Five dissimilar diseases that causeyellow leavesand brown spots ordinarily plague hydrangeas , according to Auburn University plant pathologists Austin Hagan and Jackie Mullen . type of root hogwash can also have yellow leave-taking and brown slur in hydrangeas . Root buncombe occur when hydrangeas are planted in poorly drain ground or are overwatered , accord to the US National Arboretum . Yellow leaves may be a symptom of iron want . The higher the pH of the soil ( the more alkaline ) , the less available iron is to the hydrangea . you may lend iron to the land , or increase its acidity ( lowering the pH ) by contribute aluminium sulphate or organic mulch .
Cercospora Leaf Spot
The Cercospora hydrangeae fungus can attack your hydrangea . This fungus come out as rotary brown or empurpled smear on the hydrangea leaves . The spots may turn tan or light gray in the center and are surrounded by a brownish or violet halo . bump off diseased leaves , adding N and surface watering can slow the spread of Cercospora leafspot . Outdoors , rainfall and splash water spread the fungus .
Anthracnose
The Colletotrichum gloeosporioides fungus attacks hydrangea leave and bloom . The fungus prefers intemperately fertilise hydrangeas and raging , wet weather . chocolate-brown spots on the hydrangea leaves may appear like bulls - eyes . As these brown slur grow , they become angulate splotch . This fungus comes from the spores of wet works rubble . Removing fallen and diseased leaves can serve slow up the spread of anthracnose , and protective fungicide treatments every two weeks may help .
Botrytis Blight
Botrytis blight is a gray mold that germinate after cloudy , humid and showery conditions . It unremarkably affects flower petals but this reddish - browned spotting can affect hydrangea leaf . Clearing away debris often and address with antimycotic agent can help prevent the blight .
Powdery Mildew
Powdery mildew circularize quickly in greenhouse hydrangea but is n’t as obvious in landscape hydrangeas . The cottony , white fungus first appears as small white spots on the leave of absence . The E. polygoni fungus that cause powdery mildew may also lead to yellow spots and empurpled blotches on hydrangea parting .
Phytophthora Root Rot
Excess water can cause genus Phytophthora root rot in hydrangea . xanthous leaf and wilt are signs of this antecedent fungus . Plant hydrangea on raised bed to prevent root guff . Fungicides can help foreclose the disease but can not cure it once it ’s established .
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