Field thinning studies were conducted in two orchards at Geneva and Milton, N.Y., over 3 years (2003–05) using mature Gala/M.9 trees. A range of final croploads was achieved with various chemical thinning treatments, including, benzyladenine combined with carbaryl, or napthaleneacetic acid combined with carbaryl. The most-aggressive thinning treatments in the year with high rainfall achieved an average fruit size of 190–200 g; however, the yield was reduced considerably, resulting in a reduced farm gate crop value compared to less-aggressive thinning. In a dry year, the fruit sizes were smaller even with aggressive thinning. The optimum yield for maximum crop value varied for each orchard block for each year. The optimum croploads varied less than the optimum yield, since cropload normalizes the tree size between blocks. Optimum fruit size to maximize crop value varied narrowly between 155–170 g (113–100 count size) across blocks and years. This was true despite a substantial price difference between large, 80-count fruits and the moderate-size 113-count fruits. If lower prices received for processed apples were used in the analysis, then the optimum yield was significantly higher than with fresh fruit prices. In New York State, it appears that achieving 80-count fruit requires too large of a reduction in yield, which causes a reduction in crop value.
Terence L. Robinson
`Empire'/M.26 apple trees which were planted in 1978 and trained to a Y-trellis were pruned differentially from 1989-1993. Trees were dormant pruned by removing from 1-4 scaffold limbs. The annual increase in trunk cross-sectional area (TCA), and the number and length of shoots removed during summer pruning increased linearly as the severity of pruning increased. The number of shoots removed during summer pruning from the most severe pruning treatment was more than double that of the least severe treatment Cumulative fruit number and yield were reduced linearly with increasing severity of pruning while average fruit size was increased only slightly by severity of pruning. Light interception was reduced with increasing severity of pruning. Tree efficiency of converting light energy into fruit (g fruit/MJ PAR intercepted) was linearly reduced with increasing pruning severity. Most of the reduction in conversion efficiency appeared to be due to reduced partitioning of resources into fruit since partitioning index (g fruit/unit increase in TCA) was more highly correlated to pruning severity than to conversion efficiency. Conversion efficiency and partitioning index accounted for a greater portion of the yield variation than did light interception indicating that the influence of pruning on yield was more a function of changing internal physiology than reduced light interception.
Terence L. Robinson
In 1986, an orchard systems trial was planted with `Empire' and `Jonagold' on M.26 rootstock to compare the performance of the Y-trellis training system at a range of spacings and rectangularities. There were four in-row spacings ranging from 90 cm to 3.66 m and four between-row spacings ranging from 3 to 6 m, giving tree densities from 472 trees/ha up to 3588 trees/acre. Rectangularities ranged from 0.83 to 6.67. In several cases, different spacings gave the same tree density, but with different rectangularity. Trees were trained to a Y-shaped trellis with a 60° angle. Scaffold branches were trained to the wires on each side of the Y in a fan-shaped arrangement. At the closest in-row spacing only two scaffolds were allowed per tree, while at the widest in-row spacing up to 12 scaffolds were allowed per tree. At the end of 11 years, tree weight and cumulative yield per tree were negatively correlated to tree density, while light interception and cumulative yield per hectare were positively correlated to tree density. However, the relationship was weakened by differing results with different rectangularities at the same spacing. As rectangularity increased at a given density, tree size, yield, and light interception were reduced. However, at the lower densities, trees failed to completely fill the trellis when rectangularity was low, thus limiting yield per hectare. Fruit red color was reduced at the highest densities and increased with increasing rectangularity.
Terence L. Robinson and Zhongbo Ren
Eleven year-old Empire/M.7 apple trees were shaded continously for 4 years with half-tree shading cages. Shading reduced primary spur leaf duration, bourse shoot leaf area, specific leaf weight, spur diameter and bud diameter. Over the four years, shaded spurs continued to increase in length but spur diameter increased very little resulting in long and brittle spurs. However, shaded spurs continued to flower and set fruit. Leaf area development was similar inside and outside the cages at one week after bloom but by 2 weeks after bloom, spurs inside the cages had significantly lower leaf area. Shading reduced fruit set, fruit size, fruit color, fruit soluble solids and fruit dry matter. Fruit growth rate was reduced by shading early in the season but was no different than the unshaded controls by 4 weeks after full bloom.
