By: Denis Crawford | May 10, 2018
There are a number of large (15–25mm long) sap-sucking bugs, including spined citrus bug, bronze orange bug, and crusader bug, that attack citrus trees. Spined citrus bugs attack citrus fruit directly causing brown staining, drying out of fruit segments and fruit drop. Crusader bugs feed on young plant growth causing wilting of shoots above the point of feeding. Bronze orange bugs do the same thing but they also damage flower stalks causing flowers to fall, and stalks of young fruit causing fruit drop. These bugs, especially bronze orange bug, release foul-smelling defence liquid when threatened, so wear gloves if handling them. Bronze orange bugs can squirt their defence liquid quite far, so wear goggles as well.
PREVENTION AND TREATMENT
Use insect exclusion bags over fruit but if bugs are present they tend to cluster together in winter either as adults or nymphs. Wearing protective gear, knock them off into a bucket of soapy water. As a last resort, spray bugs with organic pyrethrum (take care as it will kill beneficial insects).
CITRUS GALL WASP
All varieties of citrus may be attacked by citrus gall wasp, with lemons and oranges being the most seriously affected. Tiny female wasps lay their eggs into the bark of soft twigs in spring. Larvae hatch out and burrow into plant tissue. By late spring woody tissue forms around the larvae, the twig swells and begins to develop into a characteristic gall.
The life-cycle is completed over winter and adults emerge the following spring, leaving the galls dotted with little holes. The wasps mate and begin laying eggs almost immediately, often on the same tree. Neglected trees can end up with very large galls (500mm long). Although native to eastern Australia, the pest has been found in Perth, WA.
PREVENTION AND TREATMENT
Don’t prune heavily in winter as this encourages soft new growth in spring, into which wasps can lay eggs. Don’t apply fertilisers high in nitrogen in winter or spring for the same reason. Try spraying the tree with horticultural oil in spring to disrupt wasps laying eggs.
Prune off galls, cutting well below them to make sure you are removing all larvae. Timing is critical. Wasps emerge in most areas from mid September until early November (because of warming climate, this seems to be happening earlier). You must prune before this. Burn, soak under water, cook in the sun in a sealed plastic bag or deep bury the pruned galls; putting them in green waste only spreads the pest.
For more of Denis's tips on dealing with citrus pests, get your copy of ABC Organic Gardener Issue 101.