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  • Author or Editor: Bradley H. Taylor x
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The timing and concentration of dilute foliar sprays of gibberellic acid (GA3) were tested for their flower bud thinning effect during three consecutive years on two common cultivars of peach [Prunus persica (L.) Batsch.] grown in commercial culture under midwestern conditions. There was a strong trend for June sprays to minimize the total flower bud density (buds/cm shoot) of unbranched shoots on mature `Redhaven' and `Cresthaven' trees. The GA3 treatments applied between early July and late October did not reduce the total flower bud density. Increasing the concentration from 25 or 50 mg·L-1 to 200 mg·L-1 tended to decrease total flower bud density, especially when applied May through July. During the same period the GA3 treatments reduced total flower bud density of short shoots (<10 cm), but only about two-thirds as effectively as on long shoots. The `Redhaven' live flower density on trees treated in May, June or September was up to 2 times greater then the control in March following exposure to extreme fluctuations in winter temperatures to near critical lows in 1988 and 1989. Although 50 mg·L-1 GA3 applied in June 1989 reduced total flower bud density by 70%, it resulted in a live flower density only 35% lower than the control. The treatment induced 2.3 times greater survival of the total flower buds existing after thinning when winter temperatures gradually declined to critical levels. The increased live flower density caused by the GA3 sprays translated to a cropload 1.3 to 2.25 times greater than control. The length of neither fruiting quality shoots in the bearing canopy nor 1-year-old upright branched shoots in the top of trees (watersprouts) was appreciably affected by the GA3 applications. GA3 treatments at 100 and 200 mg·L-1 in late July and early August slightly delayed time of full bloom. Defoliation was delayed slightly by treatments applied in September and late July. Moderate doses of appropriately timed GA3 sprays reduced flower bud densities without adverse effects on winter survival, yield, defoliation or bloom time. Our results support the use of GA3 as a reliable peach thinning tool.

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Most small pumpkin growers in Illinois have traditionally relied upon natural insect pollinators to achieve fruit set and development. Many growers fail to understand the importance of pollination and are not aware of the potential benefits of using honey bee colonies to improve pollination and subsequent fruit set of pumpkin. Therefore, a study was conducted over the 2000 and 2001 growing seasons to measure the effectiveness of honey bee colonies on jack-o-lantern pumpkin production. Yields (kg·ha-1) of several cultivars (e.g., `Appalachian' and `Howden') almost doubled when honey bee colonies were present during flowering. Pumpkin weights with the inclusion of honey bees averaged 31,547 kg·ha-1 compared to 22,353 kg·ha-1 for those without honey bees. However, the number of pumpkins per ha was not as drastically influenced by the addition of honey bees; total pumpkin fruits per ha averaged 1,896 with honey bees as compared to 1,704 without honey bees. These results indicate that there were sufficient natural pollinators to induce pumpkin fruit set under field conditions during the study, but fruit size can be significantly increased with the addition of a strong honey bee colony during flowering. Since pumpkins are generally sold on a weight basis, growers should realize greater revenues with the inclusion of honey bee colonies in pumpkin fields.

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The objective of this study was to measure honey bee (Apis mellifera L.) impact on seed set, fruit set, and yield of jack-o-lantern (Cucurbita pepo L.), large-sized (C. maxima Duch.), and processing pumpkins (C. moschata Duch. ex Poir.) under field conditions. There were sufficient natural pollinators [including bumblebees (Bombus spp.), carpenter bees (Xylocopa spp.), honey bees, and squash bees (Peponapis pruinosa Say)] provided under field conditions to induce fruit set of jack-o-lantern pumpkins as fruit number obtained per hectare was not affected by the addition of a honey bee colony. However, the addition of honey bees did increase fruit number per hectare of the C. moschata and C. maxima cultivars evaluated. Honey bee pollination resulted in larger-sized fruit, increasing individual fruit size of all but small-sized pumpkins (<0.5 kg). Individual pumpkin fruit weights of the Cucurbita pepo, C. moschata, and C. maxima cultivars evaluated increased by about, 26%, 70%, and 78%, respectively, when honey bee colonies were included. Natural pollination was insufficient to stimulate maximum fruit size development and seed number and seed weight per fruit. Although pumpkin fruit set will occur with natural pollinators, the addition of honey bee colonies will ensure the presence of pollinators to maximize fruit size. Since pumpkins are generally sold on a weight basis, growers may generate greater revenues with the addition of honey bee colonies in pumpkin fields.

