Finish strong

Editor’s note: In part I of this two-part article, author Richard McAvoy addressed managing Easter lily crop production up to bud set. You can read that article and see the complete 2016 production schedule in our September 2015 issue at greenhousemag.com.
 

Once lilies emerge, all focus should be on optimizing flower bud count and keeping on schedule for the early date Easter in 2016. Bud set should be completed in early- to mid-January. During this part of the crop cycle you can use insurance lighting to reach your full 1,000-hour vernalization goal, but do not attempt to speed development of the crop with high temperatures. Once bud initiation is set you will need to track height to meet production goals, leaf unfolding rates and bud development to meet targeted sales dates.
 

Greenhouse forcing

With both pot-cooled and case-cooled lilies, greenhouse forcing starts at the end of the bulb-cooling period. Typically this is 17 weeks before Easter for case-cooled bulbs and 14 weeks before Easter for pot-cooled bulbs. The difference in the two schedules just reflects the stage of shoot development. With pot-cooled bulbs, the shoots are either at the soil surface or already emerged as soon as forcing begins (Week 14). In contrast. case-cooled bulbs will take up to three weeks to emerge. So either way, the shoots on both crops should be emerging by about week 14 (Dec. 20).

Bud initiation begins soon after lilies emerge, and should be completed no later than mid-January in the 2016 crop, when shoots are 3 to 5 inches tall. The development of stem roots coincides with flower bud initiation. During this period, day and night temperatures of 60° to 65°F are desirable (63°F is ideal), but it is imperative that temperatures do not exceed 65°F until bud initiation is complete.
 

Leaf counting & forcing temperatures:

If you haven’t previously used leaf counting, this will be a good year to start. Begin using the leaf counting technique to track lily development as soon as bud initiation is complete. You should be able to start this by week 10 or 11 (Jan. 10 to 17). This will allow you adequate time to determine if lily development is on track, and if not, to make the necessary adjustments. Don’t wait to start leaf counting this year. Too often, growers do not realize their crop is behind schedule until after visible buds fail to appear at about week 6.

Run lower average daily temperatures (55° to 60°F) if lilies are ahead of schedule — an unlikely circumstance this season, or higher temperatures (70° to 75°F) if behind schedule. Begin to assess crop development early so that temperature extremes can be avoided later. Typical leaf unfolding rates vary from approximately one leaf/day at 53°F to 1.5 leaves/day at 63°F, 2 leaves/day at 72°F and 2.5 leaves/day at 82°F. Forcing temperatures between 55° to 70°F produce the highest quality lilies and are most fuel-efficient.

Once lilies reach visible bud, they will typically flower in 30 days at 70°F and 35 days at 65°F. Monitor bud development by measuring bud length. Adjust temperature as needed to stay on schedule. A “bud stick” is a useful tool to gauge the rate of lily bud development and the time needed to finish at a specific temperature. If you don’t have a bud stick refer to Table 1 to estimate the rate of bud development. I recommend you assess bud development early and adjust temperatures at that time. In late Easter seasons, growers in northern climates often hold off on forcing bud development until the last two weeks, knowing that high natural light and warm weather in early- to mid-April will assist in this effort. But this season, you will have to push in late February and early March for the early sales dates. Ask yourself, what conditions can I expect this time of year? If winter weather patterns are still likely to prevail at your site, start your push earlier.

Uneven temperatures produce uneven crops. Use horizontal airflow to equalize greenhouse air temperatures. If you need to use temperatures above 80°F to push lilies at the end, take care to maintain adequate soil moisture and humidity levels or lily development may stall and buds may abort.
 

Height control:

Growth regulators should not be applied until after flower buds have set (early- to mid-January 2016). Use DIF to control lily height during flower initiation. Equal day/night temperatures or cool morning temperatures will produce a DIF effect and keep lilies short. The conventional PGR program uses a single application of A-Rest, Concise, Topflor or Sumagic as needed when shoots are 3 to 5 inches tall. The dose used is high enough to provide control through to about week 6. However, many growers have learned to fine-tune PGR applications to exert more precise control on the crop and with far better results. A typical program may call for weekly applications as needed to either slow stem stretch with a growth retardant such as Sumagic, or increase stretch with gibberellins such as in Fascination, or to prevent leaf yellowing in closely spaced plants (also with Fascination). Growers that use such programs are successfully applying growth retardants to lilies that are past the visible bud stage.

