Rust spots on hydrangea leaves

Hydrangeas are generally pest and disease free, but when your flowers are looking less than stunning, it’s hard not to panic.

Learn about common hydrangea problems and fix them. Your plant will be back to blooming in no time.

Hydrangea Pests

1. Scale: One of the most common pests, scale can best be identified by their clusters of white eggs on stems. Treat with Insect Control.

2. Slugs: Slugs attack young hydrangeas especially. Look for holes with ragged edges in leaves. The best way to know if slugs are the culprit is to go out and check plants at night. Lay slug traps around plants.

3. Aphids: If you see small black or green bugs on leaves you may have aphids. Treatments include gently spraying leaves with a hose or spraying with Insect Control.

4. Beetles: From Japanese to Rose chafers, beetles are known for eating petals and leaves. Handpick beetles and drop them in soapy water or spray with Insect Control.

5. Fruit Worm: If you see holes in the leaves of mature hydrangeas, you may have fruit worm. Check the underside of the leaf for this caterpillar-like bug. Knock them off and check leaves for eggs.

Hydrangea Diseases

Black Spots: In extra wet conditions, a leaf-spot fungus may appear. Don’t worry, it doesn’t harm the plant and new growth shouldn’t have spots. If black spots appear in dry conditions, you may be overwatering your hydrangea.

Powdery mildew: While this doesn’t usually kill hydrangeas, it can cause leaves to drop. Look for a gray, powdery coating on foliage. Remove and destroy any affected plant parts. Apply Neem Oil 3n1 as needed.

Rust: This fungal disease looks like rust colored spots on the underside of leaves. The tops of leaves turn brown or yellow and eventually fall off. If the problem isn’t severe, prune off and destroy the affected leaves. Otherwise, use a rust specific organic fungicide such as Neem Oil 3n1.

To prevent many diseases, use a soaker hose or spray nozzle to water the roots of plants. And water in the morning, so any water on the leaves has a chance to dry.

Additionally, many problems are a result of lack of water. If flowers turn brown and die quickly or leaves have brown, brittle spots around the edges, you may be under watering.

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Still have questions about getting your hydrange to bloom, pruning or more? Learn all of our hydrangea secrets in our hydrangea growing guide.

A basic guide to pests and diseases that effect Hydrangeas!

Last Updated on August 1, 2019

Hydrangeas are well known for there large impressive showy flowers and ability to change their flower colour from pink to blue because of the soil type.

Hydrangeas are generally pest and disease free but as with all plants sometimes they can be affected by diseases or pests. We have put together a list of the most common diseases and pests which you can refer to and try and identify any problems you may have.

Pests that may effect Hydrangeas

Hydrangeas are generally not affected to badly by pest but they can sometimes be affected by a handful of insects and other pests.

  • Aphids: These come in many forms and all though they are unlikely to kill a plant they can cause the leaves to curl by sucking the sap from the leaves which also leaves honeydue on the leaves that is a waste product of aphids. This can then lead to fungus forming on the leaves and aphids can also spread viruses. Treatments include spraying with general pesticides or for a more organic approach try washing the leaves with soap. The soap clogs the pores of aphids and kills them.
  • Rose Chafers (beetles): Rose chafers are a beetle that is known for eating the flowers blossom of Hydrangea leaving small holes in the petals. They also eat the leaves between the veins of the plant causing further damage. The best organic way to try and prevent this is to check the plants and manually remove them from the plant. Pesticides can also be successful and have more immediate effects.
  • Slugs and Snails: A pest everyone will be familiar with, there are not many plants that not affected by slugs but they will eat fresh new soft foliage. Slugs and can cause in slug traps which catch them at night and are very successful. Another highly successful way is to spread slug pellets around the garden.
  • Hydrangea Scale: Hydrangea scale is probably one of the most popular pests, they are usually identified by there oval white eggs that attach themselves to the stems of the plant. The pest such the sap from the plant and cause the plants to suffer and not growth as vigorously as they would. You can try to remove the eggs manually but this is a very hard option and may not be successful. Spraying with a pesticide is probably more effective and needs to be done around mid-July to kill the young nymphs.

Diseases that effect Hydrangeas

  • Mildew on Hydrangea

    Mildew: Mildew is common on may garden plants and Hydrangeas at no exception. Mildew, as pictured left, is common in warm wet weather and is a type of fungus. Plants can be treated with a fungicide and sprayed as instructed in the back of the product packet. Having plants in an area where air can circulate around the plants will help prevent mildew.

Disease Symptoms Pathogen/Cause Management
BOTRYTIS BLIGHT Petals turn brown and fall. Leaf spots form, especially where faded petals have fallen. Flower buds are killed before opening. Botrytis cinerea Space plants to ensure good air circulation. Maintain low humidity. Avoid watering late in the day. Remove crop debris. Apply a fungicide to protect plants.
CERCOSPORA LEAF SPOT Tan spots with reddish-brown halos develop on leaves. Cercospora Apply a fungicide to protect plants. Water in a manner that keeps moisture off the leaves.
POWDERY MILDEW Yellow areas form on leaves. These may become purplish. White, cottony fungal growth forms on the lower surface of the leaf. Erysiphe polygoni Apply a fungicide to protect plants.
VIRESCENCE Flowers are green and may be stunted. Leafy shoots grow from the flower parts. Plants decline and die. Phytoplasma Discard infected plants. Maintain good insect control.
VIRUSES Leaves may be mottled, have yellow spotting, dead flecks, line or ringspot patterns. Plants may be distorted or have flower colour breaking, or few flowers. Hydrangea ringspot, tomato ringspot, impatiens necrotic spot Plant virus-indexed cuttings. Maintain good insect and mite control. Destroy infected plants.

