About this product
Webbing on a clipped box ball, leaves stripped to a skeleton, pale green caterpillars with black heads working through the topiary. Box tree moth, Cydalima perspectalis, has become the most serious threat to British box gardens in a decade and is still spreading north.
This pack holds a mix of Steinernema feltiae and Steinernema carpocapsae, two complementary nematode species that seek out the caterpillars, stop them feeding within hours and end the larval stage within days. They are harmless to bees, butterflies, ladybirds, hoverflies, birds, pets and children. The RHS has now confirmed the approach: a recent study found nematodes considerably reduce larvae numbers, and RHS entomologist Stephanie Bird has said they "can be a useful addition to the gardener's armoury for control of box moth caterpillar".
Box tree moth has two generations a year, so one treatment is not enough. Target the first generation from late April into May, and the second in July. Within each window, apply three doses two weeks apart. Nematodes are short-lived once applied, and successive doses catch caterpillars hatching at different times. Air temperature needs to be 12°C or above, so choose a mild day and apply in the cool of the evening.
One practical warning that saves money. A pack only stays viable in the fridge for two to three weeks, so do not order all three doses of a window at once. Order the first two at the start of the window, then the third a fortnight later, timed to arrive when you need it. Each pack treats approximately 60 sqm of hedge or topiary.
Nematodes handle the caterpillars you cannot see. Hand-picking handles the ones you can, and the two together work considerably better than either alone. Remove and bin webbed leaves rather than composting them, check leaf undersides for clusters of pale yellow eggs, and open up the centre of dense topiary after pruning so you can inspect it and the plant gets some airflow. Pheromone traps are worth having for monitoring adult flight, though not as a control in themselves.
If a plant is already badly chewed, do not dig it out. Box is resilient, and with the moth controlled, a feed and a mulch, most specimens recover their shape within a year or two.