The safest ways to control bollworm in tomatoes

Unless you grow your tomato crop under a moth-proof net, you'll have to contend with bollworm at some stage. Fortunately, there are effective methods of control, provided you act quickly, says Bill Kerr.

- Bill Kerr

The African bollworm (Helicoverpa armigera), also known as the Old World bollworm, has many hosts, including a number of food crops and many weeds.

The moths lay up to 700 creamy-white eggs, depositing them singly on tender shoots or flower buds. The eggs turn brownish and hatch in three to five days. The larvae immediately start feeding on the youngest leaves, and can easily be seen at this stage.

From here, the larvae bore into the fruit, stems or flowers. When targeting fruit, they usually move from one fruit to another, rendering each unmarketable.

They are typically found halfway into the fruit, where they're easy to spot. When they're resting on leaves, however, they are well camouflaged. The newly hatched larva has conspicuous spines with a dark base. All stages have a stripe along each side, and the colour can vary from green to brown.