Finishing up 2023

 As we finish up our 2023 growing seasons, it is time to re-visit our standard cleaning procedures. Throwing out the old and preparing for the new is one of the most important components to protected production.

While this is going to look different for those in soil-based systems compared to those who are set up hydroponically, there are some key practices that can be adapted to any protected space:

1. Removing ALL organic matter from the greenhouse, and greenhouse vicinity
• dried up leaves, old soil, dirty pots and growing supplies are perfect hiding spots for pests and disease to overwinter. Its important that you eliminate as much potential habitat and food source as possible
• Don't hesitate to do this in stages. Clean out the big stuff, and come back a second and third time to get rid of the bits and pieces that were not picked up the first few times. 
• Do not leave piles of plant material or old soil next to your greenhouse. As much as these serve as habits inside the production space, they will do the exact same thing outside. No matter how well the inside is cleaned, if you have a major source of insects just steps away from the greenhouse...there will be problems
2. Collect all old growing supplies from the year, and remove from the space for cleaning. Pots, carrier trays, pruners, clips, support stakes/string etc. should be dealt with to reduce pathogen and pest load into the new production cycle. Pots, carrier trays and pruners can all be sterilized and re-used, but be aware of the cleaning agent used here - some are going to cause more harm than good! Wooden stakes, while tempting to re-use these, cannot properly be sterilized because they are highly porous. Disease transfer from year to year from re-using stakes is possible.
3. Consider swapping out ground cover if you are using something more substantial than plastic mulch! While this isn't something typically tackled on a yearly basis, following a heavy disease year it can be worth considering getting a new cover put over the ground. If you are considering this, remove the old cover before going forward with suds and sanitizer! That way your ground layer will be scrubbed back to a base layer of clean, and you can be confident that nothing is hiding out in tiny cracks and crevices throughout the old ground cover.
4. Lets get soapy!
• Giving all growing surfaces a soapy scrub is going to grab hold of any bacterial, viral and fungal agents that are still in the space and wash them away. 
• The best strategy for washing a greenhouse is to start at the top and work down - and this includes your ceiling! Failure to wash the top of the grow space creates a disease bank that can literally rain down on your future crop.
• Once you have applied your soap, give the production space a thorough rinse and allow it to air dry
5. Once you have allowed the space to airdry after cleaning, it is time to bring in the big guns- Sanitizer! There are a lot of sanitizers on the market to chose from, but they do have a few things in common:
• Contact time is important. Different products have different required contact times in order to be effective. Be sure to check what the required contact time is for your product of choice, and do your best to adhere by that. Otherwise there is no guarantee that the product will sterilize to the degree that you are hoping for
• Organic matter will de-activate sterilizing agents. Any of those leaves or soil bits that got left behind in pots and seeding trays will actually render your product useless. 
• Consider how corrosive your cleaning agent is. Bleach is effective, but does impact the longevity of growing equipment, both for plastics and other materials.
• TEMPERATURE. Sanitizer efficacies significantly decrease at lower temperatures. While it is difficult to justify heating a protected space for cleanout, it is a key factor in maximizing your product efficacy.

Here are a few other considerations for your end-of season wrap-up:

-Once the production space and tools have been cleaned, be conscious of what is coming into the space. Just because you aren't actively growing plants, doesn't mean you are immune to accidental spread! Clean clothes/shoes/growing supplies should be the only thing that enter the space for as long as possible to maintain the clean slate.

-For those who are growing in soil, producers should consider removing plastic on spaces that are not being used for production. The lack of rainwater coming onto your tunnel soils will result in the accumulation of salts in the soil. One of the best ways to tackle this is to allow the snow and rain that come with the winter to run through the soil. Come growing season, this will allow for better uptake and use of supplemented nutrients, and less stress caused by buildup over time. Plastic removal can be a pain, so even doing so every few years is going to be hugely beneficial. For more information on soil salinity in high tunnels, check out this fact sheet!

