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SYCAMORE BLIGHT EPIDEMIC NOTICED BY MANY

written by

Marianne C. Ophardt

WSU Extension Faculty

for the Tri-City Herald, Kennewick, WA

It seems like the question on almost everyone’s mind this past week is what’s wrong with the area sycamore trees? The problem is sycamore anthracnose (a.k.a. sycamore blight). I talked briefly about this fungus disease two weeks ago, but with so many frantic sycamore owners I think we need to talk more in-depth about the current sycamore blight epidemic.

Most of the older sycamores in our area are not resistant to anthracnose and have been infected numerous times over the years when cool (50 to 60 degrees F), wet spring weather has prevailed. We typically don’t experience these spring conditions in successive years like we have last year and this year. Our trees have been dealt a “double whammy,” with this springs’s infection being severe.

Sycamore anthracnose is called a “leaf and twig blight” but it should be called a twig, bud, shoot, and leaf blight because the fungus can attack all of these parts of new spring growth. According to plant pathologists at Clemson University there are four distinct phases of the disease:

1. Twig blight occurs before the leaves emerge and kills the smaller twigs.

2. Bud blight occurs when cankers girdle the twigs, preventing developing buds from getting water and nutrients.

3. Shoot blight occurs when new shoots and leaves suddenly dieback because of girdling cankers.

4. Leaf blight occurs after the leaves have fully developed is characterized by angular brown lesions associated with the leaf veins. Infected younger leaves will just look brown and crinkled and drop from the tree.

Will the trees die? Probably not. Healthy, well cared for sycamores that haven’t been topped can usually withstand repeated defoliation several times in one season. The presence of many large older sycamores in the area shows that they can survive. However, severe successive infections will weaken trees and they could die.

Can the disease be controlled? You can help manage the disease by raking up and disposing (not composting) of all fallen leaves and twigs. They serve as a source of fungus spores for next year. Cankers on twigs and branches also produce spores. Where practical, prune these out. Keep the tree in good health, providing adequate water during the summer, as well as during the fall and winter. Trees that have been badly infected this spring should be fertilized now to encourage new growth.

There are numerous fungicide sprays recommended for control of the disease, but these are applied in early spring when the buds begin to swell and the bud caps are starting to break and then again 10 to 14 days later. If your sycamore is taller than ten feet, you won’t be able to apply the spray materials effectively over the entire tree and should contract with a commercial pesticide applicator/arborist for treatment.

On very large trees, some arborists may recommend systemic fungicide injections in the trunk of the tree. The injected chemical is moved via the tree’s water conducting vascular tissues throughout the tree and will protect against early spring infections. There are several products available only to licensed commercial pesticide applicators/arborists. One of these is Arbotect 20-S. Arbotect 20-S has given excellent control over multiple field-trial seasons. According to the label Arbotect 20-S is applied “after the tree has fully leafed out (post infection) through late summer or early fall. Treatments will aid in control of anthracnose for up to three growing seasons.”

There’s no way to know if we’ll have a long cool, wet spring again next year, but if you have a particularly valuable sycamore tree you may want to consider having it injected with Arbotect 20-S. Otherwise, let’s hope for a warmer, drier spring in 2012!

Published: 6/18/2011 9:08 AM

BLIGHT HITS SYCAMORES

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

‘Bloodgood’.

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

SICK SYCAMORES

written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA

Have you noticed how sick some area sycamore trees are looking? That’s because they’ve been hit hard by sycamore anthracnose, also known as sycamore blight. Sycamore anthracnose is a fungus disease that attacks developing buds, shoots, twigs and leaves. This year it’s particularly severe because the conditions were just right in early spring. The ‘just right’ conditions for an infection were cool (temperatures below 55 degrees) wet weather about the time that the buds started to swell and expand.

Perhaps you’ve also noticed that some sycamores are not as severely affected as others. Microclimates may be responsible in some cases, but different species of sycamores also vary in their susceptibility to the disease. The native sycamores, the western sycamore (Plantanus racemosa) and the American plane tree (Plantanus occidentalis) are highly susceptible. The non-natives, the Oriental plane tree (Plantanus orientalis) and the London plane tree (Plantanus acerifolia) are less affected, but are not immune to anthracnose.

Because the disease is a severe problem in areas of the country that repeatedly have cool, wet springs, several cultivars of London plane tree have been selected for resistance to the disease. Today anyone who plants a sycamore and doesn’t want to deal with repeated severe ‘blight’ infections should look for ‘Bloodgood,’ ‘Columbia,’ and ‘Liberty’ cultivars.

We know the right conditions for infection, but how does the disease start? Like other fungus diseases, infections come from fungal spores. These spores are produced in cankers on the twigs and branches of trees that were infected in the past. Old infected leaves are also a source of spores. The spores are spread by wind and water. When the conditions are right, an infection can easily occur. The spores will attack buds, shoots, or leaves, depending on the stage of growth when the infection occurs. If it happens early, just as the buds and twigs start to expand, a tree will look almost dead and will initially develop few if any leaves.

If infection happens later, then just leaves may become infected. The leaf spots caused by an infection are brown angular areas associated with the midrib or main veins in the leaf. The area first looks brown and water soaked. These spots later turn tan and dry. Severely infected leaves may drop from the tree.

Despite the obvious ugly, denuded appearance of the infected sycamores, there’s really not much to worry about. Trees in our region seem to survive these occasional severe infections. By summer, new shoots and leaves will develop and the trees won’t look so bare. Twig die-back is also a result of infection and causes bushy clusters of twig growth, giving the tree a ‘witch’s broom’ appearance. However, this is more of a cosmetic problem and is mostly evident only in the fall and winter when the tree is bare.

Fungicides can be applied for control of the disease just when the buds start to swell and again 10 days afterwards. However, it’s difficult to get this timing just right and to get good coverage over the entire crown of a large tree. There are fungicide injections that can be tried, but these must be done over a two year period by a trained arborist. Unless your sycamore is a specimen tree, it’s probably not cost effective to invest in spraying or injection treatments. While it may render the trees a bit ugly, sycamore anthracnose will not kill our area sycamores.

Published: 5/20/2006 11:18 AM

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