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Abstract

A single or four sequential foliar sprays of paclobutrazol (PBZ) and XE-1019 (Valent Corp., Walnut Creek, Calif.) to peach [Prunus persica (L.) Batsch.] supplied, respectively, 7.5 to 480 mg a.i. and 0.75 to 48 mg a.i. doses per tree. These treatments reduced the net change in total shoot length (current-season extension shoots plus lateral shoots) occurring over the 15-week period after the sprays were applied by up to 80% and 69%, compared to the control, for each compound, respectively. The average number of lateral shoots was decreased 85% and 81% by the highest dose of each material. The shoot and whole plant dry weight at the end of the growing season (15 weeks after treatment) were ≍22% and 27% lower than the control for PBZ and XE-1019, respectively. Trunk cross-sectional area, leaf area, and dry weight of leaves and roots were also smaller on the trees treated by either compound. Root : shoot ratios were not influenced by any treatment. Chemical names used: β-[(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazole-1-ethanol (paclobutrazol); (E)-1-(p-chlorophenyl)-4-,4-dimethyl-2-(1,2,4-triazol-1-yl)-1-penten-3-ol (Valent XE-1019).

Open Access

Abstract

Early season multiple spray applications of 5, 10, or 20 ppm of gibberellins A4+7 (GA4+7) reduced the severity and frequency of russet on four strains of ‘Golden Delicious’ apple (Malus domestica Borkh) fruit at three locations over 1, 2, or 3 years. The distribution of fruit in the U.S. extra fancy and fancy categories (graded for russet only) increased with increasing concentration of GA4+7 sprays. Regression analysis of data pooled from seven trials predicted for the 5-, 10-, and 20-ppm GA4+7 sprays, respectively, 68%, 74%, and 76% of the fruit falling in the combined extra fancy and fancy grades as compared to 40% on the untreated control trees. Additional experiments revealed tank-mixing GA4+7 with pesticides reduced the degree of russet suppression in one trial, but not in another. Return bloom was diminished on trees sprayed with GA4+7 in the previous year and the flower cluster density was inversely related to GA4+7 concentration. Chemical names used: (1α,2β,4aα,4bβ,10β)-2,4a,7-trihydroxy-1-methyl-8-methylenegibb-3-ene-1,10-dicarboxylic acid 1,4a-lactone (GA4+7); polyoxyethylene-polypropoxypropanol dihydroxypropane (Regulaid).

Open Access

G A3 sprays were applied to 10 primary scaffold limb replications with a handgun at three concentrations (25, 50, 100 mg/l), from May to September 1989. Flower bud thinning with G A3 applied in the year prior to bloom was examined for its effect on the developmental fate of lateral meristems. Limbs treated in late May had, on average, 45% more flower buds survive near-critical winter temperatures than did controls. During the period of greatest sensitivity to Flower Bud Density (FBD) reduction, GA3 treated limbs had vegetative bud densities (VBD) higher than control (on average 45% greater at 100 mg/l). On 9 June 100 mg/l reduced FBD by 78% compared to control and increased VBD by 57%, while on 6 July the same concentration. reduced FBD by 94% but VBD was increased by only 32%. These results appear to support the hypothesis that GA3 induced FBD reduction has more than one mode of action.

