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MARCH - APRIL 2019 Volume 16 No 2

I  I R40.00


crop production



Starting with Cannabis Page 4

Calcium Explained Page 8

Heat Storage Page 16

Zen of Peppers Page 18

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PROPRIETOR I ADVERTISING SUZANNE OOSTHUIZEN 012-543 0880 I 082 832 1604 EDITORIAL CONTENT & COMPILATION Johan Swiegers 082 882 7023 ADDRESS PO Box 759, Montana Park 0159 E-MAIL FAX 086 518 3430 ADDRESS PO Box 759, Montana Park 0159 DESIGN Fréda Prinsloo PRINTING Business Print Centre DISCLAIMER Undercover Farming accepts no responsibility for claims made in advertisements or for opinions and recommendations expressed by individuals or any other body or organisation in articles published in Undercover Farming. COPYRIGHT Copyright is reserved and the content may only be reproduced with the consent of the Editor. Subscription Online subs: Email to If you subscribe on-line, e-mail your deposit and address details to: More information from Suzannne Oosthuizen: 012-543 0880. Subscription form available on inside back page. visit us at I besoek ons by

Contents 4 5

Starting with cannabis in a greenhouse


Economies of scale in the production of Cannabis by a greenhouse grower


Calcium – how does it affect your plant and your harvest?

Bio leaf technologies (Pty) Ltd: your partner in high end growing solutions for cannabis

FRONT PAGE: Starting with cannabis in a greenhouse. See pages 4 & 6.


9 Getting rid of Fusarium 10 Undercover Farming Expo ’19 – an overview 10 Aquaculture: The importance of pH management 10 Vegtech road show 12 DIS-EASE: Understanding the signs and symptoms of


stressed plants

14 What causes inner-leaf tip-burn on lettuce? 16 Heat storage for greenhouses 18 The zen of greenhouse peppers 19 Subscription form




ew trends in the greenhouse industry jump up every now and then. The much abused cannabis and criminalities around it are seemingly being buried to a certain extent although licencing and law still abides in most countries. In South Africa law states one can now grow cannibis on your private premises. Will this reduce

cannabis selling underhand on streets by drug lords? Time will tell. For the greenhouse industry in South Africa this is a new avenue to follow in producing an alternative crop which do not appear on the regular markets but is sold to specific companies manufacturing pharmaceutical

from the SCRIPTUREs

An Easter Scripture “He (Jesus) was pierced for our transgressions, He was crushed for our iniquities; the punishment that brought us peace was upon Him and by His wounds we are healed.” Isaiah 53:5

or biological medicine. In this edition we have some information to introduce the reader to the basic concept of cannibis growing, what it takes and the economics of it. The recent Undercover Farming Conference held at the CSIR Conference centre in Pretoria went very well again and just shows there is still an increasing interest in undercover farming in southern Africa. Representatives from Kenya, Malawi, Namibia, and even as far as Iran attended the conference and exhibitors. We are proud of our industry at the tip of Africa but would like to see a higher percentage of investment in the trade by government and public investors. New techniques and advanced technologies are heard of continuously which opens the industry to investors with modern thinking and less risk. Allthough this comes at high cost initially, as it goes with economics, these input costs may hopefully drop as demand excells. We all hold thumbs for the outcome of the forthcoming elections and prayerfull hope it will result in new aspirations to increase business and agricultural opportunities for our country and therefore job opportunies for the many un-employed. Winter is creeping up on us and we should be looking hard at our greenhouse heating expenses but not at the cost of shrinking our outputs in produce. Ed.

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Starting with cannabis in a greenhouse There are some aspects of greenhouse construction that most prospective cannabis growers will want to include to provide the best environment for their crop.


ood advice is, that with any greenhouse design, it is important to keep the end purpose in mind right from the start. Greenhouses are built to provide your crop, whatever it is, with the ideal growing environment. If you are growing annuals or perennials you may need to build some flexibility in your greenhouse design to accommodate different plants with different climatic needs. If you are only growing tomatoes, your greenhouse can be designed built to focus entirely on maximizing production efficiencies and yield of that plant. Cannabis is a controlled substance, so assuming you have jumped through all the regulatory hoops to be awarded one of the coveted cultivation licenses, it is unlikely that your cannabis greenhouse will grow any plants outside the cannabis family. Thus, for growing cannabis plants, you want to focus on the ideal environment for cannabis. The 4 Stages of Growth for Cannabis Production Affect How You Zone Your Greenhouse Zone 1: Cannabis mother plants Zone 2: Cannabis clones (cuttings) Zone 3: Cannabis in the vegetative stage Zone 4: Cannabis in the flower stage Plan for Expansion from the Start If you are already growing crops successfully in a greenhouse, it is easy to focus your cannabis business energies on the crop growing side. But losing sight of this as a whole new business with different customers and different distribution channels will get you in trouble. Start your cannabis greenhouse

sized for your near future customer demands but with scalability in mind to accommodate your longer- term business goals. A little extra time at the beginning can save you months of headaches and additional costs down the road. Balance Production Efficiencies Cannabis growers are used to growing in smaller spaces than most commercial growers. Greenhouse structures and modern horticultural growing technology offer enormous production benefits compared to typical indoor growing. But where large zones increase production efficiency, they also increase crop risk from disease or infestation spreading. When you consider the monetary value of your cannabis crop, and possibly the medical imperative of providing consistent medication to your patients, there is a reasonable trade-off between production scale zones and isolation segmenting. Zone segmentation can easily be achieved with inside gable walls and sidewalls, a properly designed greenhouse heating and cooling system and good environmental controls. Blackout curtains (also known as light deprivation screens), irrigation, and fertigation systems are all designed by greenhouse industry experts to be centrally controlled for multiple zones.

