Brown scale insect being found more often on woody plants

Tuesday, April 10, 2012
9:53 AM

Question: I have been gardening for 50 years and thought I knew most of the garden pests we gardeners learn to live with. However, last summer I noticed one of my small shrubs looking very sad and taking a closer look I found a really strange looking thing on it, I am not sure what it is a bug or fungus, it is dotted about on the underside of the leaves. I decided to dig the shrub up as it was looking like it had given up altogether and I found to my horror that the same strange substance was covering the roots as well. I read your casebook every week and was wondering if you could help identify, my problem for me and advise me whether it will spread to other plants. I have enclosed a little cutting for you to examine. (F Price, Chedgrave)

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Answer:

The problem you have on your plants is one that is reasonably new and is becoming more common, Brown scale can be found on woody plants at any time of year because old dead scales remain attached to the bark. Brown scale is a sap-sucking insect that lives mainly on the stems of a wide range of woody plants.

Convex, oval, dark brown shells, 3-6mm long, occur on the woody stems. Infested plants may lack vigour and, in heavy infestations, a black sooty mould develops on the scale’s sugary excrement, which is deposited on leaves and stems.

Light infestations are of little consequence, but heavy attacks are best dealt with in early to mid-summer when the more vulnerable newly hatched scales are present.

Spray ornamental plants with Provado Ultimate Bug Killer concentrate (thiacloprid), Provado Ultimate Bug Killer Ready To Use, or (acetamiprid) Scotts Bug Clear Ultra concentrate, or (thiamethoxam) Westland Plant Rescue Bug Killer. Some fruits affected by brown scale, including plum, raspberry and black currant, can be treated with deltamethrin (Bayer Sprayday Greenfly Killer) or lambda cyhalothrin (Westland Plant Rescue Fruit & Vegetable Bug Killer).

Alternative treatments for outdoor ornamental plants and fruit trees/bushes are plant oils/extracts (Vitax Organic 2 in 1 Pest and Disease Control, Growing Success Fruit & Bug Killer or Scotts Bug Clear for Fruit & Veg), or fatty acids (Bayer Organic Pest Control, Doff Greenfly and Blackfly Killer or Doff Greenfingers Organic Pest Spray)

The best time for summer spraying is in early July when the more vulnerable newly hatched scale nymphs will be present.

For scales on deciduous edible fruits, a plant oil winter wash (Growing Success Winter Tree Wash or Vitax Winter Tree Wash) can be used. This is used against the overwintering scale nymphs in December-January when the plants are fully dormant

With grape vines, peel away the loose outer bark to expose the scales and other sheltering pests before treatment.

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