Aiding Growers To Control Fruit Size

Press, Volume CVI, Issue 31169, 20 September 1966, Page 22

Aiding Growers To Control Fruit Size

A technique by which fruitgrowers may achieve better control over the size of peaches or apples at harvesting is being investigated by the Fruit Research Division of the Department of Scientific and Industrial Research. During the last few seasons, the division has been studying the growth rates of these fruits and correlating their sizes in the early stages of development with those at harvesting. Results to date suggest that early-season measurements will provide a reliable method of determining just how much thinning is required to achieve the desired final size of fruit. More data will have to be accumulated, however, before definite recommendations can be made to growers. Fruit size is an important factor in the economics of peach growing. The canning industry prefers fruit at least 2j inches in diameter, this being the optimum size for the stoning machines. In recent years the industry has tightened its requirements considerably and has placed a steep price premium on fruit which exceeds the threshold size.

Peaches in Hawke’s Bay orchards generally set an excessive number of fruits, of which anything up to 50 per cent must be thinned off in order to promote reasonable size in those allowed to ripen. At present it is a matter of judgment on the part of the grower to determine just how much thinning is needed, but misjudgment is common, and

the result can be a loss of value in the crop. The current research project aims at replacing the uncertainty of judgment with an objective method of harvestsize prediction. Dr. R. M. Davison, the scientist who is conducting this work, has found that there is a high correlation between the diameter of fruits at the thinning stage and the diameter at harvest.

He says that in size-predic-tion based on this correlation, the early-season assessment would involve measurement of only a small sample of the fruit in the orchard—perhaps 100 fruits from a number of trees and covering the range of sizes present For consistency of results, the measurements would have to be made at the same stage of growth in each season. With peaches, the timing of the measurements could be related to the pit-hardening stage—say, 10 days after pit hardening had started. This is about the time when peaches are normally thinned. With apples, the same general findings apply. Preferred size ranges differ slightly between varieties, but are generally regarded as packing sizes of 123 to 150 fruits per bushel.

In this crop, the size correlation improves as the season progresses, and is best if the early measurements are made just before Christmas, or later. The most convenient reference date for measurement of apples is the time of blossoming, and a suitable time for measurement and thinning would be 60 to 70 days after full bloom.