To control excessive growth, vigorous `Smoothee Golden Delicious', `Jonagold', `Empire', and `Gala' apple (Malus domestica Borkh.) cultivars on Malling 7A (M.7A) rootstock planted at close in-row spacing (2.5 or 1.8 m) were mechanically root-pruned (RP), trunk-scored (TS; ringing), or both, annually for 3 to 5 years beginning in the fourth leaf. Trees were grown in a deep, well-drained, fertile soil and supplied with trickle irrigation. RP reduced terminal shoot length in 2 of 5 years on `Smoothee Golden Delicious'; trunk cross-sectional area (TCSA) was not affected by RP. TS reduced terminal length in 3 years and TCSA in each of 5 years of treatment on `Smoothee Golden Delicious'. Bloom density was not affected by RP on `Smoothee Golden Delicious' but was increased by TS in two of the three years measured. RP reduced terminal shoot length in `Gala', `Empire', and `Jonagold' in most years and TCSA in 1993 for all cultivars. TS had no effect on shoot length or TCSA in these three cultivars. Effects of RP and TS on yield and fruit size varied with year and cultivar. In general, the effects of RP and TS were inconsistent and often failed to reduce shoot growth or canopy spread. No practical advantage was recognized from these techniques for young apple trees growing on a fertile site with trickle irrigation.
Stephen S. Miller
The ‘Stayman’ apple (Malus ×domestica) is a high-quality apple with good fresh-fruit and processing characteristics. Trees are of moderate to high vigor where it is grown in large numbers in the mid-Atlantic region of the United States. However, ‘Stayman’ is prone to skin cracking, which in some seasons can result in losses that exceed 60% to 80% of the crop. A series of experiments was conducted between 1997 and 2001 to examine the effect of prohexadione–calcium (PCa) and a mixture of gibberellins A4 plus A7 (GA4+7) on shoot growth and cracking in ‘Stayman 201’ apple. PCa consistently reduced terminal shoot growth when applied in two or three sprays between petal fall (PF) and PF + 6 weeks [May and June (postbloom)]. PCa applied postbloom combined with three or four preharvest (July and August) PCa applications reduced the growth of water sprouts. The level of ‘Stayman’ fruit cracking varied with year, but in three of five experiments conducted from 1997 through 2001, five biweekly GA4+7 sprays applied alone preharvest reduced the percentage of cracked fruit at harvest. With only a few exceptions, spraying with PCa increased fruit cracking. When GA4+7 was applied to trees previously treated postbloom with PCa, the percentage of cracked fruit was often reduced, but not always, and generally not to the same level as that in non-PCa-treated trees. Fruit cracking was increased compared with the untreated control when a spray adjuvant was included with the postbloom PCa spray. PCa or GA4+7 had no effect on yield or fruit weight at harvest. The results of this study suggest caution in the use of PCa to suppress shoot growth in bearing ‘Stayman’ apple trees because of the potential for increased fruit cracking, which may be only partially reversed by the application of GA4+7.
Stephen S. Miller and Thomas Tworkoski
A series of experiments was conducted with apple (Malus ×domestica) and peach [Prunus persica (L.) Batsch] from 2003 to 2008 to evaluate the flower thinning efficacy of eugenol and a eugenol-based essential oil. Flower thinning effects by hand defoliation and alternative chemical agents were compared with eugenol in different years. Eugenol or the eugenol-based contact herbicide Matran 2 EC (or Matratec AG) produced noticeable phytotoxicity to floral parts and exposed leaf tissue within 15 min to 1 h after application and injury was proportional to rate. At the highest rates (8% and 10%), eugenol resulted in complete burning of all exposed tissue except bark tissue, in which there were no visible signs of injury. Within 3 to 4 weeks of application, phytotoxicity was difficult to observe even at the higher rates of eugenol. In companion experiments, hand defoliation of young leaves at bloom resulted in abscission of young fruitlets in apple, but not in peach, indicating that eugenol may cause thinning by multiple mechanisms. Ammonium thiosulfate (ATS) [49 L·ha−1 or 6.0% (v/v)] provided thinning in peach and showed little or no phytotoxicity, but the response was inconsistent. ATS was also inconsistent in thinning apple. The thinning response from monocarbamidedihydrogen sulphate (MCDS; Wilthin) at 3.2% (v/v) was inconsistent in peach. At the rate used, MCDS caused some phytotoxicity on peach. Applications of 1% to 2% eugenol appear promising, but good blossom coverage is critical for thinning. Furthermore, eugenol formulations need improvement to ensure uniform coverage for more predictable thinning.
