(This report written by David Doll is from the www.thealmonddoctor.com website and is reprinted with Dr. Doll’s permission).
High winds from last week’s storm caused damage to orchards throughout California. Trees were blown over, uprooted from the strong winds, which will impact crop yields and orchard stand.
This damage usually can be categorized into two categories – trees that have blown over from a failed root system or from heart rot disease.
Failed root systems
Damage to almond trees from failed root systems tends to occur in younger orchards and is characterized by leaning trees within saturated soils. These trees ‘lean’ because lateral structure roots are broken.
In the worse cases, trees may completely blow over – in which soil is still attached to the root system in an anvil shape.
Most farmers often will pull these trees back into place and stake. This practice has variable results and it is important to consider why the tree has blown over compared to the surrounding trees.
If there are structural issues with the root system, which include “J-rooting” from plantings, or disease, the tree should be replaced. Older trees most likely will have to be replaced.
Heart rot disease
This disease is one of the primary diseases affecting orchard decline. It is characterized by ‘dry rotted’ or ‘cork-like’ wood found in the center of the tree. These trees tend to be in their teens (13 years or older) and have incidence of crown gall or other trunk issues including shaker damage, previous Phytophthora canker, or broken scaffolds.
After the wound occurs, a very large group of heart rot fungi, which typically degrade lignin, invade the heartwood of the tree which breaks down the plant’s tissues. Once enough of the tissue has been broken down, the tree loses structural integrity and falls over when enough force is received.
It is thought that the initial infection of this group of diseases occurs relatively early in the tree’s life, but will take five or more years for the tree to blow over.
More research needs to be conducted, but current recommended management practices must be in use throughout the entirety of the orchard’s life – with an emphasis on the younger years.
To prevent wind-throw and delay the tree losses to heart rot, practices must be applied at the layout and planting of the orchard.
1 - Avoid planting high on berms perpendicular to prevailing winds. Orient strong roots in the direction of the prevailing wind, and design the irrigation system to ensure a wetting pattern that will favor good root distribution.
2 - Avoid heading cuts on trees, which can favor a top-heavy tree as it creates multiple branching points.
3 - Select varieties that are less upright, and plan to defoliate the trees with zinc sulfate prior to any winter storms to reduce wind resistance.
4 - Avoid damaging tree trunks with tools and plant crown gall resistant rootstocks. Not much is known about crown gall resistant rootstocks at this time.
Since this was the first major storm in a few years, tree loss was higher than normally expected. The impact of production will be dependent upon how many trees were lost.