Building the Ideal Environment 1. Geographic location. Importantly, not all greenhouse manufacturers or cannabis growing consultants have experience in different geographical locations. Many people will try and sell you the greenhouse that has been successful elsewhere, but you

Cannabis grown in perfect greenhouse conditions

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have to obtain information from different companies to decide which greenhouse system will best suit your production site. Your outside temperature fluctuations, wind speeds, humidity levels, rainfall and light levels all factor into what equipment and the style of structure that is best for you and your crop. 2. Inside greenhouse temperature. Cannabis like many crops likes different temperatures at different stages of growth. As a generalization you want your greenhouse temperatures between 18.5 to 29.5°C. Your greenhouse heating and cooling systems need to consider the temperature needs and controls for each zone. Inexperienced consultants may tell you that you don’t need as much heating because the lights generate a lot of heat, but as you will see in the sections below, cannabis typically wants only 18 or 12 hours of light, so your coldest night time temperatures will still typically have no lights on at all. 3. Managing humidity inside a cannabis greenhouse. We all know the effects humidity has on plants. Too much, and you invite disease, too little and you dry out the plant and hinder growth. As with any crop, knowing the humidity that the plant thrives in is important when designing a greenhouse. While cannabis in the vegetative stage actually likes a higher humidity level, it prefers lower humidity when in flower. Greenhouse manufacturers who understand this can help you build flexibility into your greenhouse designs. There are several dehumidification units on the market, and for areas needing the ability to add humidity misting systems can be added into the greenhouse design. 4. Ventilation recommendations for greenhouses tie into temperature and humidity needs. Greenhouse ventilation breaks down into two main categories: 1) natural ventilation covers roof vents, sidewall vents and rollup sides, and 2) forced air ventilation requires mechanical systems like exhaust fans, and sometimes cooling pads. Please note that cooling pads are not a good option for high 6

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BIO LEAF TECHNOLOGIES (PTY) LTD: YOUR PARTNER IN HIGH END GROWING SOLUTIONS FOR CANNABIS Our passion is to grow; Bio Leaf Technologies is on a continuous drive to constantly and responsibly improve and provide innovative products suitable for the agricultural sector with specific emphasis on the Cannabis growing sector. Our focus is about providing niche products with the Cannabis industry in mind, which will ultimately assist and enable all Cannabis growers and enthusiasts, in producing quality products. Bio Leaf Technologies is an accountable company that is very much aligned with Medical Standards and is therefore uniquely positioned to provide products that are suitable for use in a Medically Graded facility. Bio Leaf Technologies is the first and only company within South Africa who has developed a niche platform of products to achieve and emulate suitable conditions for the growing of Cannabis.


urrently, our business focuses primarily on four sectors within the Cannabis market: 1. Specialized Soilless Medium 2. Grow Lights (HID & LED) 3. Consultancy

SPECIALIZED GROWING MEDIUM Our growing medium products been developed specifically for various applications. Our very specific MCG Growing Medium has been developed over the years, together with Cannabis growers in order to provide, what we feel is the best specialized growing medium available in the market today. The general composition of our soilless medium includes perlite and coco peat. Our growing mediums are manufactured to strict quality standards at our ISO 9001 certified production facility.

Our products meet the requirements for growing products of food and medical grade usage. Each batch is laboratory tested to ensure consistent quality and pH to give you complete peace of mind as a grower.

GROW LIGHTS (HIGH INTENSITY DISCHARGE & LED) We are the sole distribution agents for Luxx Lighting (HID) and I-Grows (LED) within South Africa. Both products have be designed and developed by cannabis growers for cannabis growers. Our Luxx Lighting partners are associated with some of the best Cannabis growers in California “The Jungle Boys” whilst our I-grows LED partner have a massive footprint in Switzerland’s indoor commercial CBD Growing facilities.

Our offering includes: 1000w HPS DE Unit and 630w CMH Unit • NX1 Controller (Digital) Both units are the best in class when it comes to Vegetative and Flowering stages. The 1000w DE unit in particular has shown a 24% increase in PPFD readings compared to is closest competitor within SA. This will ultimately lead to substantially better yields. The same unit is also well suited in providing the best form of supplemental lighting within the greenhouse environment.

CONSULTANCY For more information, please feel free to visit our website or contact Guy Young on 083 251 333.

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Economies of scale in the production of

Cannabis by a greenhouse grower

Economies of scale is a term used to describe decreasing average cost of production (for example, the cost of producing a kilogram of cannabis) as a grower’s total output increases. It furthermore prevails if unit costs fall as output increases (if the elasticity of costs with respect to the grower’s output is less than one).


conomies of scale might be realized either if there are diminishing marginal costs or if there are fixed costs of production (fixed costs such as capital equipment and plant construction are spread over a larger scale of output). Economies of scale might also result from improvements in organizational structure, productivity gains from labour specialization (with a higher output, workers can specialize more narrowly on specific tasks that they may 7 Starting with cannabis in a greenhouse

The small cannabis greenhouse operator.


A typical commercial Cannabis production facility for pharmaceutical markets

humidity regions. In addition to ventilation to remove hot air from inside the greenhouse, most greenhouse growers put airflow fans inside the greenhouse to circulate air movement which is good for keeping healthy plants. Greenhouse manufacturers can provide you with a greenhouse plan layout showing fan locations that optimize airflow coverage. 5. Adjusting lighting levels will increase yields in a cannabis greenhouse. One of the biggest advantages that greenhouse growing offers over indoor growing is that greenhouse plants benefit from natural sunlight. Not only does sunlight naturally provide the plants what they need to

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grow, it doesn’t cost the grower any money to power. Having said that, when cannabis is in the vegetative state it performs best with around 18 hours of light. For this reason we recommend greenhouse growers include supplemental lighting in their cannabis greenhouse plan. Make sure your greenhouse lighting plans satisfy year-round production if you want to optimize yields. 6. Flowering cannabis needs blackout. While the vegetative stage enjoys greater light levels, for flowering longer periods of darkness are desired. Ensuring 12 hours of uninterrupted darkness inside your greenhouse will force the marijuana plants to flower according to your

production schedule. This is best achieved by utilizing blackout curtain technology, also known as light deprivation in the cannabis industry. Blackout has been commonly used in production greenhouses for decades for poinsettias, kalanchoes, chrysanthemums and other crops that benefit from photoperiod adjustments. Blackout curtains can cover flat roof areas running truss to truss on gutter connected greenhouses, or they can be sloped to follow the roof line of freestanding greenhouses. Remember to cover sidewalls and door openings, and use light traps for exhaust fans as well. 7. Cannabis plants thrive with CO2 enrichment. If you are using a hot water heating system CO2 can be pulled off the boiler. In other situations you may wish to use liquid CO2 to dose your cannabis crop. This is an area best discussed with greenhouse heating experts. Additional considerations include connecting your greenhouse to warehouse and office facilities for packaging, shipping, and other support functions. There are other unique requirements for cannabis that you will not have encountered with as in typical horticultural crops, such as drying rooms and vaults. Work with a company that has the expertise on cannabis production to help you – and ask for references!

