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written by

Marianne C. Ophardt

WSU Extension Faculty

for the Tri-City Herald, Kennewick, WA

Longtime readers of this column know that sycamores are not my favorite tree. One reason for this forthright antipathy is that the sycamores planted here many years ago are prone to a fungus disease called sycamore anthracnose, a.k.a. sycamore blight. Our last severe outbreak of this disease was in 2006. A quick tour of the older areas of the Tri-Cities reveals that the disease has hit the sycamores hard again this year.

This is no surprise considering the weather this spring. We had the “perfect” conditions for the disease to develop… cool (below 55 degrees), wet weather as the buds first begin to open. Under these conditions, buds, shoots, and newly expanding leaves easily become infected from the spores produced by cankers. These cankers, distinct lesions, found on branches and twigs come from infections that occurred in previous years.

If the disease attacks early in the season, buds and shoots will be killed before they have a chance to develop. Once the leaves have developed, later infections show up as brown-colored dead angular blotches that follow along the veins. These brown areas can expand to include the entire leaf. The fungus also infects twigs and branches, forming cankers that can girdle and kill them. Repeated infections over time result in the tree developing ugly “witches brooms” with clusters of dead twigs at the ends of branches.

What can be done about it? If we know when the next spring with the perfect conditions for infection will occur, there are fungicide sprays that can be applied when the buds swell and again 10 to 14 days later. Spraying of large trees over ten feet tall should be handled by a commercial pesticide applicator. This can be an expensive proposition because of the size of these old sycamores and because they need to be sprayed twice. As an alternative to spraying, trees can be injected with a fungicide. However, this must be done in early fall by a trained and licensed applicator.

Neither spraying or injection now will help trees already infected this spring. Both must be done prior to infection. Given the unpredictable nature of the weather, it’s a gamble whether or not to use a fungicide for control every year. Let me point out that sycamores in our area seem to survive repeated infections. However, they do look pretty darn ugly in the winter. Sycamores that are almost bare now, will develop more leaves as summer goes along.

While gigantic sycamores no longer fit into the typical smaller home landscapes of today, anyone who is considering planting one should look for cultivars that are resistant to the disease. Don’t plant California sycamore (Platanus racemosa) or American sycamore (P. occidentalis), both very susceptible to sycamore anthracnose. Two resistant London plane tree hybrid (Plantanus x acerifolia) cultivars are ‘Liberty’ and ‘Columbia’. Another cultivar that’s moderately resistant is


The other characteristics that have me disliking sycamores are the multitude of large leaves requiring removal in the fall, the nasty seed balls, and the sheer massive proportions of the tree that make it a target of tree butchers who practice improper pruning (topping). However, I do find sycamore bark beautiful. The tree sheds plates of older bark, leaving the trunk with a unique gray, green, yellow and white mosaic appearance. As the weather turns hot, don’t be surprised if you see area sycamore losing big and small pieces of bark from the trunk. It’s normal and isn’t related to the anthracnose problem.

Published: 6/26/2010 2:01 PM


written by

Marianne C. Ophardt

WSU Extension Faculty

for the Tri-City Herald, Kennewick, WA

This past week I was asked to diagnose samples from a number of dying or dead arborvitae. Have you noticed them around the area? What’s causing this apparent epidemic? Before the samples were brought to the WSU Master Gardener Plant Clinc for diagnosis, the ailing shrubs had been variously mis-diagnosed with a variety of problems from spider mites to drought to “blight.” Various courses of action were taken, but the arborvitae continue to die.

Arborvitae are pretty much an insect and disease-free plant in our region. Because they usually thrive under local climate and soil conditions, they might even be considered a bit overused in our landscapes. However, when this virtually trouble-free shrub turns brown in the middle of summer the pronouncement is that “spider mites” or “blight” must be at fault. However, arborvitae are almost never troubled by spider mites. In fact, in my 25 years of diagnosing sick plants in this area, I have seen only one serious spider mite infestation on an arborvitae. There are a few other insect pests that can attack arborvitae, but these are seldom a problem here.

