Undercover
farming
ucf
I
September/October 2020 Volume 17 No 5
I I R45.00 per issue
SHADE NET
hydroponics
Plant growth
aquaculture
Agricultural shade net Page 4
Young hydroponics start-up Page 6
Impact of Silicon Page 15
Aquaculture advantages Page 18
Undercover growing solutions to help your business flourish
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Irrigation
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greenhouses I shade net I hydroponics I aquaponics PROPRIETOR I ADVERTISING SUZANNE OOSTHUIZEN 082 832 1604 suzanne@axxess.co.za EDITORIAL CONTENT & COMPILATION Johan Swiegers 082 882 7023 editors@axxess.co.za ADDRESS PO Box 759, Montana Park 0159 E-MAIL magazine@axxess.co.za FAX 086 518 3430 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.
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Contents 4
PlusNet – Setting the standard in the shade net industry in Africa 6 Young Start-up pursues hydroponics farming with full commitment 8 Tech disruption will only accelerate in decades beyond Covid-19 9 The ever-popular cocopeat still used in hydroponics systems 10 About eco-friendly technologies for retaining quality on postharvest produce 11 Hoplita* komkommer, die regte keuse 12 Are you faced with disease problems on your plants? 13 Cherry Irrigation - specialists in irrigation solutions 15 What impact has silicon on greenhouse plant growth? 16 Si may reduce the need for synthetic fungicides 17 Golden Mile: Setting a high standard for refrigeration 18 Aquaculture cropping: less is more 19 Subscription form
FRONT PAGE: Plusnet, see page 4 & 5.
INSIDE ...
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Obtain your Undercover Farming magazine digitally! Online subscription Subscribe online now! E-mail your deposit and address details to: magazine@axxess.co.za More information from Suzannne Oosthuizen: 082 832 1604 See subscription form on page 16 visit us at • besoek ons by
A Scripture to strengthen your faith
The Scriptures says: Little is much if God is in it! Proverbs 15:16 (TLB) “Better a little with reverence for God, than great treasure and trouble with it.”
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ummer is here at last! Though on the Highveld, we experience temperatures ranging from 30 to 40°C as well as in the mid and Western regions of the country. High temperatures, the rain season and little air movement bring about diseases in a greenhouse and therefore we thought it good to publish some aspects of managing the pests and diseases the producer may come across. The application of Silicon (Si) is discussed by a few authorities on the subject and we hope to receive feedback from readers on their experiences of Si in greenhouse plant fertigation. This is not a new application but much reference to Si versus chemical pesticides has been made by authors towards greenhouse vegetables and flower production around the world. Will it ever be developed to free the world from pesticides? General opinion has it that too much is invested in chemical pest management over years to quit production now. Though, many greenhouse farmers operate with biological systems in order to keep away as far as possible from pesticides or herbicides. During discussions with various levels of hydroponics and aquaponics producers and their suppliers of infrastructure, the welcome news of new single, or two partners starting up greenhouse production around South Africa gives us hope for the future of the industry at large. In this respect, such a young, totally DIY start-up accomplished much and the self-built greenhouse is really neat with good-looking plants. Read his story in this edition. To end with, Chris Potgieter of an insurance company says under the heading: Business News; “In the context of the coronavirus pandemic that has upset the global economy, it’s fitting to remember that conflict and turmoil has always spurred on accelerated technological development.” Wise words that we can build on in the industry!
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Plus-Net close-up of 20% shade net covered structure for table grapes.
PlusNet – Setting the standard in the shade net industry in Africa
PlusNet/Geotex, a Division of Master Plastics PTY, is a Gauteng based manufacturing company. Geotex was founded 25 years ago, in 1995 and the PlusNet Range was added in 2000. Today PlusNet/Geotex has a fully integrated state-of-the-art production facility that produces innovated products for the agricultural, commercial and civil industry.
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The 90% decorative range manufactured Agricultural Net by PlusNet is specifically made for the lusNet has a comprehensive African commercial market. We supply range of agricultural shade to hardware stores netting (known nationwide and from our As the leading as Agri+) from factory store direct to the 20% to 60% shade, manufacturer of tailored to improve agricultural shade net, public. spectral transmittance Business the PlusNet shade and provide the optimal As the leading net product line will lighting and protection manufacturer of open up a spectrum for your crop. Covering agricultural shade net, of new and evolving orchards with lowthe PlusNet shade net percentage shade nets opportunities for new product line will open up can significantly improve product variants. a spectrum of new and the performance of the evolving opportunities orchard / vineyard. Part for new product variants. Whether of the responses can be attributed to the you provide shade net for vegetable filtering of the light spectrum by the nets, tunnels, shade houses or creative and part is due to physical protection and ‘green’ initiatives, the wide range of creating a friendlier micro-climate.
Decorative Net Our range of attractive and functional decorative shade cloths (or Deco+ range) provide cover for your crops from 80% and up to 90% shade and come in a variety of colours. The PlusNet 80% decorative range is ideal for projects where one requires more shade like at car ports or to cover a lapa. The Deco+ range is perfect for camping as you might consider using this as a privacy screen, a ground sheet or a cover around your boma area. The 80% decorative net has a UV block of 80% and provides 76% shade.
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PlusNet netting offers the client great opportunities at the best possible price.
