FRUIT DROP HURTS LARGE CROPS
SCIENTIFIC NAME: Nephelium lappaceum
FAMILY: Sapindaceae
What has promised to be the biggest rambutan crop seen in Far North Queensland has declined to modest proportions following severe green fruit drop, probably caused by weather extremes, QDPI district horticultural inspector Roger Goebel said yesterday.
An early drop following a period of extreme heat was followed on March 1st by a second drop.
Growers from Feluga to Pawngilly have reported severe fruit loss, which has altered the crop expectation from spectacular to mediocre, depending on local geography and soil type.
Mr. Goebel said main factors causing the fruit drop appeared to be excessive sunlight, low humidity and ineffective irrigation.
He said rambutans had enjoyed a fair growing season because of extended rains last year, and this had been followed by a very good flowering, with quite good conditions during and after flowering.
But this had ended with an extremely hot period after the fruit had set and were half-filled.
"It was by far the largest crop seen in FNQ" he said. "Growers expect a green fruit drop when the seed is fully developed but the aril (edible flesh) is not filled out - that normally happens.
"But with good conditions and the trees mature enough to hold a crop, its severity was unexpected."
The rambutan is an equatorial tree which can't handle water stress and reacts by dropping its fruit.
"They like heavy, overcast weather with drizzly rain," Mr. Goebel said.
"Each panicle gets around 12 fruit, each weighing about 60g - that's an awful lot of water needed to fill the fruit to normal size."
Mr. Goebel, who grows rambutans on his Etty Bay Road hobby farm, said that, to avoid excessive fruit drop, he put two smaller sprinklers (30-50 litres) instead of one large one (90 l) under each of his bigger trees. This increased the humidity and lowered moisture stress.
Other possible measures were to use finer jets for a longer mist, and even spraying at midday.
The fruit drop has caused disappointment among many growers, including Dick Finney of Pawngilly, a member of the Rambutan Association, whose members have been reporting losses around 50 per cent, and up to 100 per cent on some trees.
Mr. Finney grows about 400 trees, representing 12 varieties, mainly R134, Jit Lee, Binjari, R168 and R162. All have been dropping fruit.
The trees in the foothills of Mt Bartle Frere produce their main crop generally in March-April-May.
"There was a change of weather, from very dry to stormy, with overcast skies," Mr. Finney said.
"You would just touch them, and they would fall off.
"Only the green fruit were affected, and their sizes ranged from a marble to around an inch in diameter.
"None of the fruit which had begun to change colour were affected, and the drops occurred from branches on the inside as well as outer branches."
Mr. Finney, who has been growing tropical fruit at Pawngilly for 11 years, said while he had seen fruit drop before, it had never been in such quantities.
"What had been a good crop was reduced quickly to a mediocre one," he said.
"The irrigation and fertiliser regime was unchanged, and the drops affected fruit across the whole spectrum of age and variety.
"The only thing we can think of is the weather change, possibly preventing the tree taking up nutrients."
The Rambutan Association has asked QDPI to examine the problem.
DATE: May 1995
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