The 2013 Easter lily schedule

The secret to scheduling the Easter lily crop is proper temperature management at each stage of development. Unusual weather patterns, along with the shifting Easter date, are always part of the challenge to growing this crop. The extreme climatic conditions that much of the nation experienced during the 2012 lily season may signal a new normal for growers to contend with. With record high temperatures for much of winter 2012, many growers saw crop development ahead of schedule and low to average bud counts. January 2012 was the fourth warmest on record and March was even more extreme with record high temperatures over the eastern two-thirds of the nation from the high plains to the East Coast, extending north into Canada and south to Florida. In International Falls, Minn., temperatures spiked from a low of minus 14°F on March 9, to a high of 79°F on March 18. Chicago recorded eight consecutive days above 80°F in March, a pattern normal for mid-June, and Boston experienced the first above-80°F degree day before March 28 in 91 years. For tens of millions of Americans, it was the warmest March in their lifetimes as more than 15,000 warm temperature records were broken. The heat confused plants and insects as well, leading to an unusually early blooming of the cherry trees in Washington and apple and peach trees in the Midwest. The West Coast was the only part of the nation that experienced a cooler-than-average March. If we experience similar extremes this season, growers will need to pay close attention to crop development and adjust temperatures as needed.

In 2013, Easter Sunday falls on March 31. This is considered an early date Easter, but the schedule allows adequate time for the full 23-week program. To stay on this schedule, growers will need to begin the process by Oct. 21, and maintain proper cooling and forcing temperatures throughout. This requires that bulbs arrive on time and in good shape, and that you are prepared to handle them immediately. The key steps in the forcing program for pot-cooled bulbs include a three-week rooting period (at 63°F) followed by six weeks of bulb cooling (at 40 to 45°F). Then plants are forced in the greenhouse at 60 to 62°F until bud initiation is complete (about four weeks). Once buds are set, higher temperatures are used to force the crop during the final 10 weeks. With case- cooled bulbs, the process involves six weeks of bulb cooling at 40 to 45°F followed by a 17-week greenhouse phase during which bud initiation occurs and the crop is forced to flower. In both cases, the entire process requires 23 weeks from start to finish. If bulbs arrive late or if your sales schedule calls for lilies earlier than one week before Easter, there are a couple of ways to save time. With pot-cooled bulbs, you can reduce the length of time that pots are held at 63°F prior to the six-week cooling period. If you are tempted to cheat here, allow enough time for bulbs to show some root development, two weeks if at all possible, but at least one. As an alternative, or if your schedule is still a little tight, you can substitute “ensurance lighting” for a portion of the 1,000-hour (six-week) bulb-cooling period. The same ensurance lighting rule applies to all forcing methods including naturally cooled, pot cooled or controlled-temperature forced (CTF), and case-cooled bulbs.

Ensurance lighting is achieved by providing at least 10 foot-candles (measured at plant height) for four hours (10 p.m. to 2 a.m.) each night. Lilies exposed to these long photoperiods immediately after shoots emerge, respond as if the bulbs were exposed to additional hours of cool (40°F) temperatures. In seasons when Easter falls on an early date, growers can extend the natural day length with low intensity light to ensure that adequate vernalization occurs. Just like exposing bulbs to 1,000 hours of vernalizing temperatures, ensurance lighting reduces leaf (and flower) number and reduces the number of days from emergence to flowering. Ensurance lighting can be used to directly substitute for lost bulb-cooling time. That is, one week of ensurance lighting will substitute for one week of cold temperature vernalization. Lighting is most effective when started immediately at emergence and for a period of up to two weeks following shoot emergence. However, do not use ensurance lighting unless the crop is short of the 1,000-hour bulb cooling threshold, and then only provide as many days of ensurance lighting as needed to reach the 1,000-hours target. Just like excessive cooling, excessive lighting will reduce lily leaf number, reduce bud counts and shorten the time to flower. Incandescent, florescent, or HID lamps can be used to provide the necessary night break.

