Pine trees can make a great addition to any yard or landscaping project. Since they're green year-round, they can provide some much-needed color in some of the northern climates, as well as attracting wildlife that depends on their bark and needles to survive through the cold winter. Like any other tree, however, disease can take its toll on these hardy trees.
Pine wilt is caused by pinewood nematodes, organisms that are introduced to the tree by carrier beetles. The disease is native to North American pines, but can be a deadly, non-native invader in countries like Japan and China.
The first sign of pine wilt is visible in the needles, which will turn first grey, then yellow, then fade to reddish brown. By that time, the tree is already dying. Pine wilt kills trees very quickly; when diagnosing a tree, it's important to take into account that if the color change seems to be happening slowly, it is not pine wilt. Once the tree is dead, the nematodes and beetle carriers feed on the remnants of the tree.
There is no cure for pine wilt once it infects the tree; therefore, prevention is important. One of the best ways to prevent infection is not to introduce non-native trees to an area, and cut down on the vulnerability of the trees there. Because of the deadly nature of this disease, many countries have placed embargoes on pine wood coming from North America.
Dothistroma Needle Blight
Dothistroma needle blight is a fungal disease that has been responsible for failure to introduce ponderosa pines to states in the West. The disease first manifests itself in brown and tan spots on the needles, and within several weeks the needles begin to turn brown. Infected needles drop, and while the tree can usually survive several years of infection it will ultimately lead to the tree's death.
Like many pine diseases, prevention and control is crucial. Fungicides applied to the tree can help prevent infection, and can kill infection in its first year. Particularly affected by this disease are Christmas tree farms--these pines are not only particularly susceptible to the disease, but infection can make the trees unsellable.
Lophodermium needlecast is also caused by a fungus, and is particularly dangerous to seedlings and young trees.
One of the things that makes Lophodermium needlecast so dangerous is that symptoms manifest themselves in the same way as storage problems; individuals can unknowingly plant infected trees, thinking that the discoloration is only from shipping or handling trauma.
One of the best ways to control the disease is to make sure no infected trees get planted; as it's spread by spores released into the air, it commonly spreads throughout an entire area by one infected plant. It can be controlled by the application of fungicide at the nursery, but it's important to make sure the disease is completely gone before selling, shipping or planting any of the seedlings.