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T.J. Tworkoski and R. Scorza

Peach trees (Prunus persica L.) with diverse shoot growth habits have been developed, but little is known about their root systems. Characterizing shoot and root systems can improve basic understanding of peach tree growth and be important in the development of rootstocks and own-rooted trees. This research determined shoot and root characteristics of four peach tree growth habits (compact, dwarf, pillar, and standard). Seed from four peach growth habits were planted in 128-L containers, grown outside during the 1998 growing season, and then harvested. Compact tree leaf number (1350/tree) was twice, but leaf area (6 cm2/leaf) was half, that of pillar and standard trees. The number of lateral branches in compact trees (34) was nearly three-times more than in pillar and standard trees. The leaf area index (LAI) of pillar trees was greater than compact and standard trees (13 compared with 4 and 3, respectively) due to a narrower crown diameter. Dwarf tree shoots were distinct with few leaves (134 per tree) and a large LAI of 76. Compact trees grew more higher-order lateral roots than pillar and standard trees. More second-order lateral (SOL) roots were produced by compact than standard trees (1.2 vs. 0.8 SOL roots/cm first-order lateral root). Pillar trees had higher shoot-to-root dry weight ratios (2.4) than compact and standard trees (1.7 for both) due to smaller root dry weights. The results indicate fundamental differences in root characteristics among the peach tree growth habits. Compact trees had more higher order lateral roots in roots originating near the root collar (i.e., more fibrous roots), and this correlated with more lateral branches in the canopy. Shoot weights were the same among pillar, compact, and standard trees but root weights were less in pillar trees, resulting in greater shoot-to-root dry weight ratios. These results indicate significant differences in root as well as shoot architecture among growth habits that can affect their use as scion or rootstock varieties.

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P.L. Preusch and T.J. Tworkoski

Composted poultry litter (CPL) may be applied as a mulch in fruit orchards to manage waste and to provide a slow-release nutrient source and weed control. With proper management, poultry manure and bedding (litter) can prevent environmental degradation, such as hypoxia in aquatic communities. Peach (Prunus persica L. `Sunhigh') plots all received preemergence herbicides in May and then the following treatments in June 1998: commercial fertilizer (N at 15 g·m-2), low rate CPL (N at 15 g·m-2 as CPL at 2.9 kg·m-2), high rate CPL (N at 62 g·m-2 as CPL at 11.6 kg·m-2), and no fertilizer or mulch control. Weeds were completely controlled by mulch and herbicide during 1998 but not during 1999. By Sept. 1999, the high rate of CPL had only 27% weed cover compared with 86% for the commercial fertilizer-treated plots. Soil N was highest (NH4-N and NO3-N at 16.4 and 18.6 mg·kg-1 soil, respectively) in plots treated with commercial fertilizer, 6 weeks after treatment (WAT). Soil N did not differ among the two CPL treatments and the control at any time. At the high rate of CPL, there was NH4-N and NO3-N at 3.2 and 0.7 mg·kg-1 soil, respectively, at 6 WAT. Water-extractable P (WEP) in the soil did not differ among the CPL and commercial fertilizer treatments at 6 WAT (P at §14 mg·kg-1 soil). However, at 47 WAT, plots with the high rate of CPL had significantly higher WEP, with P at 30 mg·kg-1 soil vs. 14 mg·kg-1 soil in plots treated with commercial fertilizer. High applications of CPL could elevate P in surface runoff to levels that cause environmental degradation. In general, Mehlich 1-extractable P (MEP) did not differ among the CPL- and fertilizer-treated plots (averaging P at 45 mg·kg-1 soil). MEP was lowest in control plots (averaging P at 21 mg·kg-1 soil). Results indicate that CPL could be used as a weed suppressant without adversely affecting N release to the environment; however, P concentration in soil water may be problematic.

