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James R. Schupp

In 1984 trees of `Starkspur Supreme Delicious' apple (Malus domestica, Borkh) on 16 rootstocks were planted at 32 sites In Morth America according to guidelines established for cooperative testing by the North Central Regional Cooperative Project (NC--140). Tree loss and root suckering in the Maine planting have been low, similar to that of other sites. Tree size in Maine is smallest amoung all sites after eight seasons. Trees on Budagovsky 9 (B.9) rootstock were the most precocious, producing significantly higher flower numbers and yield in the third year. Other precocious rootstocks in this planting included C.6, M.26EMLA, M.7EMLA and P.l. After eight years, B.9, C.6 and M.26EMLA were the most productive amoung the dwarf trees. P.l and M.7EMLA were the most productive amoung the more vigorous stocks. Heavy croping trees on dwarf rootstocks leaned more due to hurricane winds than larger better anchored trees which lost a larger proportion of their crop. B.9, C.6 and P.1 may have potential as rootstocks for commercial apple orchards in New England.

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James R. Schupp

To evaluate the interactions between cultivar and rootstock, four apple (Malus domestica Borkh.) cultivars, `Pioneer Mac', `Marshall McIntosh', `Ginger Gold', and `Empire' on two rootstocks, M.26 and Mark, were planted in a split-plot design. After 5 years, `Pioneer Mac' and `Ginger Gold' had larger trunk cross-sectional area (TCSA) on M.26 than on Mark. `Marshall McIntosh' and `Empire' had larger TCSA on Mark than on M.26. Precocity, expressed as both number of flower clusters and yield, was greater for trees on Mark for all cultivars except `Ginger Gold', which had greater flower cluster numbers and yield on M.26. Fruit size was variable from year to year, depending on crop load; however, `Pioneer Mac' and `Ginger Gold' usually produced the largest fruit, while `Empire' consistently produced the smallest fruit—'Ginger Gold' appears to be incompatible on Mark. The results of this study demonstrate that cultivar × rootstock interactions can be significant and need to be considered when rootstock and planting density recommendations are made.

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James R. Schupp

In 1984 trees of `Starkspur Supreme Delicious' apple (Malus domestica Borkh) on 16 rootstocks were planted at 30 sites in North America according to guidelines established for cooperative testing by the North Central Regional Cooperative Project (NC-140). Tree loss and root suckering in the Maine planting have been low, similar to that of other sites. Tree size in Maine is smallest amoung all sites after seven seasons. Trees on Budagovsky 9 (B.9) rootstock were the most precocious, producing significantly higher flower numbers and yield in the third year. Other precocious root-stocks in this planting included C.6, M.26EMLA, M.7EMLA and P.1. After seven years, B.9, C.6 and M.26EMLA were the most productive amoung the dwarf trees, and consequently are the most efficient. P.1 and M.7EMLA were the most productive amoung the more vigorous stocks. This trial will be conducted for 3 more seasons, however it appears that B.9, C.6 and P.1 may have potential as rootstocks for commercial apple orchards in New England.

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James R. Schupp and Highmoor Farm

Mature `McIntosh'/MM.111 apple (Malus domestica, Borkh.) trees were treated to evaluate the response of root pruned trees to chemical thinning and to determine if reducing the crop load increased fruit size on root pruned trees. The trees were root pruned at full bloom in 1988 and 1989, by cutting on both sides of the row 1m from the trunk and 30cm deep. Water, 600mg/liter carbaryl, 5mg/liter napthaleneacetic acid (NAA), or NAA plus carbaryl were applied when fruit diameter was approximately 10mm. Trunk cross-sectional area (TCSA) was increased by thinning treatments in 1988, but root pruning had no effect. In 1989, root pruning reduced TCSA increment by 35%. Shoot length was reduced by root pruning both years. All treatments reduced percent fruit set in 1989, however root pruned trees and trees treated with NAA had the highest fruit numbers at harvest. Preharvest fruit drop was reduced by root pruning in both 1988 and 1989. Root pruning had no influence on the response of apple trees to chemical thinning. Removing a portion of the crop with chemical thinners was partially successful in counteracting the reduction in fruit size caused by root pruning.

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James R. Schupp, H. Edwin Winzeler and Melanie A. Schupp

Renewal of limbs by pruning to leave a short, angled, upward-facing stub is common practice for spindle-type apple (Malus ×domestica) training systems. A short, beveled stub cut is thought to stimulate renewal growth from latent buds present underneath the base of the excised branch, and to stimulate smaller, more fruitful renewal limbs with wide crotch angles. We conducted trials over the course of 2 years that involved dormant pruning of ‘Buckeye Gala’ with renewal cuts to compare two stub lengths, 0.5 and 2 cm, and three stub orientations, upward facing, downward facing, and vertical facing, to determine the effects on renewal shoot number, position, angle, and length. We found no clear advantages with either stub length that we evaluated, and there was no improvement in renewal shoot quality with a bevel cut at any orientation. Stub length and stub angle did not influence limb renewal and may be unimportant for training orchard-pruning crews and for machine-learning and robotic pruning.