-Looking to maximize the performance of over-wintered cover crops? Unheated, double poly inflated greenhouses are not going to give enough protection from those cold winter nights. The addition of one or two layers of ground cover can work wonders for your cover crop, reducing large fluctuations in temperature and buffering against cold snaps. It also helps to protect soil moisture for your cover crop. As our day lengths turn around, these plants will see a huge boost in productivity in February and March, increasing the amount of in-house biomass generated to be worked back into the soil before bringing in the cash crop. 

Row cover is best installed after a cold snap or two in the greenhouse space. This should function to kill some of the pests that may still residing in the space, before adding the additional layer of protection

Here's to a fresh start!

Posted by: Talia Plaskett

Upcoming Tour for Greenhouse Soil Health

 Extra! Extra! Learn All About It!

Judson Reid and Talia Plaskett will be making the rounds in Nova Scotia July 3-July 5 for farmer-guided discussions on soil health in tunnel spaces! These sessions will be primarily focused around nitrogen management, and the crucial considerations to make when selecting nutrient inputs to make sure that we are supporting a healthy and resilient soil system, as well as maximizing the productivity on our target crops. This conversation is easily catered to production that is organic, conventional and everything in-between.  Feel free to bring your most recent soil test and tissue test results for some feedback and general discussion surrounding what those results are telling you.

Where soil health is a complex, multi-dimensional topic, the tour team will also be talking about the use of cover cropping in protected spaces. Where cover crops are hardly a new practice, the inclusion of this concept into tunnel spaces is not as commonly practiced. Cover crops offer a handful of benefits to protected producers, where erosion may not be the primary concern, but they can help facilitate drainage, fix nitrogen directly into the soil, maintain healthy microbial communities, and help to build organic matter in these highly productive, highly utilized spaces. 

The intention of these sessions is to provide a space for current and prospective tunnel producers to talk about soil health, and how protected production can lend to some unique challenges not typically seen in outdoor settings. So grab a friend, and register today for your closest tailgate meeting, for what should make for a very interesting session! 

More information can be found here

Posted by: Talia Plaskett

Managing Nitrogen in Soil-Based, Protected Crops

The first session of our mini-series set the stage on some of the issues we are seeing regarding soil health and long-term resiliency in protected spaces. For those of you who missed the first session, or are interested in revisiting the teachings before building on it in part 2, you can find the full recording here (Managing Nitrogen in Protected, Soil-Based Systems). A summary of some of the information presented is listed below:

One of the re-occurring themes in protected soil production is an accumulation of nutrients, specifically things like Mg, Ca, and K, as a result of large deposits of compost before a cropping season. While these are necessary nutrients for healthy crop production and good quality fruit, too much of a good thing is not always a good thing. Typical supplementation focuses so heavily on achieving a target N value, that a lot of the micronutrients that come along with that N slip by unnoticed.

Not only are we concerned with high levels of certain micronutrients, but also have to be aware of the soil structure itself. One of the soil health indicators we talk a lot about is percent organic matter. While we like to see higher percentages of organic matter, it can come at a cost to other macro- and micro- nutrient availability to the plant when not executed properly. Paying attention to the cation exchange capacity value, or CEC, on a soil test, is important for those who regularly apply compost. While not mentioned in this webinar with Judson, the higher the CEC value, the tighter bond exists between the soil particles and the nutrients, which make it harder to make adjustments to the nutrient composition/balance without significant intervention.

Combine these two factors with the lack of overhead precipitation in tunnels, we see astronomical values of these micronutrients, which are going to contribute to a rising pH, and a significant hinderance on the plant's ability to take up all of the nutrients in the required quantities/balances that the crop needs. Here is an example of the soil test presented in the webinar highlighting this exact trend. The top image highlights a soil that has been supplemented but not to any excessive extent, and the second image highlights how that soil has evolved with continual additions of a compost:

When it comes to the use of compost in protected settings, conducting a compost analysis before application is strongly encouraged, as is yearly soil testing so that we see what is happening in these soils that do not have the same opportunities for drainage as an exposed soil would. Understanding exactly what you are putting into the soil, and how often, is crucial to avoiding buildup to the levels displayed here. Generally when it comes to supplying nutrients to the crop, scenarios that require supplementation are much easier to navigate compared to a heavily loaded and complex soil as what is projected above. The use of fertilizer blends can also contribute to the accumulation of certain nutrients. Consider this - the go-to fertilizer you use in your system is 20-20-20. While that is a great source of nitrogen, your P and K are already very high, and is going to add to the already-existing nutrient load. In soils such as these, single nutrient sources are going to be a much better choice as we attempt to remediate these soils into something that are resilient and will support crop production well into the future.