Mini Net Tunnels Mini Tunnels are the quickest hasslefree infrastructure available when endeavouring to open a micro agricultural business. Net tunnels are the ideal portable, affordable do-it-yourself infrastructure for instant shade for your livestock or small gardening business. Shade tunnels come in various sizes and are simple to assemble. The PlusNet Team is ready to assist you with your net-related queries or projects. For more information on the products, visit www.plusnetgeotex.co.za or contact us by email on nets@plusnet.co.za for your quote today.
PlusNet shade net covered structures for trellised tomatoes.
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Young Start-up pursues hydroponics farming with full commitment
During recent years, few small start-ups were noticed, but one with which Undercover Farming recently met in the South Eastern Cape, really proves that, once you commit to farm with hydroponics, even in adverse financial times, there are ways to overcome obstacles.
Tom and his lady friend, Jacqueline in his greenhouse he constructed by himself.
and particularly tomatoes from a young age. He was fortunate enough to spend a lot of time in Spain and Sicily and came to appreciate the quality and flavour of their fruit and vegetables. According to Tom, he became disappointed at each return to South Africa to find the same rock solid, pink/green tomatoes, om at Lot 187 was born in the completely lacking in aroma and stuffed UK and moved to South Africa into plastic sleeves on the shelves of some years ago. He is a keen all the local stores. “There were some cook and a great enthusiast quality vine tomatoes of food preservation. at certain stores Hence, he yearned to Tom has always been grow his own greens, fascinated by vegetables but the majority of products on offer were tomato varieties, and particularly of no culinary value eggplants and peppers. tomatoes from a young whatsoever” he said. He intends to make age. He was fortunate his own conserves and Tom started growing sauces from various enough to spend a lot of tomatoes at home crops for his kitchen, time in Spain and Sicily and had considerable but also to market his and came to appreciate success despite produce to surrounding challenges of the the quality and flavour outlets and restaurants. local (Southern Cape) of their fruit and climate. “Unfortunately Tom has always been vegetables. we have very saline fascinated by vegetables
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At the time of visiting the greenhouse there were 400 grafted tomato plants, 100 seed tomato plants, 200 round violet eggplants and 100 Padron, Guindilla and Piquillo peppers growing in the greenhouse. groundwater and poor soils due to our proximity to the estuary. After the Knysna fires we decided to make a firebreak at the back of the property which freed up a little bit more space. “I expanded the planting to this area and after one year on the new turf, unfortunately the insect pressures and the consequent reliance on chemicals made me reconsider my approach. I started to read up on hydroponics and under cover farming. I got a few quotes from greenhouse companies in the
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Western Cape which varied by such a degree that I decided to look for second hand structures and build myself. I was very fortunate to purchase some galvanised hoops from a lady in Swellendam and I lifted these to form a double span tunnel “Being my first year, of 27m x 14m x 6.5m,” he I am still learning explained. much in practice and Thanks to COVID 19 Tom so far, so good. I am had a winter confined to the looking to pick as ripe property and an opportunity as possible and supply to put it all together. He found much basic information while only to my local area visiting YouTube and also from at this stage, ” Tom a greenhouse technologist said while looking after which he completed setthrough his neat up, ready to plant out by early September. greenhouse. “Being my first year, I am still learning much in practice and so far, so good. I am looking to pick as ripe as possible and supply only to my local area at this stage,” Tom said while looking through his neat greenhouse. He has a 450m2, double span tunnel and runs it on rain and run-off water, uses coco coir as grow medium and uses only biological control. At the time of visiting the greenhouse there were 400 grafted tomato plants, 100 seed tomato plants, 200 round violet eggplants and 100 Padron, Guindilla and Piquillo peppers growing in the greenhouse. A very neat and most functional set-up for a ‘novice’ indeed! JS
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Tech disruption
will only accelerate in decades beyond Covid-19
The global COVID -19 pandemic and the subsequent lockdown has forced companies around the world to adjust the way they conduct their business, while others have needed to pivot by shifting their approach entirely.
An example of a vertical hydroponics unit for greens.
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hile social distancing and remote working have led to an impressive plethora of digital services entering the market, according to Chris Potgieter of a large Insurance company, these existing technologies represent a mere tip of the iceberg. “If the history of pandemics is a guide, this contagion, like all others, will spark a wave of innovation that is directly proportional to the disruption it caused.” “In the context of the coronavirus pandemic that has upset the global economy, it’s fitting to remember that conflict and turmoil has always spurred on accelerated technological development.” “Innovation is unstoppable because of human desire for discovery and progress. Necessity truly is the mother of invention, and crisis tends to bring opportunity. The lesson for investors is that despite COVID-19 and the geopolitical tensions we’re currently facing, technology will keep advancing — possibly even accelerate as a result of the pandemic — and this creates opportunities.” He says the key to recording long-term capital growth is to identify themes or trends that will define our lives in the decades to come. The recovery in muchloved tech giants in the USA and China is
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in response to how COVID-19 will drive their growth in the short term. However, “investors need to look further forward to identify the innovations and emerging technologies of the future”. Potgieter adds that the greatest advances often happen because technologies from different areas intersect and reinforce one another. This is evident today in the advances in hi-tech sectors from artificial intelligence and 5G connectivity to biochemistry and cell- and gene-therapy. “The USA and China are currently locked in a race for superiority in these fields. And as happened 50 years ago during the Cold War, this conflict will cause technology and Innovation to be developed, perfected and commercialised faster,” he says. Food technology will take on increasing importance as the world population grows. Current projections show that food production will have to increase by 50% to keep pace with a population expected to reach nearly 10 billion by 2050. There will be an inevitable strain on food and water supplies unless we make some major adjustments to how we manage these commodities. Precision farming and precision biology are two trends that have emerged to ensure that food and water remain
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abundant in the years to come, with vertical farming technology and lab-grown protein production both on the rise. “Over the next decade it is estimated that the food technology industry will grow by approximately USD 500 billion. A few major players to watch here are: Nestlé, John Deere, Unilever, Ecolab, and Xylem, as well as the University of Wageningen.” He cautions that where returns are hard to predict, investors can gain broader exposure by going through an appropriate Exchange Traded Fund (ETF). “The key takeaway for investors is that they need to pay attention to companies investing in R&D that will help them to adapt as the market changes. While we are interested in sectors like biotech and 5G, we prefer to invest in multinationals that are spending on R&D, or take sector exposure through an appropriate ETF.” “By the same token, we avoid companies that refuse to recognise and adopt innovations that will disrupt industries. Sectors we’re keeping an eye on include energy, traditional retail, food production, transport and property.” What seems fanciful today will seem second-nature tomorrow. For savvy investors who can get an early foot in the door - Potgieter sees a good possibility for creating substantial wealth.
