http://www.weeklytimesnow.com.au/article/2009/11/05/129251_horticulture.html

Fruit trees flowering earlier

Sandra Godwin
November 5, 2009


Feeling the heat: some citrus trees are flowering
earlier in Sunraysia due to the changing climate.

CLIMATE change has forced some citrus varieties in the Sunraysia to flower two weeks earlier than normal during the past decade, researchers have observed.

But it's the likelihood of more frequent extreme temperatures - not general warming and the earlier onset of spring - that growers should fear, experts say.

NSW Department of Industry and Investment research physiologist Tahir Khurshid said a test crop of Washington navel oranges at Dareton this year reached full flowering on September 22 - the earliest date in more than a decade.

Flowering usually occurred in mid-October, but in the previous 11 years, the orange trees had flowered up to two weeks earlier.

Dr Khurshid said flowering date had no ill-effects on fruit growth or maturity, although temperatures above 35C in October could cause large numbers of flowers to fall, slashing potential yields.

"Some early ripening varieties may flower late, and some late varieties may flower earlier," he said.

"The final fruit size is related to the rate of growth of the fruit, for instance navelina flower later than Washington navel, but navelina is an early variety in the market because the rate of growth is faster compared to any mid-maturing fruit like Washington, or late-maturing varieties like lane late or barnfield, because they grow at a slower rate."

Dr Khurshid said every phenological stage of the citrus production cycle could be affected by extremes of temperature at some time, making it critical for growers to avoid stressing their trees, especially navel oranges, with a lack of water between October and March.

Extreme temperatures during the fruit-set period in November can cause large numbers of fruit to abort, Dr Khurshid warned.

"There is still argument about how citrus can be affected by climate change, which I class as something which is permanent, not a variation," he said.

"As a sub-tropical fruit, citrus can be grown at latitudes between 20 degrees and 40 degrees (in Australia, from Proserpine in Queensland to King Island in Tasmania) and in some cases, out of those latitudes such as lemons in Christchurch (in New Zealand, at 43 degrees).

Dr Khurshid said the CSIRO had predicted that in the next 20 years the number of days above 40C would rise, from 14 to 47 in the Sunraysia.

Experience in the past five years had shown just three or four days of temperatures above 40C was enough to cause havoc in citrus.

Four days in a row in February 2007 caused sunburn damage to exposed fruit around the tree canopy, while last February, seven hot days in a row also caused leaf burn, which Dr Khurshid said had not been seen in the previous 10 years.

He said growers would have to prepare for the expected increase in extreme temperatures, probably by changing tree canopy shapes, irrigation management or spraying sun protectants.