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The roundheaded apple tree borer makes little headway over the course of its first winter. Catching these grubs early on reduces the amount of cambial damage significantly. Photo by Michael Phillips
The roundheaded apple tree borer
makes little headway over the
course of its first winter. Catching
these grubs early on reduces the
amount of cambial damage
significantly.

Borer Insights

by Michael Phillips

Every orchard site seems to have its own take on a "super pest." Here at Lost Nation damage caused by the larvae of the roundheaded apple tree borer rates right up there. I've probably lost several dozen young trees in learning what I'm about to share here: Such hard-earned insights hopefully can bring you up to speed quickly! The biology of this cursed beetle and several protection schemes are fully explained in The Apple Grower, but what's new is that I've finally discovered the right tool to go borer grub hunting. The key has always been to delve throughout all damaged cambium and end up with a skewered grub at the end of the search.

My tool of choice to pry out the borer grub is a 3/8" spade bit, as sold in the tool section of any hardware store. (Irwin and DeWalt are two such drill bit brands.) This bit is used solely by itself - no drill is involved. I am not "drilling" out the grub in any fashion whatsoever. The spade bit is more akin to a pocket knife, only with it's narrow drill point, that much more effective in getting down to the bottom of the meandering mess made of the cambium that leads to the culprit. The spade bit is plenty sturdy to open up damaged areas to inspection, poke gently into suspected crevices, and absolutely great at delivering the hiding grub from a root-directed tunnel. The spade bit is not unlike a harpoon in this last regard.

The Holistic Orchard: Growing Tree Fruits and Berries the Biological Way -- click for book summary
The Holistic Orchard: Growing Tree Fruits and Berries the Biological Way by Michael Phillips

DVD: Holistic Orcharding with Michael Phillips
Michael's Holistic Orcharding DVD guides you through the orchard year.

Apple Grower: A Guide for the Organic Orchardist by Michael Phillips -- click for book summary
Apple Grower: A Guide for the Organic Orchardist by Michael Phillips

What's really, really critical to understand with this insect is how important it is to successfully get the developing grub in that first fall season or early the next spring. The eggs are laid in June, July, and August in eighth-inch slits made into the bark at the soil line. One female may oviposit as many as seven eggs in seven different slits at one sitting. Sometimes another female may come by two months later and add one or two more eggs to the same unfortunate tree. A vigorous growing tree may crush some of these; birds that poke into the bark at the base of the tree may find a few. All summer long I use the blunt edge of my hand pruner to smush any fresh egg slits that I discover. But come the fall months I get serious, as in being systematic in going down orchard rows to check suspicious spots on each and every tree.

People naturally are concerned about damaging the young tree. Truth is the borer grub has totally destroyed the "cambium connection" wherever it has been feeding. Thus I always feel free to open up the damaged area and follow every meandering turn to its end. Again, I want to stress that I am doing this early along in the damage curve (so to speak) when the 1/8 to 1/2 inch grub has done minimal damage compared to what's to come. The sooner you get it, the less damage done. Cutting away the dead bark with a pocket knife or stiff poking tool like a spade bit only reveals the totality of destruction. A healing callus will develop along the edges of this damage-with or without our probing-as the tree attempts to rebuild its cambium connection with annual growth rings over the ensuing years.

Orange frass (grub poop!) coming out of the bark is one visual clue that growers look for in searching out borer grubs but not the only one. Blackened bark, sometimes sunken inward, sometimes not, just as often reveals a problem. Some borers are small enough to "contain" their frass early on within the damage area, thus you will see no frass. These are the ones more easily missed. All egg slits and any dubious places on the bark at or near the soil line should be poked to see if such lead onward. Do push back the soil for an inch or two downward when doing this check . . . my trees have peastone mulch at the base, which helps in this regard. What I'm describing is kind of like dental work: open up the cavity completely to reveal healthy tissue along the edges, take care of the cause, and then let the healing begin. Don't leave gobs of frass in place to only confuse you the next time you check a given tree.

You absolutely need to see the guts of this creature to know you've done a righteous job. Some borers go downward for awhile but then go back to the upper edge of the damage. Some dip around a root and hide on the other side. Some "merge" into a younger grub's tunnel, leaving you satisfied with a victory that still leaves the younger grub lingering behind. It really helps me to see past damage opened-up -- from entry point to the bitter end - in order to be sure.

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Cedar apple rust on the fruit can only be prevented early in the growing season. (photo: courtesy of Keith S. Yoder via the West Virginia University Fruit Web) more insights: Holistic Disease Management

Numerous tree species can fall victim to the roundheaded apple tree borer. Wild apples, hawthorn, serviceberry, and mountain maple seem to contribute to the extreme pressures at my site. I remove all unmanaged species on occasion. Migration is limited to a few hundred yards a year, which explains why this pest problem is more localized than wide spread. If you get good at doing "borer duty" in all respects, you should find a decline in borer pressure over the years.

There's only one way to sign off after giving such advice. . .

Regards, Captain Ahab

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