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The ever-popular cocopeat still used in hydroponics systems
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close-up look at the cork-like leader in coir media, having secured cells of the pith and fibrous supply to their seven factories in Sri material reveals a porous Lanka, India and Malaysia for a number of structure, which provides an years into the future. Galuku have done enormous reservoir for holding water. an enormous amount of research and Pore space amounts to about 90% of the development, specifically in commercial material volume. hydroponic horticulture, and today growers are achieving the same yields in Coco peat as a result, has a high water coco peat as what they do in rock wool. holding capacity (WHC) and a high water retention efficiency (WRE), while at the A wide range of products is available same time maintaining a high air-filled to suit the growers needs in whatever porosity (AFP). It is this climate they grow unique combination, throughout the world, Coco peat has a high which makes it a good water holding capacity including for organic hydroponics growing growers. (WHC) and a high water medium. After drying Coconut coir has been retention efficiency it also rewets relatively available as a growing (WRE), while at the easily. medium for a number same time maintaining of years, with the initial The high lignin content a high air-filled of the material ensures grade available being a that it maintains a porosity (AFP). It is this fine material designed for good physical stability use in seed raising and unique combination, with a very slow for basic potting mixes. which makes it a good decomposition process, This grade had a very hydroponics growing which means that it can high WHC, a high salt medium. be used for extended content and a low AFP periods of time and for (10-12%) which made multi-use applications, making it very it unsuitable as a hydroponic medium cost effective. the management of the water content is too difficult and there is too little air for The supply of coconut coir is reliable oxygenation of the root zone. due to the size and organization of the coconut industry with major coco peat The lack of success with this material suppliers such as Galuku, the world resulted in a resistance to the use of
It is well-known that Coco peat is a derivative of the husk of the coconut - the fruit of Cocos nucifera trees. Coco peat consists of coir pith, coir fibre and husk chips in proportions, blended specifically for different applications in horticulture. It has unique properties, which make it highly suitable as a hydroponics growing medium. coco peat as a substrate, a misplaced fear, which still exists in some quarters today. AFP refers to the air space within the medium when the medium is at full water holding capacity (as a %). WHC is the volume of the medium that is occupied by water at full water holding ability (measured as a %). The ideal AFP and WHC for hydroponics are 35-45% and 40-60% respectively, depending upon the climate and crop grown. So, even at full WHC water-logging does not occur in the correct blends. Reputable suppliers have developed high performance grades of coco peat which bear little resemblance to the original material with blended grades having AFP and WHC tailor-made to suit requirements. Controlled steering of the growth of plants is now possible with the grower able to manage water and air content on a daily or seasonal basis, with increased production and water savings a reality. Containment systems with UV protected plastic such as Easyfil planter bags, Hydro CS slabs, Gerbera discs and the like have also been developed to reduce labour costs in growing systems and to improve hygiene. Source: M von Holdt
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An increased awareness exist of the role of pre-harvest abiotic stresses on the quality of horticultural products and their retention, although there exists a need for more pertinent research and technological advances, especially under climatic change scenarios.
About eco-friendly technologies for retaining quality on postharvest produce
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nother need for such research should be that consumers are looking for the nutritional values of fruits and vegetables, for example, their constituents such as carotenoids, flavonoids and other polyphenols, phenolic acids, and other phytonutrients, which are even more susceptible to variations in temperature, relative humidity, concentrations of oxygen, carbon dioxide, etc. An attempt was made to exemplify the main horticultural crop species; frequent reference to some of these is related to the level of scientific reports, which relates to their storability (pome fruits vs. stone fruits), short lifecycle (vegetables vs. fruits), and economic importance. An example of physiological mechanisms is climacteric (for example, tomato, apple, or banana) and nonclimacteric (strawberry, citrus, and grape berries) fruits. Among the large spectrum of biochemical and structural modifications during the growth and maturation of harvested plant parts, those with a major impact on global quality and storability are referred to and discussed how abiotic stresses affect these. We focus on the role of abiotic factors on processes related to structural modifications of the flesh due to de-polymerization of principal components of cell walls and loss of cell turgor, which affect texture. Other important processes involve modifications of nutritional and organoleptic value of fruits due to an
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increase in mono- and disaccharides following starch hydrolysis and/or de novo synthesis, biosynthesis of volatile compositions, and the degradation of organic acids. Modifications of colour due to a degradation of chlorophyll and accumulation of carotenoids and/ or flavonoids in relation to light and temperature levels at the farm level have received increased attention in recent research.
