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D. Michael Glenn and G.J. Puterka

The objective of the present study was to examine the effect of a reflective, aluminized plastic film (APF), a reflective, particle-based film applied to the tree (PFT), a reflective, particle film applied to the west side of the tree (PFW), or a particle-based reflective film applied to the grass between tree rows (RPF) on ‘Empire’ apple [Malus domestica (Borkh.)] color and fruit weight in a multiyear study. The APF treatment consistently increased red color and was the only treatment to increase fruit red color from the lower portion of the west side of the tree. The PFT, PFW, and RPF treatments inconsistently improved apple red color. The APF treatment reflected ≈6 times the amount of photosynthetically active radiation (PAR) as the RPF and reflected different red/far-red light ratios (R/FR). In all years, average fruit weight was increased by the RPF, PFT, and PFW treatments compared with the untreated control and APF treatment. The mechanism responsible for the increased fruit weight may be the altered light quality, not quantity, reflected from the RPF treatments. The reflected light has enhanced far-red radiation, which may have beneficial effects on both fruit color and fruit weight. The effect of enhanced far-red radiation on increased fruit weight may be a phytochrome-mediated process affecting dry matter partitioning.

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Thomas J. Tworkoski and D. Michael Glenn

Competitive effects of different grass species were evaluated on growth, yield, leaf N, and leaf water potential of 8-year-old peach [Prunus persica (L.) Batsch.] trees and on weed abundance. Two cultivars (`Loring' on Lovell rootstock and `Redhaven' on Halford rootstock) of peach trees were planted in separate orchards in 1987. Nine orchard floor treatments were installed beneath the peach trees in 1995: Festuca arundinacea Schreber (tall fescue); Lolium perenne L., var. Manhattan II (perennial ryegrass); Lolium perenne L., var. Linn; Agrostis gigantea Roth (red top); Dactylis glomerata L. (orchardgrass); Phleum pratense L. (timothy); Bromus carinatus Hook. and Arn. (brome); weedy control; and herbicide weed control (simazine, glyphosate). In general, grasses reduced vegetative growth and yield in both cultivars. Orchardgrass was one of the most competitive species and reduced vertical water sprout length by 15% to 27% and lateral shoot length on fruit-bearing branches by 19% to 30% compared with herbicide treatments. Orchardgrass reduced yield by 37% and 24% in `Loring' and `Redhaven', respectively. All grasses were not equally competitive; `Linn' perennial ryegrass did not significantly reduce growth or yield in `Redhaven'. Control treatments with weeds also did not differ from herbicide treatments in peach tree growth and yield. Grass and weed ground covers consistently reduced peach tree leaf N by at least 10%, compared to herbicide treatment, possibly due to reduced root growth. `Redhaven' root density in the top 10 cm of soil was ≈12 cm·cm-3 in herbicide strips vs. 1 cm·cm-3 in weedy or ground-covered strips. Peach leaf water potential was not affected by grass and weeds. Weed weights were significantly reduced by all grasses compared with weedy control. The results indicate that peach cultivars respond differently to grass competition, but the relative competitiveness of each grass species was similar for both cultivars. Grass competition reduced growth, yield, and pruning weights of mature peach trees, but the reduction in vegetative growth did not significantly reduce pruning time per tree. Grasses that are less inhibitory to peach yield may be useful for weed management in orchards.

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Fumiomi Takeda, D. Michael Glenn, and Thomas Tworkoski

Three experiments were performed to determine the effect of amending the soil surface layer and mulching with hydrophobic kaolin particle on weeds and blackberry (Rubus subgenus Rubus Watson) plants. In the first study a processed kaolin material (product M-96-018, Engelhard Corporation, Iselin, N.J.), was incorporated in August into the top 3 cm of freshly roto-tilled field that had been in pasture the previous 5 years. The following spring, dry weight of weed vegetation in the control treatment was 219 g·m–2 and was significantly higher (P = 0.05) than the 24 g·m–2 harvested from the treated soil. In two other studies, planting holes for blackberry transplants were either 1) pre- or postplant mulched with a 2- or 4-cm layer of 5% or 10% hydrophobic kaolin in field soil (w/w), or 2) postplant treated with a) napropamide, b) corn gluten meal, c) a product comprised of hydrous kaolin, cotton seed oil, and calcium chloride in water (KOL), d) hand weeded, or e) left untreated. Although untreated plots had 100% weed cover by the end of July, herbicide treatments, 4-cm deposition of hydrophobic kaolin particle/soil mulch, and KOL all suppressed weeds the entire establishment year. Preplant application of hydrophobic kaolin mulch and postplant application of KOL reduced blackberry growth and killed transplants, respectively. In year 2, blackberry plants produced more primocanes that were on average 10-cm taller in weed-free plots (herbicide, 4-cm kaolin soil mulch, and mechanical weeding) than in weedy plots (control and 2-cm kaolin soil mulch). In year 3, yield was significantly lower in control plots (1.5 kg/plant) than in plots that were treated with napropamide and 2- and 4-cm hydrophobic kaolin mulch, or hand weeded during the establishment year (4 kg/plant). The results showed that 4-cm hydrophobic kaolin mulch applied after planting can suppress weeds without affecting blackberry productivity. These kaolin products are excellent additions to the arsenal of tools for managing weeds in horticultural crops.

Free access

D. Michael Glenn, R. Scorza, and C. Bassett

A chimeric, willow-leaf mutation of a standard peach [Prunus persica (L.) Batsch.] phenotype was evaluated for its water use efficiency (WUE). The willow-leaf phenotype had greater WUE than its standard-leaf parent under both nonstressed and well-watered conditions, and this was supported by isotopic carbon discrimination. Under water-stress conditions, willow-leaf trees developed less water potential gradient from the roots to the leaves. The mechanisms associated with increased WUE by the willow-leaf phenotype include a reduced water potential gradient within the plant and uncoupling of the leaf from the aerial environment. Willow-leaf peach trees in seedling populations, descended from a different willow-leaf parent, also had reduced carbon isotopic discrimination than did sibling standard-leaf seedlings.

