Question
I have some white pine trees that "black tar" all over the needles. What is causing this and how can I stop it. It was on one tree and now it is on 3. DO I need to cut all my white pine trees down.

Answer
This black is sooty mold. Sooty molds of pine trees commonly occur on all species of pine. These fungi are named for the black spots or crusts of fungal growth they form on pine needles, branches and stems. Soot molds rarely cause problems in the forest. In some cases, however, they can interfere with the proper growth of pine trees in the urban landscape and in commercial plantings.

Although a few sooty mold fungi grow on plant substances exuded by the leaves, most grow on the excrement of certain sucking insects. The most common insects associated with sooty mold infestations are aphids, scales, mealybugs, and whiteflies. These insects feed on the sugar-rich contents of the phloem of plants and excrete a substance called "honeydew" that is very high in sugar. Sooty molds live entirely on the excretions of the insects, and do not penetrate leaf or bark tissues. No direct injury to the plant results from the presence of these fungi. However, sooty molds may be indirectly detrimental to plants by excluding sunlight and interfering with photosynthesis in the leaves.

The insects sucking the juices from the pines can be controlled with insecticides. You can either spray the tree's foliage or use a systemic insecticide on the soil beneath and the tree will absorb the insecticide through the roots and take the insecticide to the leaves and twigs. Spraying a large tree can be difficult.


Chemical Control - Contact Insecticides Numerous contact insecticides are registered for aphid control. Since aphids are often placed under considerable pesticide pressure in field crops and greenhouses, they may be resistant to certain categories of insecticides. Therefore, if you do not obtain reasonable control, consider rotation to another insecticide. Contact insecticides currently registered for aphid control include: acephate (Orthene),  bifenthrin (Talstar), chlorpyrifos (Dursban),  diazinon,  malathion, nicotine sulfate, pyrethrum, rotenone, resmethrin, and tetramethrin + sumithrin.

Chemical Control - Systemic Insecticides Several systemic insecticides are useful in aphid control. Aphids have sucking mouthparts and are thus very susceptible to pesticides located in the plant vascular system. Some of the systemic insecticides also have contact activity. Systemics injected or applied to the ground are less harmful to beneficial insects. Systemic insecticides include: acephate (Orthene)


Certain persistent insecticides that move systemically in the plant may provide control through the fall. Imidacloprid (Bayer Advanced Garden Tree and Shrub Insect Control) is a newly available systemic insecticide that can provide aphid control on trees for several months following application to the soil.  This is used on larger tree that can not be reached with sprays. The tree roots take up the insecticide and when the aphids suck the plant juices they are killed.

Control the aphids and the sooty mold will wash off with rains since it has nothing to grow and feed on,