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Mei Yuan, William H. Carlson, Royal D. Heins and Arthur C. Cameron

Scheduling crops to flower for specific dates requires a knowledge of the relationship between temperature and time to flower. Our objective was to determine the relationship between temperature and time to flower of four herbaceous perennials. Field-grown, bare-root Coreopsis grandiflora `Sunray', Gaillardia grandiflora `Goblin', Rudbeckia fulgida `Goldsturm', and tissue culture-propagated Chrysanthemum superbum `Snow Cap' were exposed to 5C for 10 weeks. They were grown at 15, 18, 21, 24 or 27C under 4-h night interruption lighting. Time to visible bud (VB) and first flower (FLW) were recorded. Days to VB, days to FLW, and days from VB to FLW decreased as temperature increased. Time to flower at 15C was 70, 64, 96, and 54 days and 24, 39, 48, and 36 days at 27C for Coreopsis, Gaillardia, Rudbeckia, and Chrysanthemum, respectively. The 27C temperature apparently caused devernalization on Coreopsis because only 40% of the plants flowered. The effects of temperature on flower size, flower bud number, and plant height also are presented.

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M. Peggy Damann and Robert E. Lyons

Juvenility and flowering requirements of Chrysanthemum ×superbum Bergmans ex J. Ingram `G. Marconi' and `Snow Lady' were examined by growing plants under short days (SDs) and transferring them to long days (LDs) upon reaching specific true leaf stages. `G. Marconi' plants did not flower in continuous SDs and only sparse flowering occurred in plants transferred to LDs. `Snow Lady' plants transferred from SDs to LDs at the cotyledon stage flowered fastest from seeding (75 days) and had the fewest number of main stem leaves and total leaves (9 and 15, respectively) at the time of first flower. Plants moved from SDs to LDs at the 24 true leaf stage flowered 123 days after seeding and averaged 28 leaves on the main stem and 37 total leaves at the time of first flower. To examine apical floral initiation, plants were distributed between SDs and LDs following transplanting and five plants per treatment were sampled each week thereafter. Microscopic examination revealed floral initiation in plants sampled after just 1 week in LDs and, after 5 weeks, macroscopic terminal flower buds were present. Under SDs, apical floral initiation began after 5 weeks, yet, 9 weeks were required for floral initiation in all five plants sampled.

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Jeffrey F. Derr

Tolerance of transplanted black-eyed Susan (Rudbeckia hirta var. pulcherrima Farw.), lanceleaf coreopsis (Coreopsis lanceolata L.), shasta daisy (Chrysanthemum × superbum Bergmans ex. J. Ingram), purple coneflower [Echinacea purpurea (L.) Moench.], and blanket flower (Gaillardia aristata Pursh) to preemergence herbicides was evaluated in container trials. Herbicides were applied at the maximum use rate and twice the maximum use rate. Dithiopyr, pendimethalin, and prodiamine provided excellent control of spotted. spurge (Euphorbia maculata L.) and yellow woodsorrel (Oxalis stricta L.) with little injury to the five herbaceous perennials. DCPA, oxadiazon, and metolachlor were tolerated by all treated species, but these chemicals provided lower control of one or both weed species. Oryzalin, isoxaben + trifluralin, and napropamide caused unacceptable injury and shoot fresh-weight reductions in some of the perennials at one or both application rates. Chemical names used: dimethyl 2,3,5,6-tetrachloro-1,4-benzenedicarboxylate (DCPA); S,S-dimethyl 2-(difluoromethyl) -4-(2 -methylpropyl)-6-trifluoromethyl-3,5-pyridinedicarbothioate(dithiopyr);N-[3-(1-ethyl-1-methylpropyl)-5-isoxazolyl]-2,6-dimethoxybenzamide(isoxaben); 2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide(metolachlor);N,N-diethyl-2-(l-naphtha1enenyloxy) propanamide(napropamide);4-(dipropylamino)-3,5-dinitrobenzenesulfonamide (oryzalin);3-[2,4-dichloro-5-(1-methylethoxy)phenyl]-5-(1,1-dimethylethy1)-l,3,4-oxadiazol-2-(3H)-one (oxadiazon); N-(1-ethylpropyl) -3,4-dimethyl-2,6-dinitrobenzamine (pendimethalin); N,N-di-n-propyl-2,4-dinitro-6-(trifluoromethyl)-m-phenylenediamine (prodiamine); 2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzamine (trifluralin).