Little lime hardy hydrangeas leaves dying

Your hydrangea is probably reacting to hot, dry weather we’ve had lately, It could well be a combination of issues, it could be normal at this time of year as well.

If you spot holes in leaves, you’re dealing with some hydrangea pests — likely some kind of caterpillar-type critter. A variety of what’s known as “fruit worms” like to munch on hydrangea leaves. They usually hang out underneath leaves, so if you look under leaves, you’ll probably spot the creatures. Knock them into soapy water or use a natural product containing spinosad, a type of bacteria.

On young hydrangeas especially, holes can also occur due to slug feeding. The best way to know if slugs are the culprit is to go out and check plants at night with a flashlight. You can also lay a rolled up newspaper near the base of the shrub. Slugs should crawl into and under it before daybreak, but they might just be visiting the bed, not feeding on the plant. Slug holes usually have ragged edges.

The dry black patches are more problematic, as they can come from both too little and too much water, says the same site:

Lack of water can also cause brown, brittle spots on leaf edges, and a few branches all on one side may die out. Usually this occurs when automated sprinkler spray isn’t reaching the entire hydrangea plant. Flowers that wilt during the day time and don’t perk up at night are also a sign of under watering. Hopefully, you lay mulch down in summer to conserve moisture.

In spring and early summer hydrangea leaves can show black spots, especially during bouts of wet, rainy weather. This hydrangea problem appears severe, but it’s usually just a leaf-spot fungus that doesn’t really harm the plant. When the rainy time ceases, new growth shouldn’t have the spots. If black spots appear during drier times, you may be overwatering your hydrangea shrubs. Hydrangea like morning sun better than afternoon sun btw.

And just a note from http://homeguides.sfgate.com/treatment-spots-leaf-hydrangea-98494.html :

But one thing hydrangeas are sensitive about is water. Keep hydrangeas well-hydrated during dry spells or droughts. Always water them at the base of the plant and never from overhead, especially because leaf spot can be spread through water droplets. The Old Farmer’s Almanac recommends covering hydrangeas in the fall with at least 18 inches of straw, oak leaves (not maple), pine needles or bark mulch. It also recommends building cages out of chicken wire or snow fencing around the plants and filling them with leaves so the plants are covered for the winter, thus preventing damage from any frost.

Hope this helps.

Last Updated on March 25, 2019

The deep green foliage of the hydrangea is as attractive as the bright bulbs of blooms to many gardeners. Unfortunately, there are numerous issues that plague the delicate equilibrium needed to keep the leaves of the hydrangea lustrous and healthy. Although disease and attacks by insects are common, another problem is one with a variety of explanations – leaves curling.

If someone must ask themselves, “Why are my hydrangea leaves curling?” they might be surprised by some of the answers. At the end of the day, though, causes can be narrowed down to a few factors: water deprivation, disease, and finicky hydrangea plant types.

A Thirsty Hydrangea

As sturdy flowering shrubs, hydrangeas require a lot of water in well-drained and tended to soil to thrive and survive. Curling leaves are often caused by the hydrangea not receiving enough moisture on a regular basis. When this happens, the cells in the leaves start to die, causing them to become dehydrated, turn brown, and eventually curl from damage. Hydrangeas require so much water that their name is actually a combination of two Greek words meaning “water” and “vessel.” Gardeners who think they are watering these shrubs enough are most likely failing in their duties.

Hydrangeas will absorb water quickly, so it’s important to keep the soil around them moist. Soil that remains well-drained is also important. When a hydrangea is brought inside, it needs to be watered sometimes more than once a day. When outside, hydrangeas can sometimes go two days between watering, but it’s best to check the soil regularly to make sure everything is healthy. If drying and curling leaves are a consistent problem, gardeners should pay more attention to their hydrangea’s water levels. To help prevent the hydrangea from drying out, the shrubs should be planted in an area with partial shade and away from heavy winds.

However, be careful about over-watering hydrangeas. An unfortunate problem that occurs is the development of Botrytis or gray mold in hydrangeas when the sepals are kept too damp.

Diseases that may cause leaf curling

Lots of diseases that affect hydrangeas will harm the leaves. In particular, there are root rot, leaf spots, and powdery mildew. The majority of the diseases which harm hydrangeas will not actually kill the hydrangea but can affect its health and appearance. However, they should still be taken seriously. Some of the most common diseases to watch out for are funguses like Armillaria root rot, which will destroy roots and prevent water from reaching the leaves and blooms. Another common problem is the Cercospora fungus, which will attack foliage and cause leaf curling and death. If a disease is believed to be the cause of hydrangea leaves curling, it’s important to treat the issue as soon as possible.

Sensitive Specimens

Some varieties of hydrangea are difficult to care for because they are sensitive to the slightest change in the environment around them. Taking care of these specimens is far more of a science than an art because everything has to be precise. Some of the most difficult hydrangeas to take care of are the bigleaf and smooth hydrangeas. Both of these varieties need to have more water than any other style of hydrangea. When exposed to dehydration, the leaves of the bigleaf and smooth hydrangeas will rapidly deteriorate. The leaves curl and the stickers start to decay and turn brown. They thrive when given at least one inch of water a week and even more when the weather is hot and dry.

Many varieties of hydrangea also suffer when exposed to the cold. It’s okay when the hydrangeas are dormant and winter comes, but many types, including the aforementioned bigleaf and smooth, do not react well to spring freezes and frosts. Gardeners cannot do much to prepare for late spurts of cold weather, and the return of wintery days can toll the end of hydrangea blooms and cause leaves to start to curl and dry. The most that can be done is trying to keep track of the weather and covering hydrangeas to help protect them from cold snaps when possible with plant protection such as fleece.

