What’s Wrong with My Hydrangea? Learn to Recognize and Treat Common Diseases

Learn how to diagnose and protect your hydrangea from common diseases

Hydrangeas ( Hydrangeaspp . and cvs . , Zones 3–9 ) are timeless favorites of gardener everywhere , but these dear shrubs are also favored by a panoptic variety of pathogens . as luck would have it , there are many preventive measures we can take to keep our works good , and knowing the signs and symptom of common disease can help us make a prompt and accurate diagnosis when disease does strike . With a little planning , research , and appropriate action when need , you could keep your hydrangea hefty and flower for many years to come . Here are some of the most common hydrangea ailments , their signs and symptoms , and urge direction strategy .

Bacterial spot causes black , angular situation on both sides of the foliage . These spots may be fence by yellow halo and generally seem first on inner leaves at the bottom of the works .

Other time , are not beleaguer by the white-livered halos .

Bacterial spot

Cause : Xanthomonas campestrisbacteria

symptom and signs : Angular foliage spots first appear in the inside , lower canopy of the plant life , often when the atmospheric condition turns ardent and wet . Unlike fungal leaf spots , the discolorations are black and angular , and they pass off on both topand bottom slope of the leaf . The spots sometimes have a scandalmongering halo . Bacterialspot is commonly misidentified as Cercospora leaf spot ( p. 22 ) on oakleaf hydrangea ( H. quercifolia , Zones 5–9).Microscopy or more advanced science laboratory technique may be needed to correctlydiagnose this job .

direction : Bigleaf hydrangeas ( H. macrophyllaand cvs . , Zones 5–9 , smooth hydrangeas ( H. arborescensand cvs . , Zones 3–9 ) , and oakleaf hydrangea are mutual hosts , but all members of the genus are susceptible . This bacteria is propagate by water and enters injured tissue . To reduce its cattle farm , avoid overhead watering and work around plastered plants . Copper - based product are often suggested for treatment but are only marginally in effect ; this sonorous metal will build up in the soil over fourth dimension and can cause phytotoxicity problems if aluminium is used to acidulate the soil . For these reasons , it is best not to utilise copper - based products to control bacterial spot .

In a more serious casing , discolouration and rot will spreadto stem turn and shoots ( above )

Discoloration is the primal sign of botrytis blight . Blotchyflowers and bracts ( inset ) are former indication of transmission .

Botrytis blight, or gray mold

drive : Botrytis cinereafungi

symptom and signs : Tan to brown blotchesappear first on bracts and flowers ; these stain may become covered in lightgray or taupe mould under high humidity . Insevere cases , the fungus spreads from blighted flowers to shoot and stems .

Management : Botrytis blight tends to be mostproblematic when the weather is nerveless and wet , often in bounce and fall . Avoid overhead watering , excessive N fecundation , and injuring industrial plant , which predispose hydrangeas to infection . While bigleaf hydrangeas are often bear on most severely , most metal money are susceptible . Thinning and pruning plants to open up the canopy improves flow of air anddiscourages botrytis infection . Fungicides that contain captan or chlorothalonil are effective ; to protect pollinators , avoid apply these to bloom plants .

Powdery mildew

Cause : Several metal money of fungi , includingErysiphespp . ,Golovinomycesspp . , andMicrosphaeraspp .

Symptoms and signs : The first foretoken to come out are small , fuzzy , white patches on the upper foliage airfoil . Upon closer scrutiny , threadlike growth ( hyphae ) is visible on the folio open . afterward in summer , small black “ ball ” develop within the hyphae that protect the fungous offspring in a thick shell that will make it the winter . In terrible instance , infected leave will twist sensationalistic and drop .

direction : Bigleaf hydrangea are most susceptible to powdery mould , while oakleaf hydrangeas seem to be more resistant . keep plant well watered to denigrate drought focus and ageing also protects against powdery mold . plant do best when they are located in a land site with morning sunshine and afternoon shade . in force fungicides for controlling powdery mildew include sulfur , myclobutanil , tebuconazole , and triticonazole .

Cercospora leaf spot cause scarlet - purpleness discoloration on foliage . The spots are more rounded on bigleaf hydrangea ( top )

and more angular on oakleaf hydrangea ( bottom ) .

