Apple growers may have problems with cockatoos and parrots taking delight in the ripe produce in the Goulburn Valley but Yarra Valley orchardists have these problems and more with flying foxes or bats.

While the bats feed on apples later in the season, they prefer cherries starting in December.

The problem has increased since the movement of the muchpublicised bat colony from the Melbourne Botanical Gardens to Yarra habitats in the eastern ranges.

One Yarra Valley grower estimates his worst loss at $150 000 in one season. Cherry growers have also suffered extensive losses, with 17 growers estimating their losses at 50 tonnes of cherries in a season.

It is a six-months-of-the-year problem for growers.

There is frustratingly little progress being made in obtaining an effective solution to the problem.

While the DSE has been able to assist with the bird issues, the bats remain a difficulty.

Two recent meetings convened by the Yarra Ranges Shire Council have had grower, government and VFF representatives working through the issues to develop solutions.

The first meeting identified 12 options as possible ways to reduce or eliminate the impact of the pest.

Five were selected as realistic options for further evaluation and were considered in more detail at a second meeting in mid-April.

One option is netting with the advantage that full exclusion netting reduces flying fox and bird damage to zero. Birds learn over as little as two years that it can be an unpleasant experience under nets as high as 5 m, with no sides. This could also work with flying foxes.

Under netting there is a more even temperature that is also good for fruit and pickers.

The problem with full inclusion netting is the cost of about $30 000/ha.

Drape-over netting costs about $6000/ha, as well as requiring machinery to role out the netting at a cost of about $12 000 and add-on labour costs. It is also expensive to move as varieties mature.

Other disadvantages of netting include possible microclimate change (eg. higher humidity), bats can get under the netting when there is roof coverage (hail netting) only and that colouring of fruit, particularly apples, is impeded.

Other options include planting trees that provide a food source elsewhere.

Research is needed to investigate the native plants flying foxes are currently feeding on and to investigate how natural feeding sources could be increased in the Melbourne area in the months from December to May.

Farm forestry may provide food sources attractive to flying foxes that could be enhanced on migratory routes.

A NSW study has found that flying foxes are attracted to bananas hanging in onion bags from trees.

A possible theory is they may be attracted to the higher concentrations of ethylene in ripe fruit.

Flying foxes have been found and photographed in a packing shed eating fruit stored there.

This may support the theory that ethylene may be the attractant.

Delaying ethylene production in fruit by delaying maturity, resulting in lower levels of ethylene, may be a way to keep flying foxes from the feed source.

Decoy feeding elsewhere on the property is another option being investigated as well as repellents that mask the attractants in the food source.

- Ross Wall

chief executive officer

Fruit Growers Victoria