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J. Scott Cameron, Carol A. Hartley, Carl H. Shanks Jr., and Jeannie K. L. Garth

At two-week intervals from 17 June to 15 July, three groups of `Meeker' red raspberry plants were infested with two-spotted spider mites (Tetranychus urticae) in a greenhouse. While populations on individual plants were allowed to develop freely, control plants were kept free of mites with a chemical miticide. Gas exchange measurements were made on 27 July prior to visible mite damage, and on 7 October after injury was apparent. The relationships between mite populations and leaf gas exchange and chlorophyll characteristics were described using a logarithmic function.

Physiological responses to mite feeding were observed prior to visible leaf injury. On both dates, CO2 assimilation rates decreased (p ≤ 0.001) with increasing mite numbers per leaflet. On 27 June, a significant relationship (R2 = 0.61***) was found between mite number and mesophyll conductance (gm). On 7 October, significant relationships (p ≤ 0.001) were also observed with gm, stomatal conductance (gs), and transpiration (E). Total chlorophyll content of leaves decreased with increasing mite populations, but chlorophyll a/b ratio and dry weight per leaf unit area were unchanged.

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J. Thomas Raese and S. R. Drake

Sprays of calcium materials were applied at high volume rates (620 g Ca/400 liters) with a handgun during early June, late June, and mid-July versus mid-July, early August, and late August for five years, 1985 to 1989. Leaf injury was most severe for the late sprays but no spray injury was observed on the fruit surfaces. Bitter pit was markedly reduced with all sprays except CaSO4. In some years, bitter pit was controlled better with the early sprays. Either early or late sprays improved fruit quality including overall appearance, reduced scald development, improved red color of the skin, increased fruit firmness and reduced incidence of bitter pit in cold air (0°C) storage. Soluble solids and acidity in the fruit was not affected by calcium sprays. Leaf Ca was higher from the late spray applications than from the earlier applications. All calcium chloride spray materials resulted in increased fruit peel and cortex Ca. Calcium nitrate sprays tended to increase fruit nitrogen concentrations leading to undesirable higher N:Ca ratios in the fruit.

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Youbin Zheng, Linping Wang, and Mike A. Dixon

Electrolytically generated copper is increasingly used to control diseases and algae in the greenhouse industry. However, there is a shortage of information regarding appropriate management strategies for copper in ornamental crop production. The objectives of this study were to characterize the response of three ornamental crops (Dendranthema ×grandiflorum L. `Fina', Rosa ×hybrida L. `Lavlinger', Pelargonium ×hortorum L. `Evening Glow') to different solution levels of Cu2+ (ranging from 0.4 to 40 μm) and to determine the critical levels above which toxic responses became apparent. The following measurements were used to assess the treatments: leaf chlorophyll fluorescence (Fv/Fm), leaf chlorophyll content, and visible injury of leaf and root. Excessive copper reduced plant root length, root dry weight, total dry weight, root to shoot ratio, leaf area, and specific leaf area in all three species. The critical solution level of Cu2+ that resulted in significantly reduced plant dry weight for chrysanthemum was 5 μm; for miniature rose, 2.4; and for geranium, 8 μm. Plant visible root injury was a more sensitive and reliable copper toxicity indicator than visible leaf injury, leaf chlorophyll content, Fv/Fm, or leaf and stem copper content. Generally, all the species exhibited some sensitivity to Cu2+ in solution culture, with chrysanthemum and miniature rose being most sensitive and geranium being least sensitive. Caution should be taken when applying copper in solution culture production systems.