Even if you are inclined to be more conservative in your PGR practices, split applications are preferred as they produce the most desirable plants. With split applications, use half the normal dose at the first application and then a one-quarter to one-half dose in subsequent applications (depending on the number of applications you plan to use and the amount of control needed). Lilies exposed to high concentrations of growth retardants have a greater tendency to develop lower leaf yellowing in the later stages of production. Some growers have been applying low concentrations of Sumagic (or similar products) just as the shoot emerges and then following with a second application when the bud initiation period is over. I prefer to allow bud initiation to be completed before altering natural hormone levels in the plant. Plus, if you are maintaining 63°F day and night, as you should, you already have a zero DIF regime that will limit stretching during this phase. If you still wish to apply PGRs at this time, I recommend the lowest effective dose (an eighth to a quarter of the normal dose). Just apply enough to hold the plant for seven to 10 days rather than the typical 3 to 5 weeks.

Leaf yellowing can develop gradually in the greenhouse or suddenly and severely after lilies are sold. Gradual leaf yellowing can be a sign of chronic stress due to a persistent and unfavorable environmental condition or a telltale symptom of a diseased root system. Improper nutrition, poor media aeration or overwatering, and low light and poor air movement from tight plant spacing, are conditions that are conducive to leaf yellowing.

Sudden and severe leaf yellowing at the end of the crop is most likely to occur on lilies in poor root health and suffering from the poor nutritional and carbohydrate status associated with a bad root system. Prolonged cold storage prior to shipping and poor shipping conditions can also favor sudden, catastrophic yellowing.

To prevent early- and mid-season leaf yellowing (from seven to 10 days before visible bud until seven to 10 days after visible bud), spray Fascination at 10/10ppm. (Note: Fresco and Fascination are similar PGR formulations; both contain two active ingredients and recommendations are provided in a format that reflects the concentration of each). Apply only to lower leaves and cover thoroughly. To prevent late-season leaf yellowing and post-harvest flower senescence, spray 100/100ppm to thoroughly cover all foliage and buds. To protect leaves from yellowing during shipping or cooling, apply when buds are 3 to 3½ inches long but not more than 14 days before the start of shipping or cooling. Side effects include increased stem stretch, so avoid contact with immature leaves during early- and mid-season applications unless increased height is your objective. Growers sometimes spray these compounds at 3 to 5 ppm at seven-day intervals or as needed to increase stem stretch.
 

Getting ready to ship:

Lilies require adequate fertilization from planting to finish but high salts in shipping can be a problem. Apply one clear watering right before shipping to lower salt levels and enhance the keeping quality for the consumer.
 

Good quality lilies can deteriorate rapidly after leaving the greenhouse. Avoid holding sleeved and boxed lilies for long periods of time, especially when temperatures are high in the shipping container. EthylBloc can also be used to increase post-harvest flower life. EthylBloc works by inhibiting the damaging effects of ethylene (a naturally occurring plant hormone that greatly accelerates the onset of leaf yellowing, and flower aging and death). Plants produce ethylene naturally but ethylene can also result from the incomplete combustion of fuels in a greenhouse, shipping or warehouse environment.

The active ingredient in EthylBloc, 1-methylcyclopropene or 1-MCP, is released as a gas and therefore lilies must be treated in an enclosed environment. A sealed shipping container or truck, or sealed greenhouse can be used to treat plants. Flowers must be fully developed before treatment. To extend flower-life, treat lilies with EthylBloc just prior to harvest, or immediately after harvest, or just prior to shipping, or upon arrival from a supplier, or just prior to sale. Note that repeat applications are not harmful and are recommended on species such as lily that bloom sequentially over time.

Richard McAvoy is professor and extension specialist at the University of Connecticut.