The ideal time to go looking for pathogens in woodlands is Spring. Many species affect spring ephemeral plants, which are only visible for a few months early in the year. Here are a few common species to look out for, arranged by host. I have also included here species of hedges and scrub like Nettles and Bramble.
Extremely common. Look for yellowed, vein-delimited leaf spots with large black pycnidia. Generally each spot has one to four pycnidia. Later, a cylinder of spores is squeezed out of the pycnidium by pressure — see the pictures on the Plant Parasites of Europe database.
Somewhat common. Look for large yellowed vein-delimited patches with white conidiophores on the underside. Related taxa on other Apiaceae are often lumped under this name.
Widespread and common in Britain. The host plant is essentially extinct in Ireland and “doubtfully native” anyway1.
Common and easy to spot. Forms blackish brown telia in distinctive rings.
Very common but subtle and difficult to spot. It causes the adult leaves to be slightly dwarfed, yellowed, and downturned (left). It is easier to find in dense aggregations of seedlings in the late autumn and winter, when it causes yellowing and mealy brownness on the cotyledons (right). In both cases beige conidiophores are visible on the underside. Often these are not very dense (middle) so you should check with a hand lens.
A downy mildew that forms whitish conidiophores on the underside of the leaves. Look for yellowed, downturned patches on the leaves.
A rust which forms whitish aecia on the undersides of the leaves. Look out for very tall, thin, slightly yellowed leaves.
This is an extremely common species, almost ubiquitous in Ireland wherever the host is found. The upper leaves show yellowed spots and turning the leaf over reveals the white underneath, which is actually made up of tiny conidia.
This rust only forms blackish brown telia, distinguishing it from other rusts on this host, which only form aecia.
Aecia of the rust species Uromyces rumicis and U. poae are both found on Ficaria, but they cannot be distinguished without high-powered microscopy. They should all be recorded as Aecidium ficariae. There is another rust, Uromyces alpinus (=Schroeteriaster alpinus), that forms aecia which are colourless according to Plant Parasites of Europe.
For more discussion of distinguishing the two species see Zwetko & Blanz (2012)2.
Look out for yellowed leaves which are slightly curled downwards and often slightly taller than uninfected leaves. On the underside you will find brownish conidiophores.
Orange aecia and blackish telia with large teliospores that are visible to the naked eye and very distinct under a hand lens. Extremely common but diverse and the many species are rather difficult to distinguish. They are reasonably host-specific: Phragmidium on Raspberry Rubus idaeus can be distinguished as Phragmidium rubi-idaei but Roses and Brambles each have multiple species that generally require microscopy. Apparently Phragmidium violaceum on Brambles Rubus fruticosus agg. can be distinguished by purple discolouration of the leaf. For more information including spore measurements check the Plant Parasites of Europe database.
Somewhat common but very distinctive. Patchy, dark grey leaf spots above, with dense, distinctly “floury”-looking conidia below.
This is actually a complex of different species, each of which has a telial stage on a different sedge. On Nettles they are all identical, forming clusters of orange aecia on leaves and petioles. Somewhat common and very distinctive where the host is found alongside sedges.
Common. Look for enclosed ‘pouches’ which the larvae develop inside. Don't confuse with D. dioicae!
In constrast to D. urticae, the larvae of this species are rolled inside the leaf but not fully enclosed within the tissue itself.
