Undercover
farming
ucf
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JANUARY/FEBRUARY 2021 Volume 18 No 1
I I R45.00 per issue
tomatoes
DISEASES
cannabis
ENERGY
Tomato trellising & Pruning Page 4
Prevent powdery mildew Page 10
Cannabis undercover Page 12
Eskom changes mind Page 15
Undercover growing solutions to help your business flourish
Turnkey Solutions
Greenhouse Structures
Irrigation
Cape Town
Climate Control
Crop Management Technology
Growing Products
Johannesburg
Telephone
021 987 6980
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011 974 5254
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Vegtech, 25 Kiaat Road, Kraaifontein
Address
Vegtech, 23 Brewery Street, Isando,
Industria, Cape Town, 7570. Email
info@vegtech.co.za
Johannesburg, 1600. Email
www.vegtech.co.za
info@vegtech.co.za
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.
Contents 4
Tomato production in a greenhouse is a devoted trade 5 Increase tomato production by pruning and trellising 8 How Controlled and Slow-Release Fertilizers Function 10 How Powdery Mildew affect Peppers and how to Prevent Stress on Plants 12 Growing Cannabis under Protective Cover or not? 14 Signposts in vegetable production 15 Eskom changes mind about Renewable Energy Power 16 pH Management Crucial for Success 18 Deciding on the Cover of a Greenhouse 19 Subscription form
FRONT PAGE: Tomato production in a greenhouse is a devoted trade, see page 4.
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Subscription details on p19 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 for 2021
Hope and Security “For I know the plans I have for you,” declares the Lord, “plans to prosper you and not to harm you, plans to give you hope and a future. Then you will call on me and come and pray to me, and I will listen to you. You will seek me and find me when you seek me with all your heart.” Jeremiah 29:11-13
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t is remarkable how our country differs in its climate zones. These influence the agricultural production of our great variety of foodstuffs tremendously. One cannot believe that parts that have not seen rain in eight years experiences flooding! Yet, towards the south the farms are bone dry and even on the south-eastern side, dams are almost just mud puddles and sheep farmers need to get rid of their animals and even farm workers. The greenhouse industry, although it largely controls its own climate, also depends on a continuous water supply. Many have borehole water supply, but in severe drought periods, the borehole levels drop below reach. With a rather bleak economic year behind, there are rumours of a further Covid spike. Public in general by now are used to media chasing up storms to increase readership and therefore take things in their stride – not denouncing Covid regulations, but living a ‘new normal’, as it is called. Therefore, in the fresh production sector, we are confident that the greenhouse industry will play an ever-increasing part in its plight of producing quality and nutritious fresh produce on the tables of many. During conversations around the country, it came under our attention that the industry as a whole is positive in its outlook. Turnkey companies rely more on obtaining most equipment here and manufactures locally in order to save on import costs but largely to have stock at hand in order to complete projects timely. There is a move towards electronic distance control in undercover farming and more about this will be published in future editions. The shade net industry is progressing with leaps and bounds locally but also in adjacent countries as more fruit tree, nuts and berry producers become aware of the benefit of undercover cropping. There is a growth in demand for 10x30 greenhouses by small operators which is a good thing as it emphasizes the positive outcomes of undercover farming, even for single operators or communities. Greenhouse keeping is a most hands-on activity and one must adopt the aptitude to really make it work as an entrepreneur. This year holds in new challenges but also many interesting new adventures for us all. Let us look forward to a great 2021!
