Urgent action needed on fruit fly

Home gardeners need to start offensive action early if they want to avoid sharing stone fruit and grapes with Mediterranean fruit fly over the summer, according to the Department of Agriculture and Food.

Department community liaison officer Ernie Steiner advised baiting as the most important weapon, but recommended a combination of tools for the best results.

"The Medfly life cycle is closely related to temperature," Mr Steiner said. "As temperatures increase the flies become much more active and the generation time can reduce to only about four weeks.

"If people hit them now before numbers build up, they will be in a much better position than waiting until fruit is nearly ripe. By that stage almost nothing deters fertile egg-laying females from stinging fruit."

Traditional cover spray products that contained fenthion or dimethoate are no longer permitted in home gardens. However, several products containing either maldison or spinosad are available in home pack sizes for use in foliar fruit fly baits.

Label directions for these products should be followed carefully and some need to be mixed with protein and sugar to be effective.

Mr Steiner said baiting was an effective weapon, but worked best over larger areas where neighbours combined their efforts.

"Unfortunately, fruit flies do not respect fences," he said. "So your good work can be undone if neighbours are not playing their part also."

Bait should be splashed onto tree foliage once, or preferably twice, a week. As coarse droplets it provides a lethal feeding patch that attracts and then despatches the flies.

Gardeners don't need to treat the whole tree, just a single patch, using 50120 millilitres depending on the label directions, varying the location each time.

Mr Steiner said the cost of organic fruit fly baits varied greatly according to the pack size. Larger, more economical pack sizes are sold by rural suppliers in four-litre containers.

Traps that contain a liquid to attract and drown fruit flies can also be effective. These are available commercially, for example CeraTrap, or can be made using plastic drink bottles with entry holes for the flies.

Readily purchased yellow-topped fly traps filled with a 'home brew' attractant also work well.

The mixtures usually contain some form of protein and sugar with a fruity aroma that attracts both male and female flies. Recipes for attractants are available on the department's website.

Good orchard hygiene, removing fallen fruit that become ideal fly breeding sites, is also important. Such fruit should be 'solarised', which means leaving it in the sun for several days in sealed black plastic bags to kill the flies before disposal.

Fruit trees that are difficult to manage should be pruned to manageable size or removed, Mr Steiner recommended. If fruit is not to be eaten, it should be stripped from trees well before ripening and destroyed.

Some gardeners use netting to protect valuable crops. This can involve small bags for bunches and single fruit, or larger sections for whole trees. More durable products than traditional mosquito netting are available from interstate suppliers online.

More details are available from the department's website at agric.wa.gov.au or from the Pest and Diseases Information Service (PaDIS) on 1800 084 881.