2012 Easter Lily schedule

Lilies, including Asiatic, can suffer from bud blast if they are exposed to stress from drought, excessive heat or disease associated with condensation dripping from the glazing.

Easter 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.

If your target overall display height is 18 inches, you need to produce a lily with a final stem length of 12 inches. You can use the charts provided (Figures 1 and 2) to track the weekly progress of your lilies to target plants with either a 12-inch, 14-inch or 16-inch length stem.

Lily stem length increases at a more rapid rate following the appearance of visible buds. 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.
 

Factors affecting stem length
The final stem length of an Easter lily is influenced by a number of factors such as maturity of the bulbs coming out of the production fields, number of leaves before visible bud, day length during forcing, daily temperature regime (especially the day temperature/night temperature difference or DIF), light intensity and spectral quality of light at the end of the day. You can't control all of these factors so concentrate on what you can control and use plant growth regulators to help as needed.

DIF is a valuable tool. Most growers use a cool morning dip or equal day/night temperatures (zero DIF) to prevent stem stretch. DIF can be used throughout the forcing cycle but cool days are harder to achieve during March and April as temperatures start to increase. Stem stretch also increases as day length increases and the days continuously lengthen during the 14-week forcing period.

Light spectral quality is not easily controlled, but it does affect stretching. Stem stretch increases as the ratio of far-red to red light increases at the end of the day. This happens naturally during the twilight period but also occurs when the sunlight is filtered through plant leaves. Crowding of plants due to close spacing and overhanging baskets add to this filtered light affect. Pulling black cloth at the end of the day to exclude the twilight period can be used to avoid exposure to a high dose of far-red light. If done consistently, this technique can be used to restrain stem stretch.

Leaf number is not completely under your control, but bulbs that receive a full six weeks of chilling will produce fewer leaves before visible bud than bulbs that do not receive a full chilling regiment. With a mid-date Easter as in 2012, don't skimp on chilling. Program your bulbs with a full six weeks before starting greenhouse forcing.
 

Scheduling considerations
Mid-date Easter schedules are the least challenging. They allow adequate time to complete all the steps in the 23-week production program without cutting corners as is sometimes necessary with early Easter schedules. Mid-date schedules are also advantageous because they do not include a lot of extra time that may require growers to hold the mature crop in a cooler or to use other stalling tactics to slow down growth as is common with late Easter schedules.

For pot-cooled bulbs, the normal 23-week schedule includes three weeks in the pot at 60oF-62oF to stimulate root development, six weeks of bulb cooling at 40oF-45oF and then 14 weeks of greenhouse forcing at 60oF-65oF or higher as needed.

For case-cooled bulbs, the production schedule also takes 23 weeks, but this includes 6 weeks of bulb cooling at 40oF-45oF followed by 17 weeks of greenhouse forcing.
 

Critical dates
Start bulb programming no later than Oct. 30 or 23 weeks before Easter. For case cooled bulbs, this marks the start of the six-week bulb cooling period. Case-cooled bulbs should be potted and greenhouse forcing should begin no later than Dec. 11 or 17 weeks before Easter.

For pot-cooled bulbs and naturally cooled bulbs, bulbs are potted on week 23 and held at 60oF-62oF for three weeks or until Nov. 20 (Week 20). This allows roots to develop before the six-week cooling period. Next, program the potted bulbs at 40oF-45oF for six weeks (Nov. 20 to Jan. 1). Once bulb cooling is completed, begin greenhouse forcing no later than Week 14 (Jan. 1).
 

Monitoring temperature
Once lilies begin to emerge, record the average dates of emergence for early, mid and late lilies in your crop. Also record the average daily greenhouse temperature following shoot emergence. You will need this information to calculate the rate of development once you begin leaf counting.

Begin checking for bud set in mid-January. Bulbs moved to the greenhouse on Weeks 17 or 14 will complete bud set sometime around the second or third week of January.
 

It is important to maintain both day and night temperatures below 65oF during this period. A constant temperature of 60oF-62oF is ideal.

The final critical date is Feb. 26, which marks six weeks before Easter. To maintain a normal schedule, the plants should be at visible bud by this date. Plants at visible bud six weeks before Easter can be forced to bloom in 35 days at an average daily temperature (ADT) of 64oF. If visible bud occurs before Feb. 26, you can maintain cooler temperatures to slow bud development or be ready to ship or hold plants that reach the puffy white bud stage before Week 1.

