Editing Hypericum perforatum (section)

=== Diseases ===
''H. perforatum'' is affected by [[phytoplasma]] diseases, and when infected with [[Candidatus Phytoplasma fraxini|''Candidatus'' phytoplasma fraxini]] it shows visible symptoms, including yellowing and deformities called [[witch's broom]]. Its chemical profile is also altered: naphthodianthrone, [[flavonoid]], [[amentoflavone]], and pseudohypericin levels are reduced; [[chlorogenic acid]] levels are increased. Additionally, phytoplasma diseases greatly reduce the essential oil yield of the plant.<ref>{{cite journal |last1=Marcone |first1=C. |last2=Bellardi |first2=M.G. |last3=Bertaccini |first3=A. |title=Phytoplasma diseases of medicinal and aromatic plants |journal=Journal of Plant Pathology |date=2016 |volume=98 |issue=3 |pages=379–404 |doi=10.4454/JPP.V98I3.060 |jstor=44280481 }}</ref>

Dieback among populations of St John's wort is also caused by fungal [[anthracnose]], such as ''[[Glomerella cingulata|Colletotrichum gloeosporioides]].'' This fungus causes the stems to lose their bark ([[girdling]]) and turn brown, and dries the aboveground parts of the plant. The infection often kills the plant within the first year of its growth, or reduces productivity over a three-year deterioration.<ref>Ernst 2003, pp. 23, 41.</ref>