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Harrow shining more light on year-round production

Greenhouses have always had the environment to permit four-season growing, but winter light levels in Canada have been the main limiting factor. Until now.

May 11, 2016  By Dave Harrison

OMAFRA’S Cara McCreary and AgCanada’s Dr. Rose Labbé are working on a number of lighting trials and the effect on greenhouse insects.

June 2016 – The Harrow Research and Development Centre is busily working to illuminate important new winter markets for Canadian greenhouse vegetable producers, all thanks to its year-round production initiatives.

Winter crops would fill store shelves with locally grown tomatoes, cucumbers and peppers, allowing retailers to have a single year-round source of these vegetables.

The greenhouses have always had the environment to permit four-season growing, but winter light levels in Canada were the main limiting factor. However, work by Harrow research teams is fine-tuning the necessary supplemental light recipes for winter crops.


The results have been quite impressive, as we learned on a recent tour of the AgCanada facility located within minutes of North America’s largest concentration of greenhouse vegetable production. The year-round production project is a five-year effort that will wrap up in 2018.

We spent a day in early April touring the Harrow facility to view some of its latest projects, a tradition at the magazine that goes back some 15 years or so. It’s a great opportunity to provide an overview of some of the studies underway.

In addition to year-round vegetable production, we also viewed some strawberry trials. There is growing interest in the crop, and Harrow is determining the best varieties and treatments to make it commercially viable.

(My tour timing was a little off. I had just missed strawberry harvesting by a day or two. How much better could an early April visit to Harrow be than with a sampling of ripe, fresh strawberries!)

Our visit also included an update on the growth of the Ontario industry, and a look at trends.

Great strides are being made into cost-effective year-round greenhouse vegetable production, and Harrow is at the forefront of Canadian studies.

The greenhouse team is about halfway through a five-year research program that will conclude in 2018. Dr. Xiuming Hao is heading the group.

Canadian retailers are increasingly looking to year-round sources of locally grown vegetables. Greenhouses with supplemental lighting will allow growers to meet the demand, says Hao.

“Year-round production is important for growers to increase their market share. Lighting is a big trend for the industry.”

He and his colleagues have done considerable work already with lighting and extending the season.

From 2004 to 2008 they focused on year-round English cucumber and mini-cucumber production, and with impressive results. Using HPS (high pressure sodium) lights, they increased annual cucumber yields by 100 to 150 per cent in comparison to unlit conventional systems.

From 2009 to 2013, they worked with hybrid lighting systems of overhead HPS lights and intra-canopy LED lights to create a vertical lighting strategy. Unlike HPS lamps that give off heat, LED bulbs are cool and can be placed very close to the plants. The hybrid lighting systems using the two lighting systems ensure optimal and uniform lighting throughout the vertical crop canopy. The LEDs allow the plant to maintain its vigour, resulting in higher late season fruit yield in comparison to use of HPS lighting only.

Harrow researchers this year are looking at year-round pepper production, and preliminary results are quite encouraging.

It’s important for growers to know that when they go into year-round production with supplemental lighting, it will mean different cultivars, and different climate control and nutrient management strategies.

In the current trial, three cultivars were evaluated and one in particular stood out. “The choice of cultivar in year-round production makes a big difference,” Hao explains.

Because light fixtures represent such a large capital investment, it’s more cost-effective to use them for longer periods of time. Some varieties respond to the extended photoperiod much better than others.

The key is to use lights for longer periods of time and have the plant respond accordingly – without triggering leaf chlorosis – to improve fruit yields and quality. (Leaf chlorosis can result if the photoperiod is pushed beyond the cultivar’s limit.)

Hao’s group has developed Dynamic Temperature Integration (TI) strategies with a pre-night temperature drop to improve the response of greenhouse tomatoes and sweet peppers to long photoperiods of lighting. The drop creates a difference in temperature between the leaves and the fruit.

“You have to be careful to only drop the temperature to a level that the crop can tolerate,” Hao emphasizes. The lower temperature is only allowed for about a half hour or so. With tomatoes, for example, you can drop the temperature to 14 C to 15 C before returning to 18 C. For peppers, you can’t go below 15.5 C to 16 C.

It’s also important that daytime adjustments are made to maintain the same 24-hour average temperature setting.

During the temperature drop, the larger surface area of the leaf means it will get colder faster. However the fruit, because of its larger volume, will lose its heat much slower and remain a few degrees warmer than the leaves. This changes the plant growth balance in favour of the fruit, resulting in accelerated fruit growth, substantially reduced leaf chlorosis, and increased total yields.

