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Common Hydrangea pests & diseases

Common Hydrangea pests & diseases

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A basic guide to pests and diseases that effect Hydrangeas!

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

With hydrangeas, the most common pests and diseases include leaf spot which can be brought about by problems with water and soil. There is also a risk of powdery mildew when the plant doesn't get enough air circulation and there's too much water in the soil. Another risk is mold and aphids such as hydrangea scale so be cognizant of where you live and what issues you might face giving your soil environment and weather.

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 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.

2 thoughts on “Common Hydrangea pests & diseases

  1. One of my there second year potted hydrangeas suddenly has white discolouring round all leaf edges. Not responded to general purpose bug spray. Pretty sure it is nowt scale or mildew. Any ideas/advice, please?

  2. I put too much malathion on my hydrangeas and now the flowers are brown. What do I do? Thank you for all the help you can give me

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