Controlled atmosphere storage of fruits and vegetables Controlled atmosphere (CA) storage commonly uses low oxygen (O2) levels and high carbon dioxide (CO2) levels in the storage atmosphere combined with refrigeration. In CA storage, inside a food storage room is the gas composition that continually monitors and adapts to maintain the optimum concentration within completely close tolerances. Because CA storage is capital intensive and expensive to operate, it is more appropriate for those foods that are
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agreeable to long-term storage such as apples, kiwifruit, and pears. CA packaging is the enclosure of food in a gas impermeable package inside which the gaseous environment with respect to CO2, O2, N2, water vapour, and other trace gases has been changed and is selectively controlled to increase shelf life. Considering the definition, there are no CA packaging systems in commercial use. However, using the combination of O2 and ethylene (C2H4) absorbers, together with CO2 release agents in packaging, at least during the early stages of the storage life of the packaged product, could be classified as CA packaging. Some functions exist for the generation and maintaining of CA including O2 removal, excess CO2 removal, and addition of air, to replace O2 consumed by respiration, removal of C2H4, and in some cases addition of CO2. Selection of the appropriate functions and devices for generating and maintaining CA depends on what horticultural produce is stored and the storage conditions required for each produce. Research has shown that CA storage has positive, negative, and no effect on certain quality aspects of fruits and vegetables, such as physiological disorders, flavour and off-flavour, acidity, C2H4 production, respiration rate, volatile compounds, phytochemical compounds, colour. Source: Agricultural University of Tirana, Albania
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Hoplita* komkommer, die regte keuse Hoplita* is `n F1 komkommer variëteit van Seminis wat die afgelope tyd in die Wes-Kaap baie in gewildheid toegeneem het.
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nr. Johan van Zyl, van die Vredendal area, het Hoplita* laasjaar as `n proef geplant om te vergelyk hoe dit met sy bestaande variëteite kompeteer. Tydens die proefaanplanting het Hoplita* homself bewys waarna Mnr. van Zyl hom deelgemaak het van sy saaiprogram. Volgens Mnr. Van Zyl het Hoplita* die
volgende uitstaande kenmerke: • hoë dravermoë sonder om sy vrugte te speen • konstante lengte van L/XL • eenvormigheid van vrugte regdeur die plant se groeifases • ‘n uitstekende siektepakket (Hoë toleransie teen CVYC, Ccu
en Intermediêre toleransie teen: CYSDV,Cca,Px). Met die mees onlangse aanplanting by Mnr. Van Zyl het Hoplita* tussen 4-5 vrugte per plant meer as die standaard varieteit geproduseer en kon al in sy vierde week na uitplant geoes word. Deur Richard Hansen
success is in the detail seeds | science | service SV5047CE* • • • • • • •
Plants have a very open structure Suitable for winter production Vigorous plants with short internodes Excellent fruit set Cylindrical and straight fruit High tolerance to Cca, Ccu Intermediate tolerance to CVYV, CYSDV, CMV, Px
Hoplita* • •
• • •
Vigorous plant Ideal for the summer months, but does also perform well during winter in the Lowveld Medium large fruit High tolerance of CVYV and Ccu Intermediate tolerance of CYSDV, Px, Cca
| www.nuvance.co.za |
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When starting out with greenhouse farming, often the operators in the greenhouses are not fully equipped to notice diseases and sometimes even forget the image of the particular disease on plants. This is a re-introduction to the major diseases that one may face on your greenhouse plants.
Are you faced with
disease problems on your plants?
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ny plant that deviates from its normal growing pattern can be seen as diseased. There are many factors that can contribute to the growth of plants and these factors have to be taken into account when diagnosing a potential disease problem. Depending on the living status of the causal factors, diseases can be infectious or non-infectious. Live organisms or pathogens will be the cause of infectious diseases whereas unfavourable growing conditions cause non-infectious diseases. It is very important to know the actual main cause of the disease to be able to decide on control measures. Non-infectious diseases can therefore be a result of normal stress growing conditions which includes insufficient light, extreme temperatures (too hot or cold), poor aeration or water drainage of growth
Downy Mildew on ‘Mammoth’ basil.
Spinach blight.
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medium, too much or too little water, toxic levels of certain nutrients, nutrient deficiencies, unfavourable pH (acidity or alkalinity) of the soil, high soluble salts, soil compaction, injury from pesticides and fertilizers, physical or mechanical damage and many more conditions. Of importance is that noninfectious problems do not spread from one diseased plant to another as can be the case with infectious diseases caused by living entities, but they actually arise suddenly in a specific spot and the problems show simultaneously on a number of plants in the same area. Poor plant health is mainly a result of poor growing conditions. Parasitic organisms on the other hand are the main cause of infectious diseases. These organisms include fungi, bacteria, viruses, nematodes, mycoplasmas and viroids. The infected plant in this case is referred to as the host plant, and many infectious diseases are very host specific. Basic knowledge of the plants’ ideal growing conditions, water and nutrient needs as well as the susceptibility of the plant to certain infectious diseases can enable one to have a perfect healthy crop. In order to understand where plant diseases come from one needs to have a closer look at the various pathogenic parasites causing infectious diseases, and combined with the necessary knowledge of growing conditions, we should be able to prevent the development of such
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diseases in the greenhouse. When it comes to disease control, prevention is always better than cure. It is quite often impossible to cure a plant if the disease is already in an advance stage. In such a case complete removal of a very sick plant is normally the best approach.
