Greenhouse Canada

Features Crop Culture Inputs
Working Towards Year-round Vegetable Production

This is just one of a number of Greenhouse and Processing Crops Research Centre projects, as researchers continue to provide growers across Canada with new tools to improve their profitability and move into new markets.

May 15, 2015  By Dave Harrison

June 2015 – Ask just about any greenhouse vegetable grower in Canada for their wish list, and “year-round production” would at the top of most pages. Retailers like the idea of a single supplier, and consumers throughout North America are favouring locally grown foods.

In Canada, low winter light levels are the challenge. And it’s not as simple as simply saying supplemental lighting is the answer. It has to be cost-effective, and it has to take into account how the lighting affects the plants’ nutritional needs and pest/biological interactions, among other considerations.

Researchers at the Greenhouse and Processing Crops Research Centre in Harrow, Ont., have undertaken an ambitious five-year project to develop year-round production models for tomatoes, cucumbers and peppers. The foundation for this research was laid more than a decade ago with projects related to extending the growing season.


The report will be completed in 2018.

This project was just one of many discussed during our GPCRC tour earlier this year.

As another example, and this time on the disease front, a major study is looking at a potential new fusarium threat for pepper growers, with Harrow researchers taking a very close look at the problem and identifying possible remedies.

Year-round greenhouse vegetable production in Canada is being advanced by a five-year research program now underway at the Greenhouse and Processing Crops Research Centre in Harrow, Ontario.

Heading the study team is Dr. Xiuming Hao. The project is running through to 2018.

“Greenhouses using supplemental lighting will allow growers to produce vegetables year-round,” he explained.

This is a very competitive market, and retailers are looking for year-round fresh produce supplies. “If we don’t have year-round production,” said Hao, “we risk losing some market share.”

Hao and his team have already done considerable work with lighting and season extension.

From 2004 to 2008, for example, they worked with year-round English cucumber and mini-cucumber production systems. They used HPS (high pressure sodium) lighting, and increased annual cucumber yields by 100 to 150 per cent in comparison to conventional systems not equipped with supplemental lighting.

From 2009 to 2013, they worked on hybrid lighting systems that placed HPS lights above the crop, and LEDs within the crop canopy – a vertical lighting strategy. The LED bulbs don’t get hot and can be placed close to the plants. This system ensured optimal – and more uniform – light distribution throughout the crop. In particular, the inter-lighting LEDs allowed the plant to maintain its vigour, resulting in higher fruit yield late in the season in comparison to use of HPS lighting only.

Plant growth, fruit yield and fruit quality are not only affected by the quantity of light, but also by its quality, or spectrum composition, said Hao.

LEDs allow researchers to fine-tune that spectrum composition.

Spectrum composition also affects certain compounds of the fruit. Hao and his team are working with Dr. Ron Cao and his colleagues at AAFC’s Guelph Food Research Centre to analyze how different light spectrum compositions impact plant growth, fruit yields and antioxidant levels.

The research has already identified the proper ratio of HPS lighting on top to LED inter-lighting for both mini-cucumber and tomato crops.

Another part of the research is looking at longer photoperiod schedules. Tomatoes, for example, grow best with up to 16 or 17 hours of light. Any longer than that and growers risk leaf chlorosis and the plant no longer responds.

However, supplemental lighting is a major capital expense, a fixed cost. Whether they use them for 17 or 20 hours, growers have still paid the same amount.

If growers can use lighting for longer periods of time and have the plant respond accordingly without triggering leaf chlorosis, they can improve their yields and quality.

Hao is applying Dynamic Temperature Integration (TI) scheduling to accomplish this goal. TI involves a pre-morning or pre-night temperature drop.

How do the leaves and fruit respond? The larger surface area of the leaf means it will have a quick drop in temperature, while the fruit temperature won’t drop as much or as quickly because it has a larger volume. For example, the leaf may drop to 15 C, while the fruit drops only to 17 C, a 2 C difference. Since the fruit is warmer and the leaf is cooler, it shifts the growth balance towards fruit growth, hence higher yields.

Dynamic Temperature Integration is showing the potential to improve plant response during longer photoperiod.

This temperature dip also allows growers to increase energy efficiency, reduce energy use, and because photoperiod injury is reduced, the plant responds much better to supplemental lighting.

The research so far has just looked at tomatoes because they have the biggest problem with an extended photoperiod. Peppers and cucumbers will be next.