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G A3 sprays (50, 65, 100 mg/L) were applied to six single tree replications of mature `Redhaven' and `Cresthaven' trees on 23 June 1989 to measure their effect on fruit maturity and the relationship among its indices. There was little effect of GA3 on fruit diameter except on the final harvest when the treated trees had 6% larger fruits. Seventy-two percent of the total yield of `Redhaven' control trees was mature at the first picking while only 30% of total yield from treated trees was ready on the same date. GA3 had a similar effect on fruit maturation on `Cresthaven'. Fruit on treated `Redhaven' trees were on average 1.3 kg firmer than control. Furthermore, GA3 increased the firmness over control on the shaded and sunny side and the suture of the fruit and no interaction between the location of pressure test and GA3 treatments was observed. There was a slight reduction in yellow ground color of G A3 treated fruits. The effect of GA3 on the relationship between individual fruit color and firmness will be examined. The effects of 1990 GA3 sprays on peach maturity and quality will also be presented.

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The response of foliage-air temperature differential (Tl-Ta) to vapor-pressure deficit (VPD) as a means of detecting incipient water stress was investigated in the Illinois planting of the NC-140 Uniform Peach Rootstock Trial. Stomatal conductance, foliage temperature, leaf water potential, air temperature and VPD were followed diurnally on three dates in 1989 for mature `Redhaven' on six different rootstock. On two of three sampling dates where predawn leaf water potential was greater than -0.5 MPa there was no indication of midday stomatal closure and all rootstock exhibited an inverse relationship between T1-Ta and VPD. On the date with the most negative predawn leaf water potential, T1-Ta of two plum rootstock (GF-677 and GF-655-2) was observed to be significantly greater at VPD levels above 2 kPa than the remaining rootstock. All rootstock on this date exhibited greater T1-Ta than at similar VPD levels on the other two dates. These data suggest that transpirational cooling plays a large enough role in foliage temperature regulation of `Redhaven' peach such that incipient water stress and rootstock effects on water relations can be detected through increases in foliage temperature.

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Two experiments were conducted in 1992 to examine the effects of GA 3 concentration and date of GA 3 application on peach fruit maturation and quality. Concentrations of 0, 24, 48 and 72 mg/l GA 3 were applied on 28 June. GA 3 at 48 mg/1 was applied on 25 May, 10 June, 28 June and 18 July. Mature `Canadian Harmony' trees were used in a randomized complete block design with 8 blocks. All concentrations of GA 3 applied 28 June delayed the weighted average harvest date by ≈2 days. There was a linear increase in concentration of maturity with increasing GA 3 concentrations. There was no detectable date of application effect on fruit maturation. There was a small (16%) increase in fruit firmness that was linearly related to increasing GA 3 concentration. Fruit firmness was greater with earlier dates of GA 3 application.

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Use of precocious, high-yielding, dwarfing rootstocks for apple trees in southern Illinois has been limited by the prevalence of fire blight and crown rot diseases, as well as soil and climate stresses. Apple orchards in the region are generally situated on heavy clay soils and often receive excess rainfall in spring and fall, followed by drought in summer. New dwarfing rootstocks adapted to these biotic stresses were used as interstems on robust, vigorous rootstocks, to determine if earlier and greater cumulative yields could be obtained compared to the current industry standard MM. 111. The treatments consisted of 20 various interstem/rootstock combinations with `Ruby Jon Jonathan' as the scion that were propagated and grown as feathered maidens in the nursery. The trees were planted at 4.5 × 6.0 m in a randomized complete-block design with eight replications in May 1996 at the Southern Illinois University Horticultural Research Center at Carbondale, Ill. The trees were trained in a vertical axis system with minimal initial pruning and complete deblossoming in the first 2 years. Trees were allowed to crop during the third- through ninth-leaf. Cumulative yields of the best performing interstem/rootstock combinations were two to three times greater compared with MM. 111. The trees on the most vigorous rootstocks consistently produced the largest fruit size, but four dwarfing clones, G. 30, V. 1, Bud. 9, and M. 7, used as interstems, generally produced higher yields with similar fruit size. These advantages were obtained without the negative side effects (excess root suckers, lack of scion uniformity, and increased mortality) traditionally associated with interstem performance in the lower Midwest.

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