2018 ASHS Annual Conference

Decreasing crop load to maximize fruit size and quality is a common management strategy for apple (Malus domestica) production. Current thinning strategies are limited by high cost of labor, changes in chemical regulations, and variation in plant response due to unpredictable weather. Additionally, current chemical and manual thinning strategies postpone removal of fruit until post bloom. Thinning earlier in the season causes larger gains in fruit size and more effectively minimizes alternate bearing. Artificial spur extinction (ASE) is a pre-bloom method of manual thinning that minimizes a tree’s potential crop load. Experimental trials in New Zealand and Australia showed ASE to maximize the impacts, reliability, and profitability of thinning treatments. Previous research in Pennsylvania has shown that the industry standard ASE level of 6 buds remaining per square centimeter limb cross sectional area does not reduce crop load to profitable levels in our climate. In 2017 a completely randomized trial was conducted at the Penn State Fruit Research and Extension Center in Biglerville, Pennsylvania on twenty mature ‘Gala’ apple trees divided into 5 treatments. Trees were thinned to 2, 4, or 6 buds cm^-2 limb cross sectional area (ASE2, ASE4, and ASE6), and compared to an unthinned control. Following initial fruit set, all buds on one year old wood were removed, except one treatment which remained unaltered. Yield of fruit ≥6.35cm in diameter was not significantly altered by the thinning treatments(P>0.65). However, the fruit produced by ASE4 showed a trend toward increased size, and had the highest soluble solids content (P>0.0033). In 2018 the study will be continued, repeating the evaluation of fruit quality and yield. The addition of an early season non-chemical thinning strategy that could set potential cropload before applying other thinning treatments would be a beneficial tool for many growers in PA.