Thin to Win – Stone Fruit

Henry Schneider, Fruitcheque Officer, DPI: Cobram, Sept 2007

The stone fruit trees that orchardists have decided to take through to harvest this season need a strong commitment to a thinning program in order to produce saleable, commercial sized fruit when picked. Last season in all irrigated fruit growing districts, orchardists experienced some problems with fruit size. In most cases the problem stemmed from what seemed like an average crop early in the season, suffered size losses in last seasons extremely difficult dry season with limited irrigation water allocation. This problem still looms as a possibility this season, given the early indicators of low water allocations so far and low expectations for rainfall. Stone fruit trees in the Murray and Goulburn Valleys experienced different stress levels during the growing season last year and will need careful assessment of how much thinning is required this season. This applies to both canning and market fruit. The stone fruit trees that orchardists have decided to take through to harvest this season need a strong commitment to a thinning program in order to produce saleable, commercial sized fruit when picked. Last season in all irrigated fruit growing districts, orchardists experienced some problems with fruit size. In most cases the problem stemmed from what seemed like an average crop early in the season, suffered size losses in last seasons extremely difficult dry season with limited irrigation water allocation. This problem still looms as a possibility this season, given the early indicators of low water allocations so far and low expectations for rainfall. Stone fruit trees in the Murray and Goulburn Valleys experienced different stress levels during the growing season last year and will need careful assessment of how much thinning is required this season. This applies to both canning and market fruit. The ‘Golden Rules’ for thinning stone fruit trees are - Thin early Thin the earliest maturing varieties first. Do it right the first time and thin hard enough and focus on what is left on the tree, not what is on the ground. Supervise the job

Canning as well as market peaches and nectarines will need careful and thorough early thinning to ensure commercial grade fruit Thinning may need to be harder this season if water allocations remain low. Average to large fruit should be the aim.

Trees with good budwood development last season can easily over-crop, as fruit set during the warm and dry conditions so far are likely to be high. However, trees with poorer budwood can also set a heavy crop but will have lower stored nutrients in the tree from last season; therefore these trees will need accurate assessment and probably thinned more heavily than normal to ensure fruit achieves commercial size and quality.

Secateur thinning by cutting abundantly set laterals in half, is also possible for a quick initial thinning if done by mid October. Hand thinning may then still be needed to space fruit evenly along the remaining lateral.

The risks associated with early thinning are that split stones in fruit may increase and it makes larger fruit more susceptible to cracking close to harvest. However, delayed thinning may result in smaller fruit, especially for early maturing varieties.

Another risk of early thinning is the crop can be lost due to frost damage after being thinned. This results in loss of fruit for packing as well as having spent money on the labour intensive job of thinning.

It seems sensible to use fruit thinning as an offset insurance to obtaining large to average fruit size in a difficult season compared to an average to poor fruit size. This is in a market where fruit size, despite the season, is a key driver of profitable returns.