Cercospora leaf spot

Cause : Cercospora hydrangeaefungi

Symptoms and signal : symptom of Cercospora leaf smear are most dramatic on bigleaf hydrangea , but smooth , panicle ( H. paniculata , Zones 3–9 ) , oakleaf , and mountain hydrangeas ( H. serrataand cvs . , Zones 6–9 ) are also hosts . As with many foliar disease , the symptoms are first observed on the interior leaves near the groundwork of the plant . On bigleaf hydrangeas , these spots have a round , reddish - purple halo surround a tan to grey lesion , whereas reddish - purple angular leaf spots develop on oakleaf hydrangeas . If an contagion becomes severe , to a great extent afflicted leave may deform yellow before falling off . Unlike many foliar diseases , Cercospora is worse on plant life grown in full sun .

direction : Proper location of plants — specifically , providing afternoon nuance — is a critical constituent in cope this disease . Avoid overheadwatering to reduce the spread of the pathogen . Researchers at Tennessee State University found that these varieties of bigleaf hydrangea were kind of or immune to Cercospora : ‘ Ami Pasquier ’ , ‘ Ayesha ’ , ‘ forever and a day Pink’,‘Fuji Waterfall ’ , ‘ Seafoam ’ , ‘ Taube ’ , ‘ Tricolor ’ , and ‘ Veitchii ’ . Resistantmountain hydrangea varieties include ‘ Bluebird ’ and ‘ Miyama - yae - Murasaki ’ , which can even be grown in full sun . Although integrated direction using fungicides is possible , most gardener do n’t want to apply fungicides every few weeks or whenever loaded weather go on . Fungicides containing chlorothalonil , copper , triticonazole , or propiconazole are effective when apply before symptom development to keep infection . To protect pollinator , spray susceptible foliation only and keep off any flower .

The symptoms of viruses vary widely . A plant infect with hydrangea chlorotic mottle computer virus ( will ) may exhibit foliage stain or distortion .

While a plant life with hydrangea ringspot computer virus may exhibit irregular growth or distinctive yellow spotting on leaves .

Viruses

causal agent : At least 17 reported viruses , including aster yellows

symptom : plant with a virus contagion may display leaf yellowing ( greensickness ) , mosaic , greensick and/or necrotic ringspots , leaf mottling and distortion , splodge , stunt , and sometimes bloom virescence ( flower revert to flick development ) . Some viruses , like tobacco rale virus or tomato spotted wilt disease virus , may impact the appearance and health of the plant . However , many virus are latent ( endemic to the plant)and cause only flimsy symptoms or none at all . A latent viral contagion may even protect against other , more serious viruses .

Management : There is no treatment or cure for hydrangeas infected by a computer virus , butit is crucial to name which virus is infecting a plant life and to reduce the facing pages of nonlatent viruses . Some nonlatent virus , like tobacco rale virus and tomato spotted wilting virus , have full host mountain chain and involve hundreds of plant species . Insects and roundworm act as as vectors , spreading the virus to other plants in a garden . If you suspect a plant has a viral transmission , work with your local diagnostic science lab to identify the virus so you’re able to then put through an appropriate management scheme ( either tolerate the infection or removing the flora ) . instead , you may choose to simply take away and demolish the septic plant to reject any risk of spread by louse , nematode , or human vectors . Although this scheme sounds harsh , I have been in garden where almost every plant is infected with tobacco plant mosaic or baccy rattle computer virus . lose one plant life is heartbreaking , but it will be a worthwhile forfeiture if it protects the rest of your garden .

More hydrangea resources for diagnosing and treating diseases

Janna Beckerman , Ph.D. , is a prof and extension plant life pathologist at Purdue University specializing in diseases of horticultural harvest .

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Bacterial spot causes black, angular spots on both sides of the leaf. These spots may be surrounded by yellow halos and generally appear first on inner leaves at the bottom of the plant.

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Bacterial spot causes black, angular spots on both sides of the leaf. These spots may be surrounded by yellow halos and generally appear first on inner leaves at the bottom of the plant.

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Other times, are not surrounded by the yellow halos.

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In a more serious case, discoloration and rot will spreadto stems and shoots (above)

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Discoloration is the key sign of botrytis blight. Blotchyflowers and bracts (inset) are early indications of infection.

Dusty-looking leaves are a sign of powdery mildew. These fungal infections can be unsightly and may even cause some foliage loss, but they are seldom fatal to the plant.