A study of Ecke poinsettia (Euphorbia pulcherrima Willd. Ex Klotz) cultivar differences to lime source, lime rate, molybdenum rate and molybdenum application method

Poinsettia cultivars have been shown to respond differently to lime additions and molybdenum additions and deficiencies. ‘Gutbier V-14 Glory’ (1992–93), ‘Annette Hegg Diva Starlight’ (1992–93)), ‘Eckespoint Lilo’ (1992) and ‘Gross Supjibi’ (1993) poinsettia cultivars were compared for their response to lime source, target pH and molybdenum rate. There were cultivar differences in response to lime source during both years. ‘Eckespoint Lilo’, ‘Gutbier V-14 Glory’ and ‘Annette Hegg Diva Starlight’ (1992) increased in plant fresh and dry weight with decreasing target pH. Bract number in ‘Gutbier V-14 Glory’ (1992) decreased with increasing molybdenum rate. Molybdenum tissue content was higher in dolomitic treatments for ‘Gutbier V-14 Glory’ and ‘Annette Hegg Diva Starlight’ (1993). Tissue phosphorous, calcium, magnesium, manganese and molybdenum increased with increasing target pH in ‘Gutbier V-14 Glory’ plants (1993). Tissue phosphorous and molybdenum were shown to increase with increasing molybdenum rate and tissue iron decreased in ‘Gutbier V-14 Glory’ and ‘Annette Hegg Diva Starlight’ plants (1993).; Cultivar response differences to molybdenum deficiency and nitrate reductase enzyme activity have been shown in poinsettias. Molybdenum deficiency symptoms were absent on ‘Eckespoint C-1 Red’ plants, which contained equal or less molybdenum than ‘Annette Hegg Brilliant Diamond’ and ‘Gutbier V-14 Glory’ plants. ‘Eckespoint Lilo’ and ‘Freedom Red’ poinsettias were compared for growth and tissue molybdenum, nitrate and nitrite reductase activity. Plant growth factors of plant height, width, fresh weight, dry weight and bract number were not affected by molybdenum application method for either cultivar. Molybdenum rate had an affect on the fresh weight, plant height and width of ‘Eckespoint Lilo’ plants, but there were no specific trends with increasing molybdenum rate. Foliar applications were not sufficient in supplying adequate molybdenum at the rates that were used, whereas soil applications were sufficient. Nitrate reductase enzyme activity increased with increasing molybdenum rate in ‘Freedom Red’ plants, but did not in ‘Eckespoint Lilo’ plants. Higher rates of molybdenum would be needed in the foliar treatments of both cultivars to bring the tissue levels of molybdenum within the normal range. Even with tissue molybdenum below the normal range, these two cultivars did not exhibit visual molybdenum deficiency symptoms.