Not sure they are a disease, but they are certainly a pest.
The next plot to mine has been empty for some years. So for several years one of the other plot holders has borrowed my strimmer and strimmed it annually before the thistles seeded. However, at the beginning of last year he had returned to Eastern Europe and I was ill so the thistles flowered and then....
So my plot was filling up with thistles.
I almost gave up, but with the onset of the virus I thought growing veg would be a good idea.
Lots of new people have taken plots but they all turned down the thistle plot.
So in the end I took it on, and my husband spend the first month of the lockdown digging it over.
Since then I have pulled up more than 1000 thistles. But they have underground rhisomes so as soon as you pull them up they pop up with more. Pull up one, and two appear and then there is a row of them.
I planted the plot with courgettes and pumpkins which I know discourage weeds. But it seems that creeping thistle are exempt. (as are nettles, comfrey, fat hen) Though the couch has not put in as much of an appearance as I had feared.
So the question is how do you get rid of creeping thistles? They are the ones with small pinkish flowers.
The farmers sprayed some of the thistles near the hedge with some weedkillers but this seems to have stayed in the soil and a few of my squashes and courgettes are not best pleased. I managed to move several, and once the soil is washed off they are doing well and producing normal non pointed leaves.
In general the plots is growing things superbly. Several people have been annoyed they did not choose the plot. In order to be quick, I dumped piles of manure and then planted four pumpkins, squashes or courgettes round each pile. Hopefully they keep the moisture in the soil, so less water is needed. With the recent rain the plants have now taken off big time, but so have the thistles.
I also have dwarf beans and thistles, carrots and thistles, a flower border with assorted thistles, tomatoes, cucumbers and chillis with thistles, and baby corn with thistles. I pull up 50 a day but that is not enough.
And horseradish!! That needs to go too but is in the middle of the raspberries.