Given all of this information, what can we do to better balance out our nutrient supplementation to prevent this from happening? One of the best strategies is going to be split nutrient, application throughout the season. This is a much more targeted approach, where we know:

    1) nutritional targets for the crop in question

    2) recent soil tests outlining nutrient composition

    3) BONUS when we consider the long-term nutrient output of supplements such as                      compost or manure

From here, we are able to formulate a plan that sees regularly scheduled nutrient introduction via fertigation into the tunnels, specifically targeted for when the plant needs those nutrients the most. In doing so, we can reduce the loss of nitrogen to the environment, prevent unnecessary buildup that impede production success, maximize the impact that each $$ of fertilizer has on crop performance, and generally contributes to resilient and long-lasting productivity of those greenhouse soils.

Interested in learning how to set yourself up for split applications during the season? Join Judson Reid and Talia Plaskett at noon (AST) on April 13th for a ‘Lunch and Learn’ session on how to set yourself up for split applications of nitrogen throughout the season! This is a great opportunity to help establish the fertigation plan for 2023 and fine-tune your calculator skills to make sure that you are getting the maximum impact for every drop of fertilizer injected into the soil. For more information, or to register for the session, please check out our learning portal.
 

Posted by: Talia Plaskett

 

 

Setting the Stage for 2023

 As we head towards the end of the season, it is time to start thinking about the cleanout process. Throwing out the old and preparing for the new is one of the most important components to protected production.

While this is going to look different for those in soil-based systems compared to those who are set up hydroponically, there are some key messages below that can be adapted for any producer. For those who are growing in soil, producers should consider removing plastic on spaces that are not being used for production. The lack of rainwater coming onto your tunnel soils will result in the accumulation of salts in the soil if left unchecked. One of the best ways to tackle this is to allow the snow and rain that come with the winter to run through the soil. Come growing season, this will allow for better uptake and use of supplemented nutrients, and less stress caused by buildup over time. Plastic removal can be a pain, so even doing so every few years is going to be hugely beneficial where it is not feasible to do more regularly. For more information on soil salinity in high tunnels, check out this fact sheet!

Here are a few key parts to your end-of season wrap-up:

1. Removing ALL organic matter from the greenhouse, and greenhouse vacinity
• dried up leaves, old soil, dirty pots and growing supplies are perfect hiding spots for pests and disease to overwinter. Its important that you eliminate as much potential habitat and food source as possible
• Don't hesitate to do this in stages. Clean out the big stuff, and come back a second and third time to get rid of the bits and pieces that were not picked up the first few times. Vacuums and leaf blowers can be excellent tools for capturing/collecting small organic bits that seem to escape the grasps of a broom
• Do not leave piles of plant material or old soil next to your greenhouse. As much as these serve as habits inside the production space, they will do the exact same thing outside. No matter how well the inside is cleaned, if you have a major source of insects just steps away from the greenhouse...there will be problems
2. Collect all old growing supplies from the year, and remove from the space for cleaning. Pots, carrier trays, pruners, clips, support stakes/string etc. should be dealt with to reduce pathogen and pest load into the new production cycle. Pots, carrier trays and pruners can all be sterilized and re-used, but be aware of the cleaning agent used here - some are going to cause more harm than good! Wooden stakes, while tempting to re-use these, cannot properly be sterilized because they are highly porous. Disease transfer from year to year from re-using stakes is possible.
3. Consider swapping out ground cover! While this isn't something typically tackled on a yearly basis, following a heavy disease year it can be worth considering getting a new cover put over the ground. If you are considering this, remove the old cover before going forward with suds and sanitizer! That way your ground layer will be scrubbed back to a base layer of clean, and you can be confident that nothing is hiding out in tiny cracks and crevices throughout the old ground cover.
4. Suds up the space
• Giving all growing surfaces a soapy scrub is going to grab hold of any bacterial, viral and fungal agents that are still in the space and wash them away. 
• The best strategy for washing a greenhouse is to start at the top and work down - and this includes your ceiling! Failure to wash the top of the grow space creates a disease bank that can literally rain down on your future crop.
• Once you have applied your soap, give the production space a thorough rinse and allow it to air dry
5. Once you have allowed the space to airdry after cleaning, it is time to bring in the big guns- Sanitizer! There are a lot of sanitizers on the market to chose from, but they do have a few things in common:
• Contact time is important. Different products have different required contact times in order to be effective. Be sure to check what the required contact time is for your product of choice, and do your best to adhere by that. Otherwise there is no guarantee that the product will sterilize to the degree that you are hoping for
• Organic matter will de-activate sterilizing agents. Any of those leaves or soil bits that got left behind will actually render your product useless. 
• Consider how corrosive your cleaning agent is. Bleach is effective, but does impact the longevity of growing equipment, both for plastics and other materials.
• TEMPERATURE. Sanitizer efficacies significantly decrease at lower temperatures. While it is difficult to justify heating a protected space for cleanout, it is a key factor in maximizing your product efficacy.

