Pollen Tube Growth Characteristics of Selected Crabapple Cultivars and Managing Apple (Malus x domestica) Crop Load and Early Season Diseases with Organic Bloom Thinning Chemicals

Reducing apple (Malus x domestica Borkh.) crop load during bloom is a reliable option for increasing fruit quality and return bloom. In this thesis, multiple approaches to improving bloom thinning practices are discussed. The first project analyzed the pollen tube growth of several crabapple cultivars. Previous research had improved the use of bloom thinning chemicals, by coordinating the application timing with the pollen tube growth between pollination and fertilization. However, pollen tube growth rates have only been measured in a few genotypes. In Chapter 2, the pollen tube growth rates of five crabapple cultivars were measured in the styles of 'Fuji', 'Golden Delicious', and 'Pink Lady' flowers, at four temperatures 12, 18, 24 and 30 C. Complex relationships were found among paternal pollen tube growth, maternal cultivar, and temperature. Chapters 3 and 4 describe projects where organically-approved chemicals, including the biofungicide, Regalia, were evaluated for their ability to simultaneously reduce crop load and decrease early season disease infection. These chemicals were applied in conventionally managed orchards (Chapter 3), and in an organically-managed 'Honeycrisp' orchard (Chapter 4). The number of chemicals approved for bloom thinning is limited, especially in the Eastern U.S. where lime sulfur and oil applications are not permitted during bloom. These studies indicate Regalia, applied during bloom, can reduce crop load and provide early season disease control. The research presented in this thesis provides new knowledge that can be incorporated into crop load management practices in both conventional and organic apple orchards.