D. Michael Glenn and Stephen S. Miller
This study examines the effect of multiple spray applications of Apogee on shoot growth and whole-canopy photosynthesis (WCPn) rate in young, bearing apple trees. Apogee increased fruit numbers and reduced shoot growth and inconsistently reduced leaf area but the reduction in photosynthetic area did not result in reduced WCPn or a detrimental effect on the fruit number:fruit size relationship. Since WCPn was not affected when leaf area was reduced by Apogee treatment, it suggests a greater photosynthetic efficiency of leaves on Apogee treated trees due to reduced shading. The use of Apogee for canopy management may produce a side-effect of increasing fruit set, which may be managed through a crop thinning program.
Alan R. Biggs and Stephen S. Miller
Twenty-three apple (Malus ×domestica Borkh.) cultivars were tested in the field and laboratory for their relative susceptibility to the white rot pathogen, Botryosphaeria dothidea. Wounded fruit were inoculated in the field at 2 to 3 weeks preharvest with mycelium from 14- to 21-day-old cultures. In the laboratory, detached fruit were similarly inoculated. Fruit were rated for relative susceptibility to the fungus with two criteria: disease severity of attached fruit in the field based on lesion growth (mm/degree-day) and disease severity of detached fruit in laboratory inoculations of wounded fruit (mean lesion diameter after 5 days). Based on the laboratory and field data from 2 years of study, cultivars were classified into three relative susceptibility groups: most susceptible: `Fortune' and `Pristine'; moderately susceptible: `Golden Supreme', `Creston', `Ginger Gold', `Sansa', `Golden Delicious', `Senshu', `Orin', `Sunrise', `GoldRush', `Arlet', `Braeburn', `Cameo', `Enterprise', `Fuji', `Shizuka', `Gala Supreme', and NY 75414; and least susceptible: `Honeycrisp', `Yataka', `Suncrisp', and `PioneerMac'. Compared to previous cultivar rankings, the results of the present study indicate that some new apple cultivars from the first NE-183 planting show greater resistance to Botryosphaeria dothidea than current standard cultivars.
Alan R. Biggs and Stephen S. Miller
Twenty-three apple (Malus ×domestica) cultivars were tested in the field and laboratory for their relative susceptibility to the black rot pathogen, Botryosphaeria obtusa. Wounded fruit were inoculated in the field at 2 to 3 weeks preharvest with mycelium from 14- to 21-day-old cultures. In the laboratory, detached fruit were inoculated similarly. Fruit were rated for relative susceptibility to the fungus by determining disease severity of attached fruit in the field based on lesion growth (mm/degree-day) and detached fruit in laboratory inoculations of wounded fruit (mean lesion diameter after 4 days). Based on the laboratory and field data from two growing seasons, cultivars were classified into three relative susceptibility groups—most susceptible: `Orin', `Pristine', and Sunrise'; moderately susceptible: `Suncrisp', `Ginger Gold', `Senshu', `Honeycrisp', `PioneerMac', `Fortune', NY75414, `Arlet', `Golden Supreme', `Shizuka', `Cameo', `Sansa', and `Yataka'; and least susceptible: `Creston', `Golden Delicious', `Enterprise', `Gala Supreme', `Braeburn', `GoldRush', and `Fuji'. Compared to previous cultivar rankings, the results of the present study indicate that no new apple cultivars from the first NE-183 planting show greater resistance to Botryosphaeria obtusa than current standard cultivars.