Once sterilized, be conscious of what is coming into the space. Clean clothes/shoes/growing supplies should be the only thing that enter the space for as long as possible to maintain your clean growing slate.

Here's to a clean start!

Posted by: Talia Plaskett

Things to Consider When Selecting Soilless Substrates

Soilless substrates are used across the world, offering a solution to those with difficult soils to grow on, or those who are looking to increase efficiencies when it comes to nutrient and water inputs. These substrates are comprised of non-soil components, but still provide the structural support needed by the plant in order to grow.

When it comes to the base material used for soilless grow media, there are two groups: synthetic and non-synthetic products. 

How do I chose what substrate to use?

While both synthetic and non-synthetic substrates are good options for providing structural support, nutrients and water to the plant root system through the cropping cycle, there are a few key questions to consider when purchasing a growing media:

1) What is the cost? 

Substrates are not created equally when it comes to cost. It is not recommended, however to chose the cheapest/most expensive one without understanding what you are getting with it. It is definitely an important factor to consider, but make sure that you understand the rest of the list below when making your choice. 

2) Where is the material coming from?

In COVID times, shipping delays are all too real for producers of all shapes and sizes. This should definitely be a consideration if you have yet to order your growing media for the upcoming season. There are many local substrate providers who might be able to fill your needs without having to ship overseas. 

3) What is the baseline nutritional status of the media?

While soilless substrates do not have much to offer in terms of baseline nutrients, it is important to realize that there are differences between the base materials. Some substrates are going to be more prone to having high initial salt levels compared to others, and if the media is not treated properly, these salts can be very damaging to your new crop. Be sure to ask your provider about your substrate and the treatments it has received. 

4) What is the particle density, porosity and particle size range of my substrate? 

These are key parameters that are going to determine how well or how poorly your substrate holds on to water. A substrate with tiny particles, means that the air and water spaces within your media are also going to be very small. This makes it harder for the plant to pull water out of those air spaces. It is also difficult for this water to drain out of the media, meaning the roots are more prone to sit in a wet matrix, regardless of the time of day. This has a tendency to lead to root disease and sub-optimal plant productivity. On the other end of that spectrum, large particles have very little capacity to hold onto water, meaning you are significantly increasing the number of irrigation events throughout the day to sustain plant growth. 

5) How do I want to handle my substrate?

Substrate is available for purchase in a few different forms. It can be purchased in large bulk orders, where the producer must hydrate, divide up into the individual growing containers, and then move those containers into the growing space. The other option is to purchase pre-filled slabs (also referred to as grow bags). Some crops have the option for specialized containers that help mitigate some production issues that typically develop down the line, while others don't. It is up to the producer, the target crop, and the labour force available, to decide which method is going to work best for that particular operation. 

6) What am I going to do with my substrate now that I'm finished with it?