If visible bud is attained after Feb. 26, you will need to run higher temperatures to finish lilies by the targeted shipping date on this schedule, one week before Easter. Raising the average daily temperature to 70oF reduces the bud development interval by about four days. Raising the average daily temperature to 75oF reduces the bud development interval by about another four days.
 

Crop timing
After bud set is achieved (sometime in mid- to late January), use temperature to control the rate of lily development during the remainder of the forcing period. Both leaf and flower development rates can be adjusted with temperature.

By controlling the rate of development you can control when the crop reaches the saleable stage. For example, at 72oF leaves unfold at a rate of two per day on average, while at 63oF the rate decreases to 1½ leaves per day. A lily will go from visible bud to bloom in 24 days at 81oF, 31 days at 70oF, 35 days at 64oF and 42 days at 59oF.

If plants reach visible bud five to seven weeks before Easter and temperature can be controlled within these limits, the crop should be in good shape to finish on time. 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.
 

Leaf counting
Start leaf counting after flower bud set is complete. The leaf counting technique is based on the fact that once flower buds initiate, leaf number is set and won't change. However, the exact number of leaves varies from year to year, and also will vary between bulb lots from different sources, 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.

The shoot tip should show evidence of tiny flower bud formation. If this is not the case, leaf counting was started too early. Wait one 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). 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 that needs to be maintained as the plants continue to grow.

If the current rate of development is too fast, meaning visible bud will be reached too early, reduce the temperature in the greenhouse. If the current rate of development is too slow, meaning visible bud will be reached too late, increase the average greenhouse temperature.

Determine a new current rate of leaf development each week (the rate since last count) and a new required rate. Determine the new required rate by subtraction. No other plants have to be destroyed. Simply subtract the number of fully developed leaves from the average total number of leaves previously determined. Flag the indicator plants and use a marking pen to mark the last leaf that was counted as mature.
 

Fungus gnat populations can explode if not detected early or if left untreated.

Height control
The lily schedule lists recommended target heights each week during development. These targets can be adjusted to fit your specific needs (e.g. increase plant height if taller finished plants are desired). This schedule is designed to produce a finished plant of about 16 inches. For lilies of this size use the target heights shown in Figure 1. If shorter lilies are desired, use the weekly height targets in Figure 2 to produce 12- or 14-inch lilies.

This is essentially graphical tracking. The lily height is monitored on a regular basis (daily, bi-weekly or weekly). The actual plant height is compared to the idealized growth curve for the lily height desired. If the average plant height is too short, positive DIF can be used to increase stem stretch. If plant height is too tall, negative DIF can be used to slow elongation.

While using DIF to control height it is important to maintain the proper average daily temperature so that crop timing is not adversely affected. For example, assume that the leaf counting calculation calls for an average daily temperature of 63oF so that an average of 1½ leaves develop per day. Consider two possible stem growth scenarios, one that calls for increasing the stem stretch rate and the other that reduces stem stretch. For ease of calculation, assume equal day/night lengths. In the first scenario, the greenhouse temperature is maintained at 68oF days and 58oF nights to achieve a positive DIF with an overall average daily temperature of 63oF. In the second case, a 58oF day and a 68oF night temperature produce a negative DIF (to restrict stem stretch) and the same 63oF average daily temperature is maintained to achieve the desired 1½ leaves per day rate of leaf development.
 

Growth regulators
A-Rest, Abide, Chlormequat E-Pro, Concise, Cycocel, Topflor and Sumagic are all labeled for use on Easter lilies. PGR applications typically begin when lilies reach 3-5 inches tall. However, with low concentration split applications, PGRs can be applied at any point in development beginning with emergence.

A-Rest, Topflor 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 PGR used when combined with negative or zero DIF.
 

Detect problems early
Whether talking about adjustments to crop timing, manipulating crop height or controlling insect infestations and disease, early detection and quick action should be the guiding principle. Problems detected early are typically easy to resolve and result in minimal permanent damage.

While making regular observations of plant height and leaf unfolding rate plants should also be scouted for insect and disease problems. Be especially conscious of developing hot spots.

