P. chrysanthemi is a new disease not yet detected in the UK, but growers of Chrysanthemum need to be aware of this new threat, says APHA.
First described from Japan in 2010, it has subsequently been detected in Croatia and the USA. An outbreak in Germany is under official control.
Main symptoms are dieback of the root system, wilting and necrosis or black rot which affects the stem.
Infected plants can exhibit reduced growth, chlorosis, vein reddening and dieback (partial or total). In Croatia, symptoms were considered very similar to those caused by Pythium spp.
APHA has also warned about Xylella, saying high risk hosts include olive, Nerium oleander, Lavender and Rosemary."
Oak processionary moth and phytophthora ramorum are other concerns, as are pests yet to reach the UK: Popillia japonica, emerald ash borer and lime tree leaf miner.
APHA says warnings are for grower awareness and "if you suspect or find these pests, please notify PHSI or Forestry Commission".