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Peggy Damann and Robert E. Lyons

Chrysanthemum × superbum, Coreopsis lanceolata, and Coreopsis grandiflora are LD flowering perennial plants. The end of juvenility could be defined as the minimum expanded leaf number required for fastest flowering once placed in LD. This research was conducted to compare juvenility and flowering requirements in dwarf and standard cultivars of these species. Plants were maintained under SD and transferred to LD upon reaching true leaf stages beginning with 0 (cotyledons only) and progressing at 2 or 3 leaf intervals to the 24 leaf stage. Coreopsis `Sunray' and Chrysanthemum `G. Marconi' were relatively unresponsive to LD whereas LD induced flowering in 70-100% of the plants in each leaf number treatment in Coreopsis `Early Sunrise'. Plants transferred at the 15 leaf stage required the least number of LD to reach anthesis. LD promoted complete flowering in Chrysanthemum × superbum `Snow Lady' plants and 90% of the SD control plants flowered as well. SD control plants from the other 3 cultivars remained vegetative. Effects of vernalization will also be presented.

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Muhammed Maqbool and Arthur C. Cameron

Field-grown plants of Alcea rosea (L.) Cav. (hollyhock), Asparagus officinalis L., Coreopsis grandiflora Hogg ex Sweet `Sunray', Dicentra spectabilis (L.) Lem. (bleeding heart), Gaillardia ×grandiflora Van Houtte `Baby Cole', Lupinus polyphyllus Lindl. `Russell Hybrids', and Phlox subulata L. `Emerald Pink' harvested as bare-root crowns in late fall were packaged in polyethylene-lined crates and stored for 6 months. There were no significant differences in the regrowth performance of any of the perennials following storage at 0 or -2C. The amount of surface covered by fungal hyphae (surface mold) increased more than 2-fold between 4 and 6 months of storage at 0 or -2C on all species. Dicentra spectabilis and Alcea rosea were most susceptible to mold growth during storage. Alcea rosea and Coreopsis grandiflora stored poorly at all storage temperatures. In a second experiment, the regrowth performance of Artemisia schmidtiana Maxim `Silver Mound', Asclepias tuberosa L., Aster novae-angliae L., Centranthus ruber (L.) DC., Chrysanthemum superbum Bergmans ex. J. Ingram, Dicentra eximia (Ker-Gawl.) Torr., Dicentra spectabilis, Geum quellon Sweet `Mrs. Bradshaw', Hosta `Honeybells', and Lupinus polyphyllus was tested following 6 months of storage at temperatures between -10 and +5C. Regrowth performance was generally similar at -2, 0, and 5C for most species. The results indicated, however, that Centranthus ruber and Chrysanthemum ×superbum should not be stored at temperatures of -2C or below. Sufficient etiolated growth developed for most species when stored at 2C or above to cause problems during shipping, handling, and potting. In general, mold growth on crowns during storage did not reduce regrowth performance of the species tested.

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M. Peggy Damann and Robert E. Lyons

To examine the effects of chilling and a limited inductive photoperiod (LIP) on flowering of Chrysanthemum superbum Bergmans ex J. Ingram `G. Marconi' and `Snow Lady', Coreopsis grandiflora Hogg `Sunray', and Coreopsis lanceolata L. `Early Sunrise', seeds were sown and plants were maintained in the greenhouse in short days (SDs) for 7 weeks, followed by 4 months of natural outdoor chilling for all plants except 10 of each cultivar, which remained in the greenhouse under SDs for the duration of the experiment. Upon return to greenhouse conditions, 10 plants of each cultivar were placed in SDs, all other chilled plants were placed in long-days (LDs) and subsequently transferred to SDs after receiving 6, 8, 10, 12, 14, 16, 18, 20, or 22 LD cycles. Ten chilled plants of each cultivar remained in LDs for the duration of the experiment. Continuous SDs without chilling resulted in 70%, 40%, 20%, and 10% flowering in `Snow Lady', `Early Sunrise', `Sunray,' and `G. Marconi', respectively. Chilling, followed by a return to continuous SDs, improved flowering in all cultivars compared to SDs without chilling. The number of LD cycles required for 100% flowering varied with cultivar. Ninety percent of the chilled `Early Sunrise' plants flowered with no LD cycles, and 100% flowering was produced by as few as six LD cycles. In `Snow Lady', 100% flowering occurred in chilled plants with no LD cycles and those receiving at least 10 LD cycles. With only six or eight LD cycles, 90% and 80% of these plants, respectively, still flowered. The percentage of `G. Marconi' and `Sunray' plants flowering ranged from 40% to 100% in the chilled treatments, with a general trend for more flowering with an increase in the number of LD inductive cycles. Continuous LDs following chilling resulted in as high or higher percent flowering than any other treatments (100% for `G. Marconi' and 90% for `Sunray'). The effects of LIP were evident in both Coreopsis cultivars but in neither Chrysanthemum superbum cultivar. There was a linear relationship between the number of LDs received and stem length at first flower in `Sunray' and `Early Sunrise'. In both cultivars, a reduction in stem elongation of about 10 cm occurred when plants received only 6 LDs compared to 22 LDs. The number of days from the start of LDs to first flower increased linearly as the number of LD cycles before the transfer back to SDs increased.