Finally, there is the issue of environment. New gardeners don’t consider their soil quality, but experienced individuals know that flowers and other plants won’t grow if they aren’t receiving the right amount of nutrients. It’s crucial to make sure soil possesses enough nitrogen, phosphorous, and potassium to keep hydrangeas happy, healthy, and with uncurled leaves.

Gardeners who don’t want to deal with sensitive specimens should consider investing in more hardy varieties for their garden. One of the best is the panicle hydrangea, which exhibits beautiful pink and white colors and can survive sudden cold snaps. They also don’t need as much water as varieties such as the broadleaf and are not sensitive to pruning.

Pests

If a pest is the cause for a hydrangea leaf curling and turning brown, then it will take a lot of work to get the shrub healthy again. Sometimes leaves start to curl from damage at a cellular level caused by aphids and other unpleasant insects chewing away at the leaves while they are young. This damages disconnects crucial pathways in the leaves that allow for the spread of water and nutrients.

Gardeners who suspect that pests like aphids might be to blame for curling leaves should carefully examine their hydrangeas. Check for holes or corrosion caused by insects eating and their damaging saliva. If some are found, try applying a pest treatment to the entire garden to stop insects from returning. To improve the appearance of the hydrangea, carefully prune and trim away the curled and dying leaves to make room for new ones to grow.

Conclusion

Hydrangea leaves curling happens for a variety of reasons and isn’t always a cause for concern. In the majority of cases, it just means the plant needs more water on a regular basis. If that doesn’t work, make sure the soil and surrounding environment provides the proper amount of sunlight and nutrients. If problems continue, it’s time to look into more concerning causes such as disease and pests. If these are to blame, quick action is needed to save the hydrangea from becoming food for unwanted visitors.

Hydrangea leaftier larva (Photo from Diagnostic Laboratory, Crop Protection, Ministry of Agriculture, Fisheries and Quebec)

Question from V.J. in Cobourg, Ont.

How do I get rid of leaf curl on hydrangea or prevent the leaf curling pest on Annabelle hydrangeas?

Beckie’s reply:

There is a good discussion of the pest you describe on the Toronto Master Gardeners website (torontomastergardeners.ca).

According to their research, the curling of hydrangea leaves could be caused by one of two insects. “The hydrangea leaftier larva binds two or as many as four leaves together with strands of silk into a cup form and then feeds and rests between them,” according to the website. Pulling apart the leaves will reveal a half-inch-long slender green caterpillar with a black head.

The leafroller also causes similar damage, but rolls only one leaf, then feeds and rests within the rolled leaf.

Both insects cause unsightly damage, but won’t harm the shrubs. When you see the damage in early spring, remove the infested leaves and squash the caterpillars. Clean up the ground below the shrubs, too, because the caterpillars drop to the ground and pupate of the summer and emerge as adult moths the following spring.

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Hydrangea Diseases and Pests

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Hydrangeas have few serious pest and disease problems that affect their health although there are several listed here that will cause cosmetic damage. For information on the selection, care, and pruning of hydrangea please visit our Hydrangea fact sheet.
Diseases
Botrytis blight (Botrytis cinerea). Small water-soaked spots on the petals quickly expand into brown irregular blotches. Brown, withered masses of flowers may be covered with the fuzzy gray growth of the fungus. Flower buds may also be affected and leaf spots can occur when infected petals have fallen on them. Disease development is favored by cool, humid, wet conditions. The causal fungus survives almost indefinitely in plant debris. Spores are spread to healthy tissue by wind. For prevention, use the methods described below for powdery mildew.
Leaf spots caused by a variety of fungi can occur on hydrangea. A common leaf spot disease in the northeast is caused by the fungus Cercospora. Tan spots with reddish brown borders form on the leaves. Infection can be reduced by minimizing leaf wetness. If needed, protectant fungicides can be applied prior to infection. This may be desirable for hydrangeas that had a lot of leaf spots the previous year and prior to wet weather. In addition, removal of infected leaves during or at the end of the season may help reduce inoculum the following season.
Cercospora leaf spot on hydrangea, image by L. White
Powdery mildew (Microsphaera penicillata) can occur on all hydrangeas but is most serious on bigleaf hydrangea. In addition to the usual white, powdery fungal growth on the leaf surfaces, yellow or purple leaf blotches might be present. This disease doesn’t usually harm the plant but is aesthetically problematic for some gardeners. The problem will be most severe on plants in shady or crowded sites that promote high humidity. Clean up fallen leaves and dead tissues to remove the spores that may cause new infections. Chemical control is unnecessary except in severe cases. Products available to control powdery include potassium bicarbonate or horticultural oils.
Root rot (Armillaria spp.) can occur in landscape plantings, especially on oakleaf hydrangea (H. quercifolia). Plants stressed by drought or other factors are most susceptible. Symptoms first appear as wilting on one or more shoots. Watering will not return the leaves to normal. Within a few weeks, the remaining shoots will wilt and the hydrangea will die. The fungus produces white, fan-shaped mycelia mats under the bark at or near the soil line. In addition, black, shoestring-like rhizomorphs of Armillaria can usually be found on the surface of infected roots, in the surrounding soil, and under the bark. In the fall after a heavy rain, clusters of honey-colored mushrooms appear above the damaged roots.
Good growing conditions are the best defense against Armillaria root rot. Water during summer droughts and fertilize according to soil test results. There is no chemical control. Another root rot, caused by Phytophthora nicotian, is favored by poorly drained soils. Symptoms are similar to those caused by Armillaria sp. Do not plant hydrangea where flooding occurs after a heavy rain.

