What are tortrix moth caterpillars?

These small green caterpillars are the larval stage of moths belonging to a family called tortrix moths (Tortricidae). There are almost 400 species of tortrix moth in Britain, only two of these can feed on a wide range of plants and commonly cause problems in gardens and glasshouses; the carnation tortrix moth (Cacoecimorpha pronubana) and light brown apple moth (Epiphyas postvittana).

Symptoms

The caterpillars of carnation tortrix and light brown apple moth bind leaves together with silky threads and feed within this shelter causing damaged areas to dry up and turn brown. Fruit and flowers can also be damaged. In glasshouses damage can occur year round.

Control

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 control

• Some damage can be tolerated without adverse effects on plant health. Populations of caterpillars, as butterflies and moths are an important part of the garden ecosystem
• Light populations can be controlled by squeezing the bound leaves to crush the concealed caterpillars and pupae
• Encourage predators and other natural enemies in the garden such as birds, wasps and ground beetles
• Carnation tortrix and light brown apple moths can be monitored and may be kept in check by using pheromone traps. These consist of an open-sided cardboard box with a sticky sheet in its base. A pellet which releases a pheromone is placed on the sheet; this is the same chemical produced by females to attract males. In a confined space, such as a glasshouse, these traps may capture enough males to reduce the mating success of the females. These traps are available from some suppliers of biological controls

Pesticide control

• Organic sprays, such as natural pyrethrum (e.g. Bug Clear Gun for Fruit & Veg, Neudorff Bug Free Bug and Larvae Killer), can give some control of tortrix moth caterpillars. These pesticides have a very short persistence and so may require reapplication to keep caterpillar numbers in check.
• More persistent contact-action 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 of 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.

Download

Pesticides for gardeners (pdf document)

Biology

Out of doors light brown apple moth has two overlapping generations during the spring and summer. Eggs are laid in batches on the leaves of host plants and hatch after about ten days. The caterpillars then feed with foliage sown together with silken threads and pupae where they have been feeding. In glasshouses and on houseplants the lifecycle can vary, with adults and caterpillars active from late winter until late autumn.

Carnation tortrix moth has a similar lifecycle to light brown apple moth but can breed continuously in glasshouses and on houseplants.