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Why do spruce trees turn brown?

This week's article comes from one of our tree gurus, my counterpart in Clay County, Rick Abrahamson, in response to a rash of calls regarding brown needles on spruce trees.

Many factors play into browning of spruce needles. First of these is normal needle drop. Evergreens shed older needles as growth continues. This needle drop is often confused with disease or insect problems. Older needles, those on the inside of the tree, that are three to five years old will turn yellow then brown and eventually fall off the tree. Usually we don't notice this as the newer growth does a good job of hiding this fact. Needle drop in this manner is a gradual process and should not concern us.

Needle browning we should be concerned about now include herbicide, drought, animal, salt injury, nutrient deficiencies, and even air pollution can cause browning of evergreens. Determine what part of the tree has turned brown and you should be able to make a good guess as to what is happening.

n Herbicide damage -- browning of newer growth. Herbicidal injury is influenced by the type of chemical used, the application rate, temperature during application, and wind speed and direction during application.

n Drought damage -- needles gradually turn yellowish-green, and then light brown. This starts at the top of the tree and progresses downward, and from the outside in. This perhaps may be the best explanation to what we are seeing in our trees. This summer's drought has left the soil profile with very low moisture content and many trees are showing symptoms of this drought stress.

n Animal injury -- dog urine can cause some browning and drop of lower branches on arborvitae and junipers.

n Salt injury -- needles will brown from the tips downward if the tree has had direct salt spray from roads. This browning typically takes place during the late winter.

n Winter damage -- water loss during winter can cause winter burn. Keep trees watered well going into winter to reduce winter injury.

n Nutrient deficiencies -- needle discoloration due to this will get progressively worse over several years. High pH soils can cause iron chlorosis as iron is not available to plants at high levels of alkalinity.

Additional information on the causes of brown evergreens can be found at $department/deptdocs.nsf/all/agdex4144. There are also several diseases that can cause browning in evergreens and more information is needed to determine if this is that case. The two most common spruce diseases common to our area have symptoms on the lower most branches. Source: Alberta Agriculture, Food and Rural Development.