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I Volume 18 No 1 3
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I once asked a former open land tomato producer what his greatest change was that he experienced after putting up greenhouses to control his own climate and acquire year round production. The answer was simple; “I used to take my family down to the South coast twice a year; now they are going on their own!” That is what it basically boils down to; to swap from open land to controlled environment production entails your 24/7 attention to your investment. (Ed)
Tomato production in a greenhouse is a devoted trade Uniformly truss of tomatoes – a sign of a healthy plant and good management.
climate over this transition period. During ll of us involved the winter – spring – summer with greenhouses know that transition, changes are often so running a successful greenhouse subtle that they can catch the operation means that the grower unawares. operator needs to have eyes all over the It can be generally stated that place as well as being a plant, climate and successful greenhouse growers are market analyst to be those who can able to second-guess It can be generally stated “pro-actively” whatever may happen that successful greenhouse (vs. reactively) next. Also, he or she avoid potentially growers are those who has to continuously harmful can “pro-actively” (vs. train and mentor conditions reactively) avoid potentially greenhouse assistants to counter harmful conditions to to ensure success potential and minimize losses counter potential plant plant stress through human error stress and harvest reduction. and harvest or neglect. reduction. With spring and summer plants in full The main players in the seasonal production, growers must be everchanges affecting the plants will be watchful to react smartly to all the lengthened day light plus increasing changes taking place in the plant and day and night temperatures. 6
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Unnatural growth caused by EC build- up in the root medium.
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Increase tomato production
by pruning and trellising Pruning and trellising tomato plants can be done by plants with indeterminate growth habit. This will shape them for better production and enhance air circulation and ventilation, optimize space and sunlight, improve growth balance between roots, leaves and fruit, and enhance the working space. Advantages of trellising 1. Reduces the incidence of physiological disorders e.g. fruit cracking and the uneven ripening of fruit due to exposure to high solar radiation and high temperature 2. Reduces the incidence of fruit rot and soil-borne diseases 3. Maximizes the efficiency of photosynthesis 4. The upright plants have fewer disease problems with leaf spots and fruit rots because their leaves stay drier and are not in contact with pathogen laden soil Possible disadvantages 1. Requires expertise (good management and skilled workers) 2. Trellising and pruning need to be done regularly – labour intensive 3. Plants can be damaged during training and harvesting
Pruning Pruning is simply the removal of the side shoots or suckers which develop between the main stem and the leaf. It helps to maintain a balance between vegetative and reproductive growth. Generally, if you do not prune or prune few side shoots, your plant will show excessive vegetative growth which may result in smaller fruit size. Care should be taken not to prune the growing point of the main stem otherwise your plant
Growing-point Sucker/side-shoot
Side-shoots
will stop growing and bearing fruit.
Removal of sucker/side-shoot with the thumb and forefinger Suckers can be removed with thumb and forefinger by pulling outwards. They are removed while they are young and succulent (2 to 5 cm long) when they heal faster. Large suckers are not easily removed and can create a larger wound, which takes time to heal and can be an entry point for pathogens. Experimental evidence has shown that there is a high reduction in yield when side shoots are allowed to develop 15-20 cm in length because they use nutrients which should go into fruit development. When working with big-suckers, it is important to remove the growing point of the sucker, causing less shock to the plant. Removing big suckers may necessitate using a knife, shears or scissors. It is important to disinfect the instrument after cutting to prevent diseases being spread from one plant to another. Pruning of suckers is known to increase the size of the fruit and promotes early harvesting. Determinate cultivars are not supposed to be pruned, but the leaves below the
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Removal of sucker/side-shoot with the thumb and forefinger.
