Two years of field experiments were conducted in eastern New York to evaluate the efficacy of a multi-step thinning approach on reducing crop load (no. fruit per cm2 trunk cross-sectional area) and increasing fruit size of 'Empire' apple (Malus ×domestica Borkh.). Applications of Endothall (ET) at 80% bloom, NAA + carbaryl (CB) at petal fall (PF), and Accel™ + CB at 10 mm king fruitlet diameter (KFD), alone and in all combinations, were compared to a nonthinned control and to the application of NAA + CB at 10 mm KFD (commercial standard). In both 1996 and 1997, orthogonal contrasts indicated the multi-step treatment significantly increased fruit size, reduced cropload, and reduced yield compared to single applications. Effects on cropload of consecutive treatments were largely predicted by multiplying effects of individual treatments. Although all thinning treatments except for NAA + CB at PF in 1997 significantly reduced cropload, no single treatment thinned sufficiently to ensure good return bloom. Compared to NAA + CB at 10 mm KFD, multi-step thinning with NAA + CB at PF followed by Accel™ + CB at 10 mm KFD produced bigger fruits in both years, and resulted in a higher percentage of spurs carrying a single fruit in 1996. When fruit size was evaluated after removing the effect of cropload (cropload adjusted fruit weight), NAA + CB at PF, Accel™ + CB at 10 mm, and the two applied sequentially, resulted in greater cropload adjusted fruit weight than the nonthinned control in both years, whereas NAA + CB at 10 mm did not. Contrast analysis of treatments with and without ET showed no significant effect of including ET on fruit size, though total cropload was reduced at P = 0.10 and total yield was reduced (P = 0.03 in 1996 and P = 0.12 in 1997). No deleterious effects from multi-step treatments have been observed. All thinning treatments significantly increased return bloom in 1996 and 1997 compared to the control with little difference observed between treatments. Chemical names used: naphthalene acetic acid (NAA); 1-naphthyl-N-methylcarbamate [carbaryl (CB)]; 6-benzyladenine [BA (Accel™)]; 7-oxabicyclo (2,2,1) heptane-2,3 dicarboxylic acid [ET (Endothall™)]
Plant response to foliar application of plant growth regulators (PGRs) is often variable, in part due to environmental factors. Weather prior to application is thought to influence cuticle development and thus PGR uptake. For example, in growth chamber studies foliar uptake of 1-naphthaleneacetic acid (NAA) is sometimes increased when fruit trees are placed in low temperature and high humidity several weeks prior to application. Environmental conditions over an extended period of time after application may influence PGR conversion to active form (e.g., ethephon), PGR metabolism, or metabolic factors that affect PGR activity in the plant. The effects of environmental conditions on PGR uptake have been investigated extensively in laboratory studies. In many cases, uptake is clearly increased by high temperatures immediately after application. Laboratory studies report a linear positive correlation between temperature and uptake and greater temperature response above 25 °C (77.0 °F). High humidity and longer drying time often are also reported to increase PGR uptake in laboratory studies. These results are consistent with many grower observations on effects of weather on chemical thinning and have been incorporated into many product labels and extension recommendations. However, relatively few field experiments have been reported in which the relationship between PGR response and environmental conditions were assessed. Wash-off studies have demonstrated that rain shortly after application may reduce efficacy of NAA. Several studies demonstrate environmental interaction with metabolic activity involved in PGR action. For example, shading after thinner application is reported to increase fruitlet abscission and enhance effectiveness of some thinning agents. Chemical thinning of apples (Malus ×domestica) with ethephon is reported to correlate strongly with temperature in the days after application, while studies suggest that higher temperatures after aminoethoxyvinylglycine (AVG) application may reduce control of preharvest drop. However, the stage of fruitlet development at apple thinning often appears to be more important than environmental conditions at the time of PGR application. In addition, field experiments indicate that longer drying times at lower temperatures seem to largely compensate for greater uptake rates at higher temperatures. This paper discusses data from published and previously unpublished experiments in order to understand the effects of environment on PGR response variability.
Abstract
This paper reports a method of propagating Peperomia ‘Red Ripple’ 3 from leaf discs in vitro.
The effects of summer pruning on the yield and quality of apples (Malus domestica Borkh.) from mature `Rogers McIntosh'/M.7 trees were assessed in 1986-88. Summer pruning from 1 July through 1 Sept. enhanced red coloring and increased the percentage of the crop graded U.S. Extra Fancy. Fruit weight was not altered by summer pruning. Total yield was reduced by summer pruning only in 1 year, however, in no year was the harvested yield reduced. The portion of the crop that was picked in the first harvest was increased by summer pruning. Dormant-pruning time was decreased by summer pruning, and the total time required for pruning was increased only 1 of the 2 years where it was measured. Summer pruning and daminozide treatment significantly increased the estimated net returns.
-naphthalene acetic acid (NAA; 0, 0.5, and 1.0 mg·L −1 ). Apical buds (0.5 cm in length) were excised from sterile 30-d-old seedlings, placed individually into test tubes, and incubated in the growth room under controlled conditions (26 ± 1 °C, 8 h dark/16 h
, 1972 ) or NAA ( Harley et al., 1958 ; McArtney et al., 2007 ) in the heavy cropping year of a biennial bearing cycle can stimulate flower bud formation. Williams (1972) reported that postharvest application of ethephon to young vigorous ‘Wellspur
The stability of the organosilicone surfactant Silwet L-77 (L-77) was investigated in growth regulator solutions representative of those frequently used as foliar sprays in horticultural research and production. Surfactant stability was followed by measurement of surface tension at selected time intervals after addition of the surfactant. Time-course studies revealed that surface tension of Ethrel (2.08 ml·liter) and Pro-Gibb (3.13 ml·liter) solutions made up with deionized water with 0.01% L-77 increased immediately after preparation. A lag phase of constant surface tension was observed at a higher (0.1'%) L-77 concentration. The rate of increase in surface tension was higher for the more acidic Ethrel solution (pH 2.5) than for the Pro-Gibb solution (pH 3.8). The water source used for preparation of the spray solution significantly affected surfactant stability. Surface tension of Ethrel solutions (2.08 ml·liter 0.1% L-77) prepared with well water remained constant over 4 hours, whereas surface tension increased when rain or deionized water was used. Surface tension increased in Pro-Gibb spray solutions prepared with deionized water at concentrations typical for low- (1/10 x), but not high- (1x), volume spray applications or when solutions were prepared with well water. In all experiments, pH of the spray solution was the only factor that affected L-77 stability. Chemical names used: (2-chloroethyl) phosphoric acid (Ethrel); gibberellin A (Pro-Gibb); polyalkyleneoxide modified polydimethylsiloxane copolymers (Silwet L-77).
Hundreds of fruit thinning experiments have been reported for various fruits including apple (Malus × domestica) and citrus (Citrus spp.). Unfortunately, very few of these reports attempt to evaluate the economic implications of thinning. Researchers routinely report significant cropload reduction accompanied by an increase in fruit size. Although these are crucial responses to thinning, they are not always associated with an increase in crop value, which is the commercial justification for thinning. The few economic studies summarized in this review illustrate that the economic effects of fruit thinning vary widely, and successful thinning often reduces returns to the grower, at least in the year of treatment. It is important to quantify the economic benefits of thinning and identify croploads that balance the trade-off between yield and fruit size to provide optimal crop value. Future thinning research should report total yields and fruit size distributions to permit economic assessments and comparisons of treatments.