economies of scale


better perform than if they devoted only a small share of their time to that task), and technology improvements. According to authorities on the subject of cannibis production, organized crime groups are running networks of houses and overseeing high-quality operations in terms of lighting, ballasts, layout, etc. These groups are employing professional electricians, greenhouse staff and at each step, as compared with the medical access point’s providers who appear less sophisticated by comparison, with many doing their own construction and design (the consequence being a less sophisticated set-up). Few of these are actually economically viable because of their lower production versus income, notwithstanding their expense on labour and input costs. Even today’s small producers might want to hire the ‘professionals’ currently employed by organized crime groups, if they dare to risk their businesses and lives in turning to these for help. Although much focus is put on internal economies of scale (the change in costs a grower would experience because of an increase in his output) – cannabis growers may also benefit from external economies of scale. This in which increases in the output of an entire industry’s produce marginal cost savings of the total industry, against decreasing the average costs of production for many businesses all at once. External economies of scale exist if growers benefit from being close to other growers. These take the form of labour pooling, sharing common assets, better availability of intermediate inputs, and sharing know-how. An important external effect for growers might be shared enforcement risk (governmental enforcement is more difficult as the number of growers increases). For some external economies of scale, it does not matter whether growers can communicate (e.g., for enforcement swamping) but for other external

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A commercial outfit with modern technology in place.

for policies intended to mitigate those economies. What may matter is not outcomes. only the total number of growers in the area, but also the ability of those growers Another reason to pay attention to to trade information, expertise, share economies of scale is that they affect suppliers, etc. the severity of the legalization-induced If economies of If economies of scale are price decline, which in scale are present, present, estimating the turn affects regulators’ estimating the magnitude of the scale ability to drive the magnitude of effects is important for illegal market out the scale effects informing decisions of business as well is important for regarding the optimal as combat likely informing decisions number of licenses to issue. associated increases in regarding the use and abuse. optimal number of licenses to issue. If the economies of scale From a study on the economic viability of are very large, and persist indefinitely producing cannabis in greenhouses by Botec for larger and larger operating scales, Analysis Corporation. then growers producing at a large scale might exclude smallscale farmers from successfully competing. Economies of scale therefore have implications for the number (and size) of growers that would be feasible in an unregulated market. This has implications for costs, price, product variety, and regulatory burden. Strong eco­nomies of scale would favour large growers, an oligopolistic market structure, and concentrated production; accordingly, they may strengthen the arguments

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Calcium – how does it affect your

plant and your harvest?

Calcium is probably the most intricate component a greenhouse grower has to contend with in crop production. Difference in advice leads the grower often down the wrong track and he may lose crop; which he cannot afford. This is a summary of Lindi Grobler of Agri-Alchemi’s talk on Calcium at the recent Undercover Farming Conference in Pretoria.


alcium is a mineral and when looked at under a microscope, is made up of multi layers of almost block form particles. This substance in its usage form must be kept in dry containers which are air-tight as moisture can deplete its function. It is estimated that 3.7 to 6% of the Earth contains Calcium. The human being contains 1.5 % Calcium in his body of which about 90% is located in the skeleton. In our soils, Calcium is adsorbed into the clay complex and therefor higher in clay-type soil as in sandy soils. Calcium in a carbonate form will change the pH of the soil – depending on the type of soil and availability, it could add to the plant’s quality or withold vigour. The optimal position to be in as a producer, is to balance out your particular crop’s needs with the correct percentage of Calcium versus Potassium and Magnesium depending on the soil’s composition. In greenhouse grow media, the different media or mixes thereof calls for a different approach of application percentages to optimise adsorption of Calcium by plants. A lack of Calcium in the water supply may be detected when for instance dishwashing liquid does not foam when poured into the kitchen sink or a lack of precipitates in kettles or on windows. This is a simple example of detecting low Calcium concentrate. Plants by nature have difficulty in take-up of Calcium and when it adsorps too little Calcium, plant deficiencies like blossomend rot is visible for instance on the underside of tomatoes or sweet peppers. Often these occurences are mistaken as sunburn but if it was caused by sunburn, the spots would have been at the top of the fruit. This lack of Calcium disease is also visible on lettuce with tip-burn and cucumbers with umbrella scores. Calcium is taken up by the root system and continues up in the plant through the xylem structure, but then at the

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of obtaining Calcium in the fruitset areas apex of the xylem it is dropped where of the plant works well, but again, only it is without translocation downwards with careful management. in the phloem of the plant. This then causes Calcium deficiency. A very small Another way of getting Calcium to its percentage of the Calcium that is in the destination is by alleviating stress in the downward trend remains in the cell walls plant. The DNA chain in a plant consists of the plant but it is actually needed in the of amino-acids and protein and the fruit production parts of the plant. moment the chain is broken, the plant goes into stress. Limited transpiration The mission of the farmer is to get the in higher or lower than required Calcium to move where it is destined temperature or cloudy and inclement to be – the fruit tips. Calcium though, weather are sure stress inducers in the is extremely affected by other elements plant. Calcium is then in severe lack. such as Potassium, Phosphate and There are a number of products on the Nitrogen due to nutrient antagons market which can be applied by foliar (Mulders chot). Therefor, if the producer spray to alleviate does not have the The mission of the farmer stress in the plant right fertigation mix and have Calcium for the different is to get the Calcium return to where it is plant types and to move where it is most needed. even varieties, he destined to be – the fruit will have to obtain There are two tips. Calcium though, is the information solutions which extremely affected by from his seedling the producer may other elements such as grower, seedsman utilise to alleviate or consultant as they Potassium, Phosphate and stress if he is not in are the ones who can a position to limit Nitrogen due to nutrient advise him to follow high temperature or antagons (Mulders chot). and to optimise the fear of application program. at night (which may cause downy or powdery mildew). One The farmer needs to understand the must realise that the healthier a plant basics of plant physiology to comprehend grows and the better it produces good how the different elements in his soil or quality fruit, the higher the Brix count grow medium and his water structure will be. If the Brix should be around 15 influences his particular crop and what he and the producer finds it to be at 5 or needs to apply in order to maximise plant below, he must immediately realise he and eventually fruit set, quality and yield. has a Calcium deficit problem and act Temperature and humidity plays a major accordingly. role in Calcium flow in the plant in a The simple piece of equipment required greenhouse. The movement of Calcium to establish Brix on your plant is readily is controlled by environmental conditions available. Brix count in greens should and the farmer in a greenhouse can be between 8 to 10 but in berries manage this by climate control. Care and fruit rise towards 15 to 18 Brix. must be taken when foliage application is The message is thus clear – the higher done at nighttime as the temperature and the Brix in the plant, the higher the humudity of the plant and the greenhouse Calcium concentration in the plant and must be absolutely correct. The droplet subsequently a much healthier crop. size of spray is crucial – if Calcium or Farmers can Google ‘Brix on crops’ and foliar feed or irrigation is applied wrong in find the ideal Brix count for his crop. balance with the aforementioned, disaster may strike. The system must be fineThe pH measure of the plant is 6.4 to tuned to manage this application. This way be healthy and productive. If the 9