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greenhouses I shade net I hydroponics I aquaponics Increase tomato production by pruning AND trellising 4
first truss can be removed to enhance air circulation. Pruning does not affect the fruit size or the vegetative growth of determinate cultivars if pruning is done below the first truss. Pruning of suckers above the first truss will result in lower yield. When the plant matures, especially when the first two trusses have been harvested, lower leaves turn yellow. Generally, remove yellow leaves below the ripening fruit clusters. These yellow leaves should be snapped off with fingers and removed as they are not actively photosynthesizing. In addition, this will enhance air circulation around the base of the plant, and will help to reduce fungal and bacterial disease build-up. This can be done by holding the main stem with one hand and snapping off the leaf where it is attached to the main stem using the other hand. It is important not to remove the green leaves since they function as a source of food supply to the fruits. The figure below shows how a plant should look after removing the old leaves. Old leaves should be removed far from the production area and destroyed to prevent the spreading or build-up of diseases. Removal of the older leaves results in trusses facing towards the walkway, which makes easy to 7 Tomato production in a greenhouse is a devoted trade 4
These increases in climatic energy levels equate to increased water use by plants, mainly for evaporative cooling. In the case of indeterminate growers like tomatoes (that were transplanted for the summer production), a further complicating factor is the exponential plant development associated with the first rapid plant growth until roughly the onset of the harvest period. During winter, fertigation EC’s are maintained at a relatively high level in an attempt to “force” as much nutrition into the plants during these periods of lower water usage. Inversely, the EC should be gradually reduced as the warmer season progresses due to the higher water usage. If the Ec is not reduced in time, plants may reach a “salt saturation point” and “shut down” transpiration temporarily. This is to protect the cells from damage due to excessive salt build-up in the plant. Typical wilting during the midday period can be ascribed to this “shutdown”. Blossom end rot often results from this
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Removal of the older leaves results in trusses facing towards the walkway, which makes easy to harvest.
Trellising shows the stem twisted around the twine, which is attached to the stay wire.
periodic wilting. At the same time as reducing EC, the water volume will have to be increased to match the transpiration of the plants. The plants’ water volume requirement will have to be upgraded daily due to the warmer weather as well as the expected rapid growth of young pre-harvest plants. This increasing need for water is echoed by the growing need for minerals as the plants need more and more nutrients to fuel the rapid growth. The relative nutrient balances must be maintained over the growth period, with careful attention for the need in Potassium during and after flowering – especially in fruiting vegetables like tomatoes. With high radiation conditions, excessive root EC or salt build-up is one of the main factors resulting in production losses. For example, Tomato plants with thick stems, compacted internodes, deformed growth points and poor or no fruit set are examples of a too high salt load on the plant. As a broad generalization, growers tend to over-fertilize in an attempt to boost
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growth. Sometimes high root zone salinity can also be ascribed to a watering regime not suited to climate, or simply, inadequate water volume to facilitate sufficient flushing of the root zone (run-off % too low). EC levels should be low to maintain good growth and allow plants to continue transpiration throughout the day. Fertilizer mixtures containing significant levels of Chlorides (often in an attempt to lower the cost of fertigation) increase the relative EC of the mixture. Programs with no or very low Chloride levels, especially for summer, will help in reducing the ion load on the root system – allowing easier uptake of beneficial minerals and further aiding the prevention of salt build-up in the roots. Successful warm weather fertigation can be “summarized” as: a program which allows the plant to optimally utilize water for evaporative cooling, transport of sufficient and balanced nutrients plus enough oxygen for healthy root function & growth. Source: P de Vries (abridged version)
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How grafting benefits the grower
harvest. Indeterminate cultivars grow very tall, and with time the yield and fruit size become progressively smaller. Removing the growing points of a plant will stop growth and enhance fruit ripening. With approaching low temperatures (frost), it is important to prune the growing points of all the plants. This is because tomato is sensitive to low temperatures, so by removing the growing points will stop fruit bearing and ripening of fruits will be enhanced.
The growing habit of the scion changes during the different seasons – it grows more generative during summer and more vegetative during the winter. Planting the right rootstock in the right season will help your plant overcome the difficulties. The De Ruiter brands; Maxifort is a good option for summer, while a more generative rootstock like Beaufort is more suitable for winter. However, there are companies like Histhil and Eza Zaden that are also producing excellent rootstock for various greenhouse plants. Disease pressure can be another reason to graft. The main problem in SA is with Fusarium and Verticillium. The common rootstocks will provide resistance to these diseases and in combination with the stronger vigour the plant will be less susceptible to secondary diseases like bacterial wilt and bacterial canker. The regulations regarding the use of agrochemicals play a role in the selection of the correct variety and rootstock. Rootstocks with resistance to bacterial wilt are on the market as well. Several seed companies have concluded successful trials in the RSA.