In an attempt to reverse the negative effects of shading on spur vigor, foliar urea, zinc-EDTA and solubor were sprayed 3 times during the early growing season each year. Rather than increasing spur leaf area, foliar nutrient sprays significantly reduced bourse shoot leaf area and did not increase the duration of primary spur leaves. Although foliar nutrients reduced total spur leaf area, they improved fruit size, color and soluble solids slightly.
Terence L. Robinson and Warren Stiles
A field experiment was established in 1993 in a 3-year-old `Empire'/M.9 apple orchard. An incomplete factorial treatment design compared nitrogen only fertilization with nitrogen plus potassium fertilizer applied either on the ground with and without trickle irrigation or through the trickle irrigation system. Timing of potassium fertigation treatments compared season-long K fertigation to early season or late-season K fertigation. Results of main effects showed that K fertilization reduced trunk cross-sectional area increase, but increased yield, fruit size, and fruit red color. There was no benefit of fertigation compared to ground application of fertilizers plus trickle irrigation. There was no effect of source of K fertilizer (KCl vs KNO3) on tree growth, yield, fruit size, or color. Time of K fertigation showed that late-season K fertigation resulted in greater trunk cross-sectional area increase compared to early season fertigation or season-long fertigation. Fruit size was greatest when K fertigation was done in the early season. There was no effect of time of fertigation on yield or fruit red color. Potassium fertilization increased leaf K levels and reduced leaf Mg levels. Time of fertigation did not affect leaf K levels, but early season fertigation resulted in higher leaf N levels.
Sergio Lopez-Cuevas and Terence Robinson
A factorial field experiment was conducted at the New York State Agricultural Experimental Station in Geneva, N.Y., during 2004 and 2005 with `Honeycrisp' apple trees on M.9 rootstock. The main plot factors were three levels of applied nitrogen (0 kg/ha, 50 k/ha, and 100 k/ha); three levels of applied K2O (0 k/ha, 100 kg/ha, and 200 kg/ha); ± foliar nutrient sprays containing N, B, Zn, and Mg, ± foliar sprays of CaCl2 and ± trickle irrigation. The subplot factor was cropload (3, 6, 9, 12, and 15 fruits/cm2 TCA). Trees receiving irrigation or potassium had higher yields and the effect was greater as cropload was increased. There was no effect of nitrogen fertilization, foliar Ca, and foliar N, B, Zn, and Mg on yield. Irrigation and increased potassium fertilization rate reduced fruit soluble solids at harvest. Foliar calcium applications, foliar N, B, Zn, and Mg applications, and nitrogen fertilization rate did not affect fruit soluble solids at harvest. No treatment factor had an effect on fruit firmness at harvest, but, after 4 months on cold storage, fruits from irrigated trees had greater firmness. Bitter pit incidence was lower on apples from trees that did not receive irrigation compared to irrigated trees. The difference was constant under all cropload levels. Foliar calcium applications, foliar N, B, Zn, and Mg applications, nitrogen fertilization rate and potassium fertilization rate did not affect bitter pit incidence.
Terence L. Robinson* and Christopher B. Watkins
In 2001 and 2002, we imposed a wide range of croploads (0-15 fruits/cm2 of TCA) on 4- and 5-year-old Honeycrisp/M.9 trees by manual hand thinning soon after bloom to define appropriate croploads that give adequate repeat bloom and also the best fruit quality. At harvest each year we evaluated fruit ripening and quality. Samples were stored for 5 months in air at 38 °F and 33 °F and evaluated for fruit firmness and storage disorders. Cropload was negatively correlated with tree growth, return bloom, fruit size, fruit red color, fruit sugar content, fruit starch content, fruit firmness, fruit acidity, fruit bitter pit, fruit senescent breakdown, fruit rot and fruit superficial scald, but was positively correlated with leaf blotch symptoms, fruit internal ethylene concentration at harvest, and fruit soggy breakdown. There was a strong effect of cropload on fruit size up to a cropload 7, beyond which there was only a small additional effect. Although there was considerable variation in return bloom, a relatively low cropload was required to obtain adequate return bloom. Fruit red color was reduced only slightly up to a cropload of 8 beyond which it was reduced dramatically. The reduced fruit color and sugar content at high croploads could indicate a delay in maturity of but, fruits from high croploads were also softer, had less starch and greater internal ethylene. It that excessive croploads advance maturity. Overall, croploads greater than 10 resulted in no bloom the next year, and poor fruit size, color and flavor, but these fruits tended to have the least storage disorders. Moderate croploads (7-8) resulted in disappointing return bloom and mediocre fruit quality. For optimum quality and annual cropping, relatively low croploads of 4-5 were necessary.