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Getting rid of


Fusarium causes a lot of greenhouse growers headaches. The fungus ensures that crops such as lettuce, tomato or phalaenopsis become ill or even die. Fusarium can be controlled with plant protection products, but the number of authorized products is shrinking.


usarium is a pathogenic fungus and can cause damage both above and below ground. Fusarium rot affects roots of plants: vascular bundles get clogged by fungal growth and can no longer transport water and food. The result: the crop withers or even dies. Especially in the cultivation of lettuce this caused many problems in recent years. Contaminated soil or substrate must therefore be properly disinfected. Two solutions have often been applied to a Fusarium infection: removing diseased calcium

plants or using chemicals. The latter solution is becoming increasingly difficult: due to stricter legislation fewer chemicals are permitted, Fusarium is becoming more resistant to some drugs and there are many different variants of the fungus. In addition, the use of chemical agents in the vegetable industry encounters

Healthy Lisianthus

objections in society. It is therefor high time for proper alternatives. That is also the opinion of growers of lisianthus and phalaenopsis. The University of Wageningen has started with research trials on Lisianthus and phalaenopsis. Three routes are being examined. 13


score is lower, the plant under-produces. The EC of the plant should also be taken into consideration. These tests should be kept record of for future cropping purposes. However, over and above pH or EC, the Brix count is the most telling whether the plant transmits ample Calcium via the roots to the fruitset destination. If it is found that the Brix is higher and the pH lower, the producer must backtrack his actions to find where and when the change happened and why. The necessary rectifications should be made immediately. Calcium needs in various plants also vary from area to area, variety to variety, season to season; therefor the producer needs to aquire the program which suits his needs in every aspect to obtain optimum produce at the least possible loss through poor Calcium management in his plants. Looking at the environment of the plant is of utmost importance. If only one part or row of plants are affected, treat them accordingly and only them. For one it will reduce treatment cost and on the other hand inhibits unnecessary negative environmental influences. Plant transpiration is the basics at the end. If one finds it hot, cloudy or any quick environmental changes outside the greenhouse, be reminded what the plant experiences inside the greenhouse and go and check whether all programs are in place to keep stress away from your production system. As far as Calcium is considered, Lindi advises farmers to live close to their plants as there are so many variables that can go wrong if the producer does not beforehand find the correct program for his particular situation in order to avoid mostly unneccesary losses. Lindi may be contacted for her advisory services at

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Undercover Farming Expo & Conference “The focus set for the 2019 event was on the quality of technology with which greenhouse producers in Southern Africa run their operations successfully and their continuous expansion. With an ever drier climate every year, the focus on water conservation and increasing yield by employing latest technologies, the Undercover Farming Expo & Conference 2019 once more offered a high level of exhibitor occupancy as well as a most interesting speaker portfolio,” reported the Director and organiser, Suzanne Oosthuizen.


he Undercover Farming Expo & Conference was presented from 06 to 07 March 2019 at the CSIR International Convention Centre, Pretoria. Looking back over the past event, the loyal exhibitors are satisfied with the business opportunities and delegates with the quality of speakers over and above the ample time allowed for networking with professionals in the trade which again


this year, was a great success. “Our registered delegates for the conference was 165, of which 100 was small commercial farmers. The Day visitor registrations and ‘walk-ins’ at the conference totalled 1 230 visitors, which included high profile visitors such as the High Commission of Iran, The Agricultural Counsellor of the Netherlands and the Trade Commission of Israel.

“Undercover Farming management received tremendous positive feedback and most exhibitors ordered their floor space for the next event before they left the premises,” Suzanne said. The speakers shared in-depth knowledge not only of the industry, but specifically about Southern Africa’s hydroponics industry’s progress at the 2019 Conference. Speakers that presented this year were:

The importance of pH management

Effective water quality management is at the very heart of successful aquaculture, most especially in recirculating aquaculture systems (RAS). We know the story: we feed the fish, they digest the feed and give off ammonia which is toxic and would accumulate in the RAS if not dealt with.


acteria in the biofilter convert this poisonous ammonia to benign nitrate, enabling recirculation to continue without the fish health being negatively affected. In this manner the toxic ammonia is managed, but there are many subtle aspects to this equation that are perhaps not as well understood yet are equally important, such as the impact of pH. When bacteria break down the ammonia and nitrite into nitrate the process gives

off hydrogen ions which in turn consume alkalinity (carbonates and bicarbonates in the water). If the availability of free alkalinity in the system is compromised, then the hydrogen ions accumulate, causing the pH to lower and become acidic. pH is simply a measure of hydrogen ions in water; the scale is negative, so a low reading means there are more hydrogen ions present and it is indicated on a scale of 1-14 where 7 is neutral, less than 7 acidic and greater than 7 basic.

