THE IMPACTS OF ARTIFICIAL SPUR EXTINCTION AND LEAF REMOVAL ON YIELD AND FRUIT QUALITY OF ‘GALA’
Open Access
- Author:
- Wiepz, Rebecca Josephine
- Graduate Program:
- Horticulture
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- November 26, 2018
- Committee Members:
- James Rawlinson Schupp, Thesis Advisor/Co-Advisor
Kari Anne Peter, Committee Member
Richard P Marini, Committee Member - Keywords:
- Spur removal
Spur leaf
Crop load management - Abstract:
- Crop load and early season leaf area are believed to be strong indicators of yield and fruit quality at harvest. Managing crop load generally consists of removing fruit; the earlier in the season excess fruit is removed, the greater the improvements at the end of the season, particularly with reference to fruit size. Early season thinning strategies are currently limited for Mid-Atlantic growers. Spur leaves are viewed at a vital carbohydrate source, contributing to initial fruit set and therefore final fruit quality. Trials conducted in 2017 and 2018 at the Fruit Research and Extension Center in Biglerville, PA examined how 3 levels of Artificial Spur Extinction (ASE) and spur leaf removal impacted end of season fruit quality and within cluster competition on ‘Crimson Gala’/M.9 trees planted in 2009. Artificial spur extinction lowered crop density only in the second season, and then only the two most intense spur removal treatments were effective. Average fruit size was increased, but fruit size distribution was not shifted to larger sizes, and overall yield was not improved. In both seasons, crop value was highest in the untreated control with intact lateral clusters. In the first season there was a greater impact on fruit set by total cluster count than by treatment, while this reversed in 2018, suggesting the level of variability decreased, and that branch level impacts were more applicable to whole-tree crop load. The lack of separation between of crop density levels suggests that branch level manipulations don’t accurately predict yield in Pennsylvania growing systems. Additionally, ASE cannot be recommended to Mid-Atlantic growers, due to the negative effects of treatments on yield and orchard profitability. Spur leaves did not impact fruit size or quality in either season, but did impact fruitlet growth and drop rates for one week in both seasons. However, this did not result in differences in size of fruit or number of fruit per cluster at harvest. Fruit nutritional status was also not impacted by spur leaf removal. This experiment confirmed that having intact spur leaves subtending the flower cluster is not critical for fruit set as long as phloem remains intact. The setting of fruits seems to be supported by other spur leaves due to the high efficiency with which photosynthates are moved throughout the canopy.