Tomato Septoria leaf spot.
Tomato powdery mildew.
Before starting to remove plants, have a look at the possible causes of such diseased or poor performance plants. There are more than 80 000 diseases recorded worldwide, but only a small number of these diseases affect a plant or variety. Disease causing pathogens often establish themselves in areas of mass production of cultivated plants. The most common disease causing pathogens are fungi, bacteria, viruses, nematodes, mycoplasmas, and viroids. Fungi In the plant kingdom fungi are very simple, sometimes microscopic small plants
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Cherry Irrigation is an innovative company with more than 30 years’ experience in the specialist field of agricultural irrigation systems design and supply. With its head office in South Africa’s Western Cape, the company also has independent registered affiliates in Namibia and Angola, and has successfully completed irrigation projects in South Africa, Angola, Namibia, Botswana, Zimbabwe and Tanzania.
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he inhouse team designs and installs all types of irrigation systems for all types of crops, including fertigation and automation systems. The company keeps up to date with the latest trends and innovations in agricultural methods and technologies, and provides training in the use of the products that are supplied. Cherry Irrigation’s design package includes the full range of consultation, soil assessment, topographical surveys and irrigation planning, although these activities can also be offered as distinct services according to clients’ requirements.
Cherry Irrigation - specialists in irrigation solutions Hydroponics Lettuce Project Greendrop Farms MultispanTunnelProject Hoopenberg Muldersvlei
High-quality products from reputable manufacturers are a given. The team builds long-term relationships with clients by really listening to their needs and working to find the best water and energy-efficient solutions within the scope of the requirements. Specialised services offered are:
• Irrigation system designs • Drip, overhead and pivot irrigation systems • Supply, installation and maintenance of irrigation and crop management products • Pumps, filters and mainlines • Automation and fertigation systems • Soil analysis and soil maps • Electrical conductivity, pH, soil moisture and climate sensors and control • Water measurement and in-field water meter verification services • Solar solutions • Training
Contact Cherry Irrigation at +27 21 859 4246 l info@cherryirrigation.com l www.cherryirrigation.com
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which can either grow on a living plant or dead organic matter like dead leaves or manure to obtain food. In general fungi lack chlorophyll and those that live on live host plants are called parasites and the one’s that live on dead organic matter saprophytes. Some fungi survive by attacking live plants at certain times and at other times they can be saprophytic in the soil or on plant debris. A fungus normally starts its life as a microscopic spore which can be looked at as the same development of plants from seed. After germination tubular threads develop known as hyphae which grow and develop further into a mycelium. Such parasitic mycelium might have the appearance of cobweb-like, whitish threads as is the case with powdery mildew or dark coloured filaments known as sooty mold. It is also possible that the mycelium can be completely within the host plant and not visible at all, as is the case with fungi causing wilting and rotting. Fungi spread by means of their spores carried by air currents, water, birds, insects, spiders, slugs, seeds, vegetative parts of plants during propagation, pruning equipment and last but not least man. Some fungi called sclerotia do not produce spores and multiply by forming compact hyphae or the actual fungal body divides into fragments which are broken off and spread by water, wind and other means. Damp conditions favour fungi development more than dry conditions. Most fungi that infect flowers, leaves, stems or fruit require a wet surface during spore germination and penetration and moisture is also essential for rapid reproduction and spreading. Certain fungi can not survive in soil for a long period without a host plant, where others live for a long time without a host. Bacteria Most bacteria species known is harmless and are seen as more beneficial to us. Some are known to cause animal and human diseases, where others can induce diseases in plants. Bacteria need to enter plant tissue through wounds caused by mechanical damage, insects or weather or natural openings like stomata and scars. They can be present in soil, water, air, animals, plants and humans and they have the ability to multiply very quickly. Systemic infections of bacteria in plant tissue can cause typical necrotic spots, leaf spots, wilting, or soft rots of tissue due to the destruction of plant cells by the bacteria. Once bacteria have entered plant tissue there is not much one can do
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to prevent the spreading to other areas of the plant. As bacteria migrate through plants they can also cause chlorosis (yellowing) as well as water soaked spots as a result of toxins released. The spreading of infectious bacteria can occur through mechanical means when grafting or pruning, cultivation, infested seed or tubers and other vegetative parts of an infested plant. Various animals, insects, nematodes and mites, as well as splashing water and dust carried by wind can act as agents in the spreading of bacteria. Warm and wet weather favour the development of bacterial diseases and the most common one’s known to us are soft rots, stem cankers , leaf and stem blights, wilts, galls, blotches and most easily recognized leaf spots. Bacteria can be dormant for months under unfavourable conditions and can live under either on or in plants, seed, vegetative parts of plants, implements and everyday garden tools, soil, plant containers, and even certain living insects. It is known that many pathogenic bacteria are killed by very high temperatures, dry conditions and sunlight. There are also animal life in the soil that prey on many pathogenic bacteria, therefore the