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The ideal pH range for freshwater fish farming is 6.5 – 8.0, with 7.5 – 7.8 being the sweet spot for most species. As always, fry are more sensitive than adults of the same species to absolute and fluctuating pH levels. Few water quality parameters are as poorly understood as pH, causing many people to shy away from measuring and managing it. This is a mistake as the pH directly affects the bacteria in the biofilter as well as the fish themselves – see the table: 11

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2019 – An Overview Kleinskuur Farm – Colin Bremner Aquaponics – The sum of aquaculture and hydroponics – Building blocks of a business Agri-Alchemi – Lindi Grobler Calcium – the problematic nutrient Green Terrace – CEO: Mbali Nwoko From city girl to farmer – the Mbali Nwoko journey Green Meds – Gail Pedra Cannabis Farming in South Africa & Africa APAC – Francois Knowles Regulation in turbulent times Pratley South Africa – Eldon Kruger Perlite as growing medium Delphy South Africa – Herbert Stolker Re-use of run-off water in the greenhouse/tunnel industry Cherry Irrigation – Charles Cherry Irrigation principles in greenhouse production PlusNet – Deon Snyman Overview of Shade Netting and Shade Net Cover Construction Talborne Organics – Jenny Slabber Healthy, safe and sustainable organic options for the horticulture industry AgriLED – Theo Pistorius Undercover Farming: A disaster-relief and community rebuilding tool Mike Loutfie Foundation – Kholisa Ngalo Access to Fresh Produce Markets The event date for the 2020 Undercover Farming Conference will soon be set for March in the near future and all role-players, farmers and input providers in the industry will be notified in due time. The Undercover Farming Expo 2019 was yet another successful event due to the participation of industry leaders and Suzanne aptly conveyed her thanks on behalf of the industry and her company for all participants.

pH too low (<6.0) pH too high (>8.0) Biofilter bacteria Ammonia toxicity struggle Burns the skin High CO2 Increased metal toxicity ↑ Methaemoglobin Low pH has an antibacterial action, consequently, if the system pH is too low the bacteria in the biofilter struggle to convert the ammonia via nitrite to nitrate. If a lower pH is desirable, such as for aquaponics, then this can be overcome by using a larger biofilter to compensate for the slower bacterial activity. There is a complex equilibrium relationship between carbon dioxide, carbonic acid, carbonates and pH in water, but the essence of this is that a low pH results in the balance swinging towards increased

dissolved carbon dioxide levels. This in turn is stressful to the fish as it impairs heart and brain function, so it is important to ensure the pH levels are correct. The solubility of metals increases as pH decreases, making the metals more toxic to fish at lower concentrations. Similarly, a decrease in pH causes an increase in methaemoglobin which is inefficient at attaching to oxygen molecules, causing the fish to struggle to obtain sufficient oxygen from the water when the pH is depressed. High pH is less frequently problematic than lower pH, due to the natural fall of pH in a mature RAS. When it does occur, the high pH causes ammonia to become more toxic and the pH directly burns the skin of the fish. Within reason, fish do adapt to a pH that is stable, even if slightly outside the ideal range, so be cautious when raising the pH to increase the level

by no more than a maximum of 0.5 pH units per day. This takes a bit of practice as each system, feed type and buffer are subtly different, but we find that around 100g of buffer is required per kilogram of feed. Calcitic lime (builder’s lime) is very useful as a buffer as it is inexpensive, freely available, soluble and effective, whilst not having negative effects on the fish or downstream environment. Many other buffer options exist, but for fish farming this is our preferred choice. Given the importance of always maintaining the correct pH, I recommend measuring pH daily and adding buffer every time the pH drops below 7.0. Small amounts of buffer added as frequently as is required will assist in sustaining a healthy RAS for the fish and filter bacteria. By: Leslie Ter Morshuizen

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DIS-EASE: Understanding the signs and symptoms of stressed plants

Greenhouse producers need to find the cause of pest and disease attack on their crops to solve problems causing DIS-EASE or stress conditions rather than to spray chemicals season after season to deal with symptoms, without ever resolving the cause.

T 2.




\he most likely cause of pest and disease on plants are the following: 1. Incorrect watering – too much or too little, not adjusting for season and climate. Poor feeding practise – applying excess, or too little or not using the correct fertilizer balance for the plants requirements Soil structure and Aeration – sandy soil leeches water and fertilizer too quickly and heavy clay soils cause poor drainage and waterlogging. pH of soil – too low causes acidic soils and too high causes alkaline conditions, both extremes can inhibit uptake of nutrients. Plant positioning and grouping – high water requirement and low water plants grouped together.

INCORRECT WATERING Too little water, hot & dry conditions

transpiration which regulates plant temperature.

REMEDY SYMPTOMS Water more often, and for longer Powdery mildew, insect attack like mealy periods to ensure a reserve of water and bug, Australian bug, scale and red spider prevent plant stress. mite. Wilting leaves Add water retention and stems, eventual Plants are made mostly products and compost. death. dependant on water, Mulch soil surface. Plants are made and like all other living Too much water, hot mostly dependant creatures are absolutely & wet or cool & wet on water, and like all dependant on a regular conditions other living creatures and adequate supply are absolutely SYMPTOMS dependant on a of water which is Downy mildew, fungal regular and adequate disease like botrytis, essential for processes supply of water black spot, rust, root like hydration, carrying which is essential rots, damping off nutrients to all parts of for processes like disease and pests plant tissue, transpiration hydration, carrying like aphids and white nutrients to all parts which regulates plant fly. Dead or brown of plant tissue, leaf spots and temperature. 13

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healthy soil = healthy plants = healthy people 12 Undercover farming I March - April 2019 I Volume 16 No 2


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blotches, yellowing of leaves, leaf drop, collapse of plant and roots blacken and die off. Too much moisture leads to rotting and fungal disease. REMEDY Reduce watering in rainy periods, or in cooler months when less water is lost through transpiration (like people sweat to regulate body temperature) in leaves. Ensure adequate drainage in beds and pots. Add compost and water holding products to absorb and hold excess water.

POOR FERTILIZER PRACTISE Plants, like people, need a healthy balanced diet and an adequate supply of all essential major, minor and micronutrients to optimise performance. Many pests and disease conditions are caused by poor quality fertilizers that might be cheap but do not satisfy the full requirements of the plant, or it leaches out very easily with watering or rain, and the nutrients are only available for plant uptake while they pass the root zone. Therefore, very frequent re-applications of fertilizers are necessary to adequately feed the plant, or nutritional stress develops. Low nutrient levels or too rich and fast a supply can also bait in pests and cause disease. SYMPTOMS Plants deficient in nutrients have soft growth like drooping leaves and stems. Leaves that yellow, show mottled spots, interveinal patterns or scorched tips with reduced or no blooms and fruit. SYMPTOMS Excess or imbalanced fertilizers with high Nitrogen levels, result in fast and Getting rid of Fusarium

soft growth of leaves and stems that attract sucking pests such as Aphids and White fly. Excess phosphate can lock-up and block uptake of micronutrients essential for plant functions by disturbing the soil chemistry resulting in slow growth.