Healthy plant on left, suspected root rot on right
Other diseases that can affect hydrangea include blister rust (Pucciniastrum hydrangea), bacterial wilt (Pseudomonas solanacearum), viruses, and virescence (caused by a phytoplasma). The blister rust fungus produces masses of orange spores on the underside of the leaves. Blighting of the young leaves and flowers can be caused by the bacterium P. solanacearum, especially after heavy rain during hot weather. Symptoms of viruses include leaf mottling, spots, ring or line patterns, flower color breaking, and distortion. Virescence is characterized by green, stunted flowers or leafy shoots growing from the flower parts.

Insects and Other Pests
Aphids can sometimes build up to high populations on the new growth of hydrangeas. At high numbers, aphid feeding may cause some leaf yellowing or distortion. In addition, aphids excrete a liquid waste high in sugars called honeydew. Sticky, clear honeydew can coat the leaves and other surfaces below the aphids. Sooty mold, a black coating of fungal growth, may form on the honeydew. While these fungi do not directly infect the plant, a lot of sooty mold can block sunlight from the leaves, resulting in decreased photosynthesis. Ants are also attracted to honeydew and some ant species will groom aphids by rubbing their antennae to stimulate honeydew production. They also defend aphids against parasites and predators. To control an aphid infestation, hose them off with a strong spray of water or apply insecticidal soap.
Black vine weevil (Otiorhynchus sulcatus). The larvae of this weevil injure hydrangea by feeding on the roots. After devouring the small roots, the small grubs move on to chew the bark from larger roots, often girdling them. The tops of girdled plants turn yellow then brown, followed by the death of the plant. The adult is 1/2″ long, black, with a beaded appearance on the thorax and scattered yellow hairs on the wing covers. Adults are flightless and feed on the leaves at night, leaving notches along the margins. Adults and large larvae overwinter, emerging from May-July. After feeding for 3-4 weeks, egg-laying begins. Insect pathogenic nematodes can be used for control of larvae in the soil. If necessary, chemical control can be used when there is adult feeding and before egg laying starts. The usual timing is during May, June, and July.
The four-lined plant bug (Poecilocapsus lineatus), below left, and the tarnished plant bug (Lygus lineolaris) cause round, brown sunken areas around the feeding puncture wounds (below right). Eggs are laid in soft stem tissue. They hatch around mid-May and the young bugs suck sap from the leaves. They molt five times and mature around the middle of June. Adults are about 1/3″ long. The four-lined plant bug is yellow with four lengthwise black stripes on its wings. Leaf spots can become holes. The tarnished plant bug is brown, 1/5″ long, with a yellow “Y” shape pattern on its back. There is one generation per year of the four-lined plant bug and two to five generations per year of the tarnished plant bug. Control is not usually necessary for these pests but if needed, use insecticidal soap or ultrafine horticultural oil.

Hydrangea leaftiers (Olethreutes ferriferana also known as Exartema ferriferanum), are quite noticeable when present. While this pest does not have a big impact on the health of the plant, it can reduce the number of flowers. After overwintering in the pupal stage, small brown and white moths emerge in the spring, mate and lay eggs on the tips of hydrangea branches (all types). The newly hatched caterpillars web a few leaves together and feed on the inner (top) surfaces of the leaves and, if present, the flower bud. The webbed together leaves look like little tents and there can be quite a few on a single plant. During the summer, larval feeding is completed and the insect drops to the ground to pupate. There is only one generation per year. If control is desired or needed, the leaves can be pulled gently apart and the caterpillar can be removed and killed. Biological insecticides containing the active ingredient Bacillus thuringiensis kurstaki (Btk) can be used during the caterpillar stage.
Japanese beetles can be a problem on oakleaf hydrangea but seldom bother the other types. Adults are metallic green and consume leaf tissue while leaving behind the veins, resulting in a lacy looking ‘skeleton’ of the leaf. A good way to get rid of these beetles is to knock them off the leaves into a container of soapy water to kill them. Insecticides are also effective but should never be applied during bloom to protect pollinators and other beneficial insects.
Rose chafer (Macrodactylus subspinosus) sometimes feeds on hydrangea and when abundant can injure plants by skeletonizing the leaves. They will also feed on the flower petals, especially of white flowers. Adult rose chafers are slightly more than 1/3″ long tan beetles with long spindly legs. They occur in large numbers where soils are sandy. Adults appear around mid-June and feed for about a month to 6 weeks. Females lay 24-36 eggs singly in the ground a few inches beneath the surface. They soon hatch and the grubs feed on the roots of grasses and other plants. In late autumn they burrow several inches into the ground to overwinter. The next April or May they return to near the surface and pupate. Beetles emerge 2-4 weeks later. Chemical control is not usually effective because more rose chafers can quickly move into treated areas.
Two-spotted spider mite (Tetranychus urticae) feeding on leaves presents as a stippled or freckled appearance and/or webbing. Spider mites are most active during hot, dry weather. Like aphids, they have piercing and sucking mouthparts and each little ‘freckle’ is an injury associated with a feeding site. In most cases, spider mites on outdoor plants are controlled by naturally occurring predators. Spider mite outbreaks often occur after the application of a broad spectrum insecticide that kills beneficial insects along with the pests. Plants that are well watered during dry periods may withstand spider mite injury.
Other insects and pests that can sometimes cause damage to hydrangeas include oystershell scale (Lepidosaphes ulmi), and stem, leaf, and root-knot nematodes.
Despite good cultural practices, pests and diseases at times may appear. Chemical control should be used only after all other methods have failed. For pesticide information or other questions please call toll free: 877-486-6271.  
UConn Home and Garden Education Center, 2018
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, the Dean of the College, Cooperative Extension System, University of Connecticut, Storrs. The Connecticut Cooperative Extension System is an equal opportunity employer and program provider. To file a complaint of discrimination, write USDA, Director, Office of Civil Rights, Room 326-W, Whitten Building, Stop Code 9410, 1400 Independence Avenue, SW, Washington, DC 20250-9410 or call (202) 720-5964.

