Rowing out in the midst of orange rust

By David Wartinbee
This week I put my boat in at the upper launch of Skilak Lake. The water around the launch area, and all along the rocky shoreline, was covered with a bright, Creamsicle-orange layer. Immediately, I guessed that this was a layer created by spruce needle rust spores, remembering that similar orange-colored floating masses were reported in Kivalina and at Twin Lakes last year.
I photographed the large floating layer and collected samples to examine in the lab. Then I set about to see if many of the surrounding spruce trees showed the characteristic infection of yellowed needles at the tips of the branches. In the areas near the boat launch, I found no trees showing the infection.
However, when I went to the far side of the lake, I found a large number of heavily infected trees. The winds had been from the southwest for a couple days and had apparently blown the spores to this northern shoreline.
The following day I was approached by two different individuals who asked about cream-colored or orange-colored layers they had seen on lakes near their particular homes. A day later, while fishing the Kenai River below Skilak Lake, I encountered thinner layers of the orange mass floating downriver. Because the brightly colored collections of spores have recently been seen on Skilak Lake, Arc Lake, the Kenai River and other lakes, I decided to revisit the topic of spruce needle rust.
The particular fungus has been reported in Alaska for many years in a variety of locations. One common theme seems to be that the outbreaks appear more often when the weather has been cool and damp. Does that sound like what we have seen this summer?
This particular rust, Chyrsomyxa ledicola, alternates hosts by infecting Labrador tea plants and then infecting spruce trees. Interestingly, those areas on the south side of Skilak Lake where I found the heavily infested trees were also areas where Labrador tea was a common undergrowth plant.
When a spruce tree is infected, generally the newest needles from this spring’s growth are injured. The needles turn yellow and lesions start to appear on the surface. Masses of bright orange spores are formed by spermatagonia within the lesions. The spores pile up and are briefly held together by a thin layer of plant tissue. These piled-up spores are what cause the needles to appear to have tiny lumps on them. Eventually the mass of spores breaks free and gets blown around by the wind. When I put samples from Skilak Lake under the microscope, the orange mass floating was nothing more than masses of these orange spores.
The infected needles will eventually wither and drop off, but this loss is apparently not lethal. New growth will come the following year from the surviving apical meristem (branch tip). Spruce trees are able to bounce back after even several years of continuous infection, since the majority of the photosynthesizing needles are not impacted.
I looked around my yard and found numerous spruce trees with obvious infections. Over the next few weeks, keep a lookout for yellowing needles on your spruce trees and large spore aggregations on our local water bodies. Also remember that these aggregations of spores can result from spores that were released a long distance from where they are spotted. Don’t worry too much about these infections doing permanent damage, though. These infections are dramatic-looking, but rarely damaging enough to kill the tree.

David Wartinbee, Ph.D, J.D., is a biology professor at Kenai Peninsula College’s Kenai River Campus. He is writing a series of columns on the biology of the Kenai River watershed.

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Posted by on Sep 5th, 2012 and filed under Point of View. You can follow any responses to this entry through the RSS 2.0. Both comments and pings are currently closed.

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