Rust on groundsel
Observation - Rust on groundsel - UK and Ireland. Description: A young, small, weedy Groundsel, Senecio vulgaris, self-seeded in a backyard plant-pot in which pans
A young, small, weedy Groundsel, Senecio vulgaris, self-seeded in a backyard plant-pot in which pansies were growing earlier in the year.
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The Groundsel has clusters of crown-shaped orange structures, which I understand are aecia (the spore stage I), on the upper side of its leaves (none, as yet at least, on its stem). On the underside in the corresponding positions are smaller orange structures.
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In addition, right across the leaf surface there are a great many small creamy-white marks, which held against the light or magnified appear as pale, almost transparent blisters. These break open at one small point at their edge. I assume these are also a result of the rust pathogen.
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The leaves also have a few small Chromatomyia fly leaf-mines; this Agromyzid is rampant on Sonchus oleraceus in adjacent plant-pots, from which it has spread to the Groundsel.
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UPDATE 12 Jan 2020: I brought my potted Groundsel indoors so as to take more photos. The Groundsel, which is only about 4" high, is doomed. Several of its young leaves have died back. New aecia have now appeared on the main stem and the bases of the petioles.
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In addition, some of the white blisters, which I wondered might be the albugo or white rust Pustula tragopogonis, which is commonly found on Groundsel, have matured and split open and rolled back on the undersides of leaves. New pustules have appeared on the previously unaffected leaves, indicating that the infection is systemic. Moreover, some of the older blistered leaves now have what appear to be white fungal threads with an occasional dispersed black smuttiness on their surfaces. I am unsure how to interpret this, not being a mycologist, but my intuition is that there are two pathogens involved.
.
The Groundsel has clusters of crown-shaped orange structures, which I understand are aecia (the spore stage I), on the upper side of its leaves (none, as yet at least, on its stem). On the underside in the corresponding positions are smaller orange structures.
.
In addition, right across the leaf surface there are a great many small creamy-white marks, which held against the light or magnified appear as pale, almost transparent blisters. These break open at one small point at their edge. I assume these are also a result of the rust pathogen.
.
The leaves also have a few small Chromatomyia fly leaf-mines; this Agromyzid is rampant on Sonchus oleraceus in adjacent plant-pots, from which it has spread to the Groundsel.
.
UPDATE 12 Jan 2020: I brought my potted Groundsel indoors so as to take more photos. The Groundsel, which is only about 4" high, is doomed. Several of its young leaves have died back. New aecia have now appeared on the main stem and the bases of the petioles.
.
In addition, some of the white blisters, which I wondered might be the albugo or white rust Pustula tragopogonis, which is commonly found on Groundsel, have matured and split open and rolled back on the undersides of leaves. New pustules have appeared on the previously unaffected leaves, indicating that the infection is systemic. Moreover, some of the older blistered leaves now have what appear to be white fungal threads with an occasional dispersed black smuttiness on their surfaces. I am unsure how to interpret this, not being a mycologist, but my intuition is that there are two pathogens involved.