Even though Easter 2013 is early, avoid the temptation to speed up lily growth in the first few weeks after emergence. Too often, growers run temperatures in the 70 to 75°F range during this critical period in a misguided effort to get ahead of schedule. The result is excessive lily height, poor bud counts and prolonged cold storage periods at the end of the crop. At emergence, hold a constant day and night temperature of 60 to 63°F until bud initiation is complete. Bud initiation is typically set when shoots are about 3 inches to 5 inches tall, mid- to late-January. The development of stem roots coincides with flower bud initiation. During this period, it is imperative that temperatures not exceed 65°F. If you find yourself short on time, increase the rate of lily development after bud initiation is complete. Do not attempt to make up lost time with high temperatures during the bud initiation period.

With a tight schedule, pay careful attention to performance variations of bulbs from different sources, as bulb lots often differ in both leaf count and finishing time. These differences can be detected early in the forcing process but growers who fail to respond end up off schedule. You can gauge differences in the maturity and finish time of various bulb lots by counting leaves as soon as bud set is complete.
 

Table 1: Lily height is always a critical concern. The final height is dependent on how well you control stretch during the entire forcing period. Typically growers target a final height that falls within a narrow range. The Easter lily schedule in this article is designed to produce a lily with a final overall stem length of 16 inches. With a pot height of 6 inches, this would be a plant with a final overall display height of 22 inches. Lilies typically double in size in the five-week period from visible bud to bloom, but it takes nine weeks of forcing prior to visible bud to reach the first 50 percent of final lily height.

Leaf counting and crop timing
Start checking leaf counts in mid-January (week 11). If bulb set is not yet complete, wait one week and try again. This will allow you plenty of time to determine if lily development is on schedule and to make the necessary temperature adjustments as needed. Use average daily temperature to control the rate of lily development for the remainder of the forcing period. The rates of both leaf and flower development can be modulated with temperature. By controlling the rate of development, you can control when the crop reaches the saleable stage. For example, at an average daily temperature (ADT) of 72°F, leaves unfold at a rate of two per day on average, while at 63°F, the rate decreases to one and a half leaves per day. Likewise, a lily will go from visible bud to bloom in 24 days at 81°F, 31 days at 70°F, 35 days at 64°F and 42 days at 59°F. If you arrive at visible bud five to seven weeks before Easter, and you can control temperature within these limits, you should be in good shape to finish on time. Finally, plants that bloom early can be held in a cooler for up to two weeks. Storing finished lilies for longer than two weeks is not recommended. Many growers were forced to store lilies for long periods in 2012 due to the unusually warm March.

The leaf counting technique is based on the fact that once flower buds initiate, leaf number is set and will not change. But the exact number of leaves varies from year to year, between bulb lots, and with bulbs exposed to different cooling conditions.

After bud initiation, select five lilies for every 1,000 plants in each lily group (per bulb source, emergence time, etc.). Select plants representative of the overall crop, and then remove, count and record the total number of leaves. Use magnification and a needle to remove and count the smallest, un-expanded leaves. (Note: The shoot tip should show evidence of tiny flower bud formation. If bud formation is not evident, wait a week and try again.) Record the number of fully developed leaves (those at a 45-degree angle to the stem or greater) and the number of undeveloped leaves (those at an angle less than 45 degrees to the stem). Now, divide the number of fully developed leaves by the number of days since shoot emergence. This is the “current rate of leaf development.” Divide the number of undeveloped leaves by the number of days remaining until visible bud. This is the “required rate of leaf development” or the rate you need to maintain as you move forward.

Click the table above to see the full 2013 Easter lily schedule

If the “current rate of development” is too fast, meaning you will reach visible bud too early, reduce ADT in the greenhouse. If the “current rate of development” is too slow, meaning you will reach visible bud too late, increase the ADT.

Determine a new current rate each week (the rate since last count) and a new required rate. Determine the new required rate by subtraction — you do not have to destroy any more plants. Simply subtract the number of fully developed leaves from the average total number of leaves previously determined. You can flag your indicator plants and use a marking pen to mark the last leaf you counted as mature.