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Steven B. Polter, Douglas Doohan, and Joseph C. Scheerens

Terbacil at 0, 0.8, 1.6, 3.2, and 6.4 oz/acre (0, 0.06, 0.11, 0.22, and 0.45 kg·ha-1) a.i. was applied immediately after planting, at the thee-leaf stage and at the six-leaf stage to greenhouse grown strawberry (Fragaria × ananassa) cultivars Jewel, Mira, and Allstar. Strawberry was most tolerant of terbacil when the herbicide was applied before leaf emergence. `Mira' was more tolerant of terbacil than was `Jewel'. `Jewel' and `Allstar' exhibited similar levels of tolerance. In a second experiment terbacil at 4.8 oz/acre (0.34 kg·ha-1) was applied to the soil, to the foliage, and to the foliage followed by a water rinse. Injury was greatest when terbacil was applied directly to the strawberry foliage rather than to the soil, but was minimal when foliage was rinsed after application. In a final experiment terbacil at 4.8 oz/acre was applied to greenhouse-grown `Jewel' strawberries at the thee-leaf stage followed by a water rinse 0.5, 1, 2, or 4 hours after application. Rinsing the foliage of strawberry plants after application significantly reduced leaf injury. Delaying the rinse up to 4 hours did not lead to increased injury. Over all, the results from our study indicate the potential for using terbacil as an effective herbicide on newly established strawberries, especially if the compound is rinsed from leaves (if present) after treatment.

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George M. Greene II

When applied as a dilute spray (at 125 and 250 ppm), BAS 125W effectively reduced shoot extension growth on `York' Imperial (YI) and `Spartan' (S) apple trees but was less effectively on `Delicious' (D). In 1994, lateral shoot growth of YI/M.26 trees (1 to 2 m tall) from 10 May to 7 July was reduced (35 vs. 7 cm) by sprays applied on May 13. The initial surge of growth by vertical shoots was suppressed by the treatments (16 vs. 35 cm), but there was more regrowth (6.5 vs. 0.5 cm). Some leaf injury was seen on YI. The 1995 experiments were conducted on S/M.111 and D/M.111 in an orchard spaced 3.7 m by 7.3 m. On S, lateral shoot length on five dates from 7 June to 20 Sept. was reduced by the sprays (44 vs. 32 cm on 20 Sept.). The initial surge of growth by vertical shoots was suppressed by the treatments (30 vs. 85 cm), but there was more regrowth (34 vs. 4 cm). There were fewer apples that were <25% red and more that were 25% to 40% and 66% to 85% red. On D, lateral shoot length on five dates from 7 June to 20 Sept. was reduced by the sprays (51 vs. 38 cm on 20 Sept.). The growth of vertical shoots was not influenced by the treatments, possibly due to a light fruit load in the tops of the trees. Growers viewing the 1995 plots estimated enhanced income of $933/ha for D and $780/ha for S.

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L. Ferguson, J.A. Poss, S.R. Grattan, C.M. Grieve, D. Wang, C. Wilson, T.J. Donovan, and C.-T. Chao

Performance of `Kerman' pistachio (Pistacia vera L.) trees on three rootstocks (P. atlantica Desf., P. integerrima Stewart and `UCB-1', a P. atlantica × P. integerrima hybrid) was evaluated with 2-year-old trees grown in sand-tank lysimeters under combined SO4 2- and Cl- salinity and boron (B) stress for 6 months. Four salinity treatments were imposed by irrigating the plants with water at electrical conductivity (ECiw) of 3.5, 8.7,12, or 16 dS·m-1 each containing B at 10 mg·L-1. Growth of `Kerman' was evaluated based on increase in total leaf area, increase in trunk diameter, and total above-ground biomass production. All growth parameters decreased as salinity increased, but were not significant until ECiw exceeded 12 dS·m-1. However, growth of `Kerman' on P. atlantica and `UCB-1' was considerably better than on P. integerrima at 16 dS·m-1. The onset and severity of foliar injury differed among scions and treatments and was attributed primarily to B toxicity, rather than the effects of salinity. Concentrations of B in injured leaf tissue ranged from 1000 to 2500 mg·kg-1. Leaf injury decreased with increasing salinity, although leaf B was not significantly reduced suggesting an internal synergistic interaction between B and other mineral nutrients. However for P. vera on P. integerrima, the highest level of salinity produced the greatest injury, possibly as a combination of B plus Cl- and/or Na+ toxicity. Leaf transpiration, stomatal conductance, and chlorophyll concentration of P. vera, determined by steady-state porometry, were also reduced to a greater degree by combined salinity and B when budded on P. integerrima than on the other two rootstocks.

