Citrus borer and codling moth are two major annoyances for home orchardists. They need controlling if you want to grow good fruit.
If you are a home gardener who has just a few fruit trees, you may find various insect pests are attacking them. Sometimes the damage is only cosmetic, but sometimes the pests spoil the fruit for eating or damage the tree in other ways. People with commercial orchards are well aware of the need for a program of sprays that will control pests.
Citrus Borer
Citrus borer attacks orange, lemon and grapefruit trees. The adult is a beetle that lays its eggs on citrus trees (and others, for example, elms). The eggs hatch into larvae with strong mouthparts that can bore into young branches and tunnel through the wood. As well, the larva cuts a circle just below the surface of the bark, which causes that part of the branch to drop off the tree.
If a citrus tree is showing poor growth, with whole branches drying and dying, often with holes surrounded by sawdust, it is probably infested with citrus borer.
To control an infestation you should cut off and destroy any infested branches. However, it is best not to do so during summer, because a wound opens the tree up to more infestation. Get rid of the dead wood in winter. Then you can use a syringe to squirt a small amount of kerosene into any remaining holes. It will kill the larvae but will not really harm the tree. Finally, block any remaining holes with putty, chewing gum or something similar.
Codling Moth
The larva of the codling moth burrows into the centre of pipfruit like apples, pears and quinces. In spring and early summer the grey and brown moths lay their tiny eggs on the fruit, or on leaves near the developing fruit. The eggs hatch into larvae that tunnel into the fruit and eat the seeds, extensively damaging the core and the fruit around it. Often the larvae die inside the fruit, but not before leaving an unattractive brown mass of faecal pellets (called ‘frass’) in their tunnels. This can sometimes be seen on the surface of the fruit, at the entry point to a tunnel.
To control this pest, trees must be sprayed with a suitable insecticide (for example, carbaryl) in early spring and every few weeks during fruiting, stopping one month before the fruit is ready to be harvested.
Alternatively, a pheromone that disrupts mating of adult moths can be sprayed near fruit. This organic method of control is still under investigation, but looks very promising.
