Notching is a technique to stimulate shoot growth from paradormant buds with the long-term objective of increasing the cropping potential of fruit trees by developing new fruiting scaffolds. Notching is not commonly practiced by apple (Malus ×domestica) growers in the southeastern United States because results can be inconsistent; notched buds frequently develop into weak spurs producing a few leaves rather than strong extension shoot growth. Therefore, a study was initiated to investigate the potential of 6-benzyladenine (6-BA) to enhance the shoot growth response from notched buds on 2- or 3-year-old wood. Notching paradormant buds on the leader of young ‘Granny Smith’/‘M.26 EMLA’ (‘M.26’) trees at the pink bud stage resulted in new growth developing on 59% of notched buds; however, fewer than 4% of these extended beyond 1.0 cm in length. Spray application of a solution of 1.5 g·L−1 6-BA into the notch increased budbreak to 95% and the proportion of new growth that developed into shoots to 89%, with a mean new shoot length of 7.9 cm. In a timing study on ‘Granny Smith’/‘M.26’, the optimum budbreak and shoot growth responses to notching plus 6-BA treatment were observed between budbreak and 2 weeks after budbreak. Notching paradormant buds on the leader of ‘Fuji’/‘M.9 T337’ (‘M.9’) trees increased budbreak, with 83% of the new growth developing into extension shoots. Spray application of 0.75 g·L−1 6-BA into the notch did not increase budbreak or extension growth of ‘Fuji’/‘M.9’ compared with notching alone. Spray application of a solution of 6-BA directly into a notch made above a paradormant bud may greatly enhance budbreak and shoot extension responses in cultivars or situations where a poor response to notching alone is expected.
Steven A. Tjosvold, Meng-Jen Wu, and Michael S. Reid
Potted miniature roses (Rosa hybrida `Belle Sunblaze') held after production in simulated home conditions performed poorly due to premature yellowing and abscission of buds and leaves, and failure of buds to open. These symptoms were accelerated when the plants were exposed to low concentrations (1 ppm) of ethylene. Spray application of 100 ppm 6-benzylaminopurine (BA) reduced yellowing, but had little effect on bud yellowing and flower opening. Application of 1 mM STS prevented the abscission of leaves and buds, although it only partly reduced leaf yellowing. A combined BA and STS treatment greatly improved the postproduction quality of rose plants, particularly if applied 1 day before harvesting.
Linda S. Campbell, Timothy A. Prince, and Harry K. Tayama
Uniconazole (Sumagic) drench applications of 1.9, 2.7, and 3.8 mL per plant and spray applications of 10, 20, and 30 ppm resulted in shorter plants and more blasted flower buds compared to control plants. Drench applications also resulted in more chlorotic leaves than controls. Average lily height with Sumagic ranged from 19 to 29 cm after Sumagic drench and spray applications, respectively. Average plant height was 29 and 31 cm for ancymidol spray and drench application, respectively. Bud abortion was 10, 12, and 17% for spray treatments of Sumagic at 10, 20, and 30 ppm, respectively, while ancymidol spray caused no abortion. Bud abortions were 8, 7, and 11% from Sumagic drenches of 1.9, 2.7 and 3.8 mL/plant compared with 0% from ancymidol drenches. Plants drenched with Sumagic exhibited leaf chlorosis on day of bloom of 18, 16 and 16%, respectively, for the three respective rates of application while ancymidol caused 11.8% chlorosis. The number of buds initiated was not affected by the treatments, Further studies should be conducted to determine the effect of lower application rates of Sumagic on Easter lilies.
Linda F. Meer, James E. Faust, and Terri Woods Starman
An experiment was conducted to determine the effect of plant growth regulator, application concentration, and time of application on five cultivars of Kalanchoe (Stromboli, Majestic, Heirloom, Keepsake, and Revelry). Kalanchoe cuttings were propagated in 5.2-cm-diameter containers under a short-day photo-period, then placed into a greenhouse maintained at 20C. Spray applications of paclobutrazol (25 or 50 ppm) and uniconazole (1 or 5 ppm) were made prior to visible flower bud (VB), after VB, or before and after VB. Across all cultivars and spray application dates, paclobutrazol applied at 25 and 50 ppm reduced total plant height by 20% and 29%, respectively, while uniconazole applied at 1 and 5 ppm reduced total plant height by 16% and 24%, respectively. Plant height was reduced by 13% with the pre-VB application, 23% with the post-VB application, and 32% with the pre- and post-VB applications. In general, the greater the treatment effectiveness at reducing plant height, the greater the increase in time to flower. For example, a post-VB Bonzi (50 ppm) application caused a 6-day delay in time to first open flower. With the appropriate plant growth regulator application, all five Kalanchoe cultivars tested could be used for commercial production in 5.2-cm-diameter pots.