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Anil P. Ranwala and William B. Miller

Experiments were conducted to evaluate storage temperature, storage irradiance and prestorage foliar sprays of gibberellin, cytokinin or both on postharvest quality of Oriental hybrid lilies (Lilium sp. `Stargazer'). Cold storage of puffy bud stage plants at 4, 7, or 10 °C in dark for 2 weeks induced leaf chlorosis within 4 days in a simulated consumer environment, and resulted in 60% leaf chlorosis and 40% leaf abscission by 20 days. Cold storage also reduced the duration to flower bud opening (days from the end of cold storage till the last flower bud opened), inflorescence and flower longevity, and increased flower bud abortion. Storage at 1 °C resulted in severe leaf injury and 100% bud abortion. Providing light up to 40 μmol·m-2·s-1 during cold storage at 4 °C significantly delayed leaf chlorosis and abscission and increased the duration of flower bud opening, inflorescence and flower longevity, and reduced bud abortion. Application of hormone sprays before cold storage affected leaf and flower quality. ProVide (100 mg·L-1 GA4+7) and Promalin (100 mg·L-1 each GA4+7 and benzyladenine (BA)) effectively prevented leaf chlorosis and abscission at 4 °C while ProGibb (100 mg·L-1 GA3) and ABG-3062 (100 mg·L-1 BA) did not. Accel (10 mg·L-1 GA4+7 and 100 mg·L-1 BA) showed intermediate effects on leaf chlorosis. Flower longevity was increased and bud abortion was prevented by all hormone formulations except ProGibb. The combination of light (40 μmol·m-2·s-1) and Promalin (100 mg·L-1 each GA4+7 and BA) completely prevented cold storage induced leaf chlorosis and abscission.

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Genhua Niu, Terri Starman, and David Byrne

The responses of garden roses to irrigation water with elevated salts are unknown. Two experiments were conducted to evaluate the relative salt tolerance of 13 self-rooted rose cultivars by irrigating the plants with nutrient solutions at an electrical conductivity (EC) of 1.4 dS·m−1 (control) or nutrient saline solutions at EC of 3.1, 4.4, or 6.4 dS·m−1. In Expt. 1, ‘Belinda’s Dream’, ‘Caldwell Pink’, ‘Carefree Beauty’, ‘Folksinger’, ‘Quietness’, and ‘Winter Sunset’ plants were grown in a greenhouse from 13 Aug. to 21 Oct. (10 weeks). Shoot dry weight of all cultivars decreased as EC of irrigation water increased. ‘Winter Sunset’ was most sensitive among these cultivars to salt stress followed by ‘Carefree Beauty’ and ‘Folksinger’ with severe leaf injury at EC of 3.1 dS·m−1 or higher or death at EC of 6.4 dS·m−1. No visual damage was observed in ‘Belinda’s Dream’ or ‘Caldwell Pink’, regardless of the salinity level. In Expt. 2, ‘Basye’s Blueberry’, ‘Iceberg’, ‘Little Buckaroo’, ‘The Fairy’, ‘Marie Pavie’, ‘Rise N Shine’, and ‘Sea Foam’ plants were grown in the greenhouse from 29 Sept. to 16 Nov. (7 weeks) and irrigated with the same nutrient or nutrient saline solutions. Salinity treatment did not affect shoot dry weight of ‘Basye’s Blueberry’, ‘Little Buckaroo’, ‘Sea Foam’, and ‘Rise N Shine’. Shoot dry weight of ‘Iceberg’, ‘The Fairy’, and ‘Marie Pavie’ decreased as EC of irrigation water increased. No or little visual damage was observed in ‘Little Buckaroo’, ‘Sea Foam’, and ‘Rise N Shine’. Leaf tip burns were seen in ‘Iceberg’, ‘Marie Pavie’, ‘Basye’s Blueberry’, and ‘The Fairy’ at EC 6.4 of dS·m−1. Generally, these symptoms were less severe than those observed in Expt. 1, probably attributable partially to the shorter treatment period. Whereas shoot Na+ and Cl varied greatly among the rose cultivars, the shoot concentrations of Ca2+, K+, and Mg2+ did not. Generally, salinity-tolerant cultivars had higher shoot Na+ and Cl concentrations. In summary, in Expt. 1, ‘Belinda’s Dream’ was the most tolerant cultivar, whereas ‘Winter Sunset’ was the least tolerant followed by ‘Carefree Beauty’. In Expt. 2, ‘Iceberg’, ‘Marie Pavie’, and ‘The Fairy’ were less tolerant to salinity as compared with other cultivars, although the differences were small.