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Erik S. Runkle, Royal D. Heins, Arthur C. Cameron and William H. Carlson

`Snowcap' Shasta daisy [Leucanthemum ×superbum Bergmans ex. J. Ingram (syn: Chrysanthemum ×superbum, C. maximum)] was grown under various photoperiods and temperatures to determine their effects on flowering. In the first experiment, plants were held for 0 or 15 weeks at 5 °C and then were grown at 20 °C under the following photoperiods: 10, 12, 13, 14, 16, or 24 hours of continuous light or 9 hours with a 4-hour night interruption (NI) in the middle of the dark period. Without cold treatment, no plants flowered under photoperiods ≤14 hours and 65% to 95% flowered under longer photoperiods or NI. After 15 weeks at 5 °C, all plants flowered under all photoperiods and developed three to four or 10 to 11 inflorescences under photoperiods ≤14 or ≥16 hours, respectively. To determine the duration of cold treatment required for flowering under short photoperiods, a second experiment was conducted in which plants were treated for 0, 3, 6, 9, 12, or 15 weeks at 5 °C, and then grown at 20 °C under 9-hour days without or with a 4-hour NI. Under 9-hour photoperiods, 0%, 80%, or 100% of plants flowered after 0, 3, or ≥6 weeks at 5 °C, and time to flower decreased from 103 to 57 days as the time at 5 °C increased from 3 to 12 weeks. Plants that were under NI and received ≥3 weeks of cold flowered in 45 to 55 days. For complete and rapid flowering with a high flower count, we recommend cold-treating `Snowcap' for at least 6 weeks, then providing photoperiods ≥16 hours or a 4-hour NI during forcing.

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Erik S. Runkle, Royal D. Heins, Arthur C. Cameron and William H. Carlson

`Snowcap' Shasta daisy [Leucanthemum ×superbum Bergmans ex. J. Ingram (syn: Chrysanthemum ×superbum, C. maximum)] was grown under various photoperiods and temperatures to determine their effects on flowering. In the first experiment, plants were held for 0 or 15 weeks at 5 °C and then were grown at 20 °C under the following photoperiods: 10, 12, 13, 14, 16, or 24 hours of continuous light or 9 hours with a 4-hour night interruption (NI) in the middle of the dark period. Without cold treatment, no plants flowered under photoperiods ≤14 hours and 65% to 95% flowered under longer photoperiods or NI. After 15 weeks at 5 °C, all plants flowered under all photoperiods and developed three to four or 10 to 11 inflorescences under photoperiods ≤14 or ≥16 hours, respectively. To determine the duration of cold treatment required for flowering under short photoperiods, a second experiment was conducted in which plants were treated for 0, 3, 6, 9, 12, or 15 weeks at 5 °C, and then grown at 20 °C under 9-hour days without or with a 4-hour NI. Under 9-hour photoperiods, 0%, 80%, or 100% of plants flowered after 0, 3, or ≥6 weeks at 5 °C, and time to flower decreased from 103 to 57 days as the time at 5 °C increased from 3 to 12 weeks. Plants that were under NI and received ≥3 weeks of cold flowered in 45 to 55 days. For complete and rapid flowering with a high flower count, we recommend cold-treating `Snowcap' for at least 6 weeks, then providing photoperiods ≥16 hours or a 4-hour NI during forcing.

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Neil O. Anderson and Richard T. Olsen

California ( De Vries, 1905 ; Howard, 1945 ). The confusion persists to this day in horticulture with the recent proposal of grouping cultivated forms of shasta daisy under the Leucanthemum Maximum Group, which would encompass the former Chrysanthemum