Elm trees are of the flowering plant genus Ulmus, which first appeared about 20 million years ago in Central Asia. These deciduous and semi-deciduous trees consist of 35 species of forest and ornamental shade trees of the family Ulmaceae. Their wood is popular for furniture, and for constructing boats and farm buildings. Unfortunately, they also suffer their share of diseases and conditions, some of which cause yellowing leaves.
Elm tree leaves turning yellow: Common reasons
Disease
Elm tree leaves turning yellow could be attributed to Dutch elm disease, which is caused by a fungal infection. The disease is spread by Hylurgopinus rufipes, or native elm bark beetles. They carry fungal spores which they release into open wounds, infecting the trees. This problem is prevalent during springtime.
Elm yellows disease is a phytoplasma that can also cause yellow and wilted leaves. It is carried by elm leafhoppers called Scaphoideus luteolus, which pick up the disease from infected trees and transmit it to healthy ones while sucking the sap from the plant tissue.
These fungal diseases block the plant’s system and inhibit water and nutrients from reaching plant parts. As a result, the elm trees lose their color and plant parts wilt and die. In the case of elm yellows disease, the trees may display scattered yellowing, wilted leaves and dying branches. The yellowed leaves appear after the inner plant tissue is already discolored and infected.
To fix this issue, you need to remove and destroy the whole tree, as these diseases are not treatable and transmission to other plants is very possible. You must also collect and destroy any debris from the infected trees to avoid the spread of infection.
Poor drainage or incorrect watering
The roots of elm trees cannot breathe if the soil is too wet. They will suffocate and stop distributing water and nutrients to the other plant parts. This happens in the event of incorrect watering or poor drainage. Underwatering yields the same effects, because with scarce water the plants cannot take up nutrients, which results in yellow leaves.
To solve this problem, make sure you use porous and well-draining soil. See to it that the planters have sufficient drainage holes and avoid planting in areas where rainwater accumulates. Compost must be incorporated into the soil to improve structure and drainage.
To check the soil’s moisture, do the finger test by inserting your index finger a few inches into the soil. Water only when the soil feels dry, and do it thoroughly and deeply. However, if the soil is moist and cool, wait for a few days and allow the soil to dry slightly before watering again.
Root damage or compacted roots
Yellowing elm tree leaves may also be caused by root damage from root rot and other infections. Damaged roots cannot deliver the nutrients required by the plants. When plants outgrow their planters the roots become compacted, while elm trees planted outdoors in a compacted landscape will have limited oxygen, water and nutrient movement in the soil. As a result, their leaves will turn yellow.
To check for compacted or damaged roots, slide the plants or young elm trees carefully out of their pots. Healthy roots are whitish-yellow, while damaged ones are dark, rotten and foul-smelling. Prune unhealthy roots and gently loosen them, but if the roots are already rotten you need to dispose of them.
Soil compaction can be improved by lawn aeration and incorporating organic matter and mulch into the planting sites. Gypsum can also improve soil compaction, especially in heavy clay soils, to help keep leaves green and healthy.
Nutrient deficiency
Another reason elm tree leaves turn yellow could be nutrient deficiency. If your plants are deficient in nitrogen, the leaves will turn yellow or pale green. Nitrogen moves easily through soil, and unless it is regularly replaced through fertilizer applications, your plants could become deficient.
Here are the various nutrients and symptoms of their deficiency:
- Nitrogen deficiency manifests as general yellowing, with older and inner leaves turning yellow first. The discoloration eventually moves outward to the young leaves.
- Potassium deficiency manifests as leaf edges turning bright yellow, while the inner leaves remain green. The older leaves show symptoms first, with leaf edges starting to turn brown.
- Magnesium deficiency manifests as yellow patches between the veins of older leaves. The veins stay green as the yellowing moves from the center of the leaves, while the leaf edges turn yellow last.
- Iron deficiency manifests as yellowing between leaf veins, but it afflicts the leaves on the top of the plant and on the branch tips first.
- Sulfur deficiency manifests as yellow young leaves.
To fix these issues, proper fertilization is necessary.
Conclusion
Elm trees are cultivated for their durable wood and are considered hardy plants. However, they are also prone to diseases and conditions that cause yellowing leaves. Elm tree leaves may turn yellow due to fungal diseases like Dutch elm and elm yellows. However, the yellowing could also be due to a nutrient deficiency, root damage, or improper watering.
Image: istockphoto.com / Ihor Khomych