Barber Chair

 

Reference: Arborist News, Oct 2023, page 72

Boxwood with Boron Toxicity Symptoms

Dendro and Codit the tree detectives looked at a property, in which some boxwoods (Buxus spp.) were "off-coloured". The shrubs in question were located in the backyard, adjacent to the pool. The owner spends a lot of time taking care of the pool. Using a hand lens and a small knife, Codit examined the leaves and scraped bark from a few branches to see if the shrubs was alive (they were alive). The margin of the leaves exhibited tissue necrosis, and appeared to be scorched. But there did not seem to be any pests or diseases on the leaves. Interestingly, in a row of boxwood, only the ones at either end of the row showed the exact same symptoms. That would usually point to a pest or pathogen, however, the scorching on the leaves points to an abiotic factor. It was not drought steers, as there was an irrigation system, not cold desiccation either, as it was not winter at that time. In addition, there was no heat sources like barbecue grills nearby. After a short conversation with the owner, he revealed that the pool was fresh water, there was no leaks and he used a variety of tools and pool products when taking care of his pool. One of the tools and chemicals are a water optimizer to improve water clarity and a pool cleaning robot. The latter was submerged in the pool to clean it, and the owner drained the robot during and after operation. The spots where he drained the robot were at either ends, where the boxwoods showing the scorching symptoms were located. The water optimizer contains sodium tetraborate pentahydrate (or the cleaning compound borax). Boron as a micro-nutrient is needed by plants but it would accumulate at the leaf margins when there are too much. Other toxicity symptoms include necrosis and uniform yellowing, followed by decline and leaf drop. Dendro advised the owner not to drain the pool water at the boxwoods and the soil should be flushed with clean water to leach out the boron. His landscaper could apply sulphur or gypsum to the soil, and they could help in some cases.

Reference: Arborist News, Oct 2023, pages 17, 18, 54, 55

Dead Plants on a Hillside

Dendro and his assistant Codit travelled to another state for a trade show. While they were there, they did a client visit on his property. There were multiple trees (including Oaks) and shrubs that suddenly browned and died about a month ago, but there had been no major problems previously. The owner George showed the duo a scenery of the coastline past the house, and explained that that was the reason he bought this property. 

Dead trees on hillside.

He then led them to a group of dead trees and on the way, blueberry bushes and ferns were noticed. George shared that about a month ago he left for a short trip and after he return, he observed that the trees had brown leaves. Shrubs were also browned after another few weeks. A bare path was "created" through ferns on a slope, where it used to be full of live ferns.

A path "created" through ferns.

Codit came up with a reasoning that the causal agent is abiotic, as there are multiple species that were browned at that area. Just to be sure, Codit used his hand lens to examine different parts of the affected plants to spot for possible biotic causal agents. He then used a Dutch auger to dig up several spots, and observed that the soil seemed normal, not compacted, and not mounded up again tree collars. 

Codit postulated that there might be weather extremes like a sudden cold snap or abnormally hot weather, but George stated that the weather had been normal. Finally, he asked George whether they were any recent work or activity done on the slope and the answer was negative.

Just when the questioning was done, the neighbour was seen to have returned and entering the house. George said that this neighbour moved in six month ago and he missed his old neighbour. George's expression soured and mentioned that the new neighbour made comments that he was not able to see the water from his house due to trees blocking the view, and had actually asked George to remove some of the trees on the hillside.

Dendro shared his assessment that the damage and plant tissue death caused to multiple plant species was probably the result of herbicide application. He informed his client that testing for herbicides is possible and that there is a cost for sending plant samples to the lab. There will be one or more screening tests for multiple compounds, as they have no idea what product was applied, and the client agreed to have the lab tests done. Codit then collected foliage that are still alive but showing browning from a few plant species. Dendro assured the client that he would be informed when the results are out. 

Browning foliage on different plant species.

The lab found tebuthiuron in every plant sample that were sent in two weeks later. They shared the results with the client by phone and George asked if there is anything that could be done for the plants that are still alive. Dendro replied that the herbicide have to be broken down in the environment on its own, and there might be more plants killed by the herbicide in the meanwhile.

The client had contacted a lawyer regarding this incident, and may need to pass the info regarding the vandalism to the authorities.

Reference: Arborist News, April 2023, pages 20, 21, 22, 29, 30

Depressions in the Backyard. What could have caused it?

In this episode of Dendro and Codit the tree diagnostic duo, they received a request to go check out the yard of a homeowner. The yard had some pine trees and holes were appearing, which I suppose was not dug by said homeowner. The duo rushed over before it rains, as Dendro was worried that the rain would saturate the ground, and together with the holes may cause the trees fall over. 

They arrived at the house and noticed that the yard has a well-manicured lawn as well. The trees were 76cm in diameter (approx. 2.4m girth) and over 36.5m in height. There was a gust of wind and the caused the crown of the trees to sway slightly but there was no movement on the ground surface and lower trunk. The crowns of the trees looked healthy, and no obvious dieback and no yellow needles. 

