Mint moth

Mint moth caterpillars feed on a range of small herbaceous plants in the mint family. Their presence can be tolerated by gardeners and the adult moths, with their reddish-purple wings delicately marked with gold, are a common sight in the herb garden.

 

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Mint moth Pyrausta aurata

Quick facts

Common name Mint moth
Latin name Pyrausta aurata
Plants affected mints (Mentha species), marjoram (Origanum vulgare), meadow-clary (Salvia pratensis), lemon balm (Melissa officinalis), catmint (Nepeta cataria) and calamints (Calamintha spp.).
Caused by caterpillars
Timing spring and summer
 

What is mint moth?

The adult moth has a wingspan of up to 2cm and has reddish brown to bright purple wings with golden markings. It is the larvae of the mint moth that are responsible for causing low levels of damage to a range of herbaceous plants in the mint family, the Lamiaceae. Adults are small, attractive, moths that can be found resting on host plants during sunny summer days.

Symptoms

  • Caterpillars of this moth can be found feeding on several common garden plants
  • Young growth at the shoot tips is often damaged, leaves may be curled over, small amounts of fine webbing and tiny black pellets of caterpillar excrement will be present
  • Caterpillars grow up to 13mm long before pupating
  • Caterpillars vary in colouration, ranging from shades of pale green to a reddish/purplish brown, whatever the background colour there are two paler stripes running longitudinally down the back and regularly spaced groups of small black spots

Control

The presence of the caterpillars of this moth rarely cause significant damage in gardens and it can usually be tolerated, on a healthy plant there are usually unaffected leaves that can be used. 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 from spring onwards so action can be taken before damage has occurred. 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 control

  • 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, hedgehogs and ground beetles
  • Check plants regularly from late April for the presence of larvae and remove by hand where practical
  • Heavily infested shoots can be cut hard to remove the problem and stimulate new growth

Pesticide control

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.

Healthy plants are not usually adversely affected by ths moth. If damage cannot be tolerated and 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 Gun for Fruit & Veg, 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)

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.

Downloads

Pesticides for gardeners (pdf document)
 

Biology

The mint moth has two generations a year with caterpillars active in spring and summer. Young caterpillars feed on the underside of leaves and later web together plant material including the flowerheads. When fully grown the larvae will be approximately 13mm long and will pupate within a cocoon in the larval feeding place. There are other species of moth of the same size and colouration which do not cause problems on herbs.
 

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