Supplemental lighting will also mean different crop nutritional requirements and more irrigation. The entire system of fertilizing and irrigation will have to be adjusted and optimized, said Hao, something the current five-year study will address.

“Fertigation requirements under lighting are different from those under ambient light.”

In another study, Hao and his team are involved in a five-year study of new greenhouse cover materials.

They will be comparing regular coverings now in use with diffused polyethelene and polycarbonate materials, along with other new coverings.

Diffused covering materials offer more even light distribution, deeper light penetration to the lower canopy, and less plant stress in summer.

“Cover material has a great effect on the bottom line for growers,” Hao noted.

The study will look at the light transmission and energy conservation properties of the various coverings.

“If you walk into a greenhouse with diffused glass or diffused poly, you’ll notice there is very little shadow,” Hao explained. “It offers better light distribution throughout the crop, top to bottom.”

Diffused light is more uniform over the vertical profile of the plant. It also means more uniform leaf temperatures, and will reduce the incidence of fruiting disorders caused by high temperatures.

“The microclimate is so much better,” said Hao.

Both of these five-year projects are being funded by AAFC; the AgriInnovation Programs of Growing Forward 2 from AAFC; and the Ontario Greenhouse Vegetable Growers.

There’s a new disease threat of greenhouse pepper crops, and plant pathologist Dr. Ray Cerkauskas is conducting multi-faceted research into it.

He has been studying the etiology and control of Fusarium oxysporum.

It was first detected in a few greenhouses in the fall of 2013. Gillian Ferguson, the recently retired greenhouse vegetable IPM specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs, brought in some infected plants.

“When a problem like this comes in,” Cerkauskas explained, “you’re not sure if this is an existing disease or something new.”

The symptoms include a canker at the base of the stem, foliar chlorosis in the early stages, extensive foliar wilt, stunting of the plant, and foliar necrosis in the later stages.

The researchers found it to be a slow moving disease during the course of their study.

They evaluated the plants in four ways – overall plant, stem, roots and crown – with a 0 to 5 scale for each part.

They found that if the plant was diseased, the rockwool block pulls away very easily because there are few roots. There was also a dark discoloration of these roots compared to healthy plants.

The four ratings were combined to provide an overall disease severity index.

The first task was to identify the disease and the causal agent applying Koch’s postulates. (Robert Koch was an early microbiologist.)

Koch’s postulates include four criteria designed to establish a causal relationship between a microbe and a disease.

“You look at the plant and you look at the symptoms, and then do isolations from that plant tissue,” said Cerkauskas.

A number of organisms were detected. Each was multiplied in culture to determine its cultural features. These cultures were then used to make a suspension that was utilized to inoculate healthy plants to see what kind of symptoms would be expressed.

Once the same symptoms were observed on the newly infected plant, the targeted organism was then re-isolated from the diseased tissue to see if the same cultural features would occur.

It has also been recently found in the Almeria region of Spain. That was the first report of this disease on greenhouse sweet pepper.

The Harrow researchers are also testing a number of popular pepper varieties to determine how susceptible they are to the disease. Is there a pepper that may be more susceptible or more resistant to this disease? The disease severity index has been applied to each of them.

The next question was with the host range of this fungus, i.e., are greenhouse tomatoes and cucumbers also susceptible to the fungus? Growers who had a pepper crop with a fusarium problem would want to know if it could affect different crops planted the next season, such as tomatoes or cucumbers.

Growers are used to completely cleaning and disinfecting the greenhouse after the pepper crop is pulled out. As well, all infected debris should be removed from anywhere near the greenhouse.

However, if some of the fungal material remained despite all the precautions, what happens to the new tomato or cucumber crops?

In this study, Cerkauskas found there were no visible symptoms with cucumbers, and only some minor symptoms on the roots and crown of a few tomato plants.

“Tomato is in the same family as pepper, so you might expect to see a little symptom development with them.”

Cucumbers and tomatoes can be symptomless hosts, it was found, but the fungus is still present and colonizing the roots. Without a thorough end-of-season cleanup and the removal of all plant debris from those crops, it could lead to a subsequent infection of the next pepper crop.

In another study, Cerkauskas is looking to see if the problem could be controlled with reduced-risk materials, including the newer class of fungicides and biologicals. Because this is a new disease, these products are not yet registered for control of it.

And in a fourth study, the researchers are using molecular means to identify the exact type of fusarium causing the problem. The DNA is being extracted at Harrow to be analyzed at the Robarts Research Institute in London, Ont.

