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Plant Health Care in Richmond, VA

Tree, shrub decline may be people-made

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Tree, shrub decline may be people-made

In recent weeks samples of trees and shrubs have been brought into the Extension office with issues that may have been avoided. The samples included an ornamental pear with yellowing leaves, a lilac with its leaf edges turning brown and a maple tree with dead branches.

In each case there were no clear signs of a disease or insect on the leaves or branches. This indicates the problem may be a trunk or root related issue, environmental stress or incorrect cultural practices.

To determine possible causes, a number of questions are asked about the issue, the plants care and anything that may have been done to or near the plant.

In the case of the ornamental pear, leaves began turning yellow a few years ago with more leaves yellowing and dropping each year. There are no common leaf diseases of ornamental pear nor did the leaves have fungal or bacterial leaf spots.

Due to the fact the tree exhibited this symptom for more than one year, with each year becoming progressively worse, a root or trunk problem was suspected. When asked if anything had been done near the tree in the last few years, it was shared a deep berm had been added around the trunk as a planter.

While there may be no way to confirm this was the cause of decline, it certainly can lead to a tree declining. Adding soil over tree roots reduces the amount of oxygen in the soil. Roots require oxygen as much as they need moisture. Low soil oxygen leads to low functioning roots and root death.

Soil piled against the trunk of a tree can also lead to decay fungi invading the wood. At this point, the damage is done. The tree might adapt to the berm and possibly recover or the berm could be removed and the tree may recover.

In the case of the lilac, the leaf symptoms were clearly scorch. Leaf scorch appears as a uniform browning of leaf edges and browning may extend down between leaf veins. Scorch indicates leaves are losing moisture faster than roots are replacing the moisture.

We have seen an increase in scorch this year, most likely due to above average temperatures and windy conditions. However, leaf scorch can be a symptom of a root and/or trunk related issue such as rot or canker disease. Even overwatering as well as underwatering can result in leaf scorch.

When asking questions about the lilac, I learned these were larger plants that were planted recently. I was told the lilacs had been watered a lot, so lack of water should not be the problem.

Statements about watering a lot are always worth following up and I learned these lilacs were being watered once a day. Daily watering will almost always lead to a plant issue if not plant death. Keep in mind roots need oxygen as much as they need water.

If a plant is watered daily, soil pores remain filled with water and oxygen is displaced. If roots go too long without oxygen, they stop functioning or die. While the lilac leaves were scorching because the leaves were not receiving enough moisture, this was due to the soil being so wet the roots could not function to take up needed moisture.

In situations like this, I recommend to stop watering on a daily basis. Keep the soil consistently moist, but not saturated. The lilacs could develop new roots and still survive.

In the case of the maple, three or four large branches on one side of the tree appeared dead. This almost always leads me to believe a maple may be infected with a disease called verticillium wilt or there is a major root or trunk issue.

Vertillium is a pathogen present in almost all soils. Trees resist infection until they are stressed. In this case, questions were asked to determine what stress may have brought this on and it was learned a fairly deep layer of soil had been added over the roots to establish a lawn.

Again, the addition of soil reduced oxygen levels in the soil and killed roots or reduced root functioning. This stressed the tree and possibly led to the tree being infected by verticillium wilt or branches simply dying because roots were dying.

To avoid unwanted stress and decline in landscape trees and shrubs, do not add soil over the tops of the roots and avoid overwatering. Excess irrigation is not healthy for plants and it is a waste of a valuable resource.

Kelly Feehan is a UNL extension educator-horticulture. Reach her at kfeehan.

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Written by vaphc

June 7, 2012 at 12:49 pm

Posted in Uncategorized

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