Trellising Trellising is done by tying twine from the bag to the stay wire above the plant. The stem is then twisted around the twine to give support. Trellising should be done two weeks after transplanting. If transplants are not trellised at early stage, they become crooked and trellising then will result in breaking or damaging the plant. Normally a tomato plant may grow approximately 5 – 6 m in a 6 month growing season. It is therefore important that the stay wires are strong enough to carry the mass of a whole row of plants with fruit. The total mass of the plants and fruit in a 45 m row is more than 1 ton. Therefore, considerable damage to plants will result if the stay wire breaks at the height of the production season. By: Martin Maboko
Grafting and fruit quality Fruit is the genetic result of the scion and not a direct result of the grafting. Indirect effects such as water and nutrient availability or carbohydrate metabolism, can alter the quality and all these factors may be highly variable based on the rootstock genotype. Cost of grafting Additional labour, grafting clips and rootstock seed add to the cost of a seedling. On commercial specialty types of tomato only 250gm more fruit per plant pays for the grafting. In various super-chain trials, growers are already picking more fruit per plant on their grafted seedlings. For the standard round-type of tomato grafting offers the benefit of a longer picking time and therefore more trusses per plant. With growers increasing their yields from 180 to 220 tons per hectare, grafting is not costly, but a financial survival tool. Important to understand though, is that whatever scion you will grow on any rootstock, the key to success depends on plant balance! (R Gillies) A tomato scion grafted on rootstock to increase production and free the plant from root diseases. Pic: JS
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The use of controlled-release (CRF) and slow-release (SRF) fertilizers allows growers to supply nutrients for an extended duration without the specialized equipment needed to apply water-soluble fertilizers.
How
Controlled and Slow-Release Fertilizers Function
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hese fertilizers are added to the media at mixing or applied to the media surface after planting. Nutrient runoff can be reduced using CRF and SRF, especially compared to applying water-soluble fertilizer through overhead sprinklers. Should the greenhouse grower rely on CRF alone, it is not always the best decision for nutrient management. For example, even distribution of CRF prills (a pellet or solid globule of a substance formed by the congealing of a liquid during an industrial process) from plant to plant is difficult when growing in cell packs or trays. The correct CRF should be matched to the crop and growing environment so that nutrients are released at the rate required for optimal plant growth – too rapid a release rate can cause media-electrical conductivity to increase too high and damage roots, or too slow a release can result in nutrient deficiencies. In some cases, a combination of CRF and water-soluble fertilizer provides the best match of nutrient supply to crop needs. Controlled-Release Fertilizer (CRF) CRFs are primarily water-soluble
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fertilizer salts or blended fertilizer substrates containing N-P-K or N-P-K plus micronutrients covered in a membrane that limits the solubility of the fertilizer. The membrane technology varies between companies and can be resin-, plastic- or polymer-based. Nutrients are released in two ways: Some CRFs have an initial release of nutrients either caused by imperfections in the coating of the prill or the use of uncoated fertilizer prills in the formula. Some CRF formulas, for example top-dress formulas, may have 70 per cent or less of the nutrients listed as coated (30 per cent uncoated). Sometimes, fertilizer prills are damaged, for example, when adding to a media during mixing. Depending on the salt used to make the uncoated fertilizer, it may completely dissolve with the first watering, and therefore should be thought of as a starter fertilizer (if incorporated at planting) or a fertilizer drench (if top dressed). To test for initial release, put a teaspoon of CRF in a litre of water and allow the solution to sit at room temperature overnight. The more the EC of the solution increases, the greater the initial
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release. Nutrients are mainly released from a CRF prill following absorption of water through the membrane. The water dissolves the fertilizer inside the prill. The dissolved nutrients then diffuse back out through the coating into the soil solution. Once the CRF prill has absorbed water, soil temperature determines the release rate of nutrients. Depending on the product, the ideal release temperature (i.e., the temperature used to predict the duration of the fertilizer release) can vary from 21°C to 25°C. For example, one type of CRF has an ideal release temperature of 21°C. For a fertilizer with a six-month release rate, 90 to 95 per cent of the nitrogen fertilizer contained in the prills will be released over six months if the temperature of the medium is maintained at an average of 21°C. The higher the average soil temperature above the ideal release temperature, the more quickly nutrients will be released from the fertilizer prill, shortening the duration of the fertilizer. In contrast, lowering the average soil temperature below the ideal release temperature will slow the nutrient release rate and 9
greenhouses I shade net I hydroponics I aquaponics Controlled & Slow-Release Fertilizers Function
increase the fertilizer duration. Using the example above, if the average soil temperature increased from 21°C to 26°C, the release duration would decrease from six months to four months, whereas decreasing the average soil temperature to 15°C would cause the release duration to increase to seven to eight months.