Stephen S. Miller and George M. Greene II
Replicated studies were conducted from 1996 to 1999 to evaluate the effect of a metalized reflective film (RF) on red color development in several apple (Malus ×domestica) cultivars that often develop poor to marginal color in the mid-Atlantic growing region. Film was applied to the orchard floor in the middle between tree rows or under the tree beginning 5 to 7 weeks before the predicted maturity date. Light reflected into the canopy from the RF was measured and compared with a standard orchard sod, a killed sod or various polyethylene films. Fruit color was estimated visually and with a hand-held spectrophotometer. Fruit quality (firmness, soluble solids, starch index) was determined from a representative sample of fruit. RF increased the level of photosynthetic photon flux (PPF) reflected into the canopy resulting in darker, redder colored `Delicious', `Empire', and `Fuji' apples with a greater proportion of surface showing red color. RF increased canopy temperature and fruit surface temperature. A white polyethylene film increased reflected PPF and fruit color, but generally not to the extent of the metalized RF. Large [>13 ft (4.0 m) height] well-pruned `Delicious' trees showed increased fruit color, especially when the RF was placed under the canopy, but `Empire' trees of similar size and a more dense canopy showed no effect. The effect of the RF was most pronounced in the lower portion [up to 8 ft (2.4 m) height] of the canopy. A high-density RF was as effective as a low-density RF and the high-density film was about 60% less expensive. A high-density RF may be a cost effective method to enhance red color on selected apple cultivars in the mid-Atlantic region. Comparisons between ethephon and the RF were variable: ethephon appeared to have more effect on color in `Empire' than the RF, but less effect than the RF on `Hardibrite Delicious'. Ethephon consistently advanced fruit maturity. Chemical name used: (2-chloroethyl)phosphonic acid (ethephon).
Stephen S. Miller and Mark W. Brown
Stephen S. Miller and Ross E. Byers
Seven-year-old `Blake'/`Lovell' peach [Prunus persica (L.) Batsch] trees were subjected to four pruning levels (none, light, heavy, and dehorned) each at three times (April, May, and June) in a factorial arrangement following freezing injury in January 1994. Pruning had a significant effect on canopy height, canopy volume and fruit yields. Peach trees pruned in April or dehorned (severe pruning) had less canopy volume in the first fruiting season (1995) after the pruning treatments were initiated than trees pruned in May or June and light or heavy pruned trees. In 1995, yields were lower for trees pruned in June, nonpruned or dehorned trees in 1994. These treatments also produced fewer large fruit at harvest and thus reduced dollar returns per hectare in 1995. In 1996, fruit numbers and fruit sizes did not differ among treatments, but dehorned trees had lower returns per hectare because trees were smaller. The results of this study indicate that peach trees subjected to moderate winter injury should be pruned no later than 2 to 3 weeks after bloom using a heavy level of pruning. There appears to be no economic advantage to dehorn pruning even though canopy volume can be reduced resulting in a smallertree with high quality wood. The results clearly illustrate the long-term negative effect of dehorn pruning on yields resulting from reduced canopy volume. Mean number of cankers per tree increased over time from 1995 through 1998, but pruning treatments did not affect the number of cankers produced. Pruning treatments did affect the size of cankers and the number with visible gumming.
Stephen S. Miller and Ross E. Byers
When temperatures reach -26 °C and lower, even for brief periods of time, damage to fruit buds and woody tissue of the peach tree is common. Low temperature injury on peach can lead to bark damage, gummosis, increased incidence of perennial canker, partial or complete crop losses, reduced shoot growth and/or tree death. In Jan. 1994 the Eastern Panhandle of West Virginia and surrounding states experienced three successive nights of temperatures at -28 °C or lower. Beginning in Apr. 1994, 7-year-old `Blake'/Lovell peach trees were subjected to four pruning levels (none, light, heavy, and dehorned) each at three times (April, May, and June) in a replicated factorial arrangement. Specific pruning treatments were applied only in 1994; a local commercially recommended level and time of pruning were applied to all trees from 1995 through 1998. Treatments had a significant effect on canopy volume and fruit yields. Trees receiving no pruning or dehorned trees and trees pruned in June had lower yields in 1995 than trees pruned in April or May or trees receiving a light or heavy pruning. These treatments also produced fewer large fruit at harvest. Lower yields and smaller fruit led to reduced dollar returns per hectare in 1995. Yields from 1996 through 1998 were lower for trees that were dehorned pruned in 1994 although there were little or no differences in fruit sizes between treatments. Time and/or level of pruning had effects on the number of cankers and number of large (>5.1 cm) cankers.