Monday, March 23, 2015

Are all types of black spots on Hoya signs of diseases by fungal infections ?

What are these black spots on the Hoya leaves ?
Botrytis and Rhizoctonia are commonly cited as fungal infections of Hoya.
On the picture above these small pots on the leaves may be caused by fungi that are not Botrytis ( Botrytis are typified by large grayish areas on leaf margins or centers ) . We have not noticed that such spots were associated with weakness or death, stem or root rot (Phytophthora, Pythium and Rhizoctonia spp.).

We might also conjecture that these tiny dark spots have a neutral or positive role regarding the immune system of the plant. Overuse of pesticides and other artificial conditions of growing may impart Hoya plants a nice look, green leaves without defects but in reality they are weakened because their immunity is not boosted as in a natural environment.

Black spots can also be anthocyanins that protect against light exposure after leaf cell damage.

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