Jason L. Osborne and Terence L. Robinson
In 2004, we conducted a chemical thinning field study in Appleton, N.Y., on 5-year-old `Rising Star' peach trees on Lovell rootstock. Treatments included soybean oil or petroleum oil applied at 8% about 30 days before budbreak. Ammonium thio-sulfate (ATS) 3.5 gal/acre, ATS 5.0 gal/acre, lime sulfur (1%, 3%) plus Crockers fish oil 2 gal/acre, and Wilthin 6 pt/acre were applied at FB; and the grower standard hand-thinning treatment at 45 DAFB. Trees treated with thinning agents were not given supplemental hand thinning. The high rate of ATS, 5.0 gal/acre and Wilthin 6 pt/acre had the greatest thinning effect and reduced fruit set by 55% and 61%, respectively, compared to the untreated control. The high rate of ATS also increased fruit size 25%, but reduced yield by 45%. Soybean and petroleum oil treatments did not significantly reduce fruit set. Lime sulfur plus fish oil treatments 1% and 3% also did not significantly reduce fruit set. Although a significant reduction in yield was observed in the high rate ATS and Wilthin treatments, a greater proportion of the crop was in the larger size categories. In 2005, treatments included soybean oil 8% plus Latron B 1956 applied 18 days and 25 days before FB, Lime sulfur (2%, 4%) plus Crockers fish oil (2%) applied at FB, Ammonium thio-sulfate (ATS) 3.5%, 5.0%, Wilthin 1.9, 2.8 L (Entek, Inc.), plus Regulaid 473 mL per 935 L/ha applied at FB, Entry 1.5, 3.0%, Tergitol TMN-6 0.75, 1.5%, hand-thin flowers to a crop load of seven fruits per cm2 at FB and hand-thin fruit to 7 fruits per cm2 applied 45 days after FB.
Terence L. Robinson and Warren C Stiles
A field experiment was established in 1992 with `Empire' apple trees on either M.7 or M.9 rootstock. Preplant fertilization with NPKB plus lime compared to the lime only control did not increase tree growth during the first 4 years, but did increase cumulative yield (10%) and average fruit size (7%). The addition of annual applications of ground-applied NKB after planting increased total shoot growth 17%, as well as yield (26%) and fruit size (14%) compared to the lime only control. Trickle irrigation significantly increased trunk cross-sectional area (17%), shoot growth (16%), yield (18%), fruit size (5%), and yield efficiency (7%). The interaction of ground fertilization and trickle irrigation showed that trickle irrigation increased the benefits of ground applied fertilizers. Without trickle irrigation, ground-applied fertilizers increased shoot growth only 6% and yield 14% compared to the unfertilized controls, but, with the addition of trickle irrigation, the ground-applied fertilizers increased shoot growth 21% and yield 21% over the irrigated but unfertilized control. Ground fertilization increased yield efficiency and fruit size by the percentage by whether or not trickle irrigation was present. Fertigation gave similar results as the trickle plus ground fertilizer treatment on tree growth, yield, fruit size, and yield efficiency. Our results indicate that trickle irrigation in the eastern United States can improve tree growth, yield, and fruit size in the first few years after planting. The addition of ground-applied fertilizer or fertigation can improve tree performance even more. However, in the humid New York climate, there does not appear to be a significant benefit from injecting the fertilizer into the trickle water compared to applying the fertilizer on the ground.
Ed Stover, Ferdinand Wirth, and Terence Robinson
Analysis of apple (Malus×domestica Borkh.) and citrus thinning experiments indicates that the relationships between cropload, fruit size, and total yield can be used to assess optimal cropload for highest crop value. Mean fruit size increased and total yield declined as the cropload (number of fruit/cm2 trunk cross-sectional area) was reduced through the use of chemical thinners. Because crop value is influenced by fruit size and total yield, intermediate croploads gave the highest economic returns in all experiments evaluated. For `Empire' apple, croploads greater than those expected to provide good return bloom often produced the highest crop value for a single year. In citrus, optimal crop values resulted from a broad range of intermediate croploads. A method is described to analyze optimum cropload from thinning experiments.