This is where things get a little hairy. Synthetic substrates cannot be composted, and usually require transport off site for disposal. Non-synthetic substrates do have the option for composting, but must be done in a strategic way to prevent the accidental creation of an oasis for lingering insects and disease. This plays in to point number 5 as well - removing the inner contents of a slab wrapped in plastic is much more time consuming to compost compared to a crop grown in a container.   

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For those who are new to growing in substrate, these questions can be overwhelming...but never fear! Your Protected Crop Specialist is here. If you have any questions on soilless substrates check out some of Perennia's resources:

• 2020 - 2021 Getting Into the Weeds Session on Soilless Substrate
• Perennia's fact sheet on Substrate
• Contact Talia Plaskett, our Protected Crop Specialist

Whats New with Biological Control?

  2021 has seen a lot of new and exciting things in the world of IPM with some of the tools available to producers for managing pest populations. Please find a quick summary of some of these new developments below with their corresponding contact information – this is a list of curated material from various sources, credit must be given where credit is due!

1)Introducing Anystis, the new generalist predator in our toolbox

 Anystis is a new generalist predator which was discovered and trialed by Vineland Research and Innovation Centre. This predator has shown control over thrips and spider mites as well as suppression of aphid populations. Not only that, but it also preys on Echinothrips and mealybugs, which currently do not have effective options when it comes to biological control agents! Not only that, but Anystis is compatible with other commonly used biocontrol agents, meaning less stress about adjusting your current regimes and more success overall when it comes to targeting your problematic pests. 

The use of Anystis has been validated in commercial greenhouse trials on gerbera and sweet pepper in Ontario, and further supported by promising results generated through recent trials at Niagara College for use in cannabis to control aphids. The predator has been transferred to Applied Bio-nomics Ltd for scaling up the rearing system and commercialization, and have a limited number of mites available for growers to try.

For more information on Anystis, contact Rose Buitenhuis, PhD Senior Research Scientist, Biological Control at Vineland Research.

 

2)Slow-release method of nematodes

The current application of beneficial nematodes is limited to sprenches, or drenches, across the surface of the growing media. The biggest targets for beneficial nematodes are the larvae of fungus gnats and western flower thrips, as well as onion thrips pupae. While the product is quite effective, the current application method to the crop sees a few technical difficulties. These drenches/sprenches are not the most effective when it comes to penetrating deeper into the growing mix, and they must be applied on a weekly basis. Not only that, but the current methods of distribution sees a very poor storage capacity – all must be distributed at once, which leaves the small producers in a bit of a financial pinch!

E-Nema is a new tech company based in Germany. They have come out with a slow-release method for these beneficial nematodes which tackles some of the difficulties associated with the existing system. These look similar to tapioca pearls, and are designed to be incorporated into the growing mix before planting. Then, over time, they will slowly release nematodes through the entirety of your growing container. These pearls are very safe, and do not contain any harmful chemicals. In addition to that, they store quite well, which is a win for smaller producers who may not need massive volumes to be distributed all at once. The reintroduction and inoculation of low doses of nematodes has proven to be more effective than coming in hot and heavy with one dose during the cycle, and this technology allows just that! 

BioBee will be the distributer for this new product, so be sure to keep your eyes peeled for that! I want to give a huge shoutout to the Cannabis Cultivation & Science Podcast for keeping up with the biocontrol world and spreading the word on cool innovations like this one!

3)New rearing methodology for Phytoseiulus persimilus

Our old reliable predatory mite is coming at us new and improved! BioBee has re-evaluated their current rearing methods for persimilis and has landed on a product that addresses some of the downfalls to the original release system. The original system sees that the predators are reared on spider mites, meaning they come out of their sachets starved and ready to tackle some serious spider mites. While that works well in heavily infested crops, it doesn’t bode well for the low pest pressure grow room, or the preventative release strategy either. This new product raises the predators on mite eggs, meaning that each sachet will come with a variety of life stages, and each sachet will have a long-life span overall as these different stages progress towards adulthood. These sachets can see up to 12 days to release the contents, giving you almost 2 weeks of release from one purchase. The new food source sees that these mites are not as hungry as they would be when raised on spider mites. This means they have time to establish in the crop, as well as hunt down those low density mites that are scattered through the room. Not only that, but there is no carrier mixed in with these predators. This is a huge win for producers of heavily-trichomed crops, as their plants will no longer be littered with pesky lingering carrier bits.

