Intruder in the Sugarbush: Sapstreak Disease

Intruder in the Sugarbush: Sapstreak Disease

Illustration by Adelaide Tyrol

On a walk through a still, snowy sugarbush, the peacefulness can be overwhelming; everything looks to be in good order. But all may not be as perfect as it seems. In any sugarbush, there is a good chance that a fungal intruder has gained entry and is wintering unseen beneath the rich, dark bark of an unlucky sugar maple. If this invader is the fungus called sapstreak disease (Ceratocystis coerulescens), then death is likely to soon claim a valuable sap producer.

This disease mainly affects sugar maples, and, because it enters trees through wounds in the lower part of the trunk or in the roots, it is more common in sugarbushes than in less frequently visited forests. Here there is more machinery, more intense management, and, especially when buckets are used instead of tubing, a lot more traffic. Sooner or later this will result in injury to a tree.
The sapstreak fungus colonizes sapwood; as it spreads, it disrupts the flow of water and nutrients from the roots to the rest of the tree. Long before there are any outward signs, a cross section of an infected tree shows a dark red or brown stain, with radiating streaks in a star-shaped pattern that give the fungus its common name.

It’s after sugaring is over that the symptoms of sapstreak disease become visible. An early summer inspection of the bush should be a shady affair, beneath the dark green leaves of well-tended trees. The first visible symptom of sapstreak is likely to be from just one tree, a tree that fails to intercept the sun as well as its neighbors, allowing a worrying amount of sunlight to penetrate the canopy. During the early stages of this disease, there are plenty of leaves, but on part or all of the crown, each leaf is smaller than normal. In subsequent years, the leaves become off-color and sparse and the crown dies bit by bit. Typically, the whole tree is dead within four years. Armillaria, an omnipresent, opportunistic fungus, often moves in to hasten the process.

Most trees with sapstreak disease are along roads or skid trails, or near the sugarhouse where comings and goings are intensified. Wounds to the roots or to the base of the tree are invariably present. Cattle in forests also cause wounds that allow sapstreak to enter – another reason to keep them out of the woods. Wounds created in spring and summer seem to be more susceptible to sapstreak disease than winter injuries, but, of course, it isn’t practical to stay out of a sugarbush in early spring.

When poorly managed timber harvesting results in wounds to a large number of trees, sapstreak disease may become a more widespread killer, with symptoms showing up three to six years after the careless logging.

Why this fungus does not infect wounds higher in the tree is not known. If spores from sapstreak are introduced into tapholes, they almost always fail to cause disease. And when an infection is initiated high in a tree, the tree succeeds in walling it off so that it does not spread. Wounds to branches rarely, if ever, get infected by sapstreak. There is some evidence that the insects that carry sapstreak spores from tree to tree are ground dwellers, but that doesn’t explain why the disease does not develop in experimentally inoculated tapholes.

When a tree infected by sapstreak is cut down, the fungus may produce abundant sticky spores in a mat over the stained surface of the wood. Some researchers believe it is important to remove infected trees to reduce the number of spores, but since the fungus is very common, this may not be worthwhile.

The value of the lowest log on the bole, which is usually the best log, is greatly reduced because of the discolored wood. Dissection of sapstreak-killed trees shows that stain columns do not extend very far up into the trunk but that the root collar and roots are completely colonized.

On a more cheerful note, this disease rarely kills a large number of trees at one time. Single trees or small groups of trees – and only those that have been wounded – will die from time to time. Although not identified until 1935, sapstreak is a native disease and one that, so far, does not seem to have spread to other countries.

Virginia Barlow is a founding editor of Northern Woodlands.

  1. Peter Lammert
    Mar 10, 2013

    Reference the loss of a portion of the butt log to the disease. Recently a wood turner in my town showed me a rather large vase shaped item that he had turned from what he called “Ambrosia Maple” that was harvested by a logger south of Damariscotta.

    To those of you who have seen lumber sawn from the butt of tapped maple trees, you may recall how Dr. Shigo’s CODIT (Compartmentalization of Decay in Trees ) is evident in how the sugar maple will restrict the spread of organisms from the tap holes (which are in fact ‘wounds’) not only to the left and right of the wound, but also above and below the tap hole. This restriction by the CODIT principle may be what is keeping the result of the wound from traveling.

    Back to the Ambrosia maple. The ‘streaks’ left by the ambrosia beetle make the wood valuable to the wood turners especially if the wounding shows completely around the tree.

    If you have a tree that succumbs to either the sap streak or the ambrosia beetle(Google it for more info plus great pictures of a cookie with the beetle stains in it ), Google Maine Wood Turners Association to see if a wood turner lives near you.
    They will pay for usable sections or you might arrange a trade for a bowl.

    Regards, Pete Lammert 207 691-2900

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