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Ross E. Byers

AVG sprays applied to `Redhaven' peach (Prunus persica L. Batsch) trees 53, 72, 80, 87, or 94 days after full bloom (AFB) slightly delayed the first harvest date. Applications at 53 or 94 days AFB slightly delayed cumulative second and third harvests. The fourth (final) harvest was not delayed by any AVG spray. Firm commercial-harvest peach and nectarine fruit submerged for 60 s in AVG solutions softened more slowly than the controls when kept at room temperature (≈24 °C) for 3 to 12 days. AVG-treated fruit dipped in ethephon after 4 days showed an increased rate of softening compared to fruits treated only with AVG. Fruit submerged in AVG solutions and stored at 1.5 or 4.5 °C for 12 to 18 days did not differ in firmness from the controls upon removal from cold storage but sometimes softened more slowly after storage. Ethylene evolution from AVG-dipped fruit was not measureable even after it was kept at room temperature for 12 days. Chemicals used: Aminoethoxyvinylglycine hydrochloride (AVG); 2-chloroethylphosphonic acid (ethephon).

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Ross E. Byers

AVG applied 2 to 6 weeks before the optimum harvest date for several cultivars dramatically reduced pre-harvest fruit drop. The loss of fruit firmness and starch loss after the optimum harvest date was reduced by AVG sprays. The development of watercore in `Starkrimson Delicious' and `York' and maturity cracking in `Rome' and `Golden Delicious' were delayed and/or prevented by AVG. Color development was slightly delayed for most red cultivars and `Golden Delicious'. Soluble solids concentration was generally unchanged. Airblast applications of 123 g·ha–1 AVG was no more effective than a standard rate of NAA (28 to 56 g·ha–1), but rates of 248 g·ha–1 AVG and above were more effective than NAA for most cultivars. When fruit were left on the tree for periods of 3 to 5 weeks after the optimum harvest date, NAA hastened the loss of fruit firmness and starch and NAA increased watercore of `Delicious' and maturity cracking of `Golden Delicious' and `Law Rome'. Soluble solids and red color were generally unaffected by NAA. Ethephon sprays hastened the rate of fruit drop. When NAA was tank mixed with ethephon, NAA delayed fruit drop caused by ethephon, but AVG did not. The use of superior oil or Regulaid surfactant did not affect NAA or AVG responses; however, the silicone surfactant Silwet L-77, in one experiment, promoted the effectiveness of AVG. Tank mixing NAA or AVG with pesticides (Guthion + Lannate + Captan) did not affect the responses of AVG or NAA on fruit drop.

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Ross E. Byers

Ethephon applied 12 to 26 days after full bloom at 1000 to 1500 mg·liter-1 not only substantially inhibited apple (Malus domestia Borkh., spur `Delicious' strains) tree growth but also caused fruit abscission. Gibberellin plus ethephon did not prevent fruit abscission when ethephon was used at these rates. Several low weekly doses of ethephon controlled tree growth without causing fruit abscission. Ethephon increased fruit soluble solids concentration and substantially reduced fruit starch in the application year. Ethephon greatly increased flowering and fruit set the following season. Fruit length: diameter ratio was not altered by the previous seasons' low weekly doses of ethephon. Chemical name used: (2-chloroethyl)phosphonic acid (ethephon).

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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.

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Ross E. Byers and R.P. Marini

Peach trees [Prunus persica (L.) BatSch.] blossom-thinned by hand were overthinned due to poor fruit set of the remaining flowers; however, their yield was equivalent to trees hand-thinned 38 or 68 days after full bloom (AFB). Blossom-thinned trees had three times the number of flower buds per unit length of shoot and had more than two times the percentage of live buds after a March freeze that had occurred at early bud swell the following spring. Blossom-thinned trees were more vigorous; their pruning weight increased 45%. For blossom-thinned trees, the number of flowers per square centimeter limb cross-sectional area (CSA) was two times that of hand-thinned trees and four times that of the control trees for the next season. Fruit set of blossom-thinned trees was increased four times. Flower buds on the bottom half of shoots on blossom-thinned trees were more cold tolerant than when hand-thinned 68 days AFB. Fruit set per square centimeter limb CSA was 400% greater the following year on blossom-thinned trees compared to controls. Removing strong upright shoots on scaffold limbs and at renewal points early in their development decreased dormant pruning time and weight and increased red pigmentation of fruit at the second picking. The number of flower buds per unit shoot length and percent live buds after the spring freeze were negatively related to crop density the previous season for trees that had been hand-thinned to varying crop densities at 48 days AFB. According to these results, blossom thinning and fruit thinning to moderate crop densities can influence the cold tolerance of peach flower buds in late winter.

