Hydrangea scale is a

Sap is a fluid that circulates through a plant's vascular system, in a similar way to blood moving through our veins. Phloem sap carries the sugars produced in the leaves by photosynthesis down to roots and other storage organs, as well as carrying minerals and hormones. Xylem sap is watery and transports nutrients absorbed by the roots upwards to the rest of the plant. Some plants leak sap from wounds or pruning cuts, and this is known as bleeding.

The immature scales (nymphs known as crawlers) are difficult to see and the presence of these insects becomes apparent in early summer when the adult scales deposit eggs on the stems and leaves. You may see:

• Eggs which are covered in white waxy fibres that form smooth, oval patches 3-4mm long. These white patches will persist on the plant long after the eggs have hatched
• Newly hatched scales (crawlers) are less than 1mm long and are pale yellow
• The crawler stage can be distributed in wind currents
• The mature scales are around 3mm in diameter, oval in shape and brown
• Heavily affected plants lack vigour and may shed leaves 

Check susceptible plants frequently from spring onwards so action can be taken before a damaging population has developed. When choosing control options you can minimise harm to non-target animals by using the methods in the non-pesticide section below. Pesticide treatments are likely to kill natural enemies and are only likely to be successful if the entire plant can be reached.

Non-pesticide

• Where possible tolerate populations of scale insects. Well-tended healthy plants are able to tolerate light populations of these insects and so they do not necessarily require control
• Heavily infested plants can be removed and replacements planted in the autumn
• Adult scales and egg masses can be removed when seen but this may not reduce large populations
• Encourage predators  in the garden, some ladybirds, parasitoid wasps and some birds will eat scale insects

Pesticides

The RHS recommends that  you don't use pesticides. Most pesticides (including organic types) reduce biodiversity, including natural enemies, impact soil health and have wider adverse environmental effects.
 
Where you cannot tolerate hydrangea scale, manage them using the information above as your first course of action.
 
Pesticide treatments are likely to kill natural enemies and so reduce the likelihood of natural control and can lead to resurgence of the target animal.

The shorter persistence pesticides (that are usually certified for organic growing) are likely to be less damaging to non-target wildlife.
 
The pesticides listed are legally available in the UK. This information is provided to avoid misuse of legal products and the use of unauthorised and untested products, which potentially has more serious consequences for the environment and wildlife than when products are used legally.
 
Always follow the instructions on the products. For edible plants, make sure the food plant is listed on the label and follow instructions on maximum number of applications, spray interval and harvest interval.

Homemade products are not recommended as they are unregulated and usually untested. 

Be aware that products such as Neem oil are not registered for use in the UK and we cannot advise on their use.

Plants in flower must not be sprayed due to the danger to bees and other pollinating insects.

• The best time for summer spraying is in July when the more vulnerable newly hatched scale nymphs are present 
• Organic sprays, such as natural pyrethrum (e.g. Bug Clear Ultra 2, Neudorff Bug Free Bug and Larvae Killer) or plant oils (e.g. Vitax Plant Guard Pest & Disease Control, Bug Clear Fruit and Veg) can give good control of scale insect nymphs. These pesticides have a very short persistence and so may require reapplication to keep scale numbers in check. Plant oil products are less likely to affect larger insects such as ladybird adults 
• Plant invigorators combine nutrients to stimulate plant growth with surfactants or fatty acids that have a physical mode of action (e.g. Ecofective Bug Control, RHS Bug and Mildew Control and SB Plant Invigorator). These are not considered organic
•  Further information about the use of pesticides available for management of scale is available on the pesticides for gardeners leaflet
   

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Pesticides for gardeners (pdf document)

Hydrangea scale is a sap-sucking insect that develops on the underside of leaves on Hydrangea and some other plants.

There is one generation a year with young nymphs hatching from eggs in mid-summer and sucking sap from the undersides of leaves. In late summer the nymphs move to the stems where they overwinter before maturing in late spring. Eggs are deposited under a covering of white waxy fibres in early summer.