Pine trees are from the genus Pinus, of the family Pinaceae. There are currently at least 126 recognized species of pine tree, as well as 35 unresolved species. These mighty trees are generally hardy and often live to a hundred years or more. However, like most trees, they are also prone to certain problems that might cause yellowing needles.
Pine tree needles turning yellow: What are the reasons?
1. Natural causes
Pine needles, especially older ones, can turn yellow due to natural causes. This usually happens during the fall season and is not a real cause for concern. The yellowing of needles will usually just occur on the branches’ inner portions, and rarely on the tips. The process usually takes about a month.
2. Sunscald and other environmental factors
Sunscald happens when dry winter wind combines with low soil moisture and intense sunlight. This results in needles yellowing at the tips, drying out on just one side of the tree, usually facing the southern sun. The pine tree may look unhealthy, but it will likely survive.
To reduce the risk of sunscald, be sure to water at least once or twice a month during winter. An anti-desiccant spray such as Wilt-Pruf provides protection from moisture loss through the needles.
Strong wind storms could also cause yellowing pine needles, as could rapid fluctuations in temperature, especially during autumn. Air pollution and road salt that splashes on pine trees can also contribute to yellowing needles.
3. Overwatering
Too much water could suffocate pine trees and symptoms of overwatering include drooping branches and yellowing needles. Test the soil for moisture before you water the pine trees by poking your finger into the ground a few inches. If the soil is muddy or wet do not water, but if it is just slightly moist you may proceed with watering the pine tree.
4. Transplant shock
Improper planting methods, such as planting pine trees too deep or not providing enough water while the roots become settled, could also result in yellowing needles. If you plant pine trees during hot weather instead of in the wintertime, this could also result in yellowing pine needles that eventually turn brown.
5. Nutrient deficiencies
Pine needles become chlorotic and yellowish if they are deficient in nitrogen. Like all plants, pine trees have nutrient requirements and when they lack these nutrients, such as nitrogen, it could cause foliage to turn yellow. Make sure to fertilize the trees according to soil test recommendations to ensure that their nutritional requirements are met.
6. Pest infestation
Pine needles turning yellow during springtime instead of during the fall season could be an indication of a pests infestation. Arachnids called eriophyid mites feed on conifers like pine trees. These mites could cause aesthetic damage to the trees, like distortion and yellowing of the needles.
Foliar nematodes known as pine wilt nematodes feed on plant tissue and cause needles to turn yellow. Some species are more susceptible to these nematodes, such as the Japanese black pine. Scale insects also feed on pine needles, specifically of the Ponderosa pine tree, causing the needles to turn yellow.
Treatment for pests may include foliar sprays like Sevin for heavy infestations, but for occasional pests you can always prune off and discard infested branches.
Common pine tree diseases and conditions:
- Annosus root rot
- Brown spot needle blight
- Cotton root rot
- Damping off
- Diplodia tip blight
- Dothistroma needle blight
- Fusiform rust
- Needle rust
- Pine wilt
- Pitch canker
Needle cast is a disease caused by fungal pathogens such as Rhizosphaera. The conifers shed large numbers of needles prematurely and only the new growth stays green. An affected tree looks as if it is dying, but this disease is treatable.
Some interesting facts about pine trees:
- They grow primarily in the Northern Hemisphere, and can be found in Asia, Africa, Europe, Canada and the USA.
- They are long-living and could live from 100 to 1000 years or more.
- Their sizes can reach from 10 to 260 feet tall, with most species reaching 50 to 150 feet tall.
- The spiral growth of needles, branches and cone scales are arranged in Fibonacci number ratios.
- Cones are an essential part of pine trees, with male cones typically 0.4 to 2 inches and female cones 1.2 to 2.4 inches long.
Conclusion
Pine needles turning yellow could be caused by overwatering, transplant shock or nutrient deficiency. It could also be due to environmental factors, pest infestation or natural causes.
Image: istockphoto.com / Vitalii Marchenko