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Growing Concerns: What’s wrong with my pine trees?

June 16, 2018 GMT

I have had a lot of homeowners asking about problems with their “pine trees.”

In most cases they are actually referring to spruce trees. Diagnosing problems in evergreens can be challenging, but knowing which species you have is very important because spruce have different problems than pine trees. In fact, different species of spruce even have different problems.

Another challenge in answering these questions is that each species can be affected by a wide range of pests, environmental stresses, chemical damage, mechanical damage and physiological disorders. Diagnosing plant problems accurately really requires observation by someone with knowledge of the signs and symptoms that are manifested with these different problems.

This presents a problem for homeowners because there are very few people in the horticulture-related professions that have this knowledge. For those of us who do, it creates a challenge because requests to do diagnostics can consume a lot of time, which can detract from getting other services done for customers.

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Homeowners can find some resources online, but they can be hard to sort through without experience in recognizing different types of symptoms. Following are a few of the common symptoms that are encountered with spruce. Excellent references can be found on line for all of these problems.

• Inner needles are turning brown and dropping making the lower portion of the tree look very sparse. This is indicative of “needle cast” diseases. There are several different diseases that cause needle cast in spruce. Knowing which species of spruce you have can help narrow down which disease is most likely. The conditions that make spruce susceptible to needle cast are similar for all of these diseases and they all have similar treatment protocols. There are some excellent references online that help in identification and provide treatment recommendations.

• Entire branches die relatively quickly, with needles turning a dark reddish brown all the way to the tips of the branches. White sap on branches is also common. This is typical of Cytospora canker which is most common on Colorado (blue) Spruce but can infect other species as well.

• New growth is twisting or curling. This is typically an indication of chemical injury from lawn weed control products. Trees will generally recover from these low level chemical exposures. This is still a stress factor on the trees, so avoid conditions that can result in repeated exposures.

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• Needles are lighter green than normal or slightly yellow over much of the tree. This can be caused by spider mites. Spruce spider mites are cool-season mites that are most active in spring and fall. They can be detected by shaking a suspect branch over a white piece of paper. Mites will show up as tiny slow moving dots on the paper. Small, fast-moving dots are typically predatory mite or insects that feed on the spider mites. Heavy infestation may require chemical treatment, but more often just making sure the tree does not get drought-stressed will allow it to tolerate the mites and the predators will keep the numbers in check.

• Whole tree dies fairly rapidly from top down. This can be caused by root rots or girdling roots, or may be a result of winter injury. The patterns of how spruces have died this spring looks indicative of winter injury. Many of the trees were probably predisposed by some of the fore mentioned problems.

Spruce problems typically affect trees that are stressed for some reason. Most often they become prevalent as trees grow and become crowded enough to limit light and air movement. The diseases and insects are typically secondary problems that can invade the weekend branches or whole trees. In these cases, embarking on a chemical treatment plan will often result in limited control and improvement. As long as the conditions stress the tree and are favorable for the pest, the problem is likely to reoccur.

Spruce is another example of a tree species that has been way overplanted. The high density of spruce in our tree population creates a great environment for the development of pests associated with them.