The signs of stress or disease in pine trees will often go unnoticed for a time. When a pine tree starts losing needles, it is in serious stress. The stress can have environmental causes or may be the result of disease. In any case, the tree is conserving resources by dropping needles. Photosynthesis may slow, preventing new growth. The process of saving a pine begins with identifying the source of the problem.
Identify the type of pine. Certain diseases are species specific. Knowing the pine species will help you eliminate certain causes. Your local garden store can help with identification. Online guides are also available.
Rule out natural causes for browning and falling needle leaves. Seasonal loss of 3-year-old needles is normal and is not a cause for alarm or treatment. This loss normally occurs in the fall.
Examine the environment around the pine. Pine needles may turn brown and fall off as a result of pollution. Runoff from engine oil, gas and salt can harm the root system of pines and contaminate the surrounding soil.
Place mulch or barriers around pines if runoff is an issue. If runoff cannot be eliminated, then reducing its impact might be possible. More likely than not, this will need to be a lifelong prevention method. As the pine and soil recover, the browning and needle cast will slow over time.
Look at the needles for evidence of spotting. Note the colour and shape of any spots that are detected. A magnifying glass may be helpful. These characteristics will be important for identification of the disease, if present. Also, note the areas of damage.
Identify the disease. Some diseases are readily identified by their unique spotting. Identification of the disease is important to determine the best course of action. Your local extension office can provide assistance.
Prune diseased or damaged branches and twigs. Damaged portions provide additional areas for disease to gain hold of the pine tree. Dispose of clippings properly to avoid reinfecting the trees.
Weed around the pine to encourage better air movement. Fungal diseases, such as Lophodermium needle cast, thrive in moist conditions. Removal of weeds will improve circulation and will help dry areas where moisture can be trapped.
Remove host species. Some pine diseases, such as white pine blister rust, require an intermediate host to complete their life cycle. Currants and gooseberries are host species for this disease. As with clippings, dispose of host plants well away from pines.
Apply a U.S. Environmental Protection Agency-approved fungicide. In cases of severe damage, pesticide application may be necessary. The fungicide must be on the pine trees before the fungus goes to spore. If not, the fungus will be able to spread to other pines.
Note the time of year that damage appears. This will help in identification of the disease, if present.
To prevent drift, never apply pesticides on windy days. Always read the material safety data sheet before applying pesticides to understand the risks of application and proper medical treatment in case of exposure.