That Bug's Got Some Gall

Gall wasps have become a significant problem in Baton Rouge.

As I continue to think about the master plan for the acreage in Clinton, trees have come into big focus for me because they would constitute, in addition to the hardscape, a part of the plan that would be difficult—or at least expensive—to undo. I could misjudge on any number of counts: size, soil requirements, location, and now, zone creep (wherein all the climate zones in North America are creeping northward. The trees, apparently, haven't bothered consulting politicians about the veracity of global warming; they've just started packing up and following the cold).

I decided to fill in the redwood-sized gaps of my knowledge by attending the most recent Plant Smart workshop produced by Baton Rouge Green. Presenting that Saturday at Hilltop Arboretum were arborist Scott Courtright, who talked about gall wasps (on which this article will focus) and preparing trees for storm season, and horticulturalist Marc Pastorak who spoke about his work with prairie plants and meadows (fascinating work to discuss another time).

Honestly, I debated whether it was worth my time to attend the talk because why in the heck would I need to know about tree pests and storm preparation? How would that possibly help me design my award-winning landscape? I can hear you more seasoned naturalists tsk tsk-ing. Don't judge; this is my journey to enlightenment. And enlightened I was.

First, take a look at the photo that accompanies this article. What do you see when you look at these specimens? Some attractive, mottled orange-yellow fruits? Delicate, star-shaped seed pods? Those were my guesses. Actually, they are the oozing, defensive excretions of a tree that is trying to protect itself from an egg (which will grow to a larvae and feed on the protective excretion) that has been injected into its bark by some parasite—in this case a gall wasp, also called a gallfly, member of genus Andricus. (There are any number of parasites that produce any number of gall types; research it on the Internet to see the variety.)

Both of these specimens were picked up by Courtright in neighborhoods around Baton Rouge. He explained that he rarely saw evidence of gall wasps in the city ten or fifteen years ago; now he sees them all the time and considers it a "drastic problem."

These infestations stunt the growth of the tree. The eggs are injected into buds, which under normal conditions, would become one of three things: a new stem, a new leaf, or a seed-producing fruit. But once an egg is injected into the bud, the bud is destroyed, hampering the tree's efforts at growth, thinning the canopy, and causing the tree to draw on the nutrient reserves stored in its trunk.  

That this is occurring in the city and isn't so much a problem in my rural neck of the woods (according to my husband, anyway, who is much more aware of the health of our trees than I am) can, at least partially, be attributed to the fact that the wasps are attacking stressed-out trees whose most ideal environment is not the concrete-encrusted, crowded, nutrient-sparse environs of urbanity. Like the very young and very old of our species, who more easily fall victim to parasites, urban trees are at much greater risk than their rural brethren.  

Here is what the LSU AgCenter has to say on its website about controlling this problem:

Chemical control in the gall stage is not effective. To properly time spray applications, collect some of the galls and store in plastic bags outside in the shade. When the wasps emerge, it is time to spray. Wasps that develop from galls on hardened twigs will not emerge until winter. Many wasps from galls [that form on] leaves and succulent stems (new growth) emerge in late spring or early summer. Galls may be physically removed from small trees and destroyed.

Here are some other highlights from the talk:

    •    mycorrhizae (a fungus) applications are great for your trees (roses are particularly reliant on mycorrhizae, by the way)

    •    formosan termites attack living plant tissue, bad for trees

    •    Other pests on the watch list in our area: buck moth caterpillars (a.k.a. stinging caterpillars) and Ipps and Southern pine beetles

    •    trees are best mulched with their own droppings, as in "mimic Mother Nature"

The upshot: I proudly deduced this important lesson after listening to Courtright speak about the insidious gall wasp for an hour: diversify, diversify, diversify. Like a good investment portfolio, you've got to make sure you've got a variety of tree species on your property or be prepared to suffer a devastating loss when some pesky little wood-gnawer decides to move in with his pregnant wife.