Are lily borers destroying your costly bulbs?

Are there holes and tunnels in the leaves of your precious and very expensive bulbs but you can’t see anything? If so, you will need to go out at night to find the culprit! Read how to control these critters below.

The lily borer(Brithys crini pancratii) is also called the amaryllis borer, and prefer plants in the crinum, amaryllis, clivia, cyrtanthus, haemanthus and nerine families. It is native to the coastal areas of the Mediterranean, but has spread to other areas around the world, wreaking havoc on plants everywhere it goes. Once this caterpillar takes hold of a plant, it can quickly destroy it, which is why vigilance and prevention are the best way to fight this pest. Fortunately, there are both chemical and natural methods that will kill these borers.

Lily borer eggs are laid in colonies on the underside of the leaves of their host plants by a white moth with a wingspan of about 4cm. In cold winter regions the eggs are laid in early September, and in warmer and coastal regions they are laid all year round.

The larvae hatch during the warmer months, tunnelling into the leaves to feed and leaving holes, and older larvae will also tunnel into the bulbs, causing the total collapse and eventual death of the plant.  

The caterpillars mature to approximately 4cm long. They are easy to identify with their yellow bodies and bright black and orange-yellow rings, and the black dots on the head and the base, look rather like eyes. Another species resembles Zebra silkworms. They are most active at night or on overcast days.

If you catch them early enough you can pick them off by hand, or to control the larvae and break the cycle, spray with a contact insecticide like 'Margaret Roberts Biological Caterpillar Insecticide' or another suitable eco-friendly insecticide which contains pyrethrins, which will kill most caterpillar larvae on contact. Chemical controls for caterpillars will also be effective.

Spray every two weeks, from September to the end of March, and remember that the larvae must be actively feeding when you spray, so do it at night.