The pepper trials are off to a good start. At the time of our visit, the crop had been growing for six months. Hao estimates the six-month crop has already matched – or is close to matching – the annual yields of a traditional pepper greenhouse (25-30 kilograms per square metre).

He hopes to achieve 45 to 50 kg/m2 of peppers in a 12-month crop trial.

Hao showed me a stem with nine fruit on it. Each pepper was about 250 grams. The crop had grown to 2.5 to three metres tall in only six months. “Growers who have stopped by to visit have been quite impressed.”

The system needs the right cultivar, along with the right climate control, heating and nutrient management strategies to be effective. As well, it needs a pruning strategy that provides a larger canopy to intercept light.

Last year’s work with mini-cucumbers had yields of 62 to 65 kg/m2 over six months. Add to that a summer crop of about 50 kg/m2, and the total yield would be about 110 kg/m2.

By comparison, a commercial mini cucumber greenhouse will have four crops per year, and each will produce about 15 kg/m2, resulting in a total yield of about 60 kg/m2.

Supplementary lighting, then, will almost double the yields and reduce the number of crops from four to two. “We also have seen very little disease,” says Hao. The crop has been growing for six months with no powdery mildew.

In another trial with mini-cucumbers, Far-red LED lighting and HPS lighting are being studied. With HPS lighting alone, the leaves tend to be a little smaller because of the infra-red heat. The Far-red light, on the other hand, could result in larger leaves to intercept more light.

You only need a small dose of Far-red light on the top of the crop. This light signals to the plant that it is being shaded, and the leaves will stretch.

“This will mean faster growth in the early stages,” says Hao. “The stems will be longer and the leaves will be bigger.”

In 2014-15, similar trials were conducted with tomatoes. The results were higher early yields because the taller plants and larger leaves intercepted more light.

This year’s mini-cucumber trials look just as promising, though the results had not been analyzed at the time of my early April visit.

Hao and his colleagues are also looking at LED lighting with tomatoes.

The big advantage with LED lighting is its narrow spectrum and you can really optimize the light quality. HPS has a fixed spectrum, however, and can’t be changed.

Far-red light will make leaves bigger, and blue light will make leaves thicker though average size. This knowledge can be applied at different crop stages to optimize leaf and fruit growth. Growers can apply different lighting recipes for different growth stages.

Blue light also promotes development of antioxidants.

As an example, the Plant Factory in Japan provides red light for the first 20 days of its lettuce crop for larger leaf development. However, they switch to blue light for the final three days to improve antioxidant and pigmentation levels.

With the current LED trials at Harrow, Far-red light is applied overhead, while blue light is placed within the canopy to promote fruit quality and antioxidants.

More premium grade tomatoes are produced with blue light in the canopy.

As well, blue light has been found to produce more antioxidants in mini-cucumbers.

“We need to find the optimal vertical lighting recipes for the top and bottom/fruit of the crop,” says Hao, who adds that nutritional management will also need to be adjusted to match the growth of the plants.

These lighting trials are being funded by the AAFC; the AgriInnovation Programs of Growing Forward 2 from AAFC; and by the Ontario Greenhouse Vegetable Growers.

Hao is also leading a new three-year LED research project funded by AAFC. It will look at LED applications in all three major greenhouse crops – tomatoes, peppers and cucumbers.

Hao will focus on the physiology, yields and fruit quality aspects of the trials.

Others team members include:

  • Dr. Rose Labbé, entomologist at Harrow Research Centre, will study the effect of lighting on greenhouse biocontrols and pests.
  • Dr. Aiming Wong, of London Research Centre, will study how LEDs might be applied to greenhouse vegetable crops to increase plant tolerance or resistance to viruses and diseases.
  • Dr. Rong Cao, of Guelph Research Centre, is a specialist in nutritional values of food. He will look at how LEDs affect the nutritional value and antioxidant levels of greenhouse vegetables.
  • Dr. Bernie Grodzinski, a professor at the University of Guelph, will look at how LEDs can speed up the translocation of photo-assimilates from the leaves to the fruit to increase yields.

Entomologist Dr. Rose Labbé is the newest member of the greenhouse team at the Harrow Research and Development Centre, arriving in July 2015.

The greenhouse industry is expanding its year-round production capabilities, and that requires supplemental lighting during the winter. Considerable work on year-round production is being carried out at Harrow. Labbé’s work with pests and beneficials will dovetail quite nicely with work being done by colleague Dr. Xiuming Hao on crop production systems.

Hao has a number of lighting systems, including LEDs, set up for his trials.

“We are incorporating some of our research to see whether biocontrols might be establishing better under the lights,” Labbé explains.

Her team is using a combination of lab trials to study basic behaviour, development times, fecundity rates, and longevity of some of the most common generalist predators, including Orius and Dicyphus.

