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Chad Finn, Michele Warmund, and Chris Starbuck

The vegetative growth and fruit yield of three types of micropropagated `Redwing' red raspberry (Rubus idaeus L. var. idaeus) nursery stock were compared. The three types of nursery material included: 1) stage IV (S-IV) actively growing plants; 2) dormant-stage IV (DS-IV) plants; and 3) nursery-matured (NM) S-IV plants, grown for 8 to 12 weeks in the field before harvest for cold storage. On 1 Apr. 1991, primocane-fruiting `Redwing' plants of each type were planted 0.6 m apart in ridged, drip-irrigated, and straw-mulched rows spaced 3 m apart in six, three-plant replications. In the establishment year, a small, but commercially viable, crop was harvested from 16 Aug. 1991 to 28 Oct. 1991. The S-IV and NM plants produced greater yields than DS-IV plants in the establishment year. However, by the end of the second year, the S-IV plants had the greatest fruit yield, followed by NM, with the DS-IV plants continuing to have the lowest yield. Fruit size of the S-IV plants was largest in both years. While there were differences in dry weight during the planting year, by the experiment's conclusion, the dry weights were similar among all nursery types. When planting `Redwing', the less-expensive, easier-to-handle, and higher-yielding S-IV plants would be recommended over the other nursery types.

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Steven P. Castagnoli, Leslie H. Fuchigami, Tony H. H. Chen, and Liping Zhen

Studies were performed on the development of dormancy, cold hardiness, and desiccation tolerance, and the effect of manual defoliation timing on performance of `Fuji' and `Braeburn' apple nursery stock. Dormancy development, response to defoliation, and desiccation tolerance of apple differed from those reported for other temperate woody plant species. Dormancy development in `Fuji' was approximately two weeks ahead of `Braeburn', and was strongly regulated by temperature. Photoperiod had no influence on dormancy development of `Fuji'. Desiccation tolerance of both varieties was greatest just prior to the onset of dormancy and early dormancy. This pattern in the seasonal development of tolerance to desiccation is not typical of temperate woody plant species. Early defoliation was detrimental to performance of `Braeburn', but had little effect on `Fuji'. Early defoliation promoted earlier spring budbreak in `Fuji'. Development of freezing tolerance in both apple varieties was typical of other woody plants, and coincided with the onset of dormancy. Maximum hardiness was achieved after the requirements for dormancy were completely satisfied.

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Fenton E Larsen and Stewart S. Higgins

Artificial defoliation of deciduous fruit tree nursery stock is often necessary so that plants can be dug early enough to escape inclement fall weather. In this research, we assessed the efficacy of abscisic acid (ABA) as a defoliant. ABA was applied as a foliar spray at one of three concentrations—500, 1000, or 2000 ppm a.i. Trees were sprayed either once or twice for a total of six chemical treatments, plus untreated controls. The defoliation and growth responses of eight cultivars were evaluated with the cooperation of commercial nurseries in Washington State. While all treatments caused significantly greater defoliation than was observed in untreated trees, ABA at 500 ppm applied once or twice, or 1000 ppm applied only once, was generally sufficiently effective only on `Bartlett', `Gibson Golden Delicious', and `Law Red Rome', but not on `Imperial Gala', `Scarlet Spur Delicious', `Granny Smith', `Braeburn', or `Red Fuji'. Single or double applications of 2000 ppm or double applications of 1000 ppm often produced faster defoliation than double applications of 500 ppm, but defoliation was not always superior after 4 weeks. No pre-digging field damage was noted, but some treatments appeared to reduce trunk diameter increase after replanting, with no consistent trends among cultivars, except with `Bartlett' pear, which was frequently negatively affected. ABA appears to be very promising as a nursery tree defoliant.

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Jeffery K. Iles

Rewholesalers, garden centers, and other sellers of deciduous shrubs routinely receive bare-root stock in late winter or early spring for potting; however, bare-root plants are sometimes slow to establish in containers. Potted liners with well-developed root systems show potential for shortening the production cycle and permitting the development of higher-quality plants earlier in the growing season. To study the effect of nursery stock type and size on subsequent growth, two bare-root sizes and one potted liner size of `Cardinal' red osier dogwood (Cornus sericea L.), `Goldflame' spirea (Spiraea xbumalda Burv.), and `James MacFarlane' lilac (Syringa xprestoniae McKelv.) were grown in polyethylene containers of different sizes. Bare-root plants (15 and 30 cm in height) were grown in 2.7- and 6.1-L, and 6.1- and 10.3-L containers, respectively. Potted liners (0.4-L container size) were grown in 6.1- and 10.3-L containers. Plant performance was evaluated 10 and 20 weeks after potting. In general, plant quality ratings increased with container volume for all species. For `Goldflame' spirea and `James MacFarlane' lilac, best plant quality ratings occurred with 30-cm plants grown in 10.3-L containers. But for `Cardinal' redosier dogwood, plant quality ratings were highest and not significantly different for 30-cm bare-root plants and potted liners grown in 10.3-L containers.