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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.

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Ross E. Byers and Alson H. Smith Jr.

An analysis of daytime high temperatures for the 10-year period from 1984 to 1993 indicated that, in the 21 days after full bloom (AFB) in 7 of 10 years, there were 3 days or more above 29.5C. In the 15- to 21-day period AFB, when fruit are considered at their optimum diameter (8 to 12 mm) for thinning, only 3 days above 29.5C were recorded. In the 15 to 21 days AFB, the high temperature was only 24C for 7 out of 10 years. Thus, growers would have to spray at temperatures 5.6C degrees lower if they were to choose to spray the warmest 3 days during the 15- to 21-day period when fruit are 8 to 12 mm in diameter. NAA caused thinning of `Golden Delicious' fruit at 8-mm fruit diameter. Tank mixing of one of several pesticides (regulaid or guthion, captan, carzol, imidan, polyram, lorsban, omite, or lannate) had no effect on NAA efficacy. Comparison of identical chemical thinning treatments (carbaryl + Accel + oil) applied to `York' and `Red Delicious' apple trees indicated that more thinning occurred with the PF treatments than at 8 mm. Average 2-day high temperatures at PF were 7.1C higher at PF for the `Red Delicious' experiment and 5.6C higher for the `York' experiment. The higher temperatures at PF could account for the differences in thinning response and not the spray timing. Pollination and fertilization inhibitors caused some fruit thinning at the highest rates and multiple applications. The MYX4801 caused more thinning and more injury to fruit than other materials. Endothall gave good thinning without fruit injury. Wilthin (GWN-6592) did cause some thinning, but fruit injury was a problem in one experiment.

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David E. Davis, John A. Barden and Ross E. Byers

In 1997 and 1998, we determined the effects of defoliation on return bloom and fruit set following a light cropping year. In one study, `Braeburn' trees were hand-thinned to a crop density (CD) of 3 fruit/cm 2 trunk cross sectional area (TCSA) in late May 1997, and then either completely defoliated or half of the tree defoliated by hand on one of five dates between June and Sept. 1997. Compared to a nondefoliated control, both whole and half-tree defoliation on all dates reduced fruit count and yield efficiency (kilograms per square centimeter of TCSA) and affected fruit weight, starch, firmness, and soluble solids in 1997. In 1998, return bloom and fruit set were reduced by most 1997 defoliation treatments. Compared to other dates, defoliation on 3 July caused the greatest reduction in return bloom in both whole and half-defoliated trees. In another study, `Braeburn' trees were hand-thinned to a CD of 5 in late May 1998; complete defoliation by hand on 1, 15, or 29 July reduced return bloom and fruit set in 1999; the 1 July treatment resulted in zero return bloom. `Golden Delicious' and `York' trees were thinned to a CD of 3 in late May 1998 and were hand-defoliated on 21 July or 12 August by removing every other leaf or removing three of every four leaves over the entire tree. In 1999, return bloom and spur and lateral fruit set were reduced by all defoliation treatments. Fruit set was most reduced by the 12 Aug. treatment. Fruit set for `York' was lower than for `Golden Delicious' in all cases.

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Ross E. Byers, D.H. Carbaugh and L.D. Combs

Aminoethoxyvinylglycine (AVG) applied as a spray to 'Arlet' apple trees inhibited fruit drop and increased the pull force necessary to detach the fruit. AVG delayed the loss of fruit firmness, starch degradation, fruit shriveling, and red color development. 1-Methylcyclopropene (1-MCP), applied as a gas or spray to trees in the field, did not affect fruit drop or pull force. The combination of AVG + 1-MCP (spray or gas) provided better control of fruit drop, slowed the loss of fruit firmness, starch degradation, and decrease in pull force than AVG alone. Thirty five days after the optimum harvest date, fruit firmness from trees sprayed with AVG + 1-MCP was maintained at 74.3 N. Fruit of the control was significantly lower at 61.4 N firmness. The delay in harvest caused untreated control fruit stems to turn brown and die, but stems on AVG treated trees remained green and fruit continued to grow. In the 35 days after the optimum harvest date, treated fruit increased 2.5 cm in fruit diameter. Chemicals used: Aminoethoxyvinylglycine (AVG), 1-Methylcyclopropene (1-MCP), and trisiloxane ethoxylate methyl ether (an organosilicone surfactant, Silwet L-77).