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 This paper discusses data from published and previously unpublished experiments in order to understand the effects of environment on PGR response variability.
Z. Y. Mao and D. W. Greene
Penetration of foliar-applied chemicals can be influenced by a number of environmental conditions including: light, temperature, and humidity. These change during the day. 14C-benzyladenine (BA) was applied to the upper or lower surface of McIntosh apple leaves from 6:0 0 to 21:OO hours at 3 hour intervals. The amount of BA entering a leaf over a 24-hour period was not influenced by the time of application. Temperature was correlated with BA retention in the wax layer (correlation coefficients, r=0.06 4 and r=0.70 for the upper and lower surfaces, respectively) and with penetration through the upper surface (r=0.58). BA penetration into the leaf was not correlated with light intensity, relative humidity, or time of droplet drying.
W.J. Bramlage, S.A. Weis and D.W. Greene
In a population of `Delicious' apples (Malus domestica Borkh.) with varying seed number at harvest, fruit size and Ca concentration in fruit increased with seed number. Neither K nor Mg concentration in fruit was related to seed number. In another population of `McIntosh' apples from 50 commercial orchard blocks, the percentage of fruit that developed senescent breakdown, a Ca-deficiency disorder, decreased linearly as seed number per fruit increased. Low seed number is probably a factor contributing to Ca deficiency in apple fruit.
P.D. Petracek, F.P. Silverman and D.W. Greene
D.W. Greene*, A.N. Lakso and T.L. Robinson
Several thinning experiments were initiated in 2003 to test the hypothesis that monitoring fruit growth is an appropriate and accurate method to predict final fruit set early enough to apply supplemental thinners if appropriate. A total of eight thinning treatments were applied in Massachusetts and New York. On the day of thinner application 70 to 100 spurs were tagged on 4-8 trees (replications). All fruit within a spur were individually identified and fruit were measured. At 2 to 3 day intervals fruit diameter was measured at a designated point on the fruit. Growth rate of the fastest growing 20 fruit on the untreated trees was used as the criteria to determine growth rate of fruit that would persist to harvest. A fruit on a treated tree was predicted to abscise if growth rate slowed to 50% or less of the growth rate of the 20 fastest growing fruit on untreated trees. Cold weather in 2003 following thinner application slowed the response time to thinners. Thinning treatments were applied to Delicious, Golden Delicious, McIntosh, and Gala at 7-9-mm stage. BA, carbaryl, and combinations of NAA and carbaryl were used. In Massachusetts accuracy of prediction of final fruit set at 7-11 days after application ranged from 87% to 100% with and average of 95% accuracy compared to final observed drop at the end of June drop in July. In Geneva, N.Y., the temperature was so unseasonably cold following application that prediction of final set at 7 to 11 days after application was between 68% and 79% with an average of 74% accuracy. We conclude that prediction of final fruit set following growth rate of individual fruit shows promise as an accurate predictor of final fruit set early enough to apply supplemental thinners if appropriate.
D.M. Glenn, W.V. Welker and George M. Greene
Mature peach trees were grown in six different-sized vegetation-free areas (VFAs) (0.36 to 13 m2) with and without stage 3 drip irrigation for 6 years. As VFA size increased, so did the trunk cross-sectional area, canopy diameter, total yield/tree, large fruit yield/tree, and pruning weight/tree. The yield efficiency of total fruit and large fruit initially increased with the increasing size of VFAs and then remained stable over the range of VFAs. Applying supplemental irrigation increased yield of large fruit and leaf N percentage in all VFAs. Cold hardiness was not affected by VFA size or irrigation treatment. The smaller VFAs resulted in smaller, equally efficient trees. Sod management was an effective, low-cost approach to controlling peach tree size, and, when combined with irrigated, high-density production, potentially increased productivity.
S.S. Miller, R.W. McNew, B.H. Barritt, L. Berkett, S.K. Brown, J.A. Cline, J.M. Clements, W.P. Cowgill, R.M. Crassweller, M.E. Garcia, D.W. Greene, G.M. Greene, C.R. Hampson, I. Merwin, D.D. Miller, R.E. Moran, C.R. Rom, T.R. Roper, J.R. Schupp and E. Stover
Cultivar and planting site are two factors that often receive minimal attention, but can have a significant impact on the quality of apple (Malus ×domestica) produced. A regional project, NE-183 The Multidisciplinary Evaluation of New Apple Cultivars, was initiated in 1995 to systematically evaluate 20 newer apple cultivars on Malling.9 (M.9) rootstock across 19 sites in North America. This paper describes the effect of cultivar and site on fruit quality and sensory attributes at a number of the planting sites for the 1998 through 2000 growing seasons. Fruit quality attributes measured included fruit weight, length: diameter ratio, soluble solids concentration (SSC), titratable acidity (TA), flesh firmness, red overcolor, and russet. Fruit sensory characteristics rated included crispness, sweetness, and juiciness, based on a unipolar intensity scale (where 1 = least and 5 = most), and acidity, flavor, attractiveness, and desirability based on a bipolar hedonic scale (where 1 = dislike and 5 = like extremely). All fruit quality and sensory variables measured were affected by cultivar. The two-way interaction of cultivar and planting site was significant for all response variables except SSC, TA, russet, crispness, and sweetness ratings. The SSC: TA ratio was strongly correlated with sweetness and acidity sensory rating, but was weakly correlated with flavor rating. The results demonstrate that no one cultivar is ideally suited for all planting sites and no planting site is ideal for maximizing the quality of all apple cultivars.