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Hannah Mathers

Weed growth in container-grown nursery stock is a particularly serious problem. Inexpensive and easily accessible carriers for safe application of concentrated preemergent herbicides have been investigated. Monaco and Hodges (1974) evaluated standard pine bark used in potting media. Coating broadcast fertilizers with preemergents has also been recently examined in agronomic crops (Koscelny and Peeper, 1996; Rabaey and Harvey, 1994). The four objectives of this experiment were: 1) determine the efficacy and duration of weed control of a range of preemergent herbicide-impregnated carriers, applied as a top-dressing. The preemergents to be tested are: Goal, Surflan, Rout, Gallery, Gallery/Surflan, Ronstar and Regal 0; 2) determine the efficacy and duration of weed control of a range of preemergent herbicide-impregnated slow and controlled release fertilizers, applied preplant incorporated in the potting mix; 3) assess the phytotoxicity of the chemical-treated carriers on the ornamental plants evaluated; and 4) determine which weeds were controlled. Of the carriers investigated, bark was the best treatment regardless of pre-emergent used. However, Surflan and Gallery were slightly better than Goal. The effectiveness of the bark in controlling weeds is worth investigating in further studies. A significant species effect with the efficacy data was observed. Euonymus `Emerald Gaiety' was significantly better at competing with the weeds present than the other species evaluated. Top dressing gave significantly fewer weeds, with rated data, vs. incorporation. The effect was most pronounced for Kansel or Fert. plus Ronstar. Osmocote micro-fert. gave less weeds, top-dressed, when weed weights were analyzed. However, using the weed weight data, there were no significant differences whether the carriers were applied top dress or incorporated. Phytotoxicity was not significantly different with incorporation vs. top dressing.

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Xiaomei Cheng and Kendra Baumgartner

Indigenous arbuscular mycorrhizal (AM) fungal communities were characterized by examining spores in five fumigated and five nonfumigated vineyards in Northern California. None of the vineyards surveyed lacked spores, but species composition differed among the vineyards. Most of the fungi were in the genus Glomus; Paraglomus occultum Morton & Redecker, G. etunicatum Becker & Gerd., and G. aggregatum Schenck & Smith emend. Koske were the most common species identified. Fungal diversity was greater in nonfumigated than in fumigated vineyards. Field-propagated grapevine nursery stock was examined as a potential source of AM fungi for fumigated vineyards. We quantified fungal colonization of new roots initiated from field-grown benchgrafts and potted benchgrafts of Cabernet Sauvignon on three rootstocks (101-14, 110R, and St. George). After 7 months of growth in the greenhouse, new roots initiated from dormant roots of field-grown and potted benchgrafts were colonized by AM fungi. Mycorrhizal colonization of new roots of field-grown benchgrafts was significantly higher than that of potted benchgrafts. Our results suggest that field-propagated nursery stock can serve as a source of AM fungi and may be better suited for fumigated and/or low phosphorus soils than potted benchgrafts.

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Jennifer L. Dwyer, N. Curtis Peterson, and G. Stanley Howell

The nursery industry continues to develop improved methods for successfully overwintering container-grown nursery stock. Experiments were conducted using several different species of woody ornamentals ranging from species known to be cold hardy to cold tender. Eighteen species were subjected to temperatures ranging from 20F to -20F and observed for post-stress performance and viability. Rates and timing of acclimation, mid-winter hardiness, and deacclimation of seven species were determined by examining the shoots for injury after subjecting them to controlled freezer conditions. The roots of the same seven species were exposed to three different overwintering systems: in a polyhouse, pot-to-pot above the ground, and pot-in-pot below the ground. Cold hardiness of root and shoot systems and the effects of warming temperatures on shoots were determined as well as the post-stress performance of each species. Results of this research will be presented.

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Mohammed Z. Alam and Calvin Chong

nursery stock grown in a compost-based medium with recycled nutrients HortScience 39 60 64 Chong, C. Purvis, P. Lumis, G. Holbein, B.E. Voroney, R.P. Zhou, H. Liu, H.W. Alam, M

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L.P. Baldridge and S.E. Newman

Most field production of woody ornamental plants involves clean cultivation of rows, performed by either mechanical or chemical means. Grass cover has been shown to reduce erosion, but may have a detrimental effect on the growth and vigor of young trees. Clover cover has been shown to not adversely affect plant growth. The objective of this study was to compare the relative merits of three row covers, clean cultivated, pine bark mulch and kobe lespedeza clover, in combination with two irrigation rates, low and high, on field-grown red bud and crape myrtle plants.

Crape myrtle and red bud plants were tallest and had a larger caliper when grown with a clean row or with pine bark mulch. Kobe lespedeza clover reduced plant growth of both species when supplemental irrigation was not provided. Clover reduced plant height and caliper of red bud even when irrigated. Generally, plants grown under pine bark mulch were more efficient in water use as shown by greater stomatal conductance in August.