Septoria musiva
It is native on the eastern cottonwood poplar Populus deltoides, causing only a leaf spot symptom.
On susceptible hybrid poplars, S. musiva causes necrotic lesions on the leaves which lead to premature defoliation, and cankers on the stem and branches which can reduce growth, predispose the tree to colonisation by secondary organisms, and cause stem breakage.
[3] Sphaerulina musiva is distributed in northeastern North America sympatrically with the native eastern cottonwood P. deltoides, on which the disease is limited to a leaf spot symptom.
[3] These endemic leaf spots on P. deltoides are believed to constitute a source of inoculum for hybrid poplar plantations.
[4] S. musiva has sometimes been reported on Tacamahaca poplars indigenous to North America (P. trichocarpa and P. balsamifera) and on their hybrids.
For example, in 2006, a high incidence of stem infections caused by this fungus was observed on P. balsamifera in a plantation within its native range in northern Alberta.
[5] Until 2006, plantings of potentially susceptible clones in the Pacific Northwest region of North America remained free of Septoria canker disease but since this date, cankers caused by this disease have been observed on a regular basis in two hybrid poplar nurseries located in the Fraser Valley of British Columbia.
It attacks from the bottom up of a poplar tree, because the main source of the infection (the dead leaves) are lying on the ground.
The infection begins to spread up the host to the top branches, creating leaf spots and cankers where ever it can.
In the spring the wind picks up the Pycnidium S. musiva spores and it carries them to find a new host to start the infection all over again.
[citation needed] S. musiva affects fitness in two ways, depending on how it manifests itself, either as a leaf spot or a canker.
Population genetics approaches suggested that dissemination of the pathogen appears to be associated with the natural distribution of wild P. deltoïdes[4][8].
This is helpful for the future, however it does not solve the current problem of dealing with the infection of the already planted poplar trees.
[13] Sphaerulina musiva was first documented in 1923 in the Northern part of the United States by Johnson and Cobb, both of whom were with the US Department of Agriculture.
