Tag Archive | apple tree rodent damage

Bridge Grafting Rodent Damage Part II

A couple weeks ago I blogged about the extensive damage done to our trees this past winter by an overpopulation of rodents.  A couple dozen apple trees and several ornamentals were chewed extensively.  Some were girdled.  To save the girdled trees, an emergency repair of grafting is attempted.  If the graft takes, the tree will be able to send nutrients back into the roots so the plant can survive.  Without help, trees that have had all the bark removed around the trunk almost always die.

In a normal winter, there is some rodent damage, especially to young trees.  That’s why I protect young trunks with tree guards.  By the time fruit trees reach forty-plus years old, rodents do not usually cause severe destruction as they gnaw on the inner bark to survive.  A little gnawing can be healed.  This last winter there were so many rodents, especially voles, present in the fields and orchards that they were forced to forage in unusual places to find enough food to survive.  Here is a somewhat grisly photo of a vole the cats killed.  The silly thing wandered into the cats’ outdoor cage.  These vermin are the main culprits in tree destruction.  They have rectangular shaped bodies with short legs, lots of teeth and stubby tails.  Voles can grow up to six inches long or more, not including the tail.

To perform the life-savings grafts, it is important to harvest a bunch of one-year-old scion growth from the same species and preferably the same tree as the one being grafted.  The scions are collected in early spring while they are still dormant.  They are closely wrapped in plastic and stored in the fridge until grafting time.  When the trees begin to bud and sap is flowing, the bark loosens and can easily be slipped free of the trunk.  Budding time is when grafting is done.

When I collected the scions I also applied wound spray to the poor girdled trees to help preserve moisture, which is why the gnawed area is black.  Using a stout blade, I cut two parallel incisions into the bark above and below the injury.  The blade is used to gently work the bark away from the trunk, exposing fresh wood.  A flap of bark is left to protect the grafting sites.  A scion is selected and trimmed to the proper length.  Both ends are shaped to slightly sharpen and form a smooth surface of fresh wood.

The graft is inserted into the bark flaps of the tree, assuring the freshly cut surfaces press against one another and the tip points upward. Then I use a staple gun with 1/2″ staples to secure the graft to the tree and hold the bark flaps in place.  Over time the staples will rust and dissolve, leaving the graft to grow unimpeded.

I give the grafted scion a test tug to be sure it is held tightly.  The scion is placed with a slight outward bend so it can move with the swaying of the tree trunk as the wind blows.  This will help the graft to stay in place.  Then I thoroughly coat the entire repair including the scion with wound spray to seal out insects and disease and seal in moisture.  Any good tree wound spray will work for this procedure, I am not endorsing a particular brand.  I used up five cans of spray this spring.

These major injuries that remove the tree’s link between the roots and leaves require many grafts placed around the trunk to repair.  They can be placed every 2″-3″.  With so much work to do, the most grafts I managed to place on a tree were six.  If they take and the trees hold in there, I can add more this fall or next year.

As the grafted scion grows into the tree, it will gradually enlarge.  I’m hoping the tree will also grow bark to help cover the wounds.  Some of the damaged trees may not survive.  The rodents actually dug down to the roots and chewed the bark off the roots.  There is not much I can do to prevent or repair that damage.

A little research reveals that orchardists have success repelling rodents and rabbits by painting the entire part of the trunk and even the lower limbs that are buried in the snow or within easy reach of rabbits in winter.  So far I have not encountered any rabbit problems.  I plan to coat the tree trunks with white latex paint prior to this fall.  Maybe that will slow down the gnawing critters.


Advertisements