Height control in many cultivars of hybrid lilies remains a major problem. While A-Rest (ancymidol) and Sumagic (uniconazol) sprays have been shown by past research to be effective in height control, plants may still be too tall, and frequently have bare lower stems.
Hybrid lilies have a fundamentally different growth habit than Easter lilies. Hybrids usually emerge from the soil much faster, and the initial phase of stem elongation is very rapid, making early and decisive application of growth retardant very important. Another difficulty is the wide range of foliage canopy characteristics, ranging from nearly flattened and cupped canopies to thin spikes. These differences make it difficult to apply sprays in a uniform manner to a bench of mixed cultivars. The importance of this observation is the fact that Sumagic is active only when absorbed through stems or roots; leaf-absorbed Sumagic is essentially without height-controlling activity.
Another difficulty is the fact many lilies in the Southeast are grown in pine-bark based media. Prior research has clearly shown that A-Rest and Sumagic are absorbed to pine bark substrates, causing a loss of much (but not all) of the total retardant activity. We are therefore left with a problem: should a grower use a growth retardant spray on hybrid lilies, or a drench, each having it's own set of problems. In this experiment, we evaluated the effects of Sumagic drenches on 11 cultivars of hybrid lilies growing in a pine bark-based substrate. To evaluate the potential effectiveness of Sumagic drenches in pine bark media, we used greater than label rates in these experiments.
Bulbs were received Feb. 15, and held at 40°F until planting on Feb. 21, 1992. Three bulbs were planted per 6" standard depth pot using Fafard (Anderson, SC) lily mix, which is pine bark based. Cultivars included in this experiment were: Amber, Delicious, Dimples, Montreaux, Mt. Blanc, Sindi, Stargazer, Whitebird, Sun Ray, Sun Pearl, and Red Carpet. Bulb sizes varied among cultivars from 12/14 to 16/18 cm circumference. Temperatures were 60°F night, and day ventilation was set to 70°F. Pots were initially set pot to pot on the benches, and spaced to 8" centers after emergence. Standard cultural practices for root rot and insect control were followed.
Sumagic drenches of 0 (water), 0.1, 0.2, or 0.3 mg a.i. per pot were applied in a total drench volume of 4.25 fluid ounces/pot (125 ml/pot). (This is equal to 6.0 to 24.0 ml Sumagic per gallon of final drench when applying 4.25 ounces of drench per pot). There were 4 replicate pots per treatment. Plants had been irrigated the day prior to application, so the medium was moist, but not wet. Although each cultivar only received one drench, the applications were made on two dates, with the 2 groups of cultivars treated according to their height. The first application date was March 30, with the cultivars Amber, Delicious, Dimples, Montreaux, Mt. Blanc, Sindi, and Stargazer being treated. On April 7, Red Carpet, Sun Pearl, Sun Ray, and Whitebird were treated. Table 1 gives the initial heights of plants when drenches were applied.
Data collected included days to emergence, visible bud and to flowering; plant height on the day of Sumagic application; plant herght at flowering (measured from the soil line to the visual average height of the three plants in each pot); dates of emergence (two shoots emerged), visible bud (buds visible on two shoots), and flowering (two flowers open/pot), and the total number of flowers and buds and aborted buds per pot.
As expected, there were great differences between cultivars in days to flower, height, and number of flower buds (Table 1). The fastest forcing cultivar was 'Amber', which flowered 56 days after planting; the longest was 'Stargazer' at 105 days. These cultivars flowered on April 17 and June 5, respectively. The shortest cultivars (without growth regulator) were 'Delicious' and 'Red Carpet' at 15", the tallest were 'Montreaux' and 'Mt. Blanc', at 27-31 inches (soil line to average plant height). Add about 4-1/2" for total height, including the pot.
Sumagic drenches did not affect days to visible bud or days to flowering, although 'Sindi' may have been delayed by a day or two in reaching visible bud (Table 1). Further, Sumagic drenches at these rates had no effect on the total number of flowers per pot, or on the number of aborted flowers (Table 1).
In most cases, Sumagic drenches were very effective in reducing plant height relative to non-treated controls (Table 1), although many cultivar differences were apparent. The most responsive cultivars in this trial were 'Delicious', 'Mt. Blanc', and 'Whitebird', with 0.3 mg Sumagic causing height reductions af 42-56%, relative to the controls.
In some cultivars, such as 'Amber' and 'Dimples', final height was reduced only 10-15% by 0.3 mg Sumagic drenches. This relative lack of response could have been due to their tall height on the day of treatment. In scanning the table, the greatest response to Sumagic is usually, but not always, associated with early drench application. Even with late applications, though, variability is seen. The height of 'Montreaux' was reduced by about 30%, but was treated at about the same height as 'Amber' and 'Dimples' which showed a much less response to Sumagic.
In most cases, 0.2 mg Sumagic reduced final height nearly as much as 0.3 mg, notable exceptions being 'Delicious' and 'Whitebird'.
Sumagic can be very effective in reducing stem elongation in many hybrid lily cultivars. It is notable that "hybrid lilies" are not listed on the Sumagic label. Labeled drench rates for Easter lilies are in the range of 0.03 to 0.06 mg/pot (or, 0.05 to 0.1 mg/pot in Florida only), which are 3 to 5 times less than used in the current experiments. Clearly, the amount of Sumagic needed to reduce lily growth in pine bark-based substrates is much greater than listed on the label for Easter lilies. Also, these experiments were conducted in the Sunbelt (South Carolina). Somewhat higher rates would probably be needed in northern areas, where lower light promotes more stretching.
For first time grower trials in pine bark media, a rate of 0.1 mg/pot is appropriate for a variety of cultivars. In soils without bark, the recommended labeled Easter lily rates are appropriate. Pink flowersBy following plant height before and after application, you should be able to get an early indication of response. When effective, Sumagic will probably restrict stem growth within a day. As yet, we have no experience with multiple applications, but there is no reason to think hybrids would not respond to them.