I was surprised to find yellow banding on a few of my pines this fall. It’s not something I’ve seen much of in my garden over the years so it caught my attention when small yellow patches appeared.
Yellow banding on black pine needles
The overall health of the needles is good, and the damage is limited to a handful of needles per shoot. The photo below shows the most extensive banding.
Keen to find out what might be the cause, I sent a sample to Waypoint Analytical.
A few weeks later I got the result, but it wasn’t what I’d expected. Banding is the primary symptom of needle cast diseases, but the samples I sent were free from foliar pathogens. The banding was an abiotic symptom.
I’d also sent a sent a sample of the roots, and that’s where a candidate pathogen showed up.
The lab isolated a species from the Cylindrocarpon genus. Many species of Cylindrocarpon aren’t plant pathogens. Some, however, form parasitic relationships with their host and may be cause symptoms like the banding in my pines. As the sample the lab examined showed root rot in the feeder roots, there’s a chance Cylindrocarpon was the cause.
Cylindrocarpon hasn’t been extensively studied, so it’s not clear which fungicides are most effective controls. While I research my options, I’ll plan to repot the affected trees this winter in a drier mix – one with larger soil particles and/or less akadama.
Here’s what the tree that provided the samples looks like.
Fifteen-year-old black pine
I’d last worked on the tree in spring (see “Multiple sacrifice branches” for details). Now that it has filled in with summer growth, it’s time to thin crowded areas by removing unnecessary shoots and needles. Here’s the tree after this work.
After cutback and needle plucking
Close up of the future trunk
I plan to use a smaller container when I repot which will make it easier to keep the tree on the dry side. In the meantime, I’m allowing it to dry out between waterings to avoid additional stress on the roots.
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