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50 Metres of Roadside #wildplantdisease – A blog written by Dr. Fay Newbery

18th August 2020

My original idea for this blog was ‘To the village and back’. In the lead-up to the #wildplantdisease challenge I heard someone say: ‘There won’t be much disease around at this time of year.’ I guess I like a challenge! I thought I’d walk the half mile into the centre of our tiny village in mid-Wales and spot as many plant diseases as I could. But after 50 metres and 17 different pathogens, I decided I’d proved that there was plenty to see.

Now, I’ll admit, I’m most interested in fungal pathogens – fungi that cause diseases – so that’s all I spotted. I bet there were viruses out there too and maybe some diseases caused by bacteria but I just don’t have my eye in for those.

Most of what I saw were rusts (seven species) and powdery mildews (six species). But there were other diseases too:

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  • 1. Bramble (Rubus fructicosus agg) infected by the rust Phragmidium violaceum causing purplish-red spots on the upper surface (and yellow and black pustules beneath depending on the time of year).
  • 2. Red campion (Silene dioica) probably infected with the rust Puccinia arenariae. This should have been checked with a microscope though as Puccinia behenis also occurs but is not as commonly seen.
  • 3. Bramble (Rubus fructicosus agg) infected by the rust Phragmidium bulbosum causing yellow spots on the upper surface (and yellow and black pustules beneath depending on the time of year). The colour of the spots is not totally reliable for identifying the rusts on brambles, especially as a third rust occurs which causes yellow spots, but it’s a good starting point.
  • 4. Willow (Salix sp). Just as willows can be difficult to identify, they are also hosts to multiple rust species which are really difficult to separate. But all the rusts are species of Melampsora so I can get that far.
  • 5. Greater periwinkle (Vinca major) infected by Puccinia vincae. This rust causes infected leaves to roll upwards from the sides. It infects all the tissues in the shoot and prevents flowering.
  • 6. Field rose (Rosa arvensis). This is another plant infected by more than one species of rust fungus. When checked, the yellow and black pustules on the underside of this leaf belonged to Phragmidium mucronatum which is the most common culprit.
  • 7. Navelwort (Umbilicus rupestris) infected by Puccinia umbilici. This disease was really widespread early in the spring causing heavily infected, and often deformed, leaves. Then the drought in May saw all the leaves die but, the recent weeks of rain have produced regrowth and the fungus is back again having survived as spores on leaf debris.
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  • 8. Sycamore (Acer pseudoplatanus) infected by Sawadaea bicornis. A second powdery mildew fungus also infects sycamore and has been found in the village but Sawadaea bicornis is the most common.
  • 9. Oak (Quercus sp) infected by Erysiphe alphitoides.
  • 10. Willowherb (Epilobium sp) with pods infected by Podosphaera epilobii.
  • 11. Red campion (Silene dioica) infected by Erysiphe buhrii.
  • 12. Hogweed (Heracleum sphondylium) infected by Erysiphe heracleid.
  • 13. Greater plantain (Plantago major) infected by Golvinomyces sordidus.
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  • 14. Tar spot, cause by the fungus Rhytisma acerinum on Sycamore (Acer pseudoplatanus).
  • 15. Leaf spot on Primrose (Primula vulgaris). There are a number of fungi that can cause leaf spots on Primula species. This is likely to be one of the two Ramularia fungi that I’ve found previously in the village. Either Ramularia interstitalis or Ramularia primulae.
  • 16. Leaf spot on Stinging nettle (Urtica dioica) caused by the fungus Ramularia urticae. On the back of the leaf, each spot is covered by a white felty layer which is made up of hyphae and spores.
  • 17. Another leaf spot disease caused by a Ramularia species. This time Ramularia duesta which is common on sweet peas but here is on Everlasting pea (Lathyrus latifolius). I wonder if this infection is why the plant hasn’t flowered this year.

Seventeen diseases seems like a good haul in such a short distance but I was disappointed not to find any galls caused by Taphrina species or any Downy mildews. Why so much disease in such a short distance? There are probably two major factors at work here. Firstly, it’s approaching the end of the season for some of these plants, such as the Red campion, so the leaves are old and lacking in vigour. And, secondly, this is a stressed environment. The plants are growing either on a wall with little depth of soil, or they’re right at the edge of the tarmac. They’ve all been subjected to drought and high temperatures; many of them are being physically damaged as cars pull over on this narrow road to pass each other; and they’re all having dust from the road surface deposited on their leaves restricting photosynthesis.

Blog written by Dr. Fay Newbery, BSPP member and plant pathologist at the Royal Horticultural Society as part of the #wildplantdisease theme this week. Follow Fay on Twitter.