Author: Robert

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All things Emerald Ash Borer

Now that the emerald ash borer (Agrilus planipennis) has made its way east and has been detected as far east as Halifax, it has become more important to be conscious of what tree species you have AND what state their health is.

EAB targets species in the ash genus (Fraxinus) such as the native green ash (F. pensylvanica), white ash (F. americana), and black ash (F. nigra) especially, along with their cultivars that have been bred for planting. Though the insect attacks stressed trees primarily, healthy ones can be a target as well. Despite being an attractive beetle in the jewel beetle family (Buprestidae) it does significant damage to the important cambial tissue of the tree. This tissue is what conducts the transport of both carbohydrates, water, and nutrients from the crown to the roots and back. Disrupting this flow, even under the bark, amounts to girdling the tree, choking it, and causing what is called a physiological drought. All the watering and fertilizing in the world can’t help it once the column of transport is broken.

The life cycle is generally one year long and occurs as follows:

  • Adult lays an egg during the summer
  • Egg hatches and burrows into the cambium (the living tissue) of the tree under the bark and consumes the wood material into the fall
  • The larva stays in this form over the winter
  • It continues to consume cambial material until it pupates in April to July
  • The adult emerges from the bark forming the D shaped exit-holes, with emergence forecasting done by BioForest
  • The adult consumes tiny bits of the leaves but not in any significant amount
  • The adults mate
  • The process begins again

It is important to recognize that our native ash trees do not have any defenses against this pest. It originated in the far east of Asia and fed primarily on Mandchurian ash (F mandschurica) in its native range.

DripLine Analytics staff has experience in both maintaining a monitoring program of over 50 detection traps, assessing hundreds of ash trees for their health and structural quality, and performing actual pesticide injections on dozens of ash trees to kill any EAB larvae that were present in them using TreeAzin from BioForest.

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What is a dripline anyway?

The dripline of a tree is an imaginary line extending vertically down from the edge of the farthest reaches of its canopy. It’s effectively the area under the tree up to the horizontal limit that rainwater could “drip” down from the leaves of that specific tree. The quality of this area below the tree determines the nutrients and water available to the tree. Further, this area is critical to how well its roots will develop to provide stability and actually get to those necessary things for growth.

photo showing a visual representation of a dripline for an ash street tree
The blue lines are a visual representation of a dripline. The area underneath the tree extending to the dripline is a key area for tree management. You can see how this ash tree isn’t going to have a good time as its dripline is mostly compact impermeable materials!

What is there to analyze about a dripline?

Just take a quick look at the above image. See how there isn’t much but asphalt and concrete pavers in the dripline? That’s not good for allowing water to get to the roots of this ash tree. The soil is likely very compact (dense, hard to break up) which makes it more difficult for both roots and water to penetrate the soil but creates a good foundation for pavers. Underneath these pavers and asphalt is usually a gravel base which is nutrient poor and has a low field capacity for water, meaning any nutrients that were applied (like in a fertilizer) would quickly be carried away by the water to an area that the roots could not reach.

This is just for one single street tree. Imagine hundreds or even tens of thousands across a major city or in a park. In forests these driplines overlap and below them is a network of roots and fungi and microbes that are often lacking in urban settings but are nevertheless very important to foresters and arborists.

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Pruning Basics

There exists a narrowly defined “right way” to prune a tree. Conversely and unfortunately there is a very broad definition to the “wrong way” to prune a tree.

Poorly pruned silver maple

Ultimately each time a tree is pruned it creates a wound. Pruning should really only be done when necessary to avoid excessive damage to the tree.

  1. Identify the reason why a branch needs to be pruned;
    • Is it dead, diseased, dying, or going to cause significant issue in the future?
  2. Determine how it needs to be removed;
    • Is it large enough that it needs to be removed in more than one piece?
  3. Make your undercut to prevent tearout or peeling
    • Ensure you’re not completely severing the branch at this point
  4. Make your top cut and remove the majority of the branch
    • Ensure it is completely removed
  5. Make your finishing cut outside the branch collar or where it would be expected to form
    • This is critical to ensuring that the wound has a good chance of closing and CODIT can occur