As orchard trees begin their spring flowering and fruit set, damage by frost is an increasing risk.

DPI senior horticultural adviser Henry Schneider said dry conditions in all fruit growing districts so far this winter were increasing the risk of damaging frosts this season.

He said opening flowers and young fruitlets were most at risk of being adversely affected by frost.

"It's still early, but the season is driving ahead . . . particularly in Cobram where peaches and nectarines are already flowering and apricots are at an advanced pink bud stage," Mr Schneider said.

"As they get closer to opening they get more susceptible to frost."

Mr Schneider advised orchardists with frost fans or sprinkler systems to ensure these are ready for action and that frost warning devices have been located and tested.

He said using water to stave off the effects of frost works in two ways.

Firstly by irrigating the soil, it is able to absorb radiation or sun heat into the ground, which acts as a heat bank.

In the early morning when frosts are most common, the heat in soil is radiated out and it is estimated this can hold a frost back 1C to 2C.

Secondly, if orchardists have sprinklers or micro jets going just before the temperature hits zero, the latent heat in the water is able to keep the air warmer than zero and reduce the effects of the frost.

Mr Schneider said soil would absorb water more effectively if grass was cut back short, or there was none at all, near the roots of the fruit trees and advised those orchardists who had trees that were almost flowering, to start irrigating the ground.

He said frost warning devices were critical, especially for micro-jet systems with pipes on top of the soil.

Pipes must have water flowing through them before they freeze up.

Mr Schneider also said if there was not enough rain to wet the topsoil, irrigation systems should be started to ensure moist soil which absorbed more heat during the day.

He said all orchards might need the soil profile wetted to 30 cm to 45 cm (depending on soil type), to allow root growth from the point of bud swell onwards.

Past dry winters have shown it is essential to gain maximum fruit size at harvest.

For more information phone any of the DPI FruitCheque staff at Cobram on 5871 0600, Tatura 5833 5222 or Swan Hill 5036 4800.