After treating an insect or disease outbreak, follow up and make sure the treatment was effective. Just because action was taken doesn't mean the treatment worked. Look for evidence of disease or conditions that favor disease such as condensation on the glazing. Also, check root development. This is especially important at time of visible bud as the plants are more prone to root loss at this stage.

Monitor electrical conductivity and nutritional status of the growing medium.

Look for pockets of plants showing signs of stress. This may alert you to a physical or mechanical problem such as a clogged emitter line or dripping from overhead baskets.

Richard J. McAvoy is professor and interim head, Department of Plant Science and Landscape Architecture, University of Connecticut, (860) 486-2925; richard.mcavoy@uconn.edu.

All agrichemical/pesticides listed are registered for suggested uses in accordance with federal and Connecticut state laws and regulations as of the date of printing. If the information does not agree with current labeling, follow the label instructions. No discrimination is intended for any products not listed.

2012 EASTER LILY SCHEDULE

FORCING METHOD

Notes and comments on the 2012 Easter lily schedule
Easter 2012 falls on a mid-date (April 8). Mid-date Easter schedules are the easiest to manage. You will have plenty of time to follow the full schedule and force at normal temperatures. If you have problems contact your extension educator.

 
Pot-cooled bulbs. Pot-cooled bulbs are normally potted and held for 3 weeks at 60°F-62°F before the 6 weeks of bulb cooling (at 40°F-45°F) begins. 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 all pot-cooled methods including naturally cooled bulbs.
 

Case-cooled 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. 11, 2011. If you cool your own bulbs, start the cooling process as soon as bulbs arrive, but no later than Oct. 30, 2011 (23 weeks before Easter).
 

Insurance lighting. Insurance lighting should not be needed this year. However, 1 week of insurance lighting can be substituted for 1 week of bulb chilling if the full 6 weeks of cooling is not achieved on schedule.
 

Fertilization. Start fertilizing using a 15-0-15 or comparable formulation when lilies emerge. If phosphorus was not added to the growing medium, 20-10-20 can be used on an alternating basis with a 15-0-15. Fertilizer rates should range from 200-400 parts per million. Do not allow the medium electrical conductivity to exceed 3-3.5 mmho/centimeter (saturated media extract). Stop fertilizing 1 week prior to sale. Provide one clear watering before shipping lilies. This reduces salt levels in the growing medium and maximizes 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.
 

Leaf yellowing, flower senescence. To prevent early-season leaf yellowing (7 to 10 days before visible bud) and mid-season leaf yellowing (7 to 10 days after visible bud) apply a Fascination spray at 10/10 ppm. (Note: Fascination contains two active ingredients and recommendations include the concentration of each). Apply Fascination to only the 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 and buds. Apply when the buds are 3-3½ inches long, but not more than 14 days before shipping or cooling. Fascination protects leaves from yellowing for up to 14 days. Avoid direct contact of spray to immature leaves during early- and mid-season applications or increased stem stretch will result.
 

Uneven Easter lily growth can occur when hanging baskets shade the plants.

Disease 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 a broad-spectrum fungicide (i.e., Banrot or Insignia), or treat to control these diseases separately by selecting 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 label information on time intervals between application of biological fungicides and traditional fungicides.
 

Pest control. Aphids, fungus gnats and bulb mites are major concerns. Use only aerosols once plants are 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 bulb mites, sort out diseased and damaged bulbs before planting, handle the bulbs gently and monitor and control fungus gnats. Duraguard is labeled as a drench for soil-borne organisms that may include bulb mites.

Registration of pesticides varies by state so consult and follow labels for registered uses. To avoid any potential phytotoxicity or residue problems, spot test first before widespread use.
 

Height control. Monitor lily height regularly during forcing. If 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. Equal day/night temperatures, high night/low day temperatures or a cool morning temperature dip will keep lilies short.

Apply A-Rest, Chlormequat E-Pro, Concise, Cycocel, Topflor or Sumagic as needed when shoots are 3-5 inches tall. Split applications provide the best results. Any of the PGRs can be applied at ¼ to ½ the normal rate as needed to control height. Reduce the concentration of Sumagic used when combined with DIF.
 

Plant storage. Easter lilies can be stored for up to 14 days in the dark at 35°F-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 shaded location to avoid excessive wilting.