ACCEL®(PGR) CONCENTRATION AND TIMING ADJUSTMENTS TO EVALUATE
THINNING AND SIZE RESPONSES IN 'LIBERTY' APPLE
Laboratories) for thinning and sizing characteristics, in a randomized and replicated field study.
Determine the effect multiple applications of a low concentration of Accel®will have on final fruit size
as a dependant variable of it's thinning properties, as well as independent of it's thinning response.
Increasing size and packout is an annual challenge with small-fruited apple varieties such as
'Liberty'. Proper cultural practices can only attain a grower a determinant amount of size in most
years, and the proper use of certain Plant Growth Regulators may substantially aid in a positive
response to final fruit size. Understanding how and when to apply certain compounds will be
necessary for their efficient use in orchard management practices in the future.
Effective chemical thinning is one of the most difficult aspects of apple production to master.
Every year is unique and adds a new variable to the thinning regime. One aspect of thinning that has
been intensely researched, and is well documented, is the correlation between early thinning and the
increase in overall fruit size. Although the benefits of reducing the trees fruit load early are well
understood, the current commercial availability of materials and annual variation in climatical
conditions makes an aggressive approach to crop reduction during the bloom and petal fall stages of
fruit development, before fruit set is known, risky (4).
Accel®is a commercially available Plant Growth Regulator that is predominately used for its
chemical thinning properties, but reportedly also has the ability to enhance fruit size by increasing cell
division (1). Alternately, when used at rates below the thinning threshold (i.e. 10 gm (ai/A), an
increase in cell division has been documented without any crop load adjustment caused by the materials
thinning effect (2). A trial was conducted in 1998 at the Rutgers University, Snyder Research and
Extension Farm in Pittstown, NJ to investigate these findings. The trial was established to investigate
any size enhancing characteristics Accel®may possess that are independent of its thinning properties.
In the trial, the Accel®treatments produced a significant increase in fruit size, weight and diameter, as
compared to the untreated control, but the certainty of the direct action is in question. Our target
application rate for Accel®was 10 gm(ai)/A, but a calibration error led to the application of 15.75
gm(ai)/A per treatment. Also, the first treatment application was applied on 29 April, one day
following the Carbaryl thinning application. A possible interaction of the two thinning agents may have
combined to create an aggressive thinning combination that overthinned these treatments. A third
possibility that could have lead to the excessive defruiting of the treatments was the compact (5 days
between treatments) application schedule. It was apparent that the two treatments containing Accel®
produced a dramatic thinning effect that was not intended and significantly impacted crop load (3).
1 North Jersey Tree Fruit Technician, Rutgers University, Snyder Research and Extension Farm, 140 Locust
Grove Rd. Pittstown, NJ08867
County Agricultural Agent, Rutgers Cooperative Extension of Hunterdon County, 4 Gauntt Place Flemington,
Plant and Soil Science Technician, Rutgers University, Snyder Research and Extension Farm, 140 Locust
Grove Rd. Pittstown, NJ08867
1999 North Jersey Tree Fruit Annual Report35