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Thomas Tworkoski

Peach [(Prunus persica (L.) Batsch., `Rutgers Redleaf'] trees were grown for two seasons in a greenhouse with three pruning treatments (none, shoot tips removed, and half the shoots removed) and three grass treatments (no grass competition; perennial ryegrass, Lolium perenne L., `Linn'; and tall fescue, Festuca arundinacea Schreb, `Kentucky 31'). Competing grass reduced shoot growth, leaf area, and weight of fine roots in shallow soil, but did not affect the growth response to pruning. Regrowth from pruned trees was such that the shoot: root ratio was restored to that of unpruned trees. Leaf water potential, stomatal conductance, and photosynthesis had decreased markedly by 48 hours after irrigation ceased in trees without competition (larger trees) and to a similar level by 96 hours in trees with competition (smaller trees). Apparently, the reduced leaf area of peach trees grown with grass competition delayed water stress. Leaf abscisic acid levels were not directly affected by grass competition but increased as leaf water potential decreased. Grass competition modified morphology and reduced tree size, but did not affect shoot growth following pruning.

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Thomas Tworkoski and Stephen Miller

Combinations of diuron, simazine, and terbacil were applied every year over 15 and 16 years to the same plots. Apple (Malu×domestica Borkh.) and peach (Prunus persica L.) trees then were planted 1 and 2 years following the last herbicide application. In general, apple-tree growth was not affected, but peach tree growth was reduced by some herbicide treatments. Peach-tree growth was reduced in plots treated with terbacil and soil organic matter was lowest in these plots. Time of last herbicide treatment did not affect apple- or peach-tree growth. The results indicated that reduced fruit-tree growth was associated with reduced soil organic matter and that residual terbacil may have inhibited peach-tree growth. Chemical names used: N′-(3,4-dichlorphenyl)-N,N-dimethylurea (diuron); 6-chloro-N,N′-diethyl-1,3,5-triazine-2,4-diamine (simazine); 5-chloro-3-(1,1-dimethylethyl)-6-methyl-2,4(1H,3H)-pyrimidinedione (terbacil).

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Thomas Tworkoski and Ralph Scorza

Shoot and root characteristics of four peach tree [Prunus persica (L.) Batsch (Peach Group)] growth habits (compact, dwarf, pillar, and standard) were studied. In compact trees, 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. Leaf area index (total one-side leaf area per tree divided by the canopy cross-sectional area of the tree) of pillar trees was greater than compact, dwarf, and standard trees (13 compared with 4, 4, and 3, respectively) due to a narrower crown diameter. Dwarf trees were distinct with few leaves (134/tree) and less than half the roots of the other growth habits. Compact trees produced more higher order lateral (HOL) 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 per centimeter first order lateral root). Pillar trees had higher shoot: root dry weight (DW) ratios (2.4) than compact and standard trees (1.7 for both) due to lower root DWs. Root topology was similar among compact, pillar, and standard peach trees but root axes between branch junctions (links) were significantly longer in compact trees. Compact trees had more and longer HOL roots in roots originating near the root collar (stem-root junction) (i.e., more fibrous roots) and this appeared to correlate with more lateral branches in the canopy. These results indicate significant differences in root as well as shoot architecture among growth habits that can affect their use as scion or rootstock cultivars.

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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.

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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.

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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).

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Fumiomi Takeda, Thomas Tworkoski, Chad E. Finn, and Charles C. Boyd

One- or two-node hardwood cuttings were taken from 9-year-old ‘Triple Crown’ and ‘Siskiyou’ blackberry (Rubus) plants on 5 Nov. 2009, 3 Dec. 2009, and 21 Jan. 2010. The response of cuttings with and without partially excised axillary buds to an application of cytokinin was compared with control cuttings with intact axillary buds and no cytokinin. Differences in root development were evident in the two cultivars tested. The cuttings of ‘Siskiyou’ and ‘Triple Crown’ callused on cut ends, but many of the adventitious roots developed from the base of the axillary buds. Shoots emerged from the bud in ≈90% of ‘Siskiyou’ cuttings stuck in November, December, and January. Rooting occurred in more than 90% of cuttings stuck in November and December but declined in cuttings stuck in January. In ‘Siskiyou’, bud excision had no effect on shoot and root emergence, but cytokinin treatment suppressed rooting in cuttings collected in November and January. Shoot emergence and rooting were poorer in ‘Triple Crown’ cuttings than in ‘Siskiyou’. In ‘Triple Crown’ cuttings, partial excision of buds reduced shoot emergence only in January but had no effect on rooting at three sticking dates. Cytokinin treatment improved shoot emergence in November and December but reduced rooting in January. The enclosed system is a viable method for propagating ‘Siskiyou’ blackberry by non-leafy floricane cuttings.

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Gary W. Stutte, Tara A. Baugher, Sandra P. Walter, David W. Leach, D. Michael Glenn, and Thomas J. Tworkoski

A study was conducted to quantify the effects of rootstock and training system on C allocation in apple. Dry-matter distribution was determined at harvest in 5-year-old `Golden Delicious' apple (Malus domestica Borkh.) trees on four rootstocks (MM.111 EMLA, M.7a, M.26 EMLA, and M.9 EMLA) and in three training systems (three-wire palmette, free-standing central leader, and nonpruned). Mobilizable carbohydrate content was determined at harvest and leaf fall in trees from the same planting on MM.111 EMLA and M.9 EMLA in all three training systems. Training system effects interacted with rootstock effects in dry weights of branches and of fruit. Nonpruned system shoot and fruit dry weights reflected known rootstock vigor; whereas, pruned system (three-wire and central leader) shoot dry weights were greatest and fruit dry weights were lowest in trees on M.7a. Rootstock affected the partitioning of dry matter between above- and below-ground tree components, with MM.111 EMLA accumulating significantly more dry matter in the root system than trees on the other rootstocks. Trees in the central leader and the three-wire palmette systems partitioned more dry weight into nonbearing 1-year shoots than trees in the nonpruned system. Root starch content at harvest was greater in trees on MM.111 EMLA than on M.9 EMLA, and root sucrose and sorbitol were less in trees on MM.111 EMLA compared to M.9 EMLA. At leaf fall, starch in young roots was equal in trees on both rootstocks, and sorbitol again was lower in trees on MM.111 EMLA. Harvest starch content of roots, shoots, and branches was lower in nonpruned than in pruned trees. At leaf fall, root, shoot, and branch starch content increased in nonpruned and central leader-trained trees but did not increase in three-wire palmette-trained trees.