Height control
The 2013 schedule lists lily height targets for each week in the greenhouse. You can adjust these targets to fit your needs (e.g. increase plant height if you desire a taller finished product). This schedule is designed to produce a finished plant of about 16 inches. You can chart the height of your crop against these target heights. Monitor lily height either daily, bi-weekly or weekly, and compare the actual height to the idealized growth curve for the lily height you wish to produce. If average plant height is too short, run a positive DIF to increase stretch. If plant height is too tall, run a negative DIF to slow elongation.

While using DIF to control height, it’s critical to maintain the ADT so that crop timing is not adversely affected.

Controlling with PGRs
Lilies typically double in size in the five-week period from visible bud to bloom, but it takes nine weeks of forcing prior to visible bud to reach the first 50 percent of final lily height. A-Rest, Abide, Chlormequat E-Pro, Concise, Cycocel and Sumagic are all labeled for use on Easter Lilies. PGR applications typically begin when lilies reach 3 inches to 5 inches tall or after buds are set. However, with low concentration split applications, PGRs can be applied at any point in development beginning with emergence. A-Rest and Sumagic (or the generic equivalents) can also be used to pre-treat bulbs using bulb soaks. With sprays and drenches, split applications produce the best results. Reduce the concentrations of PGRs used when combined with negative or zero DIF.

Leaf yellowing
Crowding, root disease and poor nutrition (especially low phosphorus and nitrogen) during the final stages of development and stress from unfavorable cultural and environmental conditions, such as excessive shading and high temperatures, all favor lower leaf yellowing. Last year, leaf yellowing was a problem for some growers, most likely due to the unusual weather but also because lilies were too tall and crowded too early. If you experience conditions that favor lower leaf yellowing during the final weeks of forcing, apply Fascination or Fresco. Applications in the weeks prior to visible bud or two weeks after visible bud should be applied only to the lower leaves to avoid stem stretching. For mature lilies ready to go into cold storage, you can apply higher rates over the entire plants.

We don’t know what climatic changes 2013 will bring, but proper attention to detail and production environment control will go a ways toward mitigating extremes and allow you to bring a quality crop in on time.

Richard McAvoy is professor and extension specialist – greenhouse crops in the Department of Plant Science and Landscape Architecture at the University of Connecticut. You can reach him at (860) 486-0627 or richard.mcavoy@uconn.edu.

 
Notes & comments on the 2013 Easter lily schedule

Easter falls early in 2013. The schedule is tight but allows time to complete the full 23-week program. If you have problems contact your extension educator.

Pot-cooled bulbs are normally potted and held for three weeks at 60-62°F before the six weeks of bulb cooling (at 40-45°F) begins (see the 2013 Easter Lily schedule for details). The bulbs then require 14 weeks of greenhouse forcing. This entire process requires 23 weeks from initial potting to Easter. This same process is used for both naturally cooled or CTF bulbs.

Case-cooled bulbs require six weeks of cooling followed by 17 weeks of greenhouse forcing to flower in time for Easter. Be sure that commercially case-cooled bulbs arrive and are planted by Dec. 2. If you cool your own bulbs, start as soon as bulbs arrive but no later than Oct. 21 (23 weeks before Easter).

Ensurance lighting: Ensurance lighting may be needed this year if you are unable to complete the full six weeks (1,000 hours) of bulb cooling before the designated greenhouse forcing date. Substitute one day of ensurance light for each day of bulb chilling required for the full 1,000 hours. See article for details.

Fertigation: Start fertilizing using a 15-0-15 or comparable formulation when lilies emerge. If phosphorus was not added to the medium, 20-10-20 can be used on an alternating basis with a 15-0-15. Fertilizer rates should range from 200-400 ppm. Do not allow medium EC to exceed 3-3.5 mmho/cm based on a Saturated Media Extract. Stop fertilizing one week prior to sale. Provide one clear watering before shipping lilies — this will reduce salt levels in the potting medium and maximize keeping quality. Do not withhold water or fertilizer to slow development. Do not over water (i.e. water too frequently) or root rot problems may occur.

