Developing flower bud of a hybrid tree peony (Paeonia suffruticosa Reine Elizabeth) photographed in Norfolk UK in May. The picture shows a bud infected with the fungal pathogen Botrytis; in a healthy bud, the scales covering the bud, and those to lower left, would be green in colour. Here, the bud itself is covered with grey sporangia of the fungus. Two species of Botrytis commonly infect garden peonies. B. cinerea (grey mould, here) tends to infect aerial parts of the plant, especially flower buds. B. paeoniae infects foliage lower down on the plant. Both are more prevalent when the Spring season is wet, and when air movement around the plant is restricted due to adjacent plants. Treatment by the stage illustrated in this picture is futile; the bud will not develop and should be removed. B. cinerea is a very common but not a catastrophic disease; in dry years it will not appear.