| Witches' brooms in a fir tree are caused by fir broom rust (Melampsorella caryophyllacearum). Blueberries are an alternate host. Here's a brief description of the lifecycle: Rust spores (teliospores), are produced on swollen infected blueberry shoots, germinate on these shoots to produce another spore type (basidiospores) from mid May to late June. These spores are carried by wind to balsam fir trees where the current season growth becomes infected. The peak discharge of basidiospores on blueberry occurs for a 3-week period in late May to mid-June. Following the infection of fir, a new spore type (aeciospores) are formed on the needles and these are then wind blown to blueberry where they germinate on leaves and stems. This occurs during mid to late summer. I can't vouch for whether or not the brooms are good luck charms. Hope this answers all your questions! |
