Hydrangea Black Spot

Question

Hi – Black spot has appeared on a young hydrangea plant that hasn’t flowered yet over night. I was a bit confused with your advice – should I spray Neem Oil spray on the infected and non-infected leaves and leave it? or should I remove all infected leaves and just spray Neem oil on the non infected ones? Thanks

Answer 1

If you have just a few infected leaves, go ahead and remove them, they will fall off anyway. If there are too many to remove at once, go ahead and spray the whole plant. When leaves fall, be sure to pick them up and discard.

https://www.gardeningknowhow.com/plant-problems/disease/black-spot-fungus.htm

Answer 2

Truly black leaf spot is a leaf spot fungus that develops in rainy periods or when hydrangeas are hit with frequent sprinkler irrigation. It does not harm the plant although it can look pretty awful at times. The fungus does not spread to other plants. As previously mentioned, you can cut off the worst of the leaves (dispose of them in the trash) and modify your sprinkler settings so that the unit waters deeply but less often and does so around 6-8am.

Caution... some people sometimes refer to "dark" colored leaf spots as black leaf spots when they are technically not "black". If the above description of black leaf spot does not sound applicable to your problem, please re-post with several pictures. Examples of dark leaf spots:

* Cercospora leaf spot is another leaf spot fungus that produces somewhat round spots that with a dark halo that may be more of a dark purple than black or dark brown than black. It is common after the Summer Solstice.

* Bacterial leaf spots are often angular, and concentrated along leaf veins or margins. Cool, wet conditions favor leaf spots so it occurs in Spring or early Summer typically (rare in the Fall).

* Anthracnose leaf spots are more dark brown spots than black leaf spots whose center turns tan. Wet, warm conditions promote this problem but it is rare in homes. More common in greenhouses.

Note that green leaves produce food for the roots so avoid removing "too many" green leaves. In the summer months, the plant may not be in the mood to be developing new foliage quickly. In the Spring, replacement foliage may develop in 2-4 weeks.