REMEDY Select quality organic fertilizers which contain the full spectrum of plant nutrients best suited for growth phase like planting for healthy root and plant structural development, or green leafy growth or to encourage flowering and fruiting. Compost or manure on their own are seldom nutritious enough to ensure healthy and productive plants in our low nutrient soils. SOIL STRUCTURE & AERATION Soil structure has a major effect on a plantâ&#x20AC;&#x2122;s resistance to stress and disease and ability to grow with vigor. Sandy soil structure: Water and nutrient retention is poor leading to plant stress. SYMPTOMS Plants droop and wilt easily, colour is sickly light green or yellow, deficiency symptoms on leaves, interveinal patterns and spots. Powdery mildew and wilting disease. Pests include red spider mites, aphids, scales, mealy and Australian bugs, ant activity. Tight clay structure: Poor root development and penetration into soil. SYMPTOMS Root rots cause collapse and death in plants. Crickets thrive in clay soils which release methane gas as they eat rotting roots and plant material. Oedema (lesions and cracked blisters


Fusarium oxysporum causing wilt in Eustoma grandiflorum.

on leaves often seen on brassica family) and cracked fruits such as tomatoes with waterlogging in soils where drainage is inadequate.

REMEDY Prepare soils well before planting by adding lots of compost, earthworm castings and water retention soil conditioners to improve soil structure, friability, water holding capacity and aeration to prevent disease and pest attack. ADJUST pH & SOIL CHEMISTRY Nothing grows well in soils that are excessively acid or alkaline, even plants that have a natural preference for either, like Rooibos, Protea and Blueberries that prefer slightly acidic soils and Mediterranean crops like Olives, Grapes and Lavender that like limey or alkaline soil conditions. Any extreme tends to lock -up nutrients which result in deficiency diseases. When pH is corrected the chemistry and nutrient uptake resumes, and the soil ecosystem is healthy and active. SYMPTOMS Unproductive plants, vulnerable to pest and disease. Excess weed pressure. REMEDY Condition soils with good quality compost. To remediate acid soils regular addition of Dolomitic lime will gradually change Ph. Adjust Alkaline soils by working in acidic compost or application of small quantities of elemental sulphur (also known as flowers of sulphur) at a time can be applied and leached into soil by watering. By Jenny Slabber of Talborne Organics

First of all the use of biological crop protection products to combat Fusarium. For this, use is made of resources that are already commercially available. The second route is to encourage the plant to defend itself better against the fungus by using so-called elicitors of induced resistance. And the third route focuses on soil resilience: can the soil be manipulated in such a way, for example by adding organic substances, that there is less chance of infection with Fusarium? The outcome will be published in a future edition of Undercover Farming. Meanwhile, this information will hopefully set the minds of the abovementioned flower types producers thinking about their greenhouse disciplines to combat Fusarium! The research is done by Dr MA Streminska

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What causes inner-leaf tip-burn on lettuce? Horticultural experts say not all nutritional problems are caused by supplying too much or too little of a certain nutrient. “Tip-burn” of inner leaves is a common problem in hydroponics lettuce, where the margins of the young emerging leaves develop necrosis and burn.


he necrosis is from a calcium deficiency, but the actual problem is more the result of poor en­vironmental conditions and water uptake. The lettuce receives an adequate supply of all plant essential nutrients in the hydroponic nutrient solution, yet you find in the centre of the head’s leaves tip-burn. Inner leaf tip-burn on lettuce appears as necrosis along leaf margins at the center of the head and is a physiological disorder involving calcium and water uptake. Calcium moves through plants passively and is carried with the flow of water. As plants transpire and take up water, calcium is essentially “pulled” up from the roots and throughout the plant. Rapid transpiration promotes calcium uptake and distribution within the plant. On the other hand, low trans­ piration rates decrease calcium uptake and transport. The growing tip of lettuce is enclosed by leaves that make up the lettuce “head,”

which block air movement and create a very humid micro-environment around the growing tip. This humid microenvironment results in low transpiration of the growing tip and reduces calcium transport to the new leaves, even if the outer leaves are transpiring adequately. With low transpiration to the growing tip, insufficient transport of calcium causes the tissue along the young leaf tips to collapse and turn necrotic as the leaves expand. In this scenario, the problem is not insufficient calcium supplied to the root zone, but a physiological disorder related to poor transpiration of water and humid environmental conditions. A similar type of physiological disorder occurs with fruiting crops such as tomato, cucumber, pepper, and eggplant, but is called “blossom end rot.” Fruits have relatively low transpiration rates, and under rapid fruit growth and swelling, localized calcium deficiency occurs at the base of the fruit. The collapsed plant tissue

Thediagram shows the effect of a downward-installed fan system on plants.

also turns necrotic and resembles rotting. Vertical airflow fans force air move­ ment directly down to the crop. Drought stress, high soluble salts, and chemical phytotoxicity can also cause leaf tip-burn in lettuce and other leafy greens. However, symptoms of The inner leaves of this lettuce head clearly these problems tend reveal burned tips. to occur on older and mature leaves, whereas inner solution is a strategy to increase leaf tip-burn from poor transpiration calcium concentrations directly and calcium transport occurs in young in plant tissues. A starting rate is expanding leaves within the head. 400ppm calcium mixed using Unfortunately, there is no way calcium chloride fertilizer salts (not to salvage necrotic leaf tissue. But calcium nitrate). Always trial on a few there are strategies growers can plants before the whole crop. This use to facilitate calcium uptake and strategy can be labour intensive and prevent inner leaf tipburn. Fertilize may leave residues on leaf surfaces, with adequate amounts of calcium. and is not often used in commercial First check that adequate calcium practice for lettuce. is supplied in the nutrient program. Low relative humidity and air move­ Supplying 40-50ppm of calcium in ment increase plant trans­piration and the applied fertilizer or hydroponic facilitate calcium uptake. Consider nutrient solution is a good starting manipulating the green­house heating point. and venting systems to dehumidify the Depending on the source, the raw air during cool and cloudy weather. irrigation water may also contain Increase use of horizontal and vertical calcium. Increasing calcium in airflow fans to improve air movement. the nutrient solution can help with Conditions that promote rapid plant calcium uptake and reduce inner leaf growth and leaf expansion promote tip-burn problems, but remember the inner leaf tip-burn, and shading/ real problem is more often related to cooling under excessively high light environmental conditions that affect and temperature conditions can help water transpiration. minimize risk. Avoid antagonistic Weekly foliar sprays with calcium effects from other fertilizer nutrients. High concentrations of ammonium nitro­­­gen, potassium, and magnesium in the nutrient solution can block calcium uptake by roots. Tips to prevent nutrient antagonisms include limiting ammonium to 15% of total supplied nitrogen and maintaining the ratio of calcium:potassium at approximately 1:2 and the ratio of calcium:magnesium at approximately 2:1 in the applied nutrient solution. Avoid high soluble salts. High soluble salts reduce the ability for plants to take up water and calcium. If possible, maintain root zone elec­ trical conductivity below 2.0 mS/cm. Select resistant varieties. Work with your seed supplier to select varieties specifically bred for lower susceptibility to inner leaf tipburn.