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Henry K. Ngugi and James R. Schupp

The risk of spreading fire blight in apples after mechanical thinning with a rotating string blossom thinner was evaluated in field and potted-tree experiments. In the field experiment, using the mechanical thinner on noninoculated trees immediately after operating the equipment on inoculated trees significantly (P < 0.01) increased fire blight incidence resulting in 90 ± 20.01 (mean ± SE) infected shoots compared with 23.5 ± 8.97 diseased shoots in similar trees that were not thinned mechanically. A similar result was obtained in greenhouse experiments whereby healthy apple plants positioned adjacent to diseased plants before the group was subjected to the mechanical thinner developed more than twice the number of infected shoots as that on similar plants that were not thinned. These results indicate that under conditions conducive to infection, the mechanical blossom thinner significantly increases the risk of spreading Erwinia amylovora. The use of the thinner should therefore be limited to orchards with no history of disease in the last 3 years and on days when predicted weather is not suitable for tree infection by E. amylovora; otherwise, a severe fire blight epidemic could develop in the orchard.

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Renae E. Moran and James R. Schupp

'Macoun'/B.9 apple (Malus ×domestica Borkh.) trees were planted in May 1998 in ± compost or ± monoammonium phosphate (MAP) for a total of four preplant treatments: 1) 90 g phosphorus (P) per tree, 2) 128 kg compost per tree, 3) 90 g P and 128 kg compost per tree, and 4) and an untreated control. MAP did not increase tree growth or yield in any year of the study. Compost increased canopy width into the sixth year after planting, and increased tree height and trunk cross-sectional area (TCA) into the seventh year. Annual yield was increased by compost in the fifth and seventh years, but not fourth or sixth year after planting. Compost increased cumulative yield in the sixth and seventh years.

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James R. Schupp and T. Auxt Baugher

Hand-thinning of fruit is among the most labor-intensive orchard practices and consequently contributes significantly to peach (Prunus persica) production costs. Prior research conducted by the authors on string blossom thinners for managing peach tree cropload demonstrated that this new technology reduces labor requirement and also improves fruit size. Studies were conducted over two seasons in peach orchards trained to perpendicular V or open-center systems to evaluate possible pruning strategies to improve tree canopy access by string thinners. The objectives were to demonstrate if modifications in fruiting shoot orientation, pruning detail, and/or scaffold accessibility improved flower removal, reduced follow-up hand-thinning requirement, and/or increased fruit size. Blossom removal was improved by either detailed pruning or partial pruning (elimination of all shoots on the side of a limb inaccessible by the thinner spindle) in both training systems. Flower density and fruit set measurements revealed greater differences among pruning treatments compared with hand-thinned control treatments with both fruiting shoot orientation pruning modifications and detail pruning resulting in improved thinning. Thinning efficacy was unaffected by scaffold angle but increased as canopy accessibility ranking increased. Follow-up hand-thinning time was reduced by all treatment, system/cultivar, and year combinations except standard pruning in an open center-trained 2009 trial. Detail pruning consistently improved fruit size compared with hand-thinned control and other pruning treatments in both perpendicular V- and open center-trained orchard plots. The best treatments resulted in a thinning savings of $120/ha to $282/ha in perpendicular V plantings and $26/ha to $46/ha in open-center plantings. Realized economic savings beyond hand-thinning alone ranged from $473/ha to $2875/ha in perpendicular V trials and $28/ha to $293/ha in open-center trials.

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Renae E. Moran and James R. Schupp

'Macoun'/Budagovsky 9 apple (Malus ×domestica Borkh.) trees were planted in May 1998 in one of four preplant treatments that were soil incorporation of: 1) control, no phosphorus (P); 2) 90 g P per tree; 3) 128 kg compost per tree; and 4) 90 g P and 128 kg compost per tree. Preplant addition of P had no effect on soil organic matter, P, magnesium (Mg), and calcium (Ca) in the first three seasons after planting, but lowered soil potassium (K) in the second season. Foliar nutrients, tree growth and flowering were also not affected by P. The addition of compost increased soil organic matter and P in the first season after planting, and pH, K, Mg, and Ca in the first three seasons. The addition of compost increased foliar nitrogen and K in all three seasons, and decreased foliar Mg in the first season. Compost incorporation increased shoot length in the first season, trunk cross-sectional area in the first two seasons, tree height and the number of growing points in third season, and flowering in the third and fourth seasons. Compost addition was more effective than P fertilization for increasing tree growth during the establishment years.

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James R. Schupp and Duane W. Greene

To compare the effects of growth regulators on preharvest fruit drop and fruit maturity, aminoethoxyvinylglycine (AVG) was applied to `McIntosh' apple trees at 75, 150, or 225 mg·L-1, at 8, 4, or 2 weeks before harvest (WBH). These treatments were compared to NAA, daminozide, and to an untreated control. All AVG treatments and timings except 75 mg·L-1 applied 8 WBH delayed preharvest drop and fruit maturity. AVG applied at 225 mg·L-1was more effective in delaying drop and development of maturity than other rates when applied 8 or 2 WBH, but at 4 WBH, 150 mg·L-1 gave equivalent results to 225 mg·L-1. AVG at 150 mg·L-1 was superior to NAA or daminozide as a stop-drop agent. No concentration, or time of application of AVG influenced fruit size at harvest. AVG reduced internal ethylene concentration (IEC) in `McIntosh' apples linearly with increasing AVG concentration. There was a linear relationship between time of AVG application (8, 4, or 2 WBH) and IEC in the fruit after harvest, and the time required for harvested fruit to enter the ethylene climacteric. Development of red color was delayed by AVG. This was attributed to a delay in ripening as determined by a slower increase in IEC and starch hydrolysis. In general, earlier application of AVG resulted in reduced effectiveness of lowering IEC following harvest. Chemical names used: aminoethoxyvinylglycine (AVG), naphthaleneacetic acid (NAA), succinic acid-2,2-dimethylhydrazide (daminozide).