Fungal leaf spot on a hydrangea.

Q: I get some kind of leaf disease on my hydrangea bushes every year. I have about 15 of them in various garden locations. They start out fine but end up covered with these spots by mid-season. I tried cutting back the irrigation system, which seemed to have helped a little at first, but the spots still appeared. The blooms are fine. I’d love to know how to prevent it or treat it.

A: That sounds like a classic fungal leaf-spot disease all right (probably Cercospora). I’d go with a 3- and possibly 4-prong approach to stop it. Knocking off the overhead irrigation already was a good move.

1.) Discourage the disease by improving air flow through your plants. Few people ever thin out their hydrangeas, which can get very dense in a few years. When it’s rainy or humid, the leaves don’t dry very well, and if any of spot-causing fungus is around, the damp conditions favor its growth. Early spring is a good time to remove up to one-third of the biggest, oldest stems from throughout your plants. Cut them right back to the base. A second good time to thin is right after the plants flower.

2.) Clean up old diseased leaves. When infected leaves brown and drop, the disease spores stay in the vicinity. Depending on temperature and moisture, the problem will flare up to varying degrees year after year. The more diseased leaves you can remove and clean up from off the ground, the fewer spores will be around to re-infect.

3.) Put down a fresh mulch to discourage some of the dropped spores from splashing back up on the plant stems. Bark mulch and leaves are good choices. Compost is probably best for disease-fighting.

4.) If those alone don’t stop or drastically reduce your spotty leaves, try a fungicide. The key with any fungicide, though, is to get the spray on all the leaves before a disease flares out of control. That means use them preventively at the first signs of spotting. Some natural sprays that help are neem oil, a bacterial fungicide that contains Bacillus subtilis (i.e. the stuff in the brand Serenade) or a homemade baking-soda spray of one tablespoon of baking soda and one tablespoon of horticultural oil mixed well in a gallon of water. Chlorothalonil is a common chemical fungicide labeled for leaf spot on hydrangeas. This disease is hardly ever fatal, though, so weigh any treatment against how much cosmetic ugliness you’re willing to accept.

Hydrangeas forum: Brown spots on hydrangea leaves

Welcome, RobinP64 and how nice that you bought MM. This is a new variety from Proven Winners that sometimes has extremely serrated leaves. I tried to find it locally to no avail. Still difficult to find. I assume you got smarter and mail ordered it directly from PW then. Ha!
The leaf lesions look like a mixture of problems. Some leaf spots at the bottom of Picture 1 suggest cercospora leaf spot. Some browning of blooms at the bottom of Picture 2 suggest that either the bloom is old and turning brown or that there has been inconsistent watering and the plant decided to go directly from a light green to a brown, bypassing a more greenish tint in the blooms. There is a white powdery looking growth, possibly a fungal infection. Either powdery mildew due to overhead watering & too much humidity; too much watering; or an opportunistic infection by another fungi. There are some large lesions in the leaves that I do not recognize from my Annabelles but since you mentioned that this is MM just planted in May, I suspect the leaves got sunburn. At the wholesale nurseries, the plants are protected from direct sun 24/7, but when planted outside by us, some leaves are not able to handle that much sun and will show sunburn. After the top is sunburned, some opportunistic fungal infection may also set in taking advantage of the sunburn lesion.
Never get the leaves wet in order to avoid leaf fungal infections. Instead water the soil (sunrise is best with sprinklers, as the leaves do not stay wet for long periods) or use soaker hoses or drip irrigation. Water the soil from the crown outwards in all directions. Hint: it is time to water the plant if you insert a finger into the soil to a depth of 4″ and the finger feels dry. When you water, the water should get down to a depth of 8″ or so.
For an idea of how much water to use, start with 1 gallon of water in Spring and increase that to 1.5 gallons when temperatures are regularly above 85F. Decrease the amount of water back to 1 gallon when temperatures are usually below 85F. should temps ratchet above 95-100, consider watering an extra day per week. But remember, they need water if a finger inserted to a depth of 4″ feels dry. If you water automatically, randomly check to make sure you are not overwatering and make sure the soil is not wet/soggy.
Water once a week or once every two weeks -depending on local rains- once the plant goes dormant. Stop watering if the soil freezes where you live but restart when you see leaf out. Tweak those watering amounts based on soil types and plant size.
Leaves produced in future years should be more sun tolerant. For now, consider this an aesthetic problem and remove only the worst of the leaves as the plant still needs the leaves in order to do its business. Just cut the petiole string that connects the leaf to the stem. Then throw away in the trash these leaves so as not to spread the spores. But just cut the worst ones or leave them all alone.
Cercospora is a leaf spot disease caused by the presence of the fungi and overhead watering. But it was particularly difficult trying to distinguish it from the other fungi caused by the sunburn so maybe the best is to let things settle and not do overhead watering. In some locations, like the PNW, some people take no action. In others like mine, it rears its ugly head annually so I practice clean sanitation practices and use drip irrigation.
There are some fungicides for cercospora (they help control it but do not cure it) but I have not used them so far. The reason is that this disease becomes visible in mid to late Summer, just as the leaves are about to die off in the Fall so, eh, it does not pay to u$e it. If you see any plant debris under the MM, throw that away too.
When the plant goes dormant, dispose of all the leaves and all the blooms in the trash so as not to spread the spores. At the same time, I would also replace the mulch under the plant with new mulch, about 2-4″ of organic mulch (not rock mulch though).
Does this help?
Luis
PS – Next time, I would suggest starting a new thread as the original posters sometimes do not like it. Hopefully, Abby will not mind. ;o)

| Quote | Post #2041454 (4)

There are few things more beautiful than lush hydrangea bushes. Unfortunately, their beauty can be sullied by a number of fungal and viral diseases (and two bacterial diseases).