Figure 1. An image of persimilis predating on a two-spotted spider mite. Photo credit: Biotactics Inc. 

This new persimilis can also be purchased in bottle form. But grower be warned! It was interestingly noted that these predators are not their characteristic red colour when you receive them from the insectary. That colour develops on the persimilis as they start feeding on spider mites. This acts as an added bonus when it comes to your scouting efforts. If you note which predators have transitioned from milky to red, you can get a sense of the pest pressure in the space and how effective your release was at managing the spider mite population.

I want to give a huge shoutout to the Cannabis Cultivation & Science Podcast for keeping up with the biocontrol world and spreading the word on cool innovations like this one!

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Posted by: Talia Plaskett

Cutworms in Cool-Season Production

The University of New Hampshire is hosting a webinar for vegetable growers dealing with cutworm issues in cool-season production, December 1^st 12-1pm.

They will cover cutworm identification, life history, and what we know about control strategies. This webinar will feature a panel of experts from around the region and there will be plenty of time for questions regarding this and other pests affecting cool-season production.

If you are interested in attending the event, register here: https://extension.unh.edu/event/2021/12/cutworms-tunnel-vegetables-other-cool-season-production-issues

Protected culture fertility survey!

Growing crops under cover is a separate skillset compared to growing under the open sky.  Fertility management, integrated pest management, environmental management are all very different.  Last year a survey went out to find out more about the protected culture industry in Nova Scotia.  To drill deeper on the learnings from that survey, Rosalie Gillis-Madden, Perennia's Vegetable Specialist, Talia Plaskett, Perennia's Protected Crop Specialist, and Caitlin McCavour, Perennia's new Soil Specialist would like to identify where there are knowledge gaps and pain points in protected crop production, specifically targeting fertility management.  Our goal is to determine where outreach and support might help the industry move forward and how we might serve you better.  This applies to growers who grow in soil or in substrate, who use conventional fertility or organic nutrient sources (composts, manures, organic fertilizer, etc.)  Please take the time to complete this survey to help us determine how we might best support growers, it should take you about 10 minutes to complete.

The mission of Perennia is to help farmers, fishers, and food processors be prosperous and profitable.

Creating a Balance : Vegetative vs Generative Growth

Part 2 - It's All in Your Water

There are many factors that play a role in managing vegetative and generative growth, and it is important to consider a well-rounded approach when attempting to swing the scales. Keeping a balanced growing environment is important for a highly productive plant and changing one thing and nothing else will end up causing more harm than good.

In part 1 of this mini-series, we addressed the need for vegetative growth to have a high yielding crop. Vegetative action is required early in the crop cycle so the plants can establish themselves. By creating this strong base, the plant will be able to support a highly productive generative state later on.

The generative growth phase focuses on managing plant productivity. It is achieved through strategic stress induction in your plants. These minor stresses are going to push the plant to divert resources to reproductive organs (fruits), while ensuring that all other plant processes can be maintained. The key word here is minor – pushing the plant too far is not going to have the response you are looking for.

How Do I Manipulate the Plant?

A few of the major contributing factors to vegetative and generative growth are listed here below. We will address the impact that each factor has on crop steering.

•        Water availability
•        EC
•        Day/Night temperatures
•        Vapour Pressure Deficit (VPD)
•        Pruning
•        Fruit load

Water Availability

Watering frequency, duration and timing plays a role in pushing the plant towards a more vegetative or generative state.

In vegetative action, water is readily available for the plant when it needs it. The plant does not have to work hard to uptake water and will readily create new above- and below-ground biomass. As roots and leaves are being produced, the plant is preparing for full-blown production. Higher water content in the substrate is achieved through small, frequent irrigation events throughout the day.

Once it is time to switch to generative growth, these watering events become longer and more infrequent. As water becomes less available, less energy is put towards the production of root and shoot material, and more will be diverted to fruit production. The plant will now have to actively seek water compared to it being readily available in the vegetative stage.