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P.L. Preusch and T.J. Tworkoski

Improper management of poultry manure and bedding (litter) can cause hypoxia in aquatic communities, but poultry waste can be converted to a stable organic fertilizer by composting. Peach trees (Prunus persica L. `Sunhigh') received the following treatments in May 1998: commercial fertilizer (15 g N/m2), low-rate composted poultry litter (15 g N/m2 as 2.9 kg composted litter/m2), high-rate composted poultry litter (62 g N/m2 as 11.6 kg composted litter/m2), and no treatment control. Weeds were completely controlled during 1998, but, by Sept. 1999, the high-rate poultry litter had only 27% weed cover compared with 86% for the commercial fertilizer-treated plots. Soil N was highest in plots treated with commercial fertilizer (16.4 mg N-NH4 and 18.6 mg N-NO3 per kg soil, 6 weeks after treatment) and did not differ among the remaining treatments (in the high rate of poultry litter—3.2 mg N-NH4 and 0.7 mg N-NO3 per kg soil, 6 weeks after treatment). Water soluble P in the soil did not differ among treatments at 6 weeks after treatment (≈12 mg P per kg soil for all treatments) but, at 47 weeks after treatment, plots with the high rate of poultry litter had 30 mg P per kg soil compared with 14 mg P per kg soil in plots treated with commercial fertilizer. In general, Mehlich 1 acid-soluble P did not differ among the litter- and fertilizer-treated plots (averaging 45 mg P per kg soil). Acid-soluble P was lowest in control plots (averaging 21 mg P per kg soil). Results indicate that poultry litter could be used as a weed suppressant without adversely affecting nitrogen release to the environment. However, P mineralization may be problematic and requires further investigation.

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T.J. Tworkoski and R.S. Young

Triclopyr was applied once or twice in consecutive years to Virginia creeper [Parthenocissus quinquefolia (L.) Planch.] that was growing along the ground beneath the peach [Prunus persica (L.) Batsch.] tree canopy. All rate (0 to 1.1 kg·ha-1) and month combinations controlled Virginia creeper during the season of application. A single application of triclopyr at 1.1 kg·ha-1 was insufficient for control beyond 1 year. Satisfactory control of Virginia creeper was obtained with two applications of triclopyr at 1.1 kg·ha-1 made in either August or September. Chemical name used: [(3,5,6-trichloro-2-pyridinyl)oxy]acetic acid (triclopyr).

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T.J. Tworkoski and D.M. Glenn

Peach tree size has been restricted when trees were grown continuously with grass after tree planting. However, control of excess vegetative growth of fruit trees was inconsistent when grass was planted beneath mature trees. This research determined the effect of seven grasses on growth, leaf nitrogen concentration, and yield of 8-year-old peach trees and on weed abundance. Two cultivars (`Loring' and `Redhaven') of peach [Prunus persica (L.) Batsch] trees were planted in separate orchards in 1987 in a split-plot design with grass as a main effect and time as the subplot. Nine treatments were installed as ground covers beneath peach trees in 1995: Festuca arundinacea, Lolium perenne var Manhattan II; L. perenne var. Linn; Agrostis gigantea, Dactylis glomerata, Phleum pratense, Bromus carintus, weedy control, and herbicide control (simazine, glyphosate). In general, grasses reduced vegetative growth and yield in `Loring' and `Redhaven'. For example, compared to herbicide treatments, orchardgrass reduced sprout length by 27% in `Loring' and by 15% in `Redhaven'. Fruit-bearing branch length was reduced with orchardgrass by 30% in `Loring' and 19% in `Redhaven'. Orchardgrass affected fruit yield more than vegetative growth, reducing yield by 37% and 24% in `Loring' (predominantly in the 2- to 2.5-inch size class) and `Redhaven' (predominantly in the >2.5-inch size class), respectively. All grasses were not equally competitive, `Linn' perennial ryegrass never significantly affected growth or yield. Weedy treatments also did not differ from herbicide treatments in peach tree growth and yield. Grasses and weeds consistently reduced peach tree leaf nitrogen by 17% compared to herbicide treatment, but weed density was not correlated with reductions in yield and vegetative growth. The results indicate that peach cultivars respond differently to grass competition but the relative competitiveness of grass species was similar for both cultivars. Grass competition can reduce growth of mature peach trees but this reduction did not translate to reduced pruning time per tree.