A vertically position fan has less direct effect on a lettuce plant.

14 Undercover farming I March - April 2019 I Volume 16 No 2

By: Ryan Dickson

foliar sprays


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Heat storage for greenhouses A relatively new concept to the greenhouse industry is to use hot water storage with alternate fuel (biomass) heating systems to limited cycling. Systems, such as wood, burn most efficiently if operated at a constant fire rate. Adding a large, insulated hot water buffer tank can store excess heat during the daytime operation to be used at night when the heat demand is the greatest.


eat storage tanks are also fairly common in operations that use their boiler system to generate CO2 during the day. Like the biomass system this hot water is stored for use when CO2 production isnâ&#x20AC;&#x2122;t required. Tanks with capacities of up to 1,000,000 litres are available. They are usually steel with an interior liner or anti-rust coating and heavy insulation on the outside. An exterior aluminium jacket protects the insulation. Most tanks are assembled on site. Design of these systems allows for a smaller boiler as the water storage carries part of the night time load. Typical design looks at the maximum heat needs for the coldest day. It also considers the maximum tank water temperature that can be achieved, the lowest water temperature that can be used and the storage period. Having a heat storage tank can also add piece of mind. In the case of a boiler failure a heat storage tank can supply 12-24 hours of hot water to sustain operation until repairs can be made. Heat can be stored for short periods of time as from day to night or for longer periods such as from summer to winter. Trees store energy for a century or more. Coal and oil store the sunâ&#x20AC;&#x2122;s energy for thousands of years. Several heat storage concepts can be used in greenhouses. Letâ&#x20AC;&#x2122;s look at a few of them.

An external storage tank saves the greenhouse operator on his heating expenses.

is effective only during the day and heat Daytime storage of heat is not normally needed at this time, for night time use storage of the heat is required to make Carbon dioxide can increase plant the system efficient. Large insulated growth. One of the by-products of water storage tanks are used to store the combustion of the heat for use fossil fuels is CO2. Carbon dioxide can at night. Capturing this from increase plant growth. In the greenhouse the flue gases and One of the by-products of industry the distributing it in the system is used the combustion of fossil greenhouse costs for water storage very little. As CO2 fuels is CO2. with alternate fuel heating systems with limited cycling. Matter such as wood and coal are most efficiently if operated at a constant fire rate. Adding a large, insulated water buffer tank can store excess heat during the daytime operation to be used at night when the heat demand is the greatest. This can reduce the size of the heating system needed. Tanks with capacities of 4 000 to over 200 000 litres are available. They are usually steel with an interior liner or anti-rust coating and a heavy insulation on the outside. An exterior metal jacket protects the insulation. Smaller tanks are delivered by


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Heat Storage for Greenhouses


truck. Larger tanks are assembled on site. Design of these systems allows for a smaller boiler as the water storage carries part of the night-time load. Typical design looks at the maximum heat needs for the coldest day. It also considers the maximum tank water temperature that can be achieved, the lowest water temperature that can be used and the storage period. Maximum water temperature is around 94ºC. The lowest temperature water for distribution in steel pipes or fin radiation is around 66ºC. A lower temperature water can be used if root zone heating system is installed. Storage period may be from one to two days. Typically storage capacity is one gallon per 200 – 300 Btu/hr of boiler heat capacity. For small growers with a good wood supply and a few plastic tunnels, an outdoor wood boiler may be a good alternate fuel source that will lower heating cost. These are available with capacities up to one million Btu/hr output. Installing a 12 000 to 15 000 litre insulated water tank can provide the buffer capacity needed to store excess heat for the night.

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storage below the greenhouse floor. Capturing excess A water tank or tank filled with wet greenhouse heat sand is the storage medium. The soil On bright, sunny days in the autumn, below the floor could also be used. winter and spring, there is usually excess Collection can be either from the excess heat that needs to be vented. Capturing heat in the greenhouse or from solar this heat for night-time use is a possibility. collectors. Recovery The amount of usable is through water Having a heat storage tank heat is approximately pipes or air ducts can also add piece of mind. 200 – 400 Btu/sq spaced throughout 30cm of floor area In the case of a boiler failure the storage area. depending on which a heat storage tank can This system can area in the country add considerable supply 12-24 hours of hot your greenhouse construction cost to water to sustain operation is located. For the greenhouse. until repairs can be made. example, a 9m x 30m When evaluating heat greenhouse could storage, the storage medium needs to be have from 600,000 to 1,200,000 Btu of considered. Heat capacity is measured as excess heat. It is a low degree heat with specific heat. Water has a specific heat of maximum temperature of about 32ºC. 1.0 Btu/sq 30cm - ºC, whereas concrete, Capturing and storing this heat is not crushed rock and sand are approximately easy. It could be collected with ducting 0.2 Btu/sq 30cm - ºC. On a volume basis, near the ridge and stored below the water holds about three times as much floor in a rock bed. It could also be heat as the concrete, rock and sand. collected with a heat exchanger and the Heat storage can provide a buffer that temperature increased with a heat pump. allows a smaller heating system to be It could then be stored in an insulated hot installed. Selection of the system and its water tank. The cost of the equipment size are important to making it economic. and operation may be prohibitive. An economic study should be done first. An external storage tank saves the Research in Europe and elsewhere has greenhouse operator on his heating been exploring the installation of heat expenses.

