Mildew on Stinging Nettle

Hi,

The powdery mildew found on Stinging Nettle is Erysiphe urticae (out of 190 British records 189 are this, and just one very old record as E. trifoli – usually on legumes). A lot of the time these powdery mildews are just made up of conidia, which are hard to tell apart in different species. If you can get the tiny fruiting bodies then they are quite beautiful under the microscope and can give you a more accurate ID, but they don’t always appear.

There is a similar-looking powdery mildew on Dead Nettle and Hemp Nettle:

https://www.flickr.com/photos/33485842@N08/21591576680/in/photolist-yTYtvs

Here is a fruiting body of the powdery mildew on Berberis:

https://www.flickr.com/photos/33485842@N08/6047051680/in/pho … cfM-6CUV4Y

You have to be careful that it is a powdery mildew and not some other white substance. I was caught out by white dustings on Stinging Nettle on the edge of the lanes in our allotments – it turned out to be fine limestone dust from the newly laid surface. Leaves with bird droppings are brought to many a leader on a fungi walk!

Powdery mildews and rusts are great to look out for – but a microscope is really essential as there can be several species on one plant host.

Unfortunately the M in Mycology stands for Microscopy, as no matter how big some may be, fungi are essentially microorganisms. At least that’s how I’ve always seen it

Cheers,

Steve

. . . Could you recommend the best way of getting the fruiting bodies or spores of rusts and mildews onto a microscope slide?

. . .

Hi Jimmy,

I’m sure Steve will reply if he knows of a better method, but the best way that I’ve discovered so far uses “The Sticky Tape Technique” as described by Debbie Evans on the final page of this HFSG Newssheet: – http://herefordfungi.org/HFSG%20News%20Sheet%20No%2025%20composite.pdf

Note – – Transparent polyester film 850 is available from 3M. It is very thin, unaffected by water, and optically clear. (Cellophane tapes are generally unsatisfactory on all of these counts).

Regards,

Mike.

Hi all

I don’t think this is a powdery mildew (i.e. the Erysiphe).

James gives some excellent field notes:

“The mildew was primarily on the underside of the leaf and in many cases it had caused the leaf to curl and turn black in patches.” [my underlining].

I think this is the Ramularia urticae imperfect state of Mycosphaerella superflua. The ascus-forming stage occurs much later on the fallen dead leaves and is not often observed. The ascus-forming stage of the Erysiphe can be seen (on the underside of the leaves) at the same time as the conidial, white-powdery mildew stage on (predominantly) the lower side, which has sparse coinidia. See Alison’s recent thread here about hogweed mildew). As the fungus takes hold on the leaf the black patches on the upper surface is a good indicator that it’s worth looking (carefully) at the underside, I can see no satisfactory images of this fungus oinline so ‘here is one I prepared earlier’:

[attachment=0]Mycsup0a.jpg[/attachment]

Chris