Free access

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.

Open access

D. Michael Glenn and William V. Welker


Peach trees [Prunus persica (L.) Batsch cvs. Loring/Halford] were grown in boxes 100 × 60 × 36 cm (length × width × depth) to evaluate the effect of K-31 tall fescue sod (Festuca arundinacea Schreb.) on peach root growth and development. The entire soil surface was kept bare in one treatment, while a fescue sod was established in one-third of the box for the second treatment. Trees were planted 17 cm from one edge of the box in bare soil in both treatments. Sod reduced tree growth. The length of roots ≥1 mm in diameter was unaffected by the sod at any position in the box. The length of roots <1 mm in diameter was reduced beneath the sod and in the area between the sod and tree compared to the bare soil treatment. The plant resistance to water flow/cm root (Rp) was unaffected by the presence of grass under both stressed and nonstressed conditions. Rp was relatively constant (9.4 × 109 s cm-1) over a range of transpiration flux levels until the flux dropped below 0.3 cm3 s-1. Below 0.3 cm3 s-1 Rp increased due to soil resistance to water flow.

Free access

Carole L. Bassett and D. Michael Glenn

Reflective films are used in orchard management to improve fruit coloration. Numerous physiological studies on the effects of application of these films have been conducted, including variation of angles of light incidence and reflection, spectral determination of reflected light, and effects on photosynthesis and pigment development. At present there have been no studies on the effects of these treatments on gene expression, particularly with regard to genetic factors controlling light perception and genes targeted by specific regulators. We sampled a fully developed leaf from apple (Malus ×domestica) branches of mature trees in 2 consecutive years. The grass between the tree rows was left untreated, sprayed with a formulation of a reflective particle film (RPF), or covered with a single layer of an aluminized plastic film (APF). Leaves at the same branch position were sampled between 1000 and 1200 hr on sunny days. Nine different gene transcripts associated with light perception, sorbitol transport, and actin (control) were measured by semiquantitative reverse transcription–polymerase chain reaction and five by quantitative reverse transcription–polymerase chain reaction. Transcript abundance of most genes was unaffected by treatment or slightly enhanced by RPF. These results are consistent with earlier observations indicating that application of this film stimulated carbon partitioning to the fruit likely through the reduced red/far-red ratio of reflected light. In contrast, the level of several gene transcripts, including MdPif3, MdPhyB, and MdSot3, was reduced by application of the APF. Only one gene, MdElip1A/B, was significantly and dramatically elevated by APF.

Free access

D. Michael Glenn, C. Feldhake, F. Takeda, and D.L. Peterson

The objectives of this lysimeter study were to 1) evaluate the amount of dewfall, 2) determine the contribution of dew to daily evapotranspiration (ET) in fall-grown strawberries (Fragaria ×ananassa Duch.), and 3) determine the relationship between actual and potential ET (PET) of strawberry. Dewfall amounts averaged 0.8 mm·day–1 and accounted for 33% of the daily ET during the 27 Sept. to 6 Nov. period. Daily ET was linearly related to PET calculated from the Penman–Monteith equation, with an accuracy of ±3 mm based on lysimeter ET. Daily ET for 2- to 4-day periods was estimated with an accuracy of ±1 mm using the Penman–Monteith. We conclude that dewfall cannot be ignored in the ET of fall-grown strawberries in the mid-Atlantic section of the United States.

Free access

Daniela Giovannini, D. Michael Glenn, Ralph Scorza, and W.V. Welker

Our objective was to evaluate the dry-matter partitioning between the roots and shoots of two genetically size-controlled peach [Prunus persica (L.) Batsch] types, dwarf and pillar, compared to a full-sized standard peach type. Compared to the pillar and standard types, the dwarf type had a reduced leaf: root ratio, less allocation of dry matter to woody tissue and more to leaf tissue. Genetically size-controlled peach trees have a smaller root system, but a lower leaf: root ratio and may require modified soil and water management techniques to ensure high productivity.

Free access

D. Michael Glenn, Ralph Scorza, and William R. Okie

Two unpruned willow leaf and two unpruned standard leaf peach [Prunuspersica(L.) Batsch.] selections were evaluated for physiological components related to water use efficiency (WUE). The purpose of the study was to assess the value of willow leaf phenotypes to improve water use efficiency in peach and separate the environmental from the genetic components. The willow leaf characteristic itself did not confer improved water use efficiency. Light interception was a key determinant of WUE in these genotypes and the relationship of WUE with intercepted photosynthetically active radiation (PAR) by the entire canopy indicated a significant negative correlation. Internal shading of the tree by excessive leaf area reduced WUE and canopies that intercept more than 60% of the PAR have reduced WUE. While WUE is improved by reducing the amount of PAR interception of the canopy, productivity is reduced. Neither of the willow leaf genotypes had a significant correlation of WUE with yield (leaf and fruit weight); however, the standard leaf type cultivars, `Bounty' and `Redhaven', had significantly different regressions that indicate greater productivity in `Bounty' for a given level of WUE. `Redhaven' was the least productive cultivar; `Bounty' was the most productive, and the two willow leaf genotypes were intermediate in the relationship of intercepted PAR with yield. Therefore, genetic differences in peach growth types can be selected for both increased WUE as well as increased productivity. Future work in peach breeding to improve WUE and productivity must take into consideration light interception, productivity, and WUE in an integrated manner to make progress in the efficient use of water and light.