Getting the Best Fruit Size in Apples

The question is how we do as managers grow that perfect crop with great average fruit size and decent yields at the same time. The following factors all have a direct influence on fruit size and fruit size distribution in apples. I am assuming that when discussing these factors an adequate program is in place for competition control and IPM practices are employed.

We can start with genetics and cultivars that we grow and handle. Honeycrisp is relatively new and is genetically a large fruited cultivar that some growers, when hand thinning to touch things up, will pull off the largest fruitlets to reduce not only excessive size but to reduce the chances of bitter pit occurring because of enormous fruit size.

Cameo is another large fruited club cultivar from the U.S.A. that we now think is a variety that could be grown very well in some areas of Ontario. Other varieties like Royal Gala, Chinook, and Empire are genetically smaller fruited cultivars. Chinook in spite of having a very high quality flesh will generally not fill bins quickly at harvest because of its relatively small size.

Rootstock choices and fertility (e.g. K) play a role in maintaining fruit size. However, it is not a recommended practice to try and fertilize your way to greater fruit size if other tree factors are out of sync. We know from experience that trees like Gala, which are spur bound and of low vigour, will respond better to spur extinction practices and canopy renewal in maintaining adequate fruit size in combination with other best practices.

Multiple siring during pollination in any apple will normally produce an advantage in achieving greater fruit size over an apple that has been pollinated using only one cultivar. This is why orchard design is so important. Pollinators have a better chance of delivering pollen from more than one cultivar if blocks of trees of any one variety are not too large. Interplanting with crab pollenizers will help.

Thinning chemically and by hand (green fruit thinning) has in the past been called the single most important cultural practice that we carry on in an orchard. A poorly thinned crop cannot be expected to generate crop value even if the tonnage is there.

The regulation of soil and canopy temperature in apple is critical if one expects to have great overall fruit size. Water and water conservation practices can make all the difference in the world to tree performance from the time the tree is planted and established to the mature years of best production. Various mulches can help considerably in keeping soils cool and moist through the heat of the summer. Mulching treatments could be more critical with some strains of M9 rootstock, as this rootstock is generally not as tolerant of warm soils as some of the more vigorous semi dwarf types like M26 or MM106.

Particle films like Surround Crop Protectant have been shown in both small and large scale demonstrations to produce a larger cleaner looking fruit especially with varieties like Golden Delicious in well managed blocks. There is evidence that Surround Crop Protectant will increase the rate of photosynthesis in the tree canopy, allowing the tree to capture and move more carbon reserves directly to the crop in plantings that are on rootstocks like M9.

Growth bioregulators like Promalin and Accel, when used on certain cultivars and when weather conditions are favourable (temperature), can have a large influence on growth rates and ultimately fruit size of varieties like Empire and Golden Delicious.

Harvest management can make or break ultimate crop volumes. Years ago when we were working on calcium use in McIntosh, we found that the aggressive use of these sprays pushed maturity ahead at an accelerated rate. Fruit that were ready 10 days ahead of unsprayed checks were also a lot smaller by at least 1-2 size classes. It goes without saying that fruit that can be held on the tree an extra few days will ultimately generate huge gains in crop volume and value if the maturity is held in check. Trees of cultivars like Royal Gala will size up the second picking rapidly once the first picking of apples is taken from the orchard.