This project is funded by the Ontario Greenhouse Vegetable Growers, and Agriculture and Agri-Food Canada.

There were 230 acres of new greenhouse structures built in Ontario last year, and the majority were constructed in the Essex, Chatham/Kent region.

Of last year’s expansion, 43 per cent was in tomatoes, 31 per cent was in peppers, and 26 per cent was in cucumbers.

The province has 2,397 acres (959 hectares) in greenhouse vegetable production. Of that, 2,078 acres (841 ha) is in the Leamington area.

The major crops include tomatoes (38 per cent), peppers (34) and cucumbers (27), along with lettuce and eggplants (one per cent).

About two-thirds of total greenhouse vegetable acreage in Canada is in Ontario, followed by British Columbia (22), Quebec (seven) and Alberta (four).

The past year was quite cold, noted OMAFRA greenhouse vegetable crop specialist Shalin Khosla, and growers had to deal with high heating bills. Similarly the 2014-2015 winter was cold.

However, the 2014 production season was quite good for the three major crops.

One industry challenge is with low prices due to the influence of other producing regions, such as Mexico, the southern U.S., and Europe. Growers are continuing to become more efficient to counter those pricing pressures.

The average greenhouse vegetable operation in the province is 11.2 acres, maintaining a trend of increasingly larger greenhouses. “On average, pepper growers are larger than tomato growers,” said Khosla. “There are fewer pepper growers, but they have larger operations.”

About 80 per cent of new greenhouses constructed in 2014 were built with glass. The new structures are tall, ranging from 21 feet to 25 feet.

More growers are using hot water heating, and most are using at least one energy curtain and some have two. “It provides for a better energy management system.”

The use of biomass as a fuel has stabilized. While the price of natural gas has dropped quite a bit in recent years, so too has the price of wood biomass. While it’s trickier to heat with biomass, there are still a number of growers using it because they’ve made the investment in these systems.

Growers are increasingly energy conscious, said Khosla, spending more time and money optimizing its usage. The Ontario industry has dropped its energy utilization from 2.5 gigajoules per square metre to about two gigajoules per square metre. “Some growers are even lower than that.”

Considerable attention is paid to water management, with growers quite aggressive in recycling their nutrient solutions. More and more growers are completely recycling their nutrient solutions.

“Growers are working hard to ensure every drop of water is utilized by the plant,” he said. “They’re making sure the fertility program is perfect for the crop so there is minimum amount of wastage.”

Ontario recently passed its Nutrient Management Act, in which growers are now able to apply used greenhouse nutrient solution to farmland. There are a number of regulations that have to be followed. “It’s a good option available to them to remove nutrient solutions from the greenhouse.”

More automation is being utilized in the packing area and in moving materials throughout the greenhouse. Included are driverless cart systems following tracks from the greenhouse to the packing area, and robotic tipping, stacking and de-stacking units in the packing areas.

Research on robotic harvesting is making headway, but it may still be a few years down the road, said Khosla. “There are several research projects underway, but it’s a very big task.” Further work on greenhouse automation is underway.

“Greenhouse vegetable growers continue to strive to improve efficiency through innovation and improved management practices.”

Cara McCreary is the newest member of the GPCRC greenhouse team.

She took over in January from Gillian Ferguson, who retired earlier this year.

McCreary was most recently at the Ridgetown Campus of the University of Guelph, where she served as a research associate in the edible bean program since 2012.

She has a master of science degree in Environmental Biology from the University of Guelph, a bachelor of commerce degree in Business Administration from the University of Windsor, and an associate diploma in Horticulture from the University of Guelph.

McCreary has several years experience as a greenhouse scout, work she began while attending Ridgetown. She first began scouting in a 52-acre tomato greenhouse operation.

“That was quite an introduction to the industry,” she recalled during our interview. “One of the most spectacular things I’ve ever seen was when I walked into such a large greenhouse for the first time. It was pretty amazing.”

She then worked on a number of research programs at the University of Guelph and at Ridgetown for a couple of years while taking science courses before embarking on her master’s degree studies at U of G.

There she studied the life cycle, temperature-dependent development and economic impact of an agricultural pest, the bean leaf beetle.

She’s already spent considerable time meeting with growers to better understand their pest management challenges. She has even found time to conduct some preliminary research focusing on the impact of supplemental lighting on predatory mites and pests.

“There are a few other projects I’m hoping I can start later this year or next year.”

Print this page


Stories continue below