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T. Daw, T.J. Tworkoski and D.M. Glenn

Shoot growth of peach trees can be managed by manipulating edaphic conditions such as root volume and soil fertility. In this experiment, 2-year-old peach trees (Prunus persica L. cv. Sentry on `Lovell' rootstock) were planted in pots with a split root design, so that half the roots were not treated and the other half received one of four treatments: root volume restricted with polypropylene nonwoven fabric (FAB), fertilizer alone (FER), FAB + FER, and untreated control (UTC). Total shoot growth and root growth were measured, and root growth in the split halves was compared. FER increased leaf number and weight by 48% and 60%, respectively, but not stem growth. Leaf nitrogen concentration and photosynthesis were greatest in FER treatment. FAB did not affect shoot weight or reduce total root weight or length, although roots did not grow past the fabric barrier. FER increased root weight and length (116% and 57%, respectively, compared to UTC) on the treated half but did not affect root growth on the untreated half. Greatest root growth occurred in the root half that received FAB + FER, particularly in the 5-cm soil segment proximal to the fabric (4.6 cm•cm-3 compared to 0.8 cm.cm-3 in UTC). Shoot length was greater in FAB + FER than FAB. Thus, fertilizer applied near fabric increased root growth and the combination of fertilizer and fabric may be used to regulate shoot growth. Specific root length (root length per gram dry weight) was highest in trees with no treatment, suggesting root acclimation to low nutrient soil conditions. Lower specific root length resulted in soils that were fertilized. The results indicate that nonwoven fabric restricts root growth in peach trees and reduces shoot elongation. The combined effect of fabric plus selected application of fertilizer may be used to regulate growth of peach trees.

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T.J. Tworkoski, D.M. Glenn and W.V. Welker

Carbohydrate and nitrogen were measured during 1992 and 1993 in shoots of peach [Prunus persica (L.) Batsch.] trees that were planted in 1989 and grown in three vegetation-free areas contained within plots planted to tall fescue (Festuca arundinacea Schreber), orchardgrass (Dactylis glomerata L.), or a mixture of Lolium perenne L. and Festuca rubra L. Trees grown in 9.3-, 3.3-, and 1.5-m2 vegetation-free areas had the greatest to the least fruit yield, respectively. Fruit number and mass were negatively correlated with stem mass. Grass type had little effect on mass, carbohydrate, or N partitioning within the tree. Individual sugars and carbohydrate partitioning were not affected by grass competition. In contrast, the proportion of shoot N partitioning into stem and leaves declined markedly as the size of the vegetation-free area increased. Proximity of peach trees to grass may have limited N uptake, which, in turn, reduced fruit yield but not stem and leaf growth.

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D.M. Glenn, T. Tworkoski, R. Scorza and S.S. Miller

The lack of dwarfing rootstocks for peach has led to cultural and genetic approaches that reduce tree size and vegetative growth to establish high-density plantings. The objectives of the study were to evaluate the interactions of pruning strategies, groundcover management, tree densities, and peach (Prunus persica) architecture combined in eight peach production systems on components of yield and economic value. The use of sod management reduced pruning time and costs, but the reduction of crop load reduced net return. High-density plantings in large vegetation-free areas (VFAs) had greater economic return than low-density plantings.

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Thomas J. Tworkoski, Michael E. Engle and Peter T. Kujawski

A polypropylene fabric containing control-release pellets of the herbicide, trifluralin, can be oriented in the soil to regulate the distribution of plant roots. In 1990, trenches were dug near 10-year-old red oak (Quercus rubra L.) and 10-year-old yellow poplar (Liriodendron tulipifera L.) and fabric containing trifluralin control-release pellets and polypropylene fabric alone were installed vertically to redirect root growth. Roots grew alongside trifluralin fabric and fabric alone and did not penetrate either fabric 38 months after installation. Shoot growth of yellow poplar was reduced about 47% each year by the trifluralin fabric treatment compared to control. Red oak shoot growth was not affected by trifluralin fabric. Leaf water potential was not affected by treatment in either species. Trifluralin residues in trifluralin fabric decreased from 23.3% to 22.0% from July 1990 to October 1993. During this time, trifluralin levels increased from 0.4 to 3.6 mg·kg-1 in soil sampled 0 to 15 cm below trifluralin fabric. These results suggest that controlled-release trifluralin will provide persistent inhibition of root and shoot growth of some species and will not migrate significantly in the soil. Chemical names used: α,α,α-trifluoro-2,6-dinitro-N-N-dipropyl-p-toluidine (trifluralin).