Newsletter. Relative humidity: an important factor in the growth of Miltonia and Cymbidium. Phalaenopsis: Production advice,

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1 Newsletter VOLUME 29 No. 1 APRIL 2011 The orchid professionals since Spring 4 and Phalaenopsis: Production advice, 2011 Development of cups, collars vases The weakest 5 link! 6 the Nothing is as changeable as weather Relative humidity: an important factor in the growth of Miltonia and Cymbidium A study entitled Teeltoptimalisatie Miltonia (optimising Miltonia production) conducted by Plant Dynamics showed that the use of free daylight is limited owing to the fact that it leads to excessively high leaf temperatures. Even if the stomata are fully open, the leaf will be unable to lower its temperature sufficiently. The solution decided upon was to control conditions during the vegetative phase to encourage the development of more or larger stomata. As part of this study, Plant Dynamics conducted a new experiment with Wageningen University and Research Centre. This experiment used various pot plants (including Miltonia and Cymbidium) kept in climate-controlled chambers to see if the quantities and/or size of the stomata could be increased by means of light intensity, the light spectrum or relative humidity. A leaf better capable of cooling itself would keep its stomata open longer and would be more capable of absorbing more light to produce more sugars. The experiment worked with vapour pressure difference (VPD measured in kpa) which is the difference in vapour pressure in the leaf and the vapour pressure in the air. Calculating the vapour pressure difference requires measuring the greenhouse temperature and the relative humidity (RH) as well as leaf temperature. An attempt was made to maintain two RH levels: 50 and 80% RH. These would produce vapour pressure differences of 1.2 and 0.6 kpa. Two light levels were tested as well. It is known that for many plants, a VPD (vapour pressure difference) equal to is the level above which the stomata will be tightly closed. At high values, the stomata will close so that the leaf will transpire less and be less able to cool itself anymore. The leaf temperature will rise. At a higher leaf temperature accompanied by a constant RH, the VPD will rise. This will close the stomata even further, transpiration will drop, and leaf temperature will continue to increase. When the stomata continue on page 2

2 close, the plant absorbs little if any CO 2, thus practically eliminating photosynthesis. Once the stomata close, they will usually not reopen that day. In Miltonia, it had already been demonstrated that a VPD of 0.8 kpa is probably the upper limit at which stomata will still be just barely open (Teeltoptimalisatie Miltonia). The findings of this experiment, however, showed that subjecting Miltonia to a higher relative humidity would result in the plants producing more stomata that were also larger. Cymbidium produced more stomata, but their size did not increase. This percentage, however, was larger than that produced in Miltonia, so the effect was probably the same. This improves the leaf s ability to cool itself. Light intensity and the light spectrum had little effect on the number and size of the stomata. The measurements also demonstrated that the stomata would open much wider at a higher RH of 75% (VPD = 0.6). This would mean more growth for both of these plants. Meanwhile, the lower RH of 50% (VPD = 1.2) had little effect on vegetative growth. The previous experiment had shown that more light alone had a positive effect but only as long as the RH was higher (VPD lower). More light will always result in a higher leaf temperature and, thus, a higher VPD. As an example, you Mil could say that if the leaf temperature would rise by 2 C, the relative humidity would have to rise by more than 10% to realise the same VPD. The Dutch Horticultural sector is investing in this project through the Product Board for Horticulture. This experiment was conducted by Plant Dynamics with assistance from the suppliers of plant material and the LTO Groeiservice. Phalaenopsis: production advice, spring 2011 Light The increase in natural light means that the plant will have to receive sufficient nutrients. A fertiliser richer in N is recommended, so the N/K ratio may be increased. Even though many growers realised a sufficiently high desired light sum during the winter, the strength of the sun should not be underestimated. Naturally, light inside the greenhouse is largely calculated in terms of PAR. But the same lux levels in daylight and lamp light show a major difference in PAR. As we mentioned in the Newsletter of May 2004, lamp light providing 10,000 lux has about PAR, but the same lux level of sunlight has around 180 PAR. This is 1.5 times as much light that can be utilised for photosynthesis, so this is why we like to measure in PAR. What s more, we would also like to diffuse the light by using an LS10 shading system. An additional advantage of this diffuse light is that it penetrates better into and between the plants. If whitewashing has not been done yet, this will mean the need to watch out for excessively high light peaks and light sums. And if whitewashing has already been done, it would be a good idea to be sure that the light sum does not drop by too much. With most computers, the time when the lamps are turned on can be coordinated with sunset so that the lights automatically turn on a few minutes later until they become unnecessary. To provide plants with enough night rest (not really a rest, since the plants will start absorbing CO 2 at night), a night lasting at least