Influence of a mechanical string thinner on the physiology of apple
Open Access
- Author:
- Kon, Thomas Matthew
- Graduate Program:
- Horticulture
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- March 28, 2012
- Committee Members:
- James Rawlinson Schupp, Thesis Advisor/Co-Advisor
- Keywords:
- apple
mechanical thinning
cropload management
spur leaves
leaf area removal
wound induced ethylene
AVG
net photosynthesis - Abstract:
- The number of chemical thinning compounds available to apple growers is expected to be reduced in the future. Many of these compounds are not compatible with organic apple production, and hand thinning is a labor intensive and expensive process. The goals of this project were to test the efficacy of the mechanical string thinner in the Mid-Atlantic region, and to determine the mode of action of the string thinner. Trials conducted in 2010 and 2011 at Penn State’s Fruit Research and Extension Center in Biglerville, PA, tested six levels of thinning severity treatments (spindle speeds) to determine an effective range on field grown ‘Buckeye Gala’/M.9 apple trees. Treatments were applied to the same trees for two consecutive years to determine any cumulative effects of using the string thinner on apple. A linear reduction in blossom clusters per limb cross-sectional area, individual blossom number per spur, and leaf area per spur occurred as the level of thinning severity increased. The string thinner reduced cropload as thinning severity increased, but injury to spur leaves early in the season limited any benefit of increased fruit size. Since cropload was reduced as thinning severity increased, fruit quality was enhanced. Increased thinning severity treatments had no effect on return bloom, but increased annual trunk growth. Spindle speeds of 180 - 210 rpm provided the best overall thinning response and minimized injury to spur leaves. Further work will be required to determine if applying mechanical thinning treatments at earlier phenological stages may reduce the injury to spur leaves. A greenhouse trial was conducted on potted ‘Buckeye Gala’/M.9 apple trees to further elucidate the mode of action of the string thinner. Mechanical thinning treatments increased the rates of ethylene evolution of shoot leaves, and aminoethoxyvinylglycine (AVG) effectively reduced the rates of ethylene production, and prevented the string thinner-induced wound ethylene response. Net photosynthesis, vegetative growth, and dry matter accumulation was not impacted by thinning severity treatment or AVG. Future work will be required to determine the influence of wound induced ethylene on fruitlet abscission of apple.