CRF and pH Management Once the CRF has released the nutrient into the soil solution, the effect on media pH is similar to that of any other fertilizer blend. The fertilizer effect on media pH is based on the type of nitrogen found in the fertilizer formula. For example, the water-soluble fertilizer 20-10-20 tends to be acidic because 40 per cent of the total nitrogen is in the ammoniacal nitrogen (NH4-N) form. Ammonium has an acid reaction in growing media. The percentage of nitrogen in the ammoniacal form ranges from 45 to 56 per cent of the total nitrogen. Therefore, the pH reaction produced by each of the fertilizers should be more acidic than using 20-10-20. Like any other fertilizer, the pH reaction produced by a CRF formula can be modified by a number of factors,
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not only like with media temperature. Therefore, the nutrient release from SRFs is less predictable than from controlledrelease fertilizers.
including: 1. The amount of ammoniacal nitrogen in the soil solution is influenced by the CRF formula, incorporation rate and media temperature. The more ammoniacal nitrogen being released into the soil solution, the greater the acidic effect of the fertilizer. Conversely, the less ammoniacal nitrogen being released into the soil solution, the smaller the acidic effect. 2. Nitrification of ammoniacal nitrogen is inhibited by low substrate pH (starting at around 5.5), low substrate temperature (less than 15°C) and lack of oxygen through water-logging. Therefore under these conditions, ammoniacal nitrogen is less acidic. 3. Basic chemicals like residual limestone contained in the media or water alkalinity may neutralize the acidic effect produced by the ammoniacal nitrogen.
Slow-Release Fertilizer Slow-release fertilizers (SRF) are another group of fertilizers with limited solubility. However, SRFs differ from controlledrelease fertilizers in one important way. The release of nutrients from slow-release fertilizers depend on multiple factors,
SRF Examples Sulphur-coated fertilizers: Sulphur-coated fertilizer are urea, or urea- or ammoniumbased salt blends that are coated with elemental sulphur and other materials (like wax) to produce individual fertilizer prills similar in size and appearance to controlled-release fertilizers. Nutrients are released when water penetrates the sulphur coating through pores or imperfections in the coating. Once water has penetrated the coating, nutrient release from the prill is rapid. Since the thickness of the sulphur coat will influence the time required for water penetration, sulphur-coated fertilizers usually contain a range of coating thicknesses to obtain extended release duration. Wax sealants are sometimes applied to the sulphur coating to slow water penetration. If wax is present, then microbial activity is needed to break down the wax to allow the sulphur coat to be exposed before nutrient release can occur. If a wax coating is present, anything that affects microbial activity, such as temperature, media-moisture level, media pH or media-aeration, will also influence nutrient release. Urea Formaldehyde (UF): UF is a class of slowly soluble nitrogen fertilizers synthetically produced by combining formaldehyde with urea. The release of nitrogen from UF is a multistep process that depends primarily on microbial decomposition. Therefore, anything that affects microbial activity will affect the release of nitrogen from UF. Isobutylene diurea (IBDU): IBDU is a single slowly-soluble nitrogen fertilizer synthetically produced by combining isobutyraldehyde with urea. The release of nitrogen from IBDU is controlled by a process called hydrolysis and is affected by media moisture level and media pH, but not microbial activity. Slowly soluble fertilizers: These are fertilizer salts that have a relatively low solubility when added to water. Examples of slowly soluble fertilizers include gypsum (CaSO4•2H2O), triple superphosphate or 0-46-0 (9Ca(H2PO4)2 + CaF2), limestone or micronutrient oxides. The release of nutrients from slowly soluble fertilizers is dependent on the solubility of the individual fertilizer salt. In addition, the particle size of the salt will influence the release duration. By: Paul Fisher, Greenhouse Grower expert.