hours is recommended. Plants emerging from the winter period are used to little light. Watering Water between times only when necessary; do not set the irrigation system to automatic pilot. During the first 6 weeks, this is often very helpful for getting the plants through a difficult start. The pot then becomes more and more saturated so that care must be taken with watering. We see that it is common practice to start providing more and more fertiliser (resulting in higher EC levels) in combination with more light and CO 2. It is still necessary to measure the EC (also at the drain) and ph; the EC particularly as measured in the upper layer of substrate increases quickly since this is where the moisture evaporates most easily and leaves the salts behind. This is why the need to provide clean water with some regularity is really essential! If drain figures are measured regularly, it is actually possible to spot a trend for a constant quantity of litres. Aim for a watering frequency of once every 4-5 days. 2

3 Temperature and RH Spring is a time when extremely low RH values can occur. It is then advisable to correct this situation by using a misting system, for example (reducing the openings of window vents can be done often but only to a certain degree. So it would be advisable to check this system thoroughly actually before spring starts. This is the time of year when a misting system is particularly effective, so its and nozzles could thus stand to be serviced. The pulse length and start of misting can be set by the climate-control computer. The system s operation can also depend on light levels (more light will result in pulses that start earlier and last longer). With the many climate factors, it is preferable to keep them as constant as possible. It is known that very abrupt changes in RH can result in a Pseudomonas infection. Rising outdoor temperatures also increase insect activity. It would thus be advisable to scout thoroughly and frequently. Lamps and sticky traps are effective in this regard. Under-bench heating pipes in particular dry the substrate out; the use of overbench pipes can be reduced as insolation increases (and definitely during the flowering and vegetative phases). As spring begins, the P-band is often still set quite high. If the setting is too high, the vents will not be open enough, and greenhouse temperatures will become too warm. How far vents can be opened is sometimes limited as well; in this case, too, greenhouse temperature will automatically become too warm. So start earlier with venting or apply a more aggressive venting strategy. The influence of the weather on your venting strategy becomes less important. Even so, it can still get very cold during the night, so too much venting in the morning can cause premature spiking. Careful venting is also better for the greenhouse climate and for energy conservation. Test the cooling system before the weather turns really warm. If in doubt about using mechanical or natural cooling, remember that mechanical is more expensive but the advantage it offers is keeping moisture and CO 2 inside the greenhouse. Pot worms In recent years, controlling pot worms (Lyprauta) has actually turned out to be a major problem, but we see differences among growers as to how problematic this can be. Often, it is the combination of watering, heating and substrate that determines whether this pest can be kept under control. The composition of the substrate and when this material was harvested could also be factors in the development of a pot worm infestation. Thorough scouting with lamp traps (effective not just for Lyprauta adults) is still essential. The only way to get rid of the adults is a cycle of fogging; spraying is less effective. There are no effective chemical agents available to control the larvae. What s more, it is difficult to get to the larvae in the pot. Various results have been achieved by the use of nematodes; these treatments are usually insufficient but are still the subject of research. We recently started using a product known as Macro-Mite on the plants at our facilities during the vegetative phase, so we have to minimise our use of chemical control agents. Macro-Mite is also used by growers to keep pot worm larvae under better control. Spider mites Spider mites will be cropping up again soon. Walk through your crop frequently, often turning over the leaves as you go, and be especially attentive to varieties that are particularly susceptible or that serve to signal an infestation. The sooner you identify problems, the better. As far as bacteria are concerned, most companies have this problem well under control. Chlorine dioxide is an effective control agent, but climate regulation is still the best control measure. Scouting for diseased plants is still necessary, even in combination with a chorine dioxide system. Bud drop The risk of bud drop is always present during the winter but there are major differences in the rate of bud drop among companies. Some growers know how to respond to this effectively. We see major differences in bud drop among companies that are growing the same varieties. And some varieties are also more susceptible to this phenomenon. We advise keeping a good eye on the plants when growing susceptible varieties and monitoring greenhouse conditions carefully, particularly temperature, light and watering. Maintaining warmer temperatures (above C) during the flowering phase is asking for trouble, even with the availability of a highly effective lighting system. Artificial light simply cannot replace sunlight. We also advise against extending the daylength longer than 14 hours during both the vegetative and flowering phases. When a plant has too many spikes and flowers to maintain, the risk of bud drop is substantially higher, especially if its root system is only moderately developed. Never set the watering system on automatic pilot; instead, adjust watering to keep the roots active until the end of production. Phal. 'Queen of Hearts' 3