importance of protecting and enhancement of various microorganisms in soils. Viruses Acting like living organisms when in living cells, viruses are complex macromolecules that infect and replicate, and in most cases mutate. They are much smaller than bacteria and can only be seen with an electron microscope. The only way to detect viruses on plants is by the visual symptoms showing on leaves or their effect on growth. Symptoms of different viruses may differ depending on the plant variety or crop. The virus causes different genetic information to be sent out to the biosynthetic apparatus of the plant cell, which results in host cells to reproduce more altered viral particles. The most common diseases caused by viruses are spotted wilts, mosaic, ring spots, mottles, stunts, yellows and streaks. Many times nutrient deficiencies are mistaken for virus-induced diseases. Environmental conditions play a huge role in crops and weeds harbouring virus and quite often no symptoms show at temperatures above 30ºC. Quite often virus symptoms are confused with nutrient deficiencies and imbalances, insectinduced toxemias, pesticide injury, genetic mutations and mite feeding damage. A couple of virus diseases can spread via workers hands from diseased to healthy
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plants. The majority of diseases can be spread in nature by especially leafhoppers and aphids, a few by mealybugs, whitefly, thrips, grasshoppers, scales and even certain beetles. As a rule almost all viruses can be spread by vegetative propagation, which includes growing plants from cuttings, parts of seed, division of tubers and rhizomes, bulbs, and even parasitic plants like dodder. A small group of round 50 viruses can be transmitted by seed, pollen, fungi, nematodes, microscopic animal life as well as slugs and snails. Once a plant is infected with virus it remains like that for the rest of its life. Viroids A fairly new class of infectious particles called viroids has been identified that cause diseases that were previously mistaken for viral diseases. These viroids are 80 times smaller van the smallest virus. They act just like viruses by invading plant cells and as a result disrupting their functions. Viroids are known to cause “chrysanthemum stunt”. Mycoplasmas Mycoplasmas are one-celled, free-living organisms that cause typical “yellows” and “witches-broom” diseases. They are smaller than bacteria and reproduce by means of budding, very much the same way as yeasts will do. Leafhoppers are known to be the transmitter of mycoplasmas. Nematodes There are thousands of nematode species. Most is harmless, feeding primarily on decomposing organic matter as well as other soil organisms. Several hundreds are seen as beneficial in controlling soil pests. Plant-parasitic nematodes have needle-like stylet mouthparts which suck juices from living plants. Diseases develop as a result of nematode feeding damage which allows easy entrance for wilt and root rot producing fungi, bacteria and other nematodes. A nematode infested plant is normally more susceptible to drought, winter injury, disease and insect attack. Common symptoms of nematode injury include stunting, yellowing, loss of green colour, twig and shoot die-back, temporary wilting and lack of response to general watering and feeding. Mostly nematodes cause poor root health where in other cases root-feeding nematodes show no specific symptoms. Infested plants are weakened and can easily be mistaken for symptoms caused by drought, sunburn, frost, nutrient deficiencies, mite and or insect damage to roots, leaves, roots or stems, or common diseases like wilts, crown and root rots. By: Johan Gerber
greenhouses I shade net I hydroponics I aquaponics
What impact has
silicon on
greenhouse plant growth? Several researches have shown Silicon (Si) has the potential to be utilised in production of floriculture crops to increase flower and stem size, accelerate flowering and improve resistance to stresses including drought.
P
roducers have observed that plants seem to grow better in soil than in a container. There are a lot of things that contribute to the growth differences, but researchers in various countries decided to investigate whether nutrient levels play a role. Should one compare a field soil to a greenhouse substrate, there is a notable difference in the level of some nutrients.
One of these nutrients is silicon, hence it was decided to take a look at the effects this minor element might have on floriculture plants if it was added to a greenhouse substrate. Silicon (Si) is a non-essential nutrient for most plants. In field crops it is known to affect plant growth and quality, photosynthesis, transpiration and enhance plant resistance to stresses such
as drought. In floriculture production, most plants are grown in soilless substrates consisting primarily of peat moss or pine bark. In these substrates the silicon concentration is limited and its supplementation might be beneficial. Observing trials conducted to determine if supplemental silicon has a place in greenhouse production, included the cut flower ‘ Zinnia Elegance’, Helianthus and Gerbera ‘Acapella’. Various concentrations of silicon were incorporated into a peat-based substrate using a potassium silicate powder
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Si may reduce the need for synthetic fungicides Si is readily available in the soil, being the second most abundant element, after oxygen, present in the earth’s crust as silicon dioxide (sand) and various silicates or sheet silicates. Silicon is extracted from sheet silicates as silicic acid. Silicate minerals weather to clay, which forms the soils in which plants grow.
S
oil water generally contains 50 to 400 ppm silicic acid, which is readily absorbed by plants. Hydroponic nutrient solutions should contain potassium silicate or treated with10 parts per million of silicic acid (H²SiO³), although hydroponically grown cucumbers are often grown in nutrient solutions without added Si. Studies of plant tissue have found a range of silicon content from a fraction of 1% dry matter to as high as 10%. In plants, the silicon seems to play a role in growth, mineral nutrition, mechanical strength, resistance to fungal diseases, and reaction to adverse chemical conditions.