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R.C. Ebel, B.L. Campbell, M.L. Nesbitt, W.A. Dozier, J.K. Lindsey, and B.S. Wilkins

Estimates of long-term freeze-risk aid decisions regarding crop, cultivar, and rootstock selection, cultural management practices that promote cold hardiness, and methods of freeze protection. Citrus cold hardiness is mostly a function of air temperature, but historical weather records typically contain only daily maximum (Tmax) and minimum (Tmin) air temperatures. A mathematical model was developed that used Tmax and Tmin to estimate air temperature every hour during the diurnal cycle; a cold-hardiness index (CHI500) was calculated by summing the hours ≤10°C for the 500 h before each day; and the CHI500 was regressed against critical temperatures (Tc) that cause injury. The CHI500 was calculated from a weather station located within 0.1 km of an experimental grove and in the middle of the satsuma mandarin (Citrus unshiu Marc.) industry in southern Alabama. Calculation of CHI500 was verified by regressing a predicted CHI500 using Tmax and Tmin, to a measured CHI500 calculated using air temperatures measured every hour for 4 winter seasons (1999-2003). Predicted CHI500 was linearly related to measured CHI500 (r 2 = 0.982). However, the slope was a little low such that trees with a CHI500 = 400, near the maximum cold-hardiness level achieved in this study, had predicted Tc that was 0.5 °C lower than measured Tc. Predicted and measured Tc were similar for nonhardened trees (CHI500 = 0). The ability of predicted Tc to estimate freeze injury was determined in 18 winter seasons where freeze injury was recorded. During injurious freeze events, predicted Tc was higher than Tmin except for a freeze on 8 Mar. 1996. In some freezes where the difference in Tc and Tmin was <0.5 °C there were no visible injury symptoms. Injury by the freeze on 8 Mar. 1996 was due, in part, to abnormally rapid deacclimation because of defoliation by an earlier freeze on 4-6 Feb. the same year. A freeze rating scale was developed that related the difference in Tc and Tmin to the extent of injury. Severe freezes were characterized by tree death (Tc - Tmin > 3.0 °C), moderate freezes by foliage kill and some stem dieback (1.0 °C ≤ Tc - Tmin ≤ 3.0 °C), and slight freezes by slight to no visible leaf injury (Tc - Tmin < 1.0 °C). The model was applied to Tmax and Tmin recorded daily from 1948 through 2004 to estimate long-term freeze-risk for economically damaging freezes (severe and moderate freeze ratings). Economically damaging freezes occurred 1 out of 4 years in the 56-year study, although 8 of the 14 freeze years occurred in two clusters, the first 5 years in the 1960s and 1980s. Potential modification of freeze-risk using within-tree microsprinkler irrigation and more cold-hardy cultivars was discussed.

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Tripti Vashisth and Anish Malladi

immature fruit were removed from the selected branch. The treatments were: 1) control (no organ injury); 2) fruit injury; 3) 50% fruit injury; and 4) leaf injury. For the fruit injury treatment, all fruit on the branch were cut in half using a razor blade