Identifying source of maple tree decline can be tricky: Ask an expert

We’re well into gardening season and you may have some questions. For answers, turn to Ask an Expert, an online question-and-answer tool from Oregon State University’s Extension Service. OSU Extension faculty and Master Gardeners reply to queries within two business days, usually less. To ask a question, simply go to the OSU Extension website and type it in including your county. Here are some questions asked by other gardeners. What’s yours?

Q: I noticed that one of the maple trees in my front yard is starting to have leaves on the branches turn brown. There two more of these trees on each side that look fine and healthy. I have started to give it extra water the last week or so. I would like to find out what could be causing this so I can treat it. – Jackson County

A: Your maple trees are located in a very difficult environment due to the surrounding sidewalk and street.

Your maple tree is most likely suffering from some of the issues listed here. Symptoms of maple decline include partial or entire crown dieback, discoloration and reduced size of the leaves, crown thinning and death. Tree decline never happens overnight. Decline can be the result of a single disease or environmental event or, more common, from stress over many years. Often there is more than one stress factor. Stressed trees often are predisposed to other problems, such as those caused by insect borers, opportunistic organisms and injury from extreme climatic factors. Any of the following may contribute to tree decline.

  • Injury to the trunk from string weeders or lawn mowers (repetitive minor injuries have a cumulative effect), poor pruning practices, weather (sudden drops in temperature, wind, hail or lightning), animals feeding on the bark (deer, beaver, porcupine, mice, etc.), other injuries to the bark or disease.
  • Injury to the roots from standing water or poorly drained soils, seasonal high-water table, soil compaction, insufficient room for root growth, a change in grade of the surrounding soil, recent construction in or near the root zone (sidewalk, sewer, etc.) or root rots.
  • Injury to the whole plant from insufficient water (lack of irrigation, drought), not being climatically adapted to the area in which it is growing, being planted in subsoil or other unsuitable soils (especially true in new housing developments), transplant shock, poor fertility, chemicals or girdling roots

For established trees insufficient water over several years is the most common cause of tree decline. Trees need supplemental irrigation in the dry summer season even if the spring has been wet. Irrigation is particularly important for trees transplanted in the past three years or that are stressed from any of the factors listed above.

Water deeply and infrequently (once a week) rather than sprinkling lightly for five or 10 minutes a day. When the soil 4 inches below the surface feels dry or only slightly damp, it is time to water. Well-drained, sandy soils need more water volume, which should be applied more frequently than for a loam or clay soil. Trees, especially conifers, in drier regions often need water during the winter to prevent desiccation.

Identify sources of stress and eliminate them if possible. Mulch under the tree to keep down weeds and to prevent the need for mowing right up to the trunk. Organic mulches such as leaf litter and wood and bark chips work well. Do not use plastic because it interferes with root–soil gas exchange and water infiltration. Spread the mulch 3 to 6 inches deep in a circle at least 3 feet in radius from the trunk. Keep the mulch from direct contact with the tree trunk.

Protect trees from bark-chewing animals by placing hardware cloth or other wire mesh around the trunk. In high-traffic areas or public landscapes, try to reroute foot or vehicular traffic to prevent compacting soil in the root zone. Correctly prune out dead and dying branches to prevent insect and disease invasion. Fertilize trees with symptoms of nutrient deficiency (yellowish or off-color leaves).

Here, here and here are sources of more information. – Chris Rusch, OSU Extension Master Gardener

Ask an Expert

Slime moldOSU Extension Service

Q: This popped up very quickly on my lawn. I’ve never seen anything like it. – Washington County

A: It is a slime mold. They do not kill the lawn unless they block out the sun long enough that the grass dies (in your case, clover). Remove it with a rake.

One of the common slime molds is actually called, “dog vomit slime molds” because it looks like a dog vomited on your lawn. You can look it up online. – Brian McDonald, OSU Extension turf specialist

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Creeping bentgrassOSU Extension Service

Q: I have a mixture of lawn types that look different. The lighter green grass is green on the top and brown below. I have thatched and over seeded with a Northwest blend, but the lighter green grass prevails. Short of killing it or using a sod cutter; I was hoping to find another solution. – Marion County

A: This is creeping bentgrass. It is almost impossible to remove once it is on your lawn. You can spray it with Roundup and sod cut it out, but it will likely return from the stolons (lateral stems or runners) it produces and leaves behind after sod cutting.

Another option is leaving it. This grass requires regular irrigation three or four times per week to stop it from going brown during the summer time. I would suggest .25 inch of water applied four times a week to prevent the brown color. This turf type also looks best when mown at a lower height. One inch would be great for this turfgrass. – Alex Kowalewski, OSU Extension turf specialist

Ask an Expert

Although some varieties of pear require aging for best flavor, Bartlett pears will ripen perfectly in a day or two on the counter. Oregonian file photo. LC-

Q. What month are Bartlett pears normally ready to harvest. I know they should come off the branch easy with a bend up from the branch but when? End of August? Beginning of September? – Washington County

A: Here’s OSU Extension’s publication on picking and storing apples and pears. It can vary depending on the year, but in general Bartlett pears come to maturity right around now, in mid-to-late August. – Lorena Hoffbeck, OSU Extension Master Gardener

Ask an Expert

Garden soilRosemarie Stein/staff

Q: How much compost is too much to mix with soil? I have nearly the same amount of compost as sandy loam and am intending to mix together to fill raised beds for vegetables but have read that too much compost may be an issue if I do a 50/50 split. The compost came from Portland Bureau of Transportation a few months ago when they were giving out leaf rot; sandy loam was purchased from a landscaping supplier for our recently finished rain garden. – Multnomah County

A: Mixing all of the compost with the sandy loam may not be the best idea. If you are filling raised beds, I would put in the sandy loam and then add about 3 to 4 inches of the compost on top and mix into the soil about 6 to 8 inches.

If the leaves are not completely decomposed, they may use the nitrogen in the soil and possibly deplete that nutrient for your plants. Does the compost have a dark, friable texture? If so, it is probably completely composted. You should add nitrogen anyway to the soil for future plant needs.

Organic matter is very important and influences the physical condition and water-holding capacity of the soil. It affects the soil bacterial process and the availability of minerals.

After you mix the two, test the pH acidity or alkalinity. You can purchase test kits at nurseries. You want your soil to be slightly acid for most vegetables 6.2 to about 7.0 neutral.

Some composted materials have been as high as 8.0, too alkaline for most plants to pick up nutrients from the soil.

You can use the leftover compost as a mulch. It will hold the moisture in and keep the roots cooler.

Here is an article about compost.  Their pH numbers are a little different from mine, but that said, it has a lot of information that you may find helpful. – Sheryl Casteen, OSU Extension Master Gardener