However, there are steps you can take to keep your beauteous shrubs from falling victim to one of these diseases.

We will introduce you to the major hydrangea diseases, so you know what to look for and how to prevent and treat them.

Fungal Diseases

Botrytis Blight (Botrytis cinerea)

This fungus can severely affect the flower buds and even kill them before they open. In addition, infected flower parts can fall on the leaves and infect them.

The first symptoms are water-soaked spots on the flowers. However, these grow into reddish brown lesions.

The reddish lesions on the leaves are a sure sign of Botrytis Blight.

Botrytis is more likely to be a problem under cool and damp conditions, such as several days of cloudy, humid, and rainy weather.

You can take steps to try and prevent this infection. Keep the humidity low. Don’t water late in the day, and only water at the roots, so you don’t get the flowers and leaves wet.

If you can, keep good airflow around your plants. Space them properly, and prune branches that are closely spaced. Treat your pruning shears with bleach as you prune, so you don’t accidentally spread any disease.

Also remove dead or damaged flowers and leaves to prevent the fungus from gaining egress into the plant. Clean up debris around the plant, so that Botrytis can’t live on the dead tissue.

If you have a persistent problem, you may need to use fungicides. Options include mancozeb, iprodione, or thiophanate-methyl.

Leaf Spots (Cercospora species and Phyllosticta hydrangea)

Cercospora manifests as circular purple or brown spots on the bottom of the plant. As the lesions get larger, the leaves can turn yellow and fall off the plant.

Watering without getting the leaves wet will help to prevent these diseases. If your hydrangeas do get infected, you have several options, including compost tea, hydrogen peroxide, garlic oil, or liquid kelp.

You can also apply the fungicides chlorothalonil or thiophanate-methyl.

Anthracnose (Colletotrichum gloeosporioides)

Plants that have been heavily fertilized are more likely to contract this common fungal pathogen.

Continued rainy weather or heavy fog produces the conditions that favor infection.

The fungus produces large brown spots on the leaves or flowers that will become more lightly colored in the centers. One distinctive symptom is that spots by the veins develop at an angle.

You can also treat this disease with liquid kelp, garlic oil, hydrogen peroxide, or compost tea.

Powdery Mildew (Erysiphe polygoni)

Powdery mildew manifests as a white powdery substance on the surface of the leaves. You can see white, cottony growth on the bottom of the leaves.

A severe case of powdery mildew. Photo via Alamy.

Left unchecked, the fungus can infect the newly developing buds and stunt their growth.

Powdery mildew is most likely to be a problem on hydrangeas when the days are warm and the nights cool.

You can prevent the disease by reducing humidity and increasing air circulation.

One way to control this disease is to apply a fungicide as soon as you discover it. Another option is to use neem.

Rust (Pucciniastrum hydrangea)

Like other rusts, hydrangea rust needs two hosts to survive and does not kill either of them. This rust only infects the smooth hydrangea, H. arborescens, and hemlock as its alternate host.

The first symptoms are orange pustules on the bottoms of the hydrangea leaves and yellow spots on top.

This disease is difficult to control, but you can manage it by cleaning up infected leaves and debris that has fallen to the ground around both hosts. Thin inside the hydrangea making sure to disinfect your pruning shears.

If you know that rust is likely to be a problem, you can grow the cultivar ‘Frosty,’ which is resistant to this disease.

Bacterial Diseases

Bacterial Wilt (Ralstonia solanacearum)

This important bacterial disease first manifests as blight in the leaves and flower clusters. However, more severe infestations can cause both wilting and root rot.

Bacterial wilt occurs mainly in hot weather and heavy rains. There are no chemical options to control this disease.

Bacterial Leaf Spot (Xanthomonas campestris)

The bacteria that cause this disease can enter the plant through natural openings like stomata or through wounds.

Bacterial Leaf Spot (Xanthomonas campestris) on oak leaf hydrangea. Photo (cropped) by Elizabeth Bush, Virginia Polytechnic Institute and State University, Bugwood.org via via CC 3.0.

The first symptoms are water-soaked spots. The spots darken and become angular in shape. These spots become larger lesions and can kill the leaves.

If you have a susceptible plant, you can protect it with copper hydroxide (Kocide).

Viral Diseases

Fifteen different viruses afflict hydrangeas! Hydrangea macrophylla is the most susceptible.

Transmission can occur by knives, leaf contact, and insects like aphids. In some cases, plant parasitic nematodes can transmit the viruses.

Prevention is the key in these cases. Quickly remove infected plants and their parts. Sterilize your pruning shears before cutting the plants, and plant clean stock in soilless media to avoid the viruses that are transmitted by nematodes in the soil.

These three are the most common viral infections that you are likely to encounter:

Hydrangea Ringspot Virus

If your hydrangea has brown spots or rings on its leaves, there is a good chance that it is infected with hydrangea ringspot virus. Then the leaves of the plant will start to be distorted and rolled, and the growth of the plant will be stunted.

Aphids do not spread this disease. However, it spreads mechanically, so tools can transmit this virus. Sanitizing your pruning tools will help to prevent the spread of this disease.

Unfortunately, if your hydrangea contracts this disease, you will have to purge it. Varieties that are tolerant to this virus are available.

Hydrangea Mosaic Virus

Hydrangeas infected with this virus will have a pattern of yellow mosaics on their leaves.