In our region, arborvitae are also rarely infected with leaf or tip blights caused by fungus diseases. These can be problems in wetter and more humid climates, but they’re seldom a problem here. When “blighted” arborvitae do appear, they’re usually in landscape situations where sprinkler irrigation is frequently wetting the foliage. Control is as simple as keeping water off the leaves.

Let’s get back to the current problem of dead and dying arborvitae. If arborvitae are such stalwart plants, why are so many of them turning up dead? A close investigation of the foliage doesn’t reveal any obvious problems. The unexplained death of the top of the plant points to root problems. Poor plant growth, die-back of individual branches, general discoloration of the leaves and the eventual death of the entire plant are the progressive symptoms of root problems.

That means we should turn our attention to what’s happening beneath the soil of the ailing arborvitae. It’s very likely that the problem is root rot. Believe it or not, root rot is a fairly common problem on arborvitae in our area. Even though many think that you can not overwater in our hot, arid climate… you can! The cause of failing arborvitae is very likely to be root rot, especially if they’re being watered heavily either with a drip system or sprinkler, or sometimes even both.

Root rot in landscape trees and shrubs is caused by a variety of different fungal pathogens found in the soil. Conditions that favor the development of root rot are poor drainage, saturated soil conditions, and warm temperatures. Other factors that contribute to root rot include planting root balls too deep, compacted soil, and mulch that’s too thick or matted to allow air movement.

Another factor that I often see contributing to a root rot problem is the type of soil in the original root ball of the arborvitae before it was planted. While some arborvitae are grown in pots in a well drained soil-less potting mix, some are grown in the ground and then dug up with clay soil around their roots. Clay is a “heavy soil” and not well aerated. It holds water tightly and stays wet longer than the sandy or loamy soils that predominate area landscapes. A problem can arise when we water for the typical sandy and loamy soils. These soils drain and dry out more quickly. Local landscapes are usually watered to keep lawns and other plants growing in sandy and loamy soils from drying out. When we do this, the soil in the clay root balls stays saturated… and can lead to root rot on plants.

The only way to tell if a plant has root rot is by looking at the roots. Healthy fine feeder roots are brown on the outside but have a white internal core and white tips. Root rot is indicated if the outer layer of the finer roots is soft, brown, and pulls off easily. Roots are obviously rotten if they’re soft, partially decomposed, and break off easily.

Once a plant with root rot starts showing death and dieback on top of the plant there’s not much you can do. Your attention should be given to those shrubs that aren’t exhibiting any symptoms yet or are in the initial stages of symptom development. Control might be as simple as not watering excessively and avoiding keeping the soil saturated. However, if the root ball is surrounded with clay soil, if the shrub is planted too deeply, or if the area has poor drainage, remedial action will be more difficult. These situations should be avoided before planting.

Dr. Linda Chalker-Scott, WSU Extension Horticulturist, and other horticulturists recommend gently washing the clay soil off the roots before planting so you don’t have that slow-draining clay soil around the roots. When this is done, you’re creating a “bare-root” tree or shrub. This should only be done in the fall or early spring when the plants are in a dormant stage.

Planting too deeply is a very common problem. The top roots of the root ball should be just below the surface of the soil. Planting them two or more inches below the soil level can lead to problems, especially from root rot. It’s best to dig your planting hole only as deep as the root ball and then plant the shrubs or trees slightly above the soil line, to allow for some settling after you thoroughly water the plant. If the area has poor drainage due to compaction or other factors beyond your control, you can make your planting beds into berms or raised beds.

If all remedial actions fail to stop successive arborvitae in a planting from dying, it’s possible that a particularly virulent type of root rot, called phytophthora root rot, may be involved. There are chemicals that can be applied to the soil to keep this fungus in check, but they’re extremely expensive and must be applied regularly. Once use of the chemicals is stopped, the disease can return. Before applying these chemicals, the disease should be positively identified. In our area, there are no local laboratories that can test for the disease. Samples can be sent to one of three labs in the region, but this is also a costly proposition.

So if you’re wondering what’s “attacking” and killing local arborvitae, the culprit likely lies beneath the soil. However, the real perpetrator is usually the person who planted them or the person who waters them… or both.

Published: 9/10/2005 11:40 AM



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