4 Development of cups, collars and vases The trend to produce more plants per m 2 continues. The search for higher efficiency now includes looking for methods to increase production on the same production surface. It is clear that total production has risen substantially in recent years due to an increase in hectarage, but another factor is optimising production, including a reduction in losses! The increase in the number of plants per m 2 every year, along with a lower cost price, should ultimately increase growers earnings. To keep the selling price as high as possible, supplying products of consistant high quality has to be a priority as well. And maintaining reliably high quality could probably go even farther to improve earnings than trying to save every penny on the cost price. The effect of energy conservation is often less than what people think. Due to changes in production systems such as those for light and temperature, certain varieties may no longer fill the bill. In recent years, there have been quite a few changes, and this means that the rate at which varieties are eliminated from production is sometimes higher than new varieties being developed to respond to these changes. The result is that the commercial assortment has substantially decreased. If a grower wants 100% assurance with regard to production, ordering only certain varieties is the only solution. To produce the right quantities per variety, a grower has to count on a period of at least two years, depending on the quantities ordered and the variety s propagation factor. Unfortunately, the risks associated with limiting the number of varieties ordered is often underestimated or forgotten; later, a grower might want to change to other varieties (to one degree or another) more quickly than is possible. The greater the quantities, the greater the risks. You could compare this to the difference in handling between a sport scar and a lorry, or a speedboat and the world s biggest cargo tanker. Certain risks to be considered include: Whether or not the variety/varieties ordered will actually respond to future changes in the production system. A more limited ability to change from one variety in production to the next once the market changes (a change in the preference for flower colour or flower type, for instance). We see a lot of experimenting with the systems listed in the title of this section. Remember that, in particular, watering as well as the climate recommendations (including RH and light) provided in our newsletters are based on past production experience. More light, more nutrients, higher RH, etc. put more demands on the plant. Varieties have often not yet been tested under these conditions conditions that can sometimes be very extreme. So it is not surprising that varieties sometimes display inexplicable signs of damage. The fact is that limits are constantly being stretched, so the chance of going too far is increasing all the time. For a complete changeover, watering and production will have to be done differently. And not all varieties will respond equally well to these methods. Often, a test conducted in part of a greenhouse section or using one sprinkler outlet (and testing just a few varieties) will not compare well to large-scale production. The advantages of cups/collars/vases are: More plants/m 2 ; Less leaf damage; Few if any roots growing into other containers; Uniform watering and fewer leaves hanging over the sides of containers mean no dry plants; Better micro climate for the plant. Certain disadvantages of cups/collars/vases are: Extra investment; Cleaning/hygiene involved in reuse to avoid the risk of infection by fungi and/or bacteria; The allocation of space based on the current production plan no longer applies; Space needed for temporary storage of cups/collars/vases ; Adjustments to logistics systems and/or machines become necessary; Growing large heavy plants becomes more difficult; The effect on the percentage of multiple spikes is still unclear and differs per variety. Phal

5 The weakest link! The Weakest Link, the name of a popular TV show, is derived from the saying that a chain is only as strong as its weakest link. In plant physiology, a plant s maximum growth is also determined by the weakest link. The literature speaks of a barrel with staves: the familiar upright wooden wine vat made of wooden planks of unequal length so that its maximum capacity is determined by the shortest plank (or stave). In scientific terms, the growth of a plant is represented as the formula: 12H 2 O + 6CO 2 + light > C 6 H 12 O 6 (glucose) + 6O 2 + 6H 2 O. This means that as the quantity of light increases, more sugars (glucose) will be produced. Sugar production also increases if more CO 2 is available. By optimising this process, the final result is greater or achieved more quickly. Optimising this process also involves such factors as water, temperature, nutrients, relative humidity and daylength. And each of these factors has its own sub-factors such as the quantity of nutrients, as well as the interrelationships among these factors. A plant s quality or susceptibility to disease is also affected by these factors. When considering Cymbidium, certain short staves can still be discovered in production. The first of these is