Publication 360, Guide to Fruit Production: Cultivar Notes for Apple Thinning
Excerpt from Ch. 4, Publication 360, Guide to Fruit Production 2012-2013,
Table of Contents
Aurora Golden Gala can be extremely productive and therefore requires early and heavy thinning for acceptable fruit size. The cultivar appears to thin relatively well with moderate rates of carbaryl. It requires a follow-up hand thinning to space fruitlets 15-20 cm apart. Match crop load to trunk diameter. Many young Aurora trees have been cropped too heavily, resulting in small fruit, delayed maturity, poor colour, poor taste and generally poor quality fruit. This cultivar responds well to Surround Crop Protectant particle film to increase fruit size and improve shape and fruit finish.
This spurry upright growing cultivar has been successfully thinned in Ontario with moderate rates of Sevin XLR. A well-thinned crop of Ambrosia finishes strongly with regard to size and colour development. The picking window for Ambrosia is narrow if the crop is to be held in long-term storage. Consult OMAFRA factsheet Commercial Production of Ambrosia Apples in Ontario, Order 09-041.
Trees can normally handle heavy crop loads in a vigorous canopy. This cultivar has been shown to thin adequately with Sevin XLR (1 L/1,000 L water) on established trees.
Creston has been shown to over-thin easily with low to moderate rates of Sevin XLR. It is a productive large size cultivar that requires two pickings.
Before the application of NAA, make sure the king bloom fruitlet is set through a check of sepal posture. Petal fall of king bloom can take place as early as 3-4 days past peak pollination. If NAA is used too early (full bloom to petal fall), the overall fruit size of unthinned apples may be reduced compared to treatment at a stage when the king fruitlet is 8-10 mm in diameter.
Enterprise appears to thin adequately with moderate rates of Sevin XLR.
Fortune is a large sized, highly coloured, dual-purpose apple that requires thinning to avoid biennial bearing. Fortune requires a strong treatment of NAA in combination with Sevin XLR. Experienced growers have reported success with 10 ppm NAA plus 1 L of Sevin XLR per 1,000 L of water.
Fuji must be thinned aggressively for best results. This cultivar exhibits strong biennial characteristics and unthinned Fuji normally returns very little bloom the next year. Mature trees usually thin adequately with combinations of Sevin and NAA, but follow-up hand thinning of king fruitlets is usually necessary. Excessive crop may prevent the fruit from maturing to premium quality.
Gala is relatively difficult to thin successfully, and requires aggressive thinning on mature trees. NAA and Sevin at the rates listed for Golden Delicious have given good results, if applied when king fruitlets are 8-9 mm. Combination sprays of 6-BA and Sevin have also been very effective. Clusters must be thinned to one fruitlet or king bloom by mid to late June to achieve best fruit size. A follow-up hand thinning within 30 days of full bloom is normally required to further reduce crop load.
Late thinning sprays may increase the production of mummified fruitlets colonized by the fungus that causes black rot. Earlier applications produce fewer mummies, reducing black rot inoculum, and maturing fruit is less likely to be infected.
This cultivar appears to be more sensitive to thinners than McIntosh, Northern Spy and Empire. It can be over-thinned with high rates of NAA or strong combinations of NAA and Sevin XLR or MaxCel and Sevin XLR.
Unlike Golden Delicious, this mid-season Golden Delicious type will thin adequately with 1 L of Sevin XLR per 1,000 L water.
Goldrush requires a combination of NAA and Sevin XLR (10 ppm NAA + 1 L Sevin XLR per 1,000 L water). This cultivar is much tougher to thin adequately, but a well-thinned crop will mature more easily.
This cultivar seems to be more sensitive to thinning treatments than Empire. Thin Honeycrisp cautiously, as it can easily become oversized and is very prone to bitter pit. Where large fruit is a problem, it may be best to leave two fruitlets per cluster, or space the fruit closer together. Use of growth regulators (such as 6-BA), which enhance fruit size, may not be warranted for this large fruited cultivar. Use no more than 2.5 ppm NAA with 1 L of Sevin XLR per 1,000 L of water as a starting point on established trees. Many growers report good fruit size distribution when the largest fruitlets are removed by hand thinning following the spray thinning treatment. Honeycrisp is highly biennial in nature and may not return an adequate crop year after year.
For a discussion on crop load and trunk circumference with respect to thinning see OMAFRA Factsheet, Commercial Production of Honeycrisp Apples in Ontario, Order No. 05-047.
This cultivar thins relatively easily and has good size potential when clusters are thinned to singles. Most producers get adequate thinning with moderate rates of Sevin. Over-cropping Jonagold may result in very poor return bloom and fruit may not mature to a premium quality.
Shizuka thins similarly to Mutsu/Crispin with moderate rates of Sevin XLR.
Silken thins with 1-1.5 L of Sevin XLR per 1,000 L of water, depending on tree age. This cultivar bruises easily. Evenly spaced fruit in the canopy is desirable because it enables careful picking and handling.
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