Calendula rust: Puccinia lagenophorae

Powdery orange rust, Puccinia lagenophorae on Calendula officinalis

Calendulas, which are sometimes give the name English marigolds, are at their peak of flowering from mid to late winter and into spring. The recent warm humid and showery weather means they are more susceptible to getting this rust disease, which is thought to originate in Australia on several native plant species, but is now fairly widespread across the world. The plants lose vigor and rapidly decline in appearance with leaves often turning black as the rust spores mature.
Nothing to be done but pull the Calendulas out and dispose of in the bin. One of the weed hosts of this rust is the common groundsel bush Senecio vulgaris. This weed is fairly common in horticultural crops and I was interested to read that the rust is being used as part of a new strategy in biological weed control in Europe. Scientific research papers can be viewed if you Google Puccinia lagenophora.