Role of Silicon Studies regarding silicate applied as a fungicide at the Pacific Agri-food Research Centre (PARC) in British Columbia first explored powdery mildew (PM) control and increased yield by adding silicate to growing media, with good control of powdery mildew on grapes, melons, zucchini, and cucumber. Continuing studies reveal that the form of silicon in solution and the solution pH greatly affect the efficacy. Fungal disease resistance in greenhouse cucumbers was shown to increase substantially in response to Si fertilization. Different rates of Si fertilization (potassium silicate) on powdery mildew was tested on cucumber leaves (inoculated PM conidia), results showed that leaf area covered by powdery mildew reduced by as much as 98%, with concentrations of 100 ppm or more of SiO² giving best results. Cherif and Belanger, (1992) found that nutrient concentrations of 100 to 200 ppm SiO² significantly reduced root mortality, root decay and yield losses on plants
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inoculated with Pythium ultimum as well as treated plants being more productive than those not treated with Si.
Mode of action Silicon is transported from the roots to shoot through the transpiration stream and deposited either as hydrated silicon dioxide, silica gel or polysilicic acid. Once the silicon is incorporated into tissue, it doesn’t move, so a regular supply is necessary. Cucumbers are shown to take up Si passively. Soluble Si taken up by plants tends to accumulate in the apoplast, particularly in epidermal cell walls, thus investigators hypothesized that Si inhibits fungal disease by physically inhibiting fungal germ tube penetration of the epidermis. Subsequently investigators have found that only the trichome bases on the cucumber epidermis tend to become silicified. Si has now been observed to accumulate around fungal hyphae and infection pegs in infected host plant cells and investigators have shown that phenolic materials and chitinases also rapidly accumulate in these infected host
cells. Cucumber plants treated with Si accumulate phenolic materials much more quickly than infected cells of nonamended plants.
Si fertilization These phenolics were also conclusively shown to be fungitoxic as fungal hyphae penetrating the phenolic-laden cells of Si amended plants were found to be seriously damaged by the accumulated phenolics. It therefore appears likely that Si fertilization reduces disease susceptibility primarily by stimulating host-plant defenses, although it may be possible that already silicified epidermal cells may play a role in disease inhibition. The question comes to mind, why has Si not been added to hydroponic nutrient solutions as is often done in Europe? Do farmers buy Si based sprays and treat crops themselves or are fertilizer companies going to take the plunge? Besides being an effective fungicide, Si may well reduce the need for synthetic fungicides as well as being beneficial to our health. By: Mike Haupt
Further opinion over Si on plants It is so that Silicon (Si) really protects a plant against sucking insects or fungus on leaves as it strengthens the leaf surface. Si is a plant feed element and therefor has as a secondary effect on plant protection against pests. The argument though is that, if a plant is protected in this way then the incidents of infestation will be much lower. If Si will ever replace insecticides or fungicides, is an open question. Si protects and reduces the possibilities of the pest or plague, but if these struck already, it will not be obliterated by a Si application. Therefore the producer will still need to apply a pesticide to save his plants. There are a number of products on the market containing Si, but they are all registered as fertilizers, not fungi or pest control products. Source: Lindie Grobler; Agri-Alchemi
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Golden Mile: Setting a high standard for refrigeration
The Golden Mile near Groblersdal in Limpopo, is the region where some of the country’s best export-quality citrus fruit and grapes are grown. This is also where new standards are set for the cultivation and storage of export-grade produce. It is therefore little wonder that the demand for state-of-the-art refrigeration solutions is higher here than anywhere else in the country.
T
he solutions developed specifically for the food producers in the Golden Mile is an example for any organisation that cannot compromise on the quality of their refrigeration. The Golden Mile is essentially the one-mile radius around the highest point in the Groblersdal area, the N11 between Groblersdal and Marble Hall. It has its own microclimate, which makes it ideal for production of outstanding quality fruit in the country. The demand for export-quality produce from this small region is so high that property prices soared in recent years. The farmers who invest their time and capital into these operations sell a highquality product -that is why they expect refrigeration systems that are up to the task. Therefor it is difficult to find a farm there that uses older technology. Refrigeration is central to the production flow on these farms. The produce has to be cooled overnight to the right temperature by the time that the trucks arrive to ensure that they can make it to their destination without spoiling. This requires that the cooling rooms run at peak efficiency, with no downtime. It also means that there is an intensive maintenance component that accompanies any refrigeration system that operates in this region. If there is a problem of any kind, a maintenance crew have less than
an hour to arrive on site and fix it. These people have to be on standby for 24 hours of the day. When a producer demands seamless operation, the obvious answer is to offer him a fully outsourced refrigeration solution, where the service provider owns and operates the system while only selling refrigeration to the client as a utility. However, because these facilities stand idle for just about three quarters of the year, and then they have to ramp up to 24-hour operation for about three months, outsourcing is more complex. Fully outsourced solutions are most viable if the facility operates for at least eight months of the year. The farmers therefore own all of the refrigeration systems on their sites, while a refrigeration expert has to be contracted to conduct 24-hour live monitoring and maintenance. There are companies now that developed their own monitoring tools, which observe the operation of the refrigeration equipment in real-time. This is a crucial part of their service, as the monitoring equipment picks up problems and temperature fluctuations the moment that they start to present, so action can be taken well before the quality of the produce is put in jeopardy. This also means maintenance teams need access to all the refrigeration system’s replacement components. One cannot
have a compressor break in the middle of the night, and have to wait a week for one to be dispatched. The team needs it on hand so that they can do a swap in the minimum amount of turnaround time. Geographical distance is one of the main challenges faced by service providers. Firstly, maintenance crews need to be on-site quickly, meaning that they have to be set up and ready to be dispatched within minutes of getting a call. Secondly, the far distance of these farms from infrastructure such as grid power is a major issue. The further that these facilities are located from town, the weaker their power supply is. At the moment there are facilities that simply cannot function with the low voltage that they sometimes get from the grid. As a result, most of these facilities have now started to incorporate solar power and batteries with their refrigeration systems. It is actually an ideal match in the end according to refrigeration experts. It is reckoned that Golden Mile is truly the golden standard that displays the full capabilities of state-of-the-art refrigeration service providers. The systems and proce dures employed there are standard for all operations across South Africa, but Groblersdal is definitely where solutions are tested to their absolute limit. EPMD
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Aquaponics is simply amazing technology, and an aquaponics system is thoroughly enjoyable to operate, so it is unsurprising that we easily get carried away when growing crops using this methodology. There is also the commercial imperative to produce as much as possible from our systems, and for both reasons we find at times that we plant, or permit, too much growth in our systems.