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The zen of greenhouse peppers Greenhouse peppers can be a challenging crop to grow. Once the plants establish a pattern of growth it can be difficult to manage them in another direction. For example, if the plants are strongly vegetative, it can take some time to direct the plants to be more generative, and vice versa. It is important to establish the proper balance in the plants as early as possible in order to set the stage for continuous, sustainable production and resulting high yields.


articular points of challenge with pepper production include setting and holding the first fruit. Fruit set is targeted at the second or third note above the fork where the plant breaks into two stems. The challenge here is that the young plant is generally strongly vegetative, a requirement for good establishment in the coco coir bag and eventual filling of fruit, and such plants tend to want to remain vegetative. By establishing the proper 24-hour average temperature of about 20 to 20.5°C with a day temperature of 21°C and a night temperature reaching 16 - 17°C and holding this regime, the plants will be directed to set and hold fruit. The next point of challenge is to have an adequate fruit load established on the stems before the first fruit are picked. If the first fruit set, and subsequent flowers do not set, when the first fruit are harvested, all the energy of the plant goes towards vegetative growth. The plants will “race” to the wire with a resulting significant loss of yield. Once a good balance is established in the plants, maintaining about 5 to 6 developing fruit per stem (10 - 12 fruit/plant) at all times with fruit taking approximately 7 weeks to mature, then the crop will likely stay in balance to the end of the season. This assumes no drastic changes in the management of the crop of course. As the season progresses it is important to pay close attention to the plants, the following are a few signals that the plants may exhibit and an explanation for what the signals indicate.

Flowers Flowers upward facing, weak The plant is too generative, reduce night temperature James Calpas to drop the 24 Alberta Agriculture hour average temperature by 1°C . This will direct the plant to be more vegetative. Weak flowers usually occur during the

summer months, although they can show up earlier if the greenhouse is run too warm. James Calpas Alberta Flowers large, bullish, Agriculture thick peduncles, flowers opening downward - The plant is too vegetative. Raise the night temperature Normal flowers, the Zen state. to bring the 24-hour average James Calpas Alberta temperature up Peduncle Agriculture by 1 or 1.5°C. The fruit from these large flowers often abort or are deformed. Flowers opening


downward, right-sized

Fruit abortion - Most fruit abortion occurs within 1 week of fruit set and relative humidity in the greenhouse is related t the “unwillingness” of the rises above 85%. Fruit splitting can plant to carry the fruit. The plant is occur as a result of high root pressures either too vegetative and needs to be when the night air temperatures are directed to set and hold fruit by raising cool and root zone temperatures are the 24-hour average temperature 1°C, high. It is also important not to water or is too generative and is dropping too late in the day. young fruit because it is already Sizing but not reaching mature carrying too much of a load, Direct colour - Peppers reach mature size, these plants vegetatively by lowering but do not completely reach mature the 24 hour average temperature colour over the entire fruit, even after 1 or 2°C. 8 weeks. This condition is thought to Misshapen fruit, tails - Most problems be related with lower 24-hour average with fruit shape are related to poor temperatures. Raising the 24-hour temperature conditions during average temperature 0.5°C should help flowering. Usually seen when air to correct this problem in the crop. temperatures fall Premature fruit below 14°C for It is important to establish drop - A condition periods over the the proper balance in the when fruit mature course of a few to size, and not plants as early as possible days, primarily yet to colour, in order to set the stage for during the winter and premature continuous, sustainable months. Lygus bugs abscission, or fruit can also cause fruit production and resulting drop occurs. The shape problems, high yields. problem is seen the bugs fed by early in the season inserting their mouthparts into the very affected the first fruit to size and young peppers, much like mosquitoes appears to be related to low boron feed on people. The damage becomes levels in the feed. apparent when the fruit continues to Fruit reaching mature colour but not develop and the damaged tissue tears sizing - Small fruit usually indicated a open. Lygus bugs can even “top” he plant that is too generative, one that plant by killing the growing point. has put more resources into setting Cracking/split fruit - Fine cracks on fruit and nor enough resources the skin, russeting occurs when the 19

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at the blossom end or on the side of the fruit. Blossom end rot is due to a calcium deficiency, or reduced translocation of calcium to the fruit. It can result under conditions of lower transpiration or a shortage of water. A high E.C. in the root zone restricts the uptake of water. Maintain an active environment so that the plants are transpiring. If the problem does not rectify, apply a spray of 400 ppm calcium chloride solution to the plants. Sun scald - During the summer months under high solar radiation any fruit exposed to direct sunlight can develop sun scald. The symptoms of sun scald appear similar to those due to blossom end rot. Ensure that adequate leaf cover is maintained to shade the fruit from direct sunlight.


into developing the leaf area required to fill the fruit. These plants also have very short internodes, small leaves and appear stalled. Reduce the night temperature by 1 or 2°C to direct the plant to be more vegetative. Target internode lengths of approximately 6 - 7 centimeters. Remember hat secondary fruit produced on laterals will always be smaller than primary fruit on the main stem. Blossom End Rot - This may appear

Turning over, underside of leaves face up. This behavior is common when the plants are first set out into the production greenhouse and is also seen on established plants, usually in outside rows. The condition appears to be related to high vapour pressure deficits as when transplant are moved from the nursery into conditions of lower relative humidity in the greenhouse.

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Curling, from the edges in - Seen primarily on older leaves, although some cultivars may have more of a tendency to exhibit this characteristic, this is not considered to be a problem. If excessive curling and twisting is seen on the young growth this can be an indication that herbicides have drifted into the greenhouse. Interveinal chlorosis - As the leaf ages, over 3 months old, the tendency of developing interveinal chlorosis increases. A result of ageing and senescence s these leaves are no longer as active in the development of the plant and fruit. The plant can “mine” the leaf, removing mobile nutrients for use on other parts of the plant. This behavior is normal. Interveinal chlorosis on the younger leaves can indicate a problem with the nutrient solution or that the root zone temperatures are exceeding 23°C. It is important to keep the root zone temperatures in the 19 - 22°C range. Large leaves - Large leaves are a sign of a strong vegetative plant. Not a problem if the fruit set is also good. Small leaves - Indicates that the plant is generative, which should also be apparent by a heavy fruit set. The plant may be too generative if the fruit is taking too long to ripen and are undersized. As well as lowering the 24-hour average temperature, under summer conditions it is recommended to have about 20 ppm of ammonium nitrogen. This will help to direct the plant to be more vegetative.

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Undercover Farming Magazine March/April 2019  

Undercover Farming Magazine March/April 2019