not flowering in time for 1 November or Christmas, the major disadvantage being lower prices due to lower demand. This postponement is largely attributable to insufficient heating. If the aim is to cut Cymbidium before 1 November, the plants must have received a 24-hour temperature of 20 C since early/mid-february. Before that time, they must have been kept at a 24-hour temperature of C for approximately 3 months. Consistently maintaining a temperature of 1 C less will delay flowering by 2-3 weeks. We saw this happen last season. Due to the cold months of February, March and May, a conscious effort had to be made to provide more heat. Growers who did so were on schedule for their November production. The cold, wet months of August and September 2010 also required attention to providing enough heat. The thicker the whitewash coating on the greenhouse roof, the lower the average greenhouse temperature and, thus, the lower the average plant temperature! Low 24-hour temperatures led to a delay in flowering among the Christmas varieties produced for both cut flowers and pot plants! This delay in flowering also created a marketing problem. The Christmas production was ready to go at the same time as the Valentine s Day supply. Not only was the market flooded, but the quality of the delayed Christmas production was not up to standard, and Cym. 'Cass Flor' this contributed to lower prices. There is yet another problem that we think deserves attention. It is known that there are problems involving the quality of forced tulips, such as susceptibility to disease, that can be traced back to the weather conditions during the previous spring when the bulbs were in the field. Similarly, peonies are susceptible to Botrytis in the flowers when the plants were exposed to a wet cloudy summer the previous year. In other words, quality is already largely determined by light and temperature conditions during flower initiation. We are all familiar with the loss of plants in Cymbidium production, particularly during the summer period. In general, you can say that growers who produce under wetter, darker (darker greenhouses caused by too much whitewash) have more problems with this than growers who produce under dryer, drier conditions (new greenhouses, little if any whitewash). Even in southern European countries, we see greater losses among growers producing under wet, dark conditions. In a year with above-average sunshine and warm temperatures, the difference will not be so noticeable, but it certainly was in a year like It is assumed that the flowering of plants produced under conditions of too little light during August/September will definitely be delayed. In addition, the new shoots being initiated will be weaker and will produce weaker flower buds. As anyone would agree, this will not benefit quality. This is why we advocate admitting as much light as possible as long as temperatures will not exceed the maximum. The use of an external shading system offers a way to optimise light levels in combination with the desired temperatures. This investment is substantially less expensive for a wide span greenhouse than for a Venlo greenhouse. 5

6 Nothing is as unpredictable as the weather Practically everyone you talk to about the weather has the idea that living in the Netherlands means living in a country with highly unpredictable conditions. Even so, it s actually not as bad as all that. The Netherlands has a temperate climate without huge extremes in temperature, light, wind, etc. When you compare the climate of the Netherlands with other large amenity horticulture regions, what you notice in particular is the daylength. This is a highly determining factor and has a major impact on humans, plants and animals. It also has a major impact on the crops we grow. Consider, for example, the effect of daylength when growing chrysanthemums and poinsettias year round. Yet this effect is also noticeable when growing orchids. For many orchids: long days are beneficial for vegetative growth; short days are beneficial for generative growth; We could actually make better use of this in our production practices, but we usually depend more on the light sum and adjust daylength to this. We devoted an article published a few years ago to the effects of daylength on orchids. Graph 1 clearly shows that you can divide a year into 4 quarters according to light periods: 1. daylength shorter than 12 hours and decreasing; 2. daylength shorter than 12 hours and increasing; 3. daylength longer than 12 hours and increasing; 4. daylength longer than 12 hours and decreasing; Cym. 'Super Lady' The change in the number of hours of light initiates processes in the plant that many are insufficiently if at all aware of. We think that this phenomenon offers us ways to improve our production process even more. For some time, we at Floricultura have been producing graphs of the number of sun hours in the Netherlands. Although what you see in these graphs is not the only determining factor with regard to light, it provides a very good way of showing the trends in our climate that affect your production in the greenhouse. Days with many sun hours mean a lot of free extra heat for the greenhouse. For flowering, this can be a disadvantage (for early-flowering Cymbidium for example). We can easily see these effects by taking 2010 as an example. In that year, there were a number of cold periods. If supplemental heating was not used at these times, the result was a delay in growth and flowering. The fact that some Daylength in various production regions The Netherlands California Brazil Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec.