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How Powdery Mildew affect Peppers and how to
Prevent Stress on Plants With temperatures soaring during the high intensity of abnormal rainfall patterns and subsequent high humidity, Powdery Mildew can take its toll – if not early detected.
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Healthy n the production of sweet peppers peppers, Powdery Mildew is the most common with healthydisease and it is of vast economical looking foliage importance. The only effective way around them. to control Powdery Mildew is to have a holistic approach on the production of sweet peppers. Example of Powdery Mildew on a leaf. Powdery Mildew in peppers grows within the leaf and can be latent in the plant for 21 days before it becomes evident as having already infected the crop. It can result in defoliation of the plants, from which recovery is exceptionally slow. Hence, it is essential to monitor a crop carefully and react quickly. During its infection of the plant, Powdery Mildew utilizes nutrients from within the plant, interferes with photosynthetic processes, increases transpiration, impairs growth and increases leaf drop and flower loss. Generally, a 10% infection/infestation will result in a 10% yield loss. Conditions that encourage the growth leaf surface. of Powdery Mildew include 15.5 to The reaction of nutrient and 27°C, although powdery mildew can environmental conditions is also survive at temperatures as low as 4O°C, important as under low light conditions, low light intensity magnesium and Powdery Mildew During its infection of the concentrations in the has the ability to plant are reduced. plant, Powdery Mildew even germinate Under conditions utilizes nutrients from in the absence of of high disease within the plant, interferes water. On the other pressure, this low hand, suppressive with photosynthetic level of magnesium conditions include processes, increases could make the plants water on the plant transpiration, impairs more vulnerable as surface for extended they are unable to growth and increases leaf periods of time, build the papillae. drop and flower loss. day temperatures Also, under low light above 32°C and conditions, there is night temperatures above 18°C, direct also a reduced production of sugars sunlight or high pH conditions on the by the plant which will also affect the
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production of papillae. During winter, there are less uptake problems with magnesium and calcium; thereby also a reduced Powdery Mildew problem can be expected at this time. Understandably, the management of the irrigation and fertigation system is essential in controlling the infection. Pulsing has been found to be a highly effective irrigation technique that results in creating a low water tension in the soil medium and consequently increasing yields. Frequency of application is more important than the amount of fertilizer being applied, and this can be directly related to the increased availability of phosphorous and manganese. The importance of light in pepper production is little considered, particularly with regards to field pepper production. Plant density and the trellising of sweet peppers are all about sufficient light. A lack of light will not
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greenhouses I shade net I hydroponics I aquaponics How Powdery Mildew affect Peppers
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only lead to poor yields but in the end it will lead to a high incidence of Powdery Mildew that may destroy the crop. Plant population and the direction of the rows should all be based on exposing the plants to as much light as possible. Fields obtaining large amounts of afternoon sunshine are less susceptible. Traditionally, planting was recommended to be done in a North-South direction, but it has been found that this can lead to early infections of Powdery Mildew, especially when related to light conditions. An East–West row configuration in winter may reduce the incidence of infection. In winter, it would be wise to reduce the plant density so as to increase the amount of light received by the plants. Summer population: 35000/ha, winter population 25–30 000/ ha. This would also help reduce the incidence of Powdery Mildew in the crop. A minimum light level of 1000psu (photosynthetic sun units) is required at midday for prevention of Powdery Mildew.
Further tips to avoid Powdery Mildew: • Growing under protection under winter