Thinning is a critical but challenging practice in apple production, especially for organic producers. The objective of this experiment was to determine if exclusion netting, used to manage insect pests and stress, could reduce fruit set and thinning requirements of ‘Gala’ and ‘Honeycrisp’ apple trees in Michigan and Washington, U.S.A., respectively. Nets were closed around whole canopies at different timings based on a predetermined percentage of open flowers. In 2017 and 2018, netted trees set a full commercial crop regardless of percentage of open bloom at the time of netting, including prebloom enclosures. Fruit set and yield of netted ‘Honeycrisp’ trees were significantly lower than non-netted, nonthinned controls but similar to non-netted hand-thinned controls. ‘Gala’ fruit set and yield did not differ among treatments. Exclusion netting markedly reduced the number of mature seeds and increased the number of nonfertilized seeds in both cultivars. Pollinator exclusion to ‘Gala’ in a frost year increased parthenocarpic fruit set two-fold compared to non-netted trees. Fruit size, shape, and quality attributes of ‘Gala’ were were similar among treatments, but ‘Honeycrisp’ fruit were significantly smaller than hand-thinned, non-netted controls. Netting may constitute an alternative, viable strategy to manage fruit set but requires testing on different cultivars.

The profitability of modern apple orchard plantings depends largely on how rapidly the costs of planting are returned. Tree establishment and growth in the formative years are often can be limited by transplant shock associated with bare-root trees. In this experiment, we examined the effect of two planting systems, air-pruning containers, and field-grown liners, on above- and below-ground growth and development during the first year in the nursery. M9 ‘Nic 29’ bench grafts for three apple cultivars of different vigor classes, ‘Fuji’ (high vigor), ‘Gala’ (moderate vigor), and ‘Honeycrisp’ (low vigor). We hypothesized that air root-pruning containers would alter rooting distribution compared to field-grown liners by increasing fine root production, and this, in turn, would result in improved resource allocation and greater biomass partitioned to above-ground organs. Bench grafts were divided evenly between a field-grown liner bed (for bare root production) and an air-pruning container system. Air-pruning containers produced trees with significantly more root tips and greater total root length per tree than field-grown liners. Importantly, air-pruning containers resulted in a marked and significant increase in roots < 0.4 mm in diameter; however, field-grown liners produced trees had significantly more roots with diameters > 1.5 mm and, thus, significantly greater root dry matter content (DMC). Above-ground parameters (scion length, DMC of wood and leaves, and individual leaf area and DMC) were significantly increased for plants in air-pruning containers. Generally, the growth benefits from air-pruning containers were less pronounced in ‘Gala’ compared to ‘Honeycrisp’ or ‘Fuji’. The percentage of total DMC partitioned to the canopies of air-pruning containerized trees was significantly greater than field-grown liners.

Pollination is essential for producing temperate-zone tree fruits like apples (Malus × domestica). While traditionally considered insect-dependent, this view may result from orchard designs tailored to European honeybees. Previous research showed that low-seed apples could develop in insect exclusion nets, suggesting wind as an alternative pollinator. This study investigated the paternal origin of seeds and fruit set under nets compared to open canopies. Netted canopies of ‘Gala’, Fuji’, and ‘Honeycrisp’ set commercial fruit numbers without manual thinning. To determine the parental source of seeds, genotyping was performed using 16 SNP markers tailored for distinguishing apple cultivars, with primer design and genotyping conducted via the KASP™ system. Results showed significant genetic overlap between seeds from netted and non-netted fruits and nearby pollinizers, ruling out self-pollination. Netted canopies retained fruits with similar or fewer seeds compared to abscised fruits in open canopies, indicating fruit set depends on the population’s seed content rather than individual fruit seed count. These findings supporting the hypothesis that apple trees are adapted to utilize both wind and insect pollination. While wind pollination offers a sustainable approach, it requires adjustments in orchard design to ensure sufficient pollen transfer for reliable fertilization and yield.