Decrease leaf yellowing and delay flower senescence: To prevent early-season leaf yellowing (seven to 10 days before visible bud) and mid-season leaf yellowing (seven to 10 days after visible bud) spray Fascination or Fresco at 10/10 ppm. Apply only to lower leaves and cover thoroughly. To prevent late-season leaf yellowing and post-harvest flower senescence, spray 100/100 ppm to thoroughly cover all foliage & buds. Apply when buds are 3 to 3.5-inch long BUT NO MORE than 14 days before shipping or cooling. Protects leaves from yellowing for up to 14 days. Note: Avoid direct contact of spray to immature leaves during early- and mid-season applications or increased stem stretch will result.

Disease and pest control: Before planting, clean bulbs of debris, removing any damaged scales, especially scales that show evidence of infection. Once potted, root rots associated with Rhizoctonia, Fusarium, and Pythium are a concern. Drench immediately with Banrot or Insignia, broad-spectrum fungicides, or you can treat to control these diseases separately by selecting from the fungicides specifically registered for Rhizoctonia, Fusarium and Pythium control on lily. Materials registered for Rhizoctonia and/or Fusarium include 26GT, 26/36, Contrast (Rhizoctonia), and Terraclor WP (Rhizoctonia). Materials registered for controlling Pythium include Alude, Banol, Subdue Maxx and Truban. Check with manufacturers regarding compatibility when tank mixing fungicides. Fungicides may also need to be re-applied later in the crop — check labels for guidance. Preventive biological fungicides (RootShield, CEASE, Actinovate, Mycostop or Companion) may also be applied for disease suppression and to enhance root growth. Check with company or product labels information on time intervals between application of biological fungicides and traditional fungicides.

Aphids, fungus gnats and bulb mites are a major concern. Use only aerosols once in bud. Many chemicals are listed for aphid control, including, Safari, Flagship, Tristar, Marathon, DuraGuard, Distance, Enstar AQ, Preclude TR, Tame, UltraPure Oil, Insecticidal Soap, Talstar and Endeavor. Fungus gnats can be controlled with many of these same chemicals as well as Citation, Adept, insect parasitic nematodes (Nemasys, NemaShield, Scanmask) and Gnatrol. Bulb mites, Rhizoglyphus robini, represent one of the more troublesome insect pests on lilies and effective management requires an integrated approach. Bulb mites are considered a secondary pest and are commonly associated with decay caused by fungus gnat damage and soil-borne fungal pathogens. To best manage this problem, sort out diseased and damaged bulbs before planting, handle bulbs gently and monitor and control fungus gnats. Duraguard is labeled as a drench for soil borne organisms that may include bulb mites.

Controlling height: Use A-Rest, Chlormequat E-Pro, Concise, Cycocel or Sumagic as needed when shoots are 3 to 5 inches tall. Split applications provide the best results. You can apply any of the PGRs at one-fourth to one-half normal rate as needed, to control height. Reduce the concentrations of Sumagic used when combined with DIF. Use DIF, or cool morning DIP, to control lily height. Equal day/night temperatures, high night/low day temperatures or a cool morning temperature dip will keep lilies short. Monitor lily height regularly during forcing. If the height exceeds the target size, run negative DIF to slow stem elongation. If height is less than the target size, run positive DIF to increase stem elongation.

Storage: Lilies can be stored for up to 14 days in the dark at 35-45°F when buds turn white but before they open. Spray for Botrytis control prior to moving lilies to cold storage. Materials registered for botrytis control on lilies include 26GT, 26/36, Daconil, Exotherm Termil, Sextant, and Protect DF. Follow label directions. Water Easter lilies thoroughly before starting cold storage. After removing from the cooler, place lilies in a shady location to avoid excessive wilting.
 

All agrichemical/pesticides listed are registered for suggested uses in accordance with federal and Connecticut state laws and regulations as of print date. If information does not agree with current labeling, follow label instructions. Contact the Connecticut DEP for current regulations. Where trade names are used for identification, no product endorsement is implied nor is discrimination intended.