Pine trees in the yard with a well-manicured lawn.

The homeowner informed the duo that several pine trees died over the years due to different reasons and she had their stumps grounded down (note that the stumps were not entirely removed). Codit then noted that the root collars of the trees cannot be seen, which suggested that the ground level in the yard had been raised. He suggested to the homeowner to excavate the ground around the trees so as to expose the root collar, and put in a wide ring of mulch 5 to 8cm thick. The mulch "circles" are to keep the turf from competing with the trees for water and nutrients, and to protect the tree base from lawnmower damage.

Close-up of tree base with root collar being covered by soil.

Dendro suspected that the holes may be sinkholes, which are caused by soil being washed away or rock dissolving below ground. He then checked a few spots around the yard to see if any spots were saturated with a Dutch auger, which is generally used for examining soil profile and collecting soil for nutrient analysis. He picked a few spots away from the holes to probe the soil but was found to be dry below the turf layer. There does not seem to be cavities or holes found in those spots too. 

Dutch auger

The few spots (that were probed away from holes) were found to have dry soil.

Codit then probed the holes near the pine trees and discovered that the holes were 0.9 to 1.2m deep and as wide. The material dug out from beneath the holes had decayed wood besides soil. The homeowner realised that the holes are the locations where a pine tree died. Dendro concluded that the holes were formed when the stumps decayed and formed cavities in the ground. Furthermore, he postulated that the holes would not affect the health and stability of the remaining pine trees, as the holes were not large, and there was no sinkhole issue. The holes in the ground could be filled in.

Reference: Arborist News, Dec 2022, pg 18-20 and 54-55

Watering Trees

Watering trees after planting would help in their survival and growth, as compared to not watering at all. Trees with a lack of watering would lead to higher mortality rate, and are more susceptible to pests and diseases. As roots spread out and make contact with more soil volume, the frequency of watering could be reduced. Establishment of trees could be assessed visually by observing twig elongation. 

The volume of water required is minimally 1.5 to 3 liters per cm of tree diameter, though irrigation frequency is important, and ultimately determines whether the tree is being maintained for survival or vigour (Table 1). Please note that this guideline does not apply to trees in a tropical climate, as it is warmer and that promotes transpiration in plants.

Reference

1. Boldly Planting for the Next Generation, Oct 2021, Arborist News 

Excerpt of "Managing Soil Compaction Around Trees"

Generally, soil compaction is found at the top 30cm of the soil, which coincides with the region where most roots grow. Where possible, soil compaction should be prevented to maintain an environment suitable for root development.

Soil strength is measured by a penetrometer which measure force required for a probe to push into the soil. Penetrometer readings in excess of 2 MPa (2 megapascals = 20 bars) will restrict root elongation. As bulk density increase, soil strength is more likely to increase in step, and even more likely in drier soil than wetter conditions. Most roots are unable to penetrate moist soils of a bulk density > 1.4-1.6g cm-3 in high clay soil and 1.7g cm-3 in more sandy soil. 

Low pore space is harmful to roots and microorganisms as it would lead to hypoxic (low oxygen) conditions and reduced nutrient uptake. Tree nutrient deficiency would result even if nutrient level is good. Compacted soil can lead to both water deficiency and water logging. Erosion due to compacted surface will increase nutrient leaching and remove topsoil, which decrease tree stability.

In a classic case of a tree growing in compacted soil, a decline of the crown can be observed. In consideration of existing and newly planted trees, soil should be prevented from compaction by means of physical barriers or routing paths away from rooting zones.

Decompaction - Before trees are planted, the site could be cultivated using hand tools or equipment. As for de-compaction an area with existing trees, the best method to use air soil-excavation tools. They can facture compacted soil to around 30 cm depth and minimise disturbance to roots.

Reference:

1. International Society of Arboriculture's Arborist News, Volume 29, Number 5, October 2020

Soil Compaction article in "Arborist News" and "Horticulture: Plants for People and Places"

 

(a) Soil compaction caused by construction traffic running alongside a woodland. (b) Soil characteristics modified by soil compaction. Increasing or decreasing band width indicates the impact of soil compaction on the named soil characteristics. Dashed lines indicate that trends are likely to be non-linear. Redrawn from Hirons and Percival (2012). Crown Copyright, courtesy Forestry Commission (2012), licensed under the Open Government License v3.0

References:

1. International Society of Arboriculture's Arborist News, Volume 29, Number 5, October 2020

2. Hirons AD, Percival GC (2012) Fundamentals of tree establishment: a review. In: Johnston M,

Percival G (eds) Trees, people and the built environment. Forestry Commission, Edinburgh

3. Johnston, Mark & Hirons, Andrew. (2014). Plants for People and Places, Vol. 2 Environmental Horticulture (pp.693-711). Urban Trees (Chapter 20).