Roberto G. Lopez and Erik S. Runkle
Prohexadione-Ca (ProCa) is a relatively new plant growth regulator (PGR) that inhibits internode length in rice, small grains, and fruit trees. However, little is known about its efficacy and potential phytotoxicity on floriculture crops and how it compares to other commercially available PGR chemicals. The effects of two foliar spray applications (2 weeks apart) of ProCa (500, 1000, or 2000 ppm), paclobutrazol (30 ppm), or a tank mix of daminozide plus chlormequat (2500 and 1000 ppm, respectively) were quantified on Dianthus barbatus L. `Interspecific Dynasty Red', Ageratina altissima R. King & H. Robinson (Eupatorium rugosum) `Chocolate', Lilium longiflorum Thunb. `Fangio', and Buddleia davidii Franch. `Mixed.' All plants were forced in a glass-glazed greenhouse with a constant temperature setpoint of 20 °C under a 16-h photoperiod. Two weeks after the second spray application of ProCa at 500, 1000, or 2000 ppm, plant height of Dianthus and Lilium was shorter than control plants by 56%, 60%, and 65% and by 6%, 26%, and 28%, respectively. However, ProCa bleached and reduced the size of Dianthus flowers. ProCa at 2000 ppm and daminozide plus chlormequat were effective at controlling the height of Eupatorium (64% and 53% reduction, respectively); however, leaves of Eupatorium were discolored and showed symptoms of phytotoxicity 1 week after the first ProCa application. Only daminozide plus chlormequat were effective on Buddleia. ProCa is an effective PGR for most of the crops we tested; however, its discoloration of red flowers and foliage may limit its application for commercial use.
John M. Ruter
Paclobutrazol was applied as a foliar spray, root-medium drench, and impregnated spike to `New Gold' lantana grown in 2.8-liter pots. Plants were treated 14 June 1993 at rates of 0, 0.5, and 1.0 mg a.i. paclobutrazol/pot and were harvested 27 July 1993 when control plants required further pruning. Impregnated spikes reduced plant size and flowering to a greater degree than spray applications. Drenches reduced root dry weight and biomass compared to spray applications. Plants treated with 0.5 and 1.0 mg a.i. paclobutrazol/pot were not different in regards to plant growth and flowering. Compared to nontreated controls, plants treated with paclobutrazol had a reduced growth index, decreased shoot and root dry weight, and fewer flowers with open florets. All plants in the study were marketable, even though growth control was considered excessive. Lower rates than used in this study should be considered for controlling growth. These results suggest that impregnated spike formulations of paclobutrazol may control plant growth in pine bark-based media.
Larry R. Parsons and T. Adair Wheaton
Undertree microsprinkler irrigation has protected 1 or 2 year old trees to a height of 1 meter during severe advective freezes. During the severe December 1989 freeze, microsprinklers elevated to 0.9 meter protected 5 year old citrus trees to a height of 2 meters. Limb breakage due to ice loading was negligible. Protection was achieved with water application rates less than half that required by some overhead sprinkler models. Survival is attributed to 1) continuous spray from the microsprinkler rather than periodic spray from a rotating overhead sprinkler, and 2) effective localized application rate on branches intercepting spray is more than average overall spray application rate. Elevated microsprinklers provide freeze protection to a greater height and allow for more rapid post-freeze recovery.
W.A. Retzlaff, W.W. Barnett, L.E. Williams, and T.M. DeJong
Japanese plum (Prunus salicina Lindel. `Casselman') trees exposed to three atmospheric ozone partial pressure treatments were sprayed with a summer application of Volck Supreme oil (1% aqueous solution) to control an outbreak of spider mites (Tetranychus spp.). Phytotoxic effects were observed on the foliage of trees in the plots exposed to ambient or higher atmospheric ozone partial pressures 5 days following spray application. Foliage on trees exposed to 0.044 and 0.081 μPa·Pa-1 ozone [12-h mean (8 Apr. to 12 June 1992)] partial pressures developed water spotting and more foliage abscission than trees exposed to charcoal-filtered air (0.024 μPa·Pa-1 ozone). Thus, ozone air-pollution stress may predispose plants to increased phytotoxicity from summer oils.
Steven E. Newman, Michael J. Roll, and Ronald J. Harkrader
Quaternary benzophenanthridine alkaloids (QBAs) isolated from plants in the family Papaveraceae are effective for the control of some fungal diseases. Extracts from Macleaya cordata, a species rich in QBAs, were formulated at 150 mg·L–1 QBA for spray application to greenhouse roses infected with Sphaerotheca pannosa var. rosae (powdery mildew). The QBA formulation was applied at 10-day intervals. For comparison, copper sulfate pentahydrate, piperalin, and fenarimol also were applied to mildew-infected plants within the same greenhouse at their respective labeled rates. One day after treatment, visible symptoms of mildew infection were reduced 60% by QBA, whereas fenarimol, copper sulfate pentahydrate, and piperalin reduced the symptoms of infection 50%, 75%, and 85%, respectively. Subsequent studies demonstrated that a tank mix of QBA and piperalin provided enhanced control of powdery mildew on rose. Results from this study indicate that QBAs have the potential to be developed as a biorational fungicide for greenhouse use with both fungicidal and fungistatic activity.
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.