“LSU Ag Center, West Feliciana Parish — is this about sweet potatoes or webworms?”
That’s how I answer the telephone lately, given the volume of calls about both.
I assume everyone knows about the 4-H sweet potato fundraiser by now, so let’s address the latter.
This season, for reasons not explained to me, more webworms have been active than practically anyone can remember.
LSU Agricultural Area Extension Forester Brian R. Chandler, at the Clinton Idlewild station, confirmed this for us. He’s spent a career dealing with tree issues across the Florida Parishes, so it’s not just you and me.
While there are several species of webworm (a broad term for this type of caterpillar), the ones we’re seeing lately are Hyphantria cunea, or the fall webworm. (Thanks to Mr. Chandler for that one, too.)
These webworms will produce three or four generations per year, but what we’re seeing now is the last generation before winter. It seeks shelter in leaf litter to survive winter and may burrow into soil.
And, no, our Louisiana “freezes” will not kill them.
What’s first noticeable are the affected brown areas in the tree, especially out near branch tips where leaves are more tender. Upon closer inspection, one can see webbing surrounding the damage (think free Halloween decorations).
Inside the webbing, the leaves are partially or (by now) entirely denuded. In most cases, no permanent damage is done to the tree, yet heavier infestations may eat up every leaf on the tree, sometimes even moving down the bark or onto other trees in search of more food.
But even then, timing could be worse, as trees are about to drop their leaves soon anyway, so they should have some food stores saved for winter already. Of course, if the problem reoccurs year after year, it may be detrimental or even fatal for the tree. For young trees, it’s especially threatening.
Fall webworms are easier to control when webs are small and the caterpillars are, too.
As late as I’m writing this article, the webworms are relatively mature and tough, and so are the webs.
So, if you’re interested in killing them, removing the webs will help expose them to chemical applications and bird predation.
If spraying, the same chemicals used on just about all caterpillars are effective, including carbaryl (Sevin or other brands), pyrethroids (pyrethrin, permethrin, etc.), spinosad and others.
Thuricide Bt (and other brands) can be a useful organic alternative but it’s most effective on young caterpillars.
Whatever you decide to do for this season, I recommend scouting for fall webworms next year. The problem can be managed most effectively — and with the least amount of damage — when you catch the webworms early.
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