7 Cymbidium growers were late for their November 1st or Christmas production says it all. The following graph shows the number of sun hours for the last three years, with the grey line being the average over the period from (thus considered to be the norm). In graph 2 the norm line shows that we go from 43 sun hours in December to 209 in May. Over a period of 30 years, the month of May has the most sun hours and the months from May through September do not differ that much. It should also be noted that the trend in recent years is for an annual 10-15% increase in sun hours something that is currently far above the norm line. It is clear that we are seeing more of the sun in the last 10 years. But if we look at just the last 3 years, we see that 2010 in particular could be characterised as very changeable, with a dark February, a light April, a dark May and an extremely light month of June followed by a period from August through December when the months were somewhat darker than normal. Graph 3 shows the deviation from the norm for the values shown in the first graph. This makes it even clearer that 2010 was a year with peaks and valleys Monthly sum of hours of sunlight: average throughout the Netherlands (source: Royal Netherlands Meteorological Institute) normal % Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec. 3. Monthly sum of hours of sunlight in the Netherlands: deviation from normal (source: Royal Netherlands Meteorological Institute) 175% 150% normal % 100% 75% 50% Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec. 7

8 Copyright Floricultura BV. Parts or all of this newsletter may be copied, providing the source is specified. Our information and advice are compiled with the greatest care, but are always noncommittal. Cymbidium: advice Very early varieties During April and May, it will be necessary to maintain 24-hour averages of 20 C. Daytime temperatures can increase to approx. 25 to 26 C, but prevent leaf temperature from rising to 27 C or higher. During the day, using a misting system for a few hours is a good way to keep the temperature within limits. At the same time, the RH cannot be allowed to drop to the point at which flower bud blasting could occur. Maintaining the proper RH also ensures better growth. During this period of the year, aiming for a higher RH is necessary because it is in this period in particular that the RH is often too low. The RH can sometimes drop to extremely low values below the range of 20 to 30%. In such a case, a misting system serves not only to cool the greenhouse but also to improve the climate to such a degree that the Cymbidium continues its process of photosynthesis better instead of slowing its growth rate to a standstill. Night temperatures are still low enough during this period, but do not allow them to drop below 14 C since nighttime heat loss through the greenhouse can lead to plant temperatures lower than what they should be. The plant temperature can be too low at the time the heating system is turned on in the morning; the plant s transpiration may not be able to react quickly enough to this rapid increase in greenhouse temperature. Under extreme conditions, this could lead to flower bud blasting so that only shoots instead of spikes appear in June/July. If poor weather results in low greenhouse temperatures, heating will be required. At the end of such a day, pull the shade cloths closed to hold the heat inside and save on heating costs. Depending on the weather conditions, whitewashing should be postponed as long as possible, but a heat wave in late May will definitely require a light application of whitewash. Do not whitewash too heavily. With our unstable weather, a short hot period can turn to wet and cloudy. It would be better to whitewash in phases. Early varieties Treat the plants in the Christmas production section of the greenhouse the same as the very early varieties. It would be best not to whitewash until the summer solstice unless the weather really demands it, but here again, two applications would be better. Here, too, pay attention to the 24-hour temperatures being achieved! Mid-range varieties The greenhouse sections housing these varieties are still fairly cool and the plants will have to be put in their intended place and/or divided. Not much else needs to be done. Devoting attention to heating to keep temperatures high enough is unnecessary; actually, whitewashing can be avoided unless the weather turns extremely hot during July/August. Late varieties These are flowering or almost in bloom. These greenhouse sections are already whitewashed and a misting system could possibly be used during the day to counterbalance excessively low RH values and high temperatures. The whitewash coating must be removed from these greenhouse sections after flowering but if the weather is now extremely sunny and warm, wait a few days until more normal conditions return to keep the transition from being too abrupt. Extremely late varieties To maintain quality, the second or maybe third application of whitewash should be made now to keep heat out of the greenhouse. After flowering (in mid-july) the whitewash coating will have to be removed from the greenhouse. If weather conditions are extremely hot, however, it would be better to remove the whitewash in two phases. If we have a cold summer as we did last year from July through August, heating will be necessary if the 24-hour temperature is not reached. And if the roof is coated with whitewash, this will be even more necessary! You have to invest to reap the benefits! A few more points that apply to all flowering phases: In general, the substrate dries out faster during the spring, so proper watering is essential. Waiting until too late to water for just one afternoon can result in bud blasting. Scout frequently (once a week) for spider mites. If you see a minor infestation starting, spray locally or, if you grow organically, space the plants farther apart. Scatter snail and slug pellets on a regular basis (approx every 3 weeks) starting in April. If you wait until you see very many of these pests, you will be much too late and will think that control is fruitless. P.O. Box 100, 1960 AC Heemskerk, The Netherlands T: +31 (0) F: +31 (0) E: orchids@floricultura.com I: Cym. 8500