Figure 1. Depicted here is the general irrigation strategy for substrate-grown greenhouse crops (ex. Tomato). Water content (WC) is depicted in green. While the timing and frequency of watering for generative and vegetative phases will vary, the general concept applies. As the day ramps up, you slowly increase the amount of water you deliver to the crop. After you achieve first run-off, you can start hitting the crop with water at regular intervals (determined, in part, by the weather that day). As the end of the day approaches, irrigation stops all together. Photo credit: Greenhouse Canada, June 2010 (https://www.greenhousecanada.com/september-2010-2418/)

While the daytime irrigation strategy is important in crop steering, you must also consider what is happening through the night. The length of the dry-down period of your growing media will help to tip the scales towards vegetative or generative tendencies. A short dry-down period (usually achieved by scheduling the last irrigation event of the day 1-2 hours before sunset) encourages vegetative growth. A longer dry-down period (which would have the last irrigation event happening earlier in the day) will encourage generative tendencies.

EC Measurement

The electrical conductivity (EC) of your fertilizer solution is important to consider when encouraging vegetative or generative action. EC is an indication of the salt content in the solution and will therefore impact water availability to the plant. A higher EC value means a higher salt content, and the harder the plant must work to take up water. As the plant works harder to take up water, less resources will be sent to vegetative growth (leaves, roots) and more will be sent to the generative tissue.

Here is a rough guideline of where your target EC should be, based on the crop stage:

Plant Stage	Target EC
Germination (vegetative)	0 - 1
Plant raising (vegetative)	2.5 – 3
Harvesting (generative)	2.75 – 3.5*
Full harvest (generative)	2.75 – 4*

*Should be watering with an EC of around 3, but you will see a higher substrate EC as the salts accumulate in the grow media

Understanding how your watering habits sway the crop in one direction or the other is a good starting point. Irrigation is something that all protected producers have control over, and it is important to see that watering plays a huge role in plant phenology and overall production capacity.

Creating a system that encourages maximum production capacity is in everyone’s best interest, and it is extremely important that all factors are addressed when trying to push for a more generative crop. Adjusting the watering and EC alone are not going to be enough to hit the target yield. All plant processes are intertwined and should be carefully considered whenever adjustments are made.

Stay tuned for our next post on vegetative vs generative growth, which looks at the role of temperature and humidity in crop steering.

Posted by: Talia Plaskett

Creating a Balance: Vegetative vs Generative Growth

Part 1 - Setting the stage 

Most greenhouse vegetable producers will have come across vegetative versus generative growth in their vine crops (tomato, pepper, cucumber). Over the next few weeks, we will be exploring the differences between the two types of growth, what they look like, and how we can manipulate the plants to encourage one form of growth over the other. This information will be focused on tomato production, but it is important to note that the same concepts apply to other crops.

Vegetative growth is characterized by:

• Thick stems
• Lots of leaves and suckers
•  Leaves are long and can be twisted/curled
• Dense growing tip
• High density of leaves
• Small fruit
• Elongated fruit truss

The plant is putting most of its energy towards the production of plant material. While leaves are important for photosynthesis, tipping the balance towards a more vegetative state does not leave enough energy being diverted towards fruit production. The size and quality of the fruit coming off a vegetative plant will be significantly less than what you would want.

Figure 1. An image of an overly vegetative tomato plant. Notice the thickness of the stem, the high density of plant material, and the curling of the leaves. Photo credit: Government of Alberta, Tomato plant propagation in commercial greenhouse tomato production (https://www.alberta.ca/tomato-plant-propagation-in-commercial-greenhouse-tomato-production.aspx)

Generative growth is characterized by:

•       Thin stems
•       Fewer leaves, typically shorter in length
•       Good sized fruit
•       Slight purple tinge to the growing tip

These features indicate that the plant is putting most of its resources towards fruit production. While we want to see generative growth, it is possible to tip the balance too far. A plant that is overly generative, will not have the leaf resources available to power plant growth. Overly thin stems with few leaves will not be able to support a high fruit load, and the resulting fruit will not be of market quality.

