Hungry caterpillars great for books, bad for trees
by Louise Estabrook
Agricultural and Natural Resource Agent for Cherokee County
September 28, 2012 12:00 AM | 1822 views | 0 0 comments | 8 8 recommendations | email to a friend | print
It’s that time of year when North Georgia gardeners find themselves under attack once again.

Well, it’s not exactly the gardeners under attack — it’s our oak trees. And the attacker? The Orange-Striped Oak Worm.

Known as Anisota senatoria to those of us with a flair for Latin nomenclature, the orange striped oak worm is a major consumer of oak leaves, and sometimes other hardwood leaves, as well.

It’s the caterpillar stage of this pest that is capable of wreaking havoc on our lovely shade trees. If you’ve ever read the book, “The Very Hungry Caterpillar” by Eric Carle, then you know what voracious appetites these little larvae have. Entire branches will be stripped of leaves, seemingly overnight. And they don’t dine alone. Where there’s one, there are hundreds of them. Step out at night and stand quietly near any afflicted oak tree — just listen to the roar of an army of oak worms feeding.

The larva of the orange-striped oak worm is pretty large — 1½ inches to 2 inches long. They’re black, with thin orange lines running along the length of their body.

Once they’ve started to munch on your trees, there’s no mistaking their presence. A large caterpillar such as this voracious eating machine takes in food at one end and passes it right out the other end. Entomologists call the result “frass,” but a rose by any other name ... Well, you get the idea. A branch overhanging a car or a patio can create quite a mess.

A healthy, mature tree can tolerate quite a lot of defoliation (up to 20 percent with little to no effect), especially now as the summer draws to a close and the leaves are getting ready to drop anyway. On a mature tree, oak worm control measures are rarely necessary. The caterpillars will feed for a while, and then drop to the ground to overwinter in their pupa stage. The adult moths will reappear beginning next June, and the cycle starts over.

The problem really comes into play when a tree is already stressed or if the tree is very young. There are steps you can take to help the tree along, however.

* Keep the tree watered as well as you can.

* Remove the grass within the drip line of the branches and replace it with an organic mulch instead.

* Don’t make a mulch volcano — keep the mulch pulled away about 6 inches all the way around the trunk.

* If you fertilize nearby lawns, then that’s probably enough fertilizer for the tree. If you don’t have any grass near the tree, then it would be prudent to apply a balanced tree fertilizer according to the label directions.

Another negative scenario occurs when the tree is too young or newly planted to shake off a little defoliation. There are two ways to handle this — handpick the offending oak worms and drop them into a container of soapy water. On a small tree, this is quite easy to do, but really creepy. Wear gloves.

The other way is to spray the tree with Dipel or Thuricide, two forms of Bt (Bacillus thuringiensis). This is a biological control that causes the insects to stop feeding and interrupts the life cycle of the oak worm.

There are also more toxic chemical controls that will eliminate the pests, but they are more of a threat to the environment. If you suspect that your trees might require a more poisonous chemical control, please call the Cherokee County Extension Office, and I will give you the proper recommendations.

Information about Extension Solutions for Homes and Gardens can be found on the University of Georgia Cooperative Extension website at or by contacting the Cherokee County Extension Office at 100 North St., Suite G21 in Canton at (770) 479-0418. The Georgia Extension Master Gardener Program is a volunteer training program offered through county offices of the University of Georgia Cooperative Extension.
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