used in cases like this.

You've actually already done the smartest thing (and often recommended)....cutting off the branch they've taken over.

They will do some defoliating, but at this time of year, we don't worry about that too much. Can you live with that?

    Bookmark   August 21, 2010 at 10:20PM
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Cutting off any trees branches simply because of an insect is a pretty drastic thing to do and totally unnecessary. Applied appropriately and at the right time BtK is effective and an environmentally sound practice. These are too big for that so the strong stream of water or maybe (although it will not be that effective) an Insecticidal Soap might be used, but control is noy usually needed since these are a very good food source for many birds.

    Bookmark   August 22, 2010 at 7:08AM
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Whew! I am so relieved that these are something considered a food source for birds! I can live with those ugly things intent on eating the tree from the tip to the trunk, and hope they enjoy themselves.

So far this morning, no sign of any additional caterpillars, but of course they could be part of the black spots beneath the leaves.

Earlier this year, this particular young river birch had so many aphids on its leaves, all green and fresh a color they looked like the leaves themselves, but I thought it strange that a river birch leaf should be textured like crepe paper! And that is when I discovered it was literally COVERED in aphids. Now THAT horrified me, and I was afraid the aphids would spread to my roses.

What would cause aphids to flock to one plant and try to totally cover it? I've encountered aphids in huge quantities before, on my nasturtiums up in Massachusetts (too hot to grow them in Alabama), and those were black aphids. Never saw them any color but green before, so it was a shock that they came in colors!

I've heard that nasturtiums are sometimes planted as sacrificial plants to keep the aphids focused and thus leave other plants alone. But in my book, nothing beats a long meandering row of nasturtiums growing like Monet used them at Giverny.

    Bookmark   August 22, 2010 at 10:24AM
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rhizo_1 (North AL) zone 7

Kimmsr, this is an insect that feeds in large communities in one localized area. The removal of one branch may result in getting rid of several hundred larvae in one fell swoop, without the use of any chemicals at all. The removal of one or two branches may result in the preservation of this season's foliage. Why on Earth do anything else?

Please note that spraying with Bt should be a last resort practice, just as with any other pesticide. Resistance to Bt has shown up all over the world, largely due to agricultural use of Bt, but homeowners contribute to the problem, as well. There are millions of people in this country alone that foster butterfly and moth habitats, something worth thinking about. The indiscriminate use of Bt-kurstaki products isn't acceptable, especially if there are other measures available.

Is Bt-k a valuable and useful product? Absolutely, when used with care. Right place, right reason, right product. In this particular situation, with these particular insects, Bt-k is not a good fit.

Moccasinlanding, can I assume that you are talking about River Birch, since you live in the South? They are a pretty little tree, but 'can' be a real insect magnet. Even in a native setting, this is the case. Aphids love River Birch.

Landscape planted R. Birch are probably more susceptible to problems as there might be excess fertilization, irrigation, compaction, or other factors that can contribute to a plant's susceptibility. You'll be lucky if you can keep the population at bay with strong sprays of water or insecticidal soap (you did say it was a young tree, right?).

This winter, however, after the leaves have dropped, you can begin with some applications of dormant or other horticultural oil. Spray all along the branches and trunk, and try to get into the nooks and crannies where those eggs are hidden. I'd spray three or four times, up until the time of bud break. You'll go a long way in breaking the aphid cycle.

Have you seen any scale insects on this plant? ;-) You might as well take a good look!

    Bookmark   August 22, 2010 at 3:31PM
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Rhizo1, yes, it is a river birch. I had one before when I lived directly on the bayou, and it grew without incident of any kind. Now I planted this one two years ago to shade the western exposure of a sun porch in the summer, and for whatever reason, this year has been fraught with danger for this little tree. Beginning with the aphids soon after all the young bright green leaves opened up.

I will do as you suggest, spray with horticultural oil. By next year, this young tree will be too tall for anything but a step ladder to reach the top.

And if you think SCALE might be an issue with it too, I'm thinking this could be the source of the scale which got on my scheffelera. This birch is just outside the sun porch, the location of my scheffelera.

This spring also, I had to cut back some old fashioned azaleas which had gall on them, and all of these issues are new to me. I've really never had much problem with pests or garden diseases before. There was a bout with the azalea caterpillars, en masse like the yellow catterpillars on the birch, but that ended happily thank heaven.

I do not use fertilizers on any of my in-ground plants, except an occasional feeding of the roses at the other end of the yard. I do not have to water, but I was thinking of running some drip hoses in a nearby flowerbed. I may think twice about that now. Compaction could be an issue, since there is a nearby circular driveway, but it was installed before I planted the tree.

I did not mind trimming the branches of the birch, because it will as it grows drop those lower branches anyyway. I know how to terminate a cut to minimize disfigurement to the tree.

Thanks for your advice.

    Bookmark   August 22, 2010 at 3:58PM
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