 

Figure 2. A tomato plant that is growing generatively. Notice that the stem is significantly thinner here compared to Figure 1. The leaves are much less densely packed, and the leaves are not curling excessively. Photo credit: Talia Plaskett, Perennia.

Production of greenhouse crops requires both types of growth for optimum production. The act of rooting after transplant is considered vegetative. You want to encourage the plant to establish a good strong base in the growing media, so that it can support the plant through the growing season, and push for high yields. After a certain point, you want to start pushing the plants to a more generative state. This will encourage more fruit, and of a higher quality as well.

How do I know where I stand?

Designate one or more areas within the greenhouse as being your primary monitoring spot. This area should be representative of the growing conditions in that space – many growers will choose the centre of the tunnel/greenhouse, and pair this with the location where they are collecting information on drain EC/pH and slab weight. Each production space should be considered its own entity, as temperature, humidity, air circulation etc. will vary between bays despite our best efforts.

Within this monitoring block, a series of measurements should be taken weekly. Things like stem width (measured below the youngest flower cluster with an open flower), internode length, leaf length, weekly growth, and number of leaves/clusters will let you know how the crop is doing. Keeping this information on record will help you get an idea of how your interventions paid off, and generally how the crop is doing. These measurements can also be used to forecast future yields and therefore what will be available for retail.

Soil Salinity in High Tunnels

Drought stress on tomato leaves. Soil salinity can cause
increased susceptibility to drought stress in plants. 
Photo: Long Island Horticultural Research & Extension Center

Soil salinity can occur in high tunnel production due to some of the characteristics unique to this type of growing system. High tunnels are often used as a season extension tool, meaning that they are in production for a longer period of time and managed more intensively than a typical field. This management can include fertilizer applications, irrigation, and heavy traffic leading to compaction and poor drainage, all of which contribute to salt buildup in the soil.

The other major difference between tunnel and field production with an impact on soil salinity is that the ground under tunnels is protected from the elements, most notably precipitation. In a field situation salts would have more opportunity to be flushed through the system by rainfall, while tunnels aren’t able to take advantage of this type of natural cleansing. 

Soil salinity is a concern for a number of reasons including that plants in saline soils are more susceptible to water stress, which is particularly prevalent in a year with so little excess water around anyway. Saline soils can also lead to salt injury in plants and adverse affects on soil structure. It is important to monitor the salt levels of your soil and take preventative measures to avoid excess buildup. Some strategies for preventing or managing saline soils include utilizing mulch to reduce evaporation from the soil, deep tillage, and exposing the soil to rain by removing the plastic from the tunnel. As you start to think about coming to the end of the production cycle, it might be a good time to employ some of these strategies or plan preventative measures for next season.

For more information, check out Perennia’s factsheet: Soil Salinity in Nova Scotia High Tunnels.

Late Summer Scouting and Beneficial Insect Release

 As the air starts to move away from the heat of the summer and into cooler fall temperatures, it’s important to continue scouting your high tunnels and greenhouses for insect pests. Although the days for your crop may be numbered, many insect pests overwinter in the ground or in the debris in and around the growing space as a part of their life cycle. The more insects that overwinter successfully, the higher your pest pressure will be on next year's crop. Once pests start slowing down and hiding away for the colder months, the window of opportunity for controlling these pests closes. Beneficial insects typically do not survive the winter months, so planning to release them late summer can help to reduce pest populations while they are still active and reduce their population sizes for the following spring. For those pests that do remain active in the colder weather, it is important to keep those numbers low in the fall to limit pest pressures throughout the colder months. 

During the harvest season, it can be difficult to maintain a scouting program due to the sheer volume of work to be done on any given day. However, it is important to remember that the early days of a new crop are critical, and ensuring your plants have every advantage they can get is crucial to a successful and high yielding season. Taking that extra time to scout and release beneficials will pay off in the long run and mean less headache in the coming year.  

Cornell University Extension in New York conducted on-farm applied research on Aphid Management in Winter Tunnel Greens which offers some practical insights into late season integrated pest management.