Recently we have seen an increase in people’s concerns about pine trees. Many pines in our area have needles that are turning yellow or brown and dropping off. There are several reasons why needles will change color and drop. Proper diagnosis is important when determining what, if anything, might be ailing these trees.
If the needles turning yellow are on the inside of the tree, not the tips of the branches, then there is little to fear. Pine trees will drop older growth when triggered by weather or season, like deciduous trees dropping their leaves each fall. This change can be gradual or, sometimes, very rapid, creating a dramatic drop. During drought years, or years with insect infestations, needle drop will be greater, due to environmental stresses.
Different varieties of pines drop needles at different rates. White pines are notorious for having very dramatic needle drop, especially on mature trees. Austrian pines and Scotch pines normally will drop a significant amount of needles only about every three years. This often creates extra concerns because of the amount of time between drops. Spruce and fir also drop needles, but because this process is usually so gradual and happens a little each year, it is not very noticeable.
Needle shed is a natural process that evergreens go through. Dropping older needles is really the trees’ only defense against insect and disease issues. Particularly with insects such as scale, to drop needles is the only way for the tree to eliminate this type of infestation, without the help of an insecticide.
If the yellowing or browning, and/or needle drop occurs at the terminal ends of the branches, there are most likely other problems that need to be handled. If the needle drop seems excessive, it is likely that the tree is under stress. Things like high pH, drought conditions, lack of nutrition, and disease or insects will create extra stress on trees.
One of the issues creating browning tips on pines right now is the pine tip moth. The pine tip moth lays its eggs on the new growth of pine trees. As the eggs hatch, the caterpillars eat and live within the new growth of the tree. When feeding is concluded, the developed caterpillar leaves the new growth to inch down the trunk. On the side of the trunk, just below the soil line, it forms a white, paste-like, silken cocoon for pupating over the winter. Adult moths emerge the following spring with the return of warm weather. Although the damage is not life-threatening to the tree, it does leave the tree looking less than desirable. This insect is best controlled with the use of insecticides.
Late summer and fall is a great time of year to spray pines and spruce for diseases and insects. Dormant Oil spray will control most disease and insects that affect evergreens. The pine tip moth requires a product such as Hi-Yield’s 38 plus, combined with a surfactant. Feeding with a good fertilizer and a good acidifier will have a positive effect on these trees come spring. It is also important to supplement watering during dry periods. Since evergreens retain needles year round, the tree continues to lose moisture in the wintertime. An evergreen plant in dry soil is more likely to have winter injury through dehydration.