Aquaculture cropping: less is more
T
his can be as a outcome of planting the seedlings too close to each other, which results in the plants competing for light and growing vegetatively without much fruit set. It could be as a consequence of not pruning old growth regularly or completely removing plants once they pass their stage of maximum output of harvestable material (either leaves or fruit). Vine crops tend to remain in the beds for several months and there is a temptation with them to plant the replacement seedling at the base of the old vine during the last few weeks of harvesting from the mature plant. As there is no need for crop rotation in aquaponics, this may seem like a good way of gaining growth time in the beds, but in reality is not a sustainable plan. It could even just be a poor choice of variety i.e. using a variety that is not well suited to growth in aquaponics. The classic example here is an extremely vigorous variety of golden cherry tomato which we tried (twice!) and found to be such a productive grower that it smothered everything around it (both times) with the result that pruning was nearly impossible and effective spraying with (organic)
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pesticides was rendered impossible, resulting in a pest population explosion (again – both times!). Goldilocks, a golden cherry tomato variety that grows so rampantly in aquaponics that it smoothers neighbouring plants and blocks the pathway, even when being pruned heavily The trouble with permitting over- growth is that it reduces the open spaces between plants, restricting air flow, permitting fungal infections and pests to establish. Compounding this, pest sprays are less effective, bearing in mind that virtually all the sprays we use in aquaponics are gentle, contact treatments with no residual action. Under these conditions plants fail to thrive, and such over growth therefore actually has a detrimental impact on productivity. The solution therefore is to remove the old plants before planting seedlings, only plant varieties well suited to aquaponics, prune frequently and plant at the correct spacing. When we follow these basic rules we can continue to enjoy farming in aquaponics. This truly is a case of less is more. By: Leslie Ter Morshuizen, Aquaponics Africa.
greenhouses I shade net I hydroponics I aquaponics What impact has silicon 15 with optimum silicon treatments along with increased flower quality compared (KSiO3); rice hull ash, which is a natural to untreated controls for each of the by-product with high silicon content (20 species. percent SiO2); or five weekly substrate drenches of soluble potassium silicate To single out one of the (KSiO3). Five weekly foliar applications important reasons to advise of sodium silicate (Na2SiO3) were also silicon application is to made until runoff. . establish sufficient The silicon concentration increased in all substrate and plant silicon tissue levels. plant species that received supplemental silicon treatments. The increase in silicon Though guidelines for acceptable tissue and concentrations improved helianthus leaf substrate levels are tissue along with the increase in stem not yet established for diameter. The silicon concentration and floriculture crops. deposition in plant tissue (leaf versus stem and flower) varied among species Other indicating that aspects To single out one of the different species of fertilization important reasons to advise may take up with silicon that silicon application is to different amounts of have gained interest establish sufficient substrate silicon. Also, silicon are increased and plant silicon tissue levels. drought resistance deposition varies in different plant and increased tissues. Depending on silicon source and flower diameter. A potential cause for rate, several plant traits improved when both of these benefits is the reduction supplemental silicon was applied. in water lost by plants through evapotranspiration. Reduction of transpiration Thick straight stems were evident with rate (or increase of leaf resistance) helianthus and zinnia. In gerbera, flower has been attributed to silicon. Further diameter increased with sodium silicate silicon studies have used agricultural foliar sprays. Early flowering occurred crops and the effects were accelerated with increased environmental stresses like drought and metal toxicity. Reducing the transpiration rate could increase floriculture crop production.
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A study on the effect of supplementing silicon on stomata conducts (the mechanism plants use to open and close “water vapour” valves), proved that, under normal greenhouse conditions, leaf resistance (reduction of transpiration) increased with a high rate of sodium silicate foliar sprays. This study didn’t support an active role of silicon in stomata movement but there is an indication that a sodium silicate foliar spray application would act as a filmforming anti-transpirant that increases leaf resistance. The results after researches on the physical aspects related to silicon supplementation are encouraging. Horticultural researchers continue to explore optimum rates as high rates of many silicon sources can cause nutrient imbalances and a substrate pH shift. However, by using moderate rates growth enhancements were still achieved and no issues with growth and development were observed. Because of the alkaline nature of many silicon supplements, it is not recommended to mix soluble forms with fertilizer solutions as the resulting high pH will likely cause precipitation of nutrients. The rates of silicon supplements used in researches did not have any dramatic or residual effects on substrate pH. However, if growing conditions exist with high alkaline water or high limestone rates in the substrate then issues could arise. Source: S Marek OSU
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