This is another virus that is not transmitted by aphids. However, once again, you can spread the virus with your tools. So be sure and disinfect your pruning shears to avoid inadvertently spreading this virus.

Tomato Ringspot Virus

This virus causes the leaves to turn yellow and become distorted, and the growth of the plant will be stunted.

Nematodes, not pruning tools, spread this virus.

If you are growing your hydrangeas in containers, you can avoid tomato ringspot virus by using a soil mix that is free of nematodes.

Such Beautiful Plants and So Many Diseases

There are a number of different organisms that can infect hydrangea plants and sully their beauty.

However, you can take steps to keep your plants from becoming infected:

  • Prune your plants, so that the insides are open and will not accumulate moisture. (And disinfect your pruning shears or flower-cutting knives whenever you use them!)
  • Pick up dead flowers and leaves, since they can harbor fungi.
  • Water your plants at the bottom, so the tops will not get wet.
  • Control insects, since they spread many of these diseases.

Have you encountered a disease on your hydrangea? If so, let us know in the comments.

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About Helga George, PhD

One of Helga George’s greatest childhood joys was reading about rare and greenhouse plants that would not grow in Delaware. Now that she lives near Santa Barbara, California, she is delighted that many of these grow right outside! Fascinated by the knowledge that plants make chemicals to defend themselves, Helga embarked on further academic study and obtained two degrees, studying plant diseases as a plant pathology major. She holds a BS in agriculture from Cornell University, and an MS from the University of Massachusetts Amherst. Helga then returned to Cornell to obtain a PhD, studying one of the model systems of plant defense. She transitioned to full-time writing in 2009.

Hydrangea-Powdery Mildew

Cause Erysiphe friesii var. friesii (formerly Microsphaera friesii) has been reported from Washington and Erysiphe polygoni has been reported from British Columbia. These fungi are favored by conditions that produce high humidity but dry leaves such as heavily-shaded growing sites. It is a highly specialized pathogen that forms a close association with the host. Conditions that favor the host also favor the pathogen. Much of the fungus remains outside infected plant parts where it grows on the surface but sinks root-like structures called haustoria into plant cells to obtain nutrients. The white growth seen is composed of both mycelium and spores of the fungus.

The cultivar Veitchii was found to be resistant, Nikko Blue was susceptible, and Madame Emile Mouilliere, Forever Pink, Lilacina, and Holstein were intermediate; while Preziosa is very susceptible.

Symptoms Leaves’ undersides are covered with a white powdery growth; upper surfaces develop yellowish green blotches or turn purplish brown. Leaves may become completely covered and die early. Premature defoliation may occur on severely infected plants. Reduced leaf area and shoot elongation are also possible. Blooms may become stunted and malformed.

Cultural control

  • Keep greenhouse humidity low.
  • Space plants for good air circulation.
  • Plant or move bushes in the landscape to sunnier locations.
  • Plant resistant cultivars.

Chemical control Fungicides will do best when used before symptoms develop. Few materials have good eradicant activity. Use at 7- to 14-day intervals; using shorter intervals when environmental conditions favor disease development. Alternate or tank-mix products from different groups that have different modes of action. Limit the use of any one group during crop production. Limit the use of any one group during crop production.

  • Armada 50 WDG at 3 to 9 oz/100 gal water. Do not use a silicone-based surfactant. Not for nursery or greenhouse use. Group 3 + 11 fungicide. 12-hr reentry.
  • Banner MAXX at 5 to 8 fl oz/100 gal water. Group 3 fungicide. 12-hr reentry.
  • Bayleton 50 T&O at 5.5 oz/275 to 550 gal water. Landscape only, not for use on plants for sale. Group 3 fungicide. 12-hr reentry.
  • Bicarbonate-based products. Might be used to supplement a normal program when powdery mildew is first observed. Do not mix with acidifying agents. Thorough coverage is essential. O
    • MilStop (85% potassium bicarbonate) at 2.5 to 5 lb/A in the field or 1.25 to 5 lb/100 gal water in the greenhouse. Oregon and Washington only. 1-hr reentry.
    • Monterey Bi-Carb Old Fashioned Fungicide at 4 teaspoons/2 gal water. H
  • Broadform at 2 to 4 fl oz/100 gal water. Group 7 + 11 fungicide. 12-hr reentry.
  • Camelot O at 0.5 to 2 gal/100 gal water. 4-hr reentry.
  • Compass O 50 WDG at 1 to 2 oz/100 gal water plus an adjuvant. Do not use organosilicate additives. Group 11 fungicide. 12-hr reentry.
  • Eagle 20 EW at 6 to 12 fl oz/100 gal water. Not labelled for this pest, but highly effective against powdery mildews in general. Group 3 fungicide. 24-hr reentry.
  • Heritage at 1 to 4 oz/100 gal water plus a non-silicone-based wetter sticker. Group 11 fungicide. 4-hr reentry.
  • Insignia SC at 3 to 6 fl oz/100 gal water plus an adjuvant. Do not use with organosilicate-based adjuvants. Use preventively only. Group 11 fungicide. 12-hr reentry.
  • Myclobutanil 20 EW T&O at 6 to 12 fl oz/100 gal water plus spreading agent. May observe a PGR effect. Group 3 fungicide. 24-hr reentry.
  • OHP 6672 4.5 F at 10 to 20 fl oz/100 gal water. Group 1 fungicide. 12-hr reentry.
  • Orkestra at 6 to 8 fl oz/100 gal water. Group 7 + 11 fungicide. 12-hr reentry.
  • Pageant at 6 to 12 oz/100 gal water. Group 7 + 11 fungicide. 12-hr reentry.
  • Pipron at 4 to 8 fl oz/100 gal water. Do not treat after flower buds are visible. Greenhouse production only. Group 5 fungicide. 12-hr reentry.
  • Spectracide Immunox at 1 fl oz/gal water. H
  • Terraguard SC at 2 to 8 fl oz/100 gal water. 12-hr reentry.
  • Trigo at 1.5 to 2.4 oz/100 gal water for greenhouse or 3 to 9 oz/100 gal water for the nursery. Group 3 + 11 fungicide. 12-hr reentry.
  • Trinity at 4 to 12 fl oz/100 gal water. Group 3 fungicide. 12-hr reentry.

