The caterpillars of this moth can be found feeding on plants at all times of the year but are most common between May and October.  

• Holes are eaten in the foliage and flowers of a wide range of plants, including unopened flower buds, frequent hosts include chrysanthemums, red valerian and barberry 
• Young growth at the shoot tips is particularly favoured
• The caterpillars are up to 45mm long (1¾in) and vary in colour from brownish yellow to bright green
• They hide during the day, emerging to feed at night
• Caterpillars can be removed to alternative host plants where damage is less undesirable (e.g. common nettle, hop or bramble) or larger host plants where their feeding will have no effect on the long term health (e.g. hazel, birch or oak) 

It is only occasionally that caterpillars of this moth cause significant damage in gardens; it can usually be tolerated. Caterpillars and associated moths are important as a food source for other garden wildlife and so should be preserved where possible.

Check susceptible plants frequently so action can be taken before a damaging population has developed. When choosing control options you can minimise harm to non-target animals by starting with the methods in the non-pesticide control section. If this is not sufficient to reduce the damage to acceptable levels then you may choose to use pesticides. Within this group the shorter persistence pesticides (that are usually certified for organic growing) are likely to be less damaging to non-target wildlife than those with longer persistence and/or systemic action.

Non-pesticide 

• Where possible tolerate populations of caterpillars, as butterflies and moths are an important part of the garden ecosystem
• Encourage predators and other natural enemies in the garden such as birds, wasps, hedgehogs and ground beetles
• Check plants regularly for the presence of larvae and remove by hand where practical

Pesticides

The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner.

If numbers of larvae are too high for hand picking, control may be achieved by spraying with pesticides. Spraying at dusk is likely to give the best results. 

• Organic contact insecticides containing natural pyrethrins (e.g. Bug Clear Ultra 2, Neudorff Bug Free Bug and Larvae Killer). Several applications of these short persistence products may be necessary to give good control
• More persistent contact insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Bug Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer, Provanto Sprayday Greenfly Killer) and cypermethrin (e.g. Py Bug Killer)
• The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available

Follow label instructions when using pesticides. On edible plants make sure the food plant is listed on the label and follow instructions on maximum number applications, spray interval and harvest interval. Plants in flower should not be sprayed due to the danger to bees and other pollinating insects. Inclusion of a pesticide product does not indicate a recommendation or endorsement by RHS Gardening Advice. It is a list of products currently available to the home gardener.

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Pesticides for gardeners (pdf document)