They will also look at the potential of using supplemental LED lighting to break the diapause stage of a number of key predators, including Orius, Dicyphus and Feltiella.

The work is currently focusing on a small spectrum of blue and red light, and will be looking at other spectra going forward. The work will be important not only to growers, but also to biocontrol companies looking to establish populations of these predators in the winter months.

Labbé is also studying the establishment of predators under a variety of lighting conditions. Preliminary results suggest that relative to untreated compartments, establishment of the predators was much better under lights. Dicyphus responded especially well – two to three times better – under both the HPS and LED light treatments, compared to the compartments without lights.

“That’s pretty impressive,” notes Labbé. “We will be repeating the trials in a commercial setting.”

Work has been done with Orius in experimental greenhouses. It did very well under the lights, with about a 20 per cent increase in establishment rates.

These preliminary results suggest that lighting in general will help predators get established in early season. Predators tended to live a bit longer and were reproducing earlier under the lights.

Labbé is also conducting predator mite trials, continuing some of the work started by Dr. Les Shipp before he retired a few years ago.

One of the promising new hopefuls is Typhlodromips montdorensis, which is not yet registered in Canada. It doesn’t restrict itself to thrips, the target pest in the trials.

Typhlodromips is said to be fairly competitive with other mites in the early season. Labbé’s results, however, are very preliminary as they are only about halfway through the trials.

Another project is looking at the effect of blinking LED lights on nocturnal pests. The lights seem to be a deterrent to the unwanted visitors. “Any pests that are typically nocturnal would be susceptible to this kind of technology,” says Labbé. “It’s quite cutting edge.”

AgCanada is continually assessing the potential of new pest threats. The goal is to pre-empt their arrival by looking at new control measures, including finding new parasitoids that could be deployed.

Labbé is also part of an AAFC working group developing procedures to assist the Canadian Food Inspection Agency (CFIA) in testing for non-targeted impacts of new biocontrols being assessed during registration submissions. The goal is to have a methodology to help potential applicants in moving their product through the process. “This will be a big help to the industry in general in accessing new biocontrols.”

Greenhouse construction crews were again busy in Ontario in 2015, with acreage increasing by five per cent to 2,800 in total.

During our recent visit to the Leamington/Kingsville area, it seemed as if every concession was home to at least one construction project. Quite impressive! Expansion has become business as usual in this vibrant region, home to North America’s largest concentration of greenhouse vegetable production.

OMAFRA greenhouse vegetable extension specialists Shalin Khosla (crop production) and Cara McCreary (IPM) work closely with the AgCanada researchers on projects. They have offices at the Harrow centre.

Khosla says there have been a number of changes in the industry over the past few years.

  • First, there are more high-tech glass greenhouses being used in construction, and more growers are looking at diffused glass. As well, there is considerable interest in energy curtains, with at least one curtain – and sometimes two – being installed.

“The price of glass has come down dramatically and the price of plastic has gone up,” Khosla explains.

Growers who have moved to glass have learned to operate under it and are able to optimize their production, resulting in impressive yields. “That’s an incentive to other growers to consider glass.”

As well, double poly has to be changed every three to four years, and there are now fewer people able to do it because of the rising heights of new greenhouses.

  • Secondly, there has been a change in the crop ratio. In the past, peppers were third after tomatoes and cucumbers in terms of acreage. However, peppers have now edged their way into second place.

Organic production has been increasing, driven by consumer and retailer demand. Just about every major packing house in Ontario has some organic product lines, including tomatoes, cucumbers, peppers and lettuce.

A wide variety of specialty tomatoes, along with mini peppers and cucumbers, are also grown.

There is growing interest in lettuce, and more recently in strawberries. Of the latter, Harrow has been conducting trials the past year and with good results.

Greenhouse strawberries are fairly common in Europe, but the Ontario industry would need North American cultivars and that requires the development of a specialized knowledge base geared to local conditions.

The interest in greenhouse strawberries is deeply rooted in the Ontario industry, as Khosla recalls trials conducted about 26 years ago at Harrow!

The current research has included HPS and LED lighting systems. They’ve been looking at three growing media – rockwool, BVB (a soilless mix) and capillary mats – and two cultivars (‘San Andreas’ and ‘Albion’).

On the heating front, a number of growers have switched from steam to hot water. There are benefits with both, says Khosla, but many of the newer projects are opting for hot water, largely because they can utilize the flue gas. They also have the ability to use hot water storage tanks to improve boiler efficiency.

Automation is also key, with much of the investment in the packing sheds. Handling the large variety of cell packs, bags, trays and resealable plastic packs can be quite time-consuming, so automation is addressing this challenge.

