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Today: December 28, 2023

3 years ago

Causes for Pine Trees Losing Their Needles

Causes for Pine Trees Losing Their Needles
Close up of pine tree | Image: istockphoto.com

For all of the benefits pine trees can offer, they also suffer from their share of problems. One of the most common and vexing is when your pine tree starts losing its needles.

When this happens, it can spell the death of the tree. Unlike the leaves on deciduous trees, pine trees never regrow their needles.

If the tree loses too many, it won’t be able to survive. Therefore, it’s important to spot and treat problems before they prove fatal to your tree. Here are some of the common reasons that pines lose their needles.

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Needle Blight

Dothistroma needle blight (caused by the fungus Dothistroma pini) and diplodia tip blight (caused by Diplodia pinea) are common explanations for needle loss in pines all over the U.S..

Dothistroma needle blight generally affects the lower crown of a pine tree. East of the Great Plains, this has resulted in the death of nearly all Ponderosa pine plantings, and caused severe damage in plantings of of Austrian pines in the central and southern region of the Great Plains.

Both of these pine species are highly susceptible to this specific fungus. Along the West Coast, plantings of lodgepole and Monterey pines have been affected.

The first sign of Dothistroma appears as dark-green bands and yellow spots on the needles. The bands and spots eventually turn brown. Along the West Coast the bands turn a reddish color, which is why this infection is also known as “red band disease” in that region of the country.

According to the U.S. Department of Agriculture, the fungus is commonly found in, and frequently spread by older transplants produced by landscape nurseries.

Diplodia tip blight is most common in mature, two- and three-needle pines such as the Austrian, black, red and Mugho varieties. It has also been detected in young nursery plantings that are growing quickly.

Needles infected with Diplodia will expand and turn yellow, then brown. At the base of dead needles, small fungal fruiting bodies can often be found. Should the fungus infect wounds within the tree’s stems and branches, the disease has been known to cause girdling cankers.

The fungi that cause these diseases prefers wet, cool springtime conditions and takes advantage of injured trees. Restrict pruning to the winter when the fungus isn’t present.

Regular and thorough watering will help the tree be more resistant to problems. If infection should occur, using a strong fungicide can provide some control.

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Pine Wilt

This fatal condition is caused by a certain roundworm species called the pine wilt nematode.

This tiny, destructive worm eats the pine tree’s cells, causing it to wilt from an inability to transport water and nutrients. It is common in most mid-Western and Eastern states, most notably in North Carolina.

The pine wilt nematode, frequently spread by the longhorned beetle, generally does not attack pine trees younger than five or six years old. The most susceptible pines are mature Austrian, Cluster and Loblolly pines, as well as the black and red varieties of the Japanese pine.

These species are likely to die within 30-90 days after symptoms are initially identified.

Unlike most of its soil-dwelling brethren, the pine wilt nematode infects the upper parts of the tree. Symptoms include needle wilting, yellowing and eventual browning, leading to the death of the entire tree.

According to North Carolina State University’s College Of Agriculture and Life Sciences, pines diagnosed with this disease must be removed and burned or buried immediately to prevent the infection of other pines.

Keeping pines healthy is the number one method of preventing this disease altogether. If you want to save an infected pine, nematicides are available, but they are expensive.

Pine Bark Beetle

These insects tend to infest ailing pine trees and aren’t picky about which pine species they exploit. Adult beetles are tiny– sometimes as small as 1/16 of an inch in length.

Once they find an unhealthy pine to attack, they release a pheromone to attract other beetles. They chew their way underneath the bark creating tunnels, or galleries, where females will lay their eggs. Larvae will hatch and continue to eat away at the tree until they become adults, hindering the tree’s ability to transport nourishment and water.

If you notice many squiggly lines in the bark, it is likely the tree is hosting these destructive pests. Needles on infested pine trees will turn yellow and then red before dropping. Resin, or pitch, often develops on the surface of the bark.

You may also notice very fine boring dust accumulating in bark crevices, underneath areas of infestation and at the trunk base.

Keeping pines watered and fed properly will help them resist infection and degradation. Infected pines should be removed and burned to prevent additional infestations.

Phytophthora Root Rot

This soil-borne fungus infects pine trees, harming or killing them in the process. The pathogen will infect roots in waterlogged soil conditions, presenting itself when trees are planted in containers or in areas with poor drainage.

It a frequent issue among nurseries using overhead irrigation during the growing season.

This type of fungus attacks the roots, causing them to rot and die. Although it lives in the soil, the symptoms are presented on the above-ground portions.

Signs of an infection include:

  • reduced growth
  • reddening or browning needles
  • dying branches
  • falling needles and eventually…
  • …death

Younger pines frequently die outright when infected, while mature trees may first develop cankers on the trunk accompanied by split bark and oozing pitch.

Phytophthora Root Rot can be prevented by planting pines in well-drained locations.

Professional soil tests from your local inexpensive tree care company or university agricultural extension can tell you if this fungus is present in your soil. If infection occurs, commercial fungicides are often helpful.