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GREENHOUSE GROWER NOTES April 2006 2

Reviewing the 2006 Easter lily crop: root rot, fungus gnats and PGR issues.  Take time to document this year’s successes and mistakes to help next season.

By the time you sit down to read this article, the 2006 crop will have been shipped and you may be trying to forget how difficult a season it was. There were only three issues, and they weren’t new. But maybe you need to put down on paper, as a reminder for next year, the successes and mistakes that were made with the crop this year. If you don’t, you won’t remember until it’s too late!

Do you ever think to yourself: “Why do I grow Easter lilies year after year … beyond the obvious monetary reasons?”

For me, it’s the challenge. It proves your mettle as a grower! This is a crop where there is no simple cookbook recipe … you have to read the crop several times a week and respond accordingly. Every year is different! Only the principles of growing remain the same.

The Easter lily is a bulb, but more importantly it is a perennial that is sensitive to its environment even when it has no shoot growth. The way a lily forces in the greenhouse is very much influenced by the weather in the fields of California and Oregon and the vernalization conditions it experienced before you received it. The changing date of Easter from one year to the next creates another big wrinkle in the forcing exercise. In a figurative way, you essentially have to think like an Easter lily for about 120 days.

Poor root growth and root rot were among problems many growers experienced this year. What are some of the reasons it happened, and could it have been prevented? The short answer is ‘yes.’

Easter was late this year, so there was plenty of time to force the crop. Experience has shown that by mid-March, the higher light levels and greenhouse temperatures generally reduce the number of days from visible bud to puffy stage compared to when Easter is very early. (Easter 2008 will be the opposite challenge!) So, in January we had no need to have warm temperatures to speed up leaf unfolding and indirectly encourage more root growth.

Regardless of the supplier, many growers using case-cooled bulbs had a significant number of sprouted bulbs in the cases. This made planting a tedious process. The West Coast producers realized in early October ’05 that the shoots were beginning to move very quickly off the basal plate (a response to an earlier environmental event).

This meant that they had to dig and cool the bulbs as quickly as possible to minimize the movement off the basal plate. The early movement off the basal plate meant that case-cooled bulbs during their six weeks of vernalization were maintained longer than normal at 4-5ºC. As a result, the leaf count was, in general, lower than we have seen for a number of years.

So what, you say!

Emergence occurred quickly, and in most cases uniformly consistent, with a well-vernalized lily. Thus, the lilies had little time to develop roots before emergence.

With the late Easter date, lower leaf count (in some cases), dull overcast January and high energy costs, many growers decided to maintain heat set points of 15-16ºC. This did not encourage really active root growth.

Some growers over-watered the growing media, given the weather throughout most of January. This can happen very easily. With the low greenhouse temperatures and minimal ventilation, the media tended to stay wet too long. Transpiration rates were also low because of the slow rate of leaf unfolding and the relatively low air temperatures. In addition to the described conditions encouraging root rot pathogens, the cool and wet media also encouraged decomposition of the old roots remaining around the centre of the basal plate.

The combination of these factors attracts adult fungus gnats, and more specifically to struggling plants – those under stress. When removed from the pot and the roots washed, many poor lilies were heavily infested with fungus gnat larvae. To be graphic, they were crawling with them! In some cases, the population was sufficiently high that the stem roots were completely damaged before they had an opportunity to develop.

In today’s competitive market, no one can afford to throw out five per cent or more of their crop. That five per cent is the profit!

Lilies need to be grown moist, but not wet. The best roots are always found on the plants in the driest pots.

During the early season, the opportunities to water/fertilize the crop are limited. However, in my experience it is more beneficial to err on the dry side. If you are not sure what to do … don’t water … wait another day! Learn to water lightly and do it more frequently. This means that initially after watering, it may have only moved one-third to one-half the way down the column of media. However, when you check the following day, you will find it has moved the remainder of the way down resulting in the media being moist but not saturated with water.

Some growers got caught believing they did not have a fungus gnat population within their crop because the yellow sticky cards were not trapping significant numbers. However, the flight movement was reduced by the cool temperatures and the low light conditions of January.

Experience has shown that it is important to be proactive in the battle against fungus gnats. Application of one of the IGRs, such as Dimilin or Citation, should be seriously considered during the latter part of January when stem root growth is well underway. The stem roots are crucial to the well-being of the crop as we move into the last month of forcing.

The use of the beneficial nematode Steinernema feltiae or predatory biological agents such as Hypoaspis (predatory mite) and Atheta (rove beetle) can be effective as well if introduced at the beginning of the crop.

At the first sign of root rot, a fungicide application should be made. Root rot prevention should rely first on cultural practices and secondly on fungicides. However, application of a fungicide at visible bud is a good practice because of the stress that is put on the roots during the last four weeks of forcing. This is when the flower buds are rapidly expanding and higher temperatures may be needed to finish the crop on schedule.

Lower stem stretch early on was also a big concern for many growers. Early-season stretch is always an issue with case-cooled lilies, but it seemed to be a bigger problem than usual this year. The amount of cooling the bulbs received and their maturity has an influence.

A number of growers have questioned whether Sumagic is effective on Easter lilies under low light conditions but continued to apply Sumagic. I can only speculate because I don’t know the answer. I have observed that the early stretch was less under glass than poly, which might suggest that transpiration rates and greenhouse humidity levels may play a role. In a Sumagic pre-plant bulb dip research trial at Vineland and Guelph this year, we observed that there did not appear to be much effect even at the higher rates until after Jan. 20. Over time, the effect became increasingly stronger. It may be that under low light and minimal transpiration rates, movement of the PGR into the growing tip, where gibberellin production occurs, may not be happening until the plant is more active. The result was that some growers were very concerned at time of visible bud that the crop had the “palm tree effect” because of over-application. However by the shipping date, the plant stems had elongated sufficiently to negate most of the effect.

Sorting the lilies early and centring stems in the middle of the pot is important in developing a uniform and quality crop. Too many lilies were not well sorted and this makes PGR application and the timing more difficult. The question that has to be asked is, “can I afford not to sort and centre the shoots?” Think of the big picture! Quality always sells first.

I don’t know about you, but I find it interesting that every year growing lilies is always as challenging as the previous year. I wouldn’t want it any other way!

Wayne Brown is the greenhouse floriculture specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs, University of Guelph, in Vineland. • 905-562-4141, ext. 179; wayne.brown@omafra.gov.on.ca