University of Guelph professor Dr. Medhat Moussa is working on robotic systems for greenhouse vegetable crops.

Keen interest is also being shown in lighting. There are about 65 acres in the region using artificial lighting, with more being added each year. “A lot of growers are interested in researching and trying out LED lighting.”

Growers are very efficient with their energy management, and that’s helping keep overall costs down. “For example, they’re venting more carefully,” says Khosla. Growers are optimizing their computer programs to ensure the ideal environment for their crops.

Growers are also becoming more efficient in their use of fertilizer and water. “They’re quite precise in their watering, making sure the amount of water they’re giving the plant is exactly what the plant needs.”

There’s a lot of work being done on new water recycling and disinfection systems.

Educational programs are being developed by the Ontario Greenhouse Vegetable Growers, the Ontario Ministry of the Environment and OMAFRA to help growers comply with new water use regulations.

Under the Nutrient Management Act, for example, growers are now able to apply used greenhouse nutrient solution to farmland. There are a number of regulations that have to be followed.

Other growers have the ability to connect to municipal sewer systems.

The growing season featured a mild winter, but featured low light conditions that led to a slight delay in some of this year’s crops. Growers had to be especially careful how they watered because they could easily overdo it under such low light conditions.

Disease and pest challenges have been about normal for most greenhouse vegetable crops in Ontario over the past year, though whiteflies were a little more challenging than usual.

“Overall, there have been the usual disease and pest pressures,” notes Cara McCreary. “The key for growers is to respond quickly after a problem has been detected.”

While whitefly was a problem, many growers were able to keep it under control using a variety of tools. One example is yellow sticky tape, which is strung the length of a row just above the canopy. “It’s amazing how many adult whitefly it catches,” she says. “Adults are difficult to control, so this has been effective for many growers.”

More yellow sticky tape was strung this year, probably prompted by last year’s whitefly problem.

Some growers strung the tape atop every row, while others opted for every other row. However growers who used it over alternate rows found much higher whitefly numbers in the rows without the tape, and are doubling up their efforts this year by putting the tape over every row.

“It’s important to put it up early in the season,” says McCreary. The tape lasts for the season and is raised as the canopy grows taller.

Biocontrols are also effective. “We rely quite heavily on them for whitefly control.”

This past mild winter and fall meant a greater potential for pest problems. There would have been much more pest pressure than normal going into the winter, and potentially higher survival rates for pests over the winter. “Growers were especially alert for problems this year because of the weather. They’re very quick to respond, and that is so important.”

McCreary works closely with Dr. Rose Labbé, AAFC’s greenhouse entomologist at Harrow.

Lighting trials are among current entomology research themes. “How does supplemental lighting affect pests and do they develop more quickly or more slowly under various lighting regimes? Similarly, how does lighting affect biocontrols?”

McCreary says that research over the years has developed very effective biocontrol programs based on regular greenhouse conditions. “What we have to determine is the effect, if any, if you add lighting to the mix,” she explains. “If there is an effect, we may need to adjust the biocontrol programs.”

One key consideration is the diapause phase some beneficials enter during the winter. Generally speaking, diapause is related to temperature and daylength.

Orius, for example, is a great predator when targeting thrips, but it diapauses through the winter when light levels are much lower. This means there are a number of months it can’t be used. However, could supplemental lighting help break that diapause? The research is underway.

Strawberries are a relatively new commercial crop being grown in Ontario greenhouses. McCreary says there is definitely growing interest in it. “We don’t have a lot of experience with strawberries in greenhouses with respect to pests and other challenges.”

Harrow is conducting extensive research on the crop. Labbé and McCreary are monitoring the trials to assess the pest pressures, and are also working closely with commercial growers.

“It’s a learning curve for everyone. Even with predators and parasitoids, they have preferences with host plants.” For example, would predators that are effective in controlling a pest in a tomato crop be as effective against that same pest in a strawberry crop?

McCreary is also checking on field strawberry biocontrol programs to assess what could also work in a greenhouse.

The major pest threats for greenhouse strawberries are thrips and two-spotted spider mites. Powdery mildew is also a problem, but usually in patches.

She will also assist with efforts to register new products. “There are a limited number of products available right now.”

On a related theme, organic greenhouse vegetable production is also increasing in the province. “Growers currently have a limited range of available products and IPM programs will rely even more heavily on bio-agents.”

Work will also continue on biopesticides and beneficial microbes. Both have great potential for use by organic and conventional growers. They have reduced risk for resistance development and reduced risk for workers.

“It’s important to have access to a combination of conventional and bioagent products,” notes McCreary.

“This is important in reducing resistance.”

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