Biological control Thorough coverage of all leaf surfaces is essential.

  • Bayer Advanced Natria Disease Control RTU (Bacillus subtilis strain QST 713) is registered for the home garden. Active ingredient is a small protein. H O
  • Cease or Rhapsody (Bacillus subtilis strain QST 713) at 2 to 8 quarts/100 gal water. Active ingredient is a small protein. Efficacy in the Pacific Northwest is unknown. 4-hr reentry. O

Reference Hagan, A.K., Olive, J.W., Stephenson, J., and Rivas-Davila, M.E. 2004. Impact of application rate and interval on the control of powdery mildew and Cercospora leaf spot on bigleaf hydrangea with azoxystrobin. Journal of Environmental Horticulture. 22:58-62.

Common Hydrangea Diseases : Tips On Treating A Sick Hydrangea

Hydrangeas are fairly easy plants to grow in many regions. There are several forms from which to choose, each with its own peccadilloes and problems. Diseases of hydrangea are typically foliar, although root and flowers may also become infected by fungal or viral problems. In most cases, the plant is able to recover with proper care. Ailing hydrangea symptoms do often start at the leaves, even if the affecting disease is root or insect based. The most prevalent causes of a sick hydrangea will be described in this article.

Diseases of Hydrangea

One of the more beautiful landscape plants are the hydrangeas. Whether you like the bigleaf, oakleaf, panicle or smooth leaf variety, they are generally considered easy to care for and provide a giant display of summer color. Common diseases of hydrangea can affect plant health but also the wondrous floral display for which they are known. Treating a sick hydrangea starts with recognizing common diseases and how to prevent and treat them.

In order to discern what is going on with your plant, you need to start first by gathering any clues. Do you see any insects? Is the problem confined to the leaves or affecting stems and flowers? Once you have viewed the plant carefully, you can start deciding what might be happening to it and how to treat it.

Leaf spot diseases

Since, most ailing hydrangea symptoms are foliar, the number one cause is usually fungal. Leaf spots caused by Cercospora, Alternaria, Phyllosticta or Anthracnose stem from a fungal disease. They are most prevalent in moist conditions, although some occur in warm periods, while others form in cooler temperatures.

Preventing water from remaining on leaves and treating with a good fungicide will usually conquer the problem.

Bacterial leaf spot can be treated with a bactericide. Removing and destroying infected leaves in all cases can help prevent spread.

Viral hydrangea diseases

Viruses are transmitted to plants through insect activity, usually sucking pests, but also through mechanical means. There are 15 main viruses that affect all hydrangeas, but bigleaf varieties seem to be the most attacked. Symptoms are mottled leaves, chlorosis, blisters, rings, distortion and stunting. There are no accepted controls for viral infections.

Prevention is your best defense. Sterilize pruning shears and knives before using them on a plant. Reduce the potential of pests by good cultivation and the removal of infected plant material and weeds around the hydrangea.

The infection is systemic and will eventually infect all parts of the plant. Over time, the plant will succumb and need to be removed and destroyed to prevent infecting any other landscape plants.

Other hydrangea diseases

Rust and powdery mildew are two common issues in ornamental plants. Neither will kill the plant but they do affect the overall beauty.

Powdery mildew looks just like it sounds and stems from another fungus. It will affect leaves and the flowers, especially buds, where it can destroy the flowers. If possible, increase air circulation, reduce humidity and remove infected plant material.

Rust is another visual detraction to hydrangea. It stems from a pathogenic parasite and shows as reddish pustules on leaves. It may be spread through infected plant material or mechanical means. Opening the canopy of the plant and removing damaged material can help manage it.

Botrytis blight attacks all forms of hydrangea. Water soaked lesions occur on leaves, flowers and stems. Treating a sick hydrangea with this disease requires careful sanitation and cultivation practices, and the application of a fungicide.

Hydrangea

Hydrangea spp.

Leaf Spots (fungi – Cercospora spp., Phyllosticta hydrangeae and others): Circular-to-irregular shaped spots are produced on leaves. Use foliar protectant fungicides as needed.

Powdery Mildew (fungus – Erysiphe polygoni): A white, powdery substance appears on leaf surfaces. Yellow spots that later turn brown may appear on the upper surface. If allowed to develop, it may get into newly developing buds and cause stunting. Use a foliar fungicide that has the ability to control powdery mildew.

Botrytis Blight (fungus – Botrytis cinerea): Botrytis is probably the most serious fungus attacking this plant because it causes severe problems in the flower buds. Infected flower parts may drop on leaves and cause infection of those structures. Cool, damp conditions with an abundance of fungal spores encourage the condition. This problem is especially severe at times in commercial greenhouses. Dispose of any weak or decaying plant tissue and use appropriate protectant fungicides if necessary.

Ring Spot (virus – Hydrangea ring-spot virus): Pale colored rings may appear on leaves and some varieties may have distorted leaves. Dispose of diseased plants. Commercial plant producers should use tolerant varieties.

Nematodes (nematodes – Meliodogyne spp., Pratylenchus spp., and Ditylenchus spp.): Nematode damage occurs when this plant is set in infested beds. Plants grown in pots would not be affected if nematode-free propagating stock and sterilized soil is used.

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