Drought puts stress on evergreens

Nick Meyer, an area extension horticulture agent for Colorado State University, checks a dead pine tree along 30 Road in Grand Junction. Dryness is the main issue, but homeowners have to be careful not to overwater. One or two times a week is suggested.

If you are a homeowner with pine trees in your yard and noticing they are not the healthy green they should be, you are not alone.

A significant number of local urban pine and other evergreen trees like spruce and juniper are turning brown and declining.

Local experts attribute this to a number of environmental factors including drought and extreme winters. Biological factors like insects and the pine nematode, a microscopic worm that infects the tree, have also caused problems.

“The main problem I’m seeing is that the trees are stressed by two dry winters in a row,” Susan Rose said.

Rose works as the horticulture education specialist at the Colorado State University Extension office in Grand Junction. She has seen and diagnosed many of the unhealthy trees in the area.

By driving around town doing an informal survey, Rose said she estimated that 20 percent of the evergreen trees in the valley are in poor health. Rose has looked at more than 50 samples of trees that residents have brought in to be examined.

The past two winters and dry summers caused the most damage, Rose said. The temperature inversion experienced in the valley this past winter and extended drought caused many trees to become stressed, which made them more susceptible to other issues a healthy tree likely would not experience, like insects or the pine wilt nematode.

“The problem with (the nematode) is the trees die quickly,” said CSU entomology and agronomy area extension agent Bob Hammon.

The nematodes affect the already stressed “exotic” or non-native Scotch pine and Austrian pine, also called black pine. Hammon has not witnessed nematodes affecting native ponderosa or piñon pines. These native pine species have developed a natural resistance, said Nick Meyer, CSU extension agent for horticulture.

But, the extension office estimates that fewer trees have nematode problems and that the majority of trees are stressed from environmental factors.

Although dryness is the main issue, homeowners have to be careful not to overwater.

Rose suggests developing a sensible watering schedule and only water one or two times a week.

“We use the term avoidance — you want to avoid having these problems in the first place. Keep it watered and also consider using a fertilizer to stimulate vigor,” Meyer said. “A healthy plant is the best defense against invading pests.”

You can easily tell if trees in your yard are stressed, Rose said. The needles will start to turn brown at the tip. But, that does not mean you have to plan on removing them from your yard.

To assess unhealthy looking trees, Rose said to look at the terminal buds. The terminal bud is found at the end of a branch marking the end of that year’s growth.

If this bud looks green and only the needles are brown, chances are the tree could recover.

“If you see green growth at the ends of the branches, then you can take a sigh of relief because the needle browning is probably environmental.

But, if the whole tree is that brownish-red, you may want to take a sample and have it investigated,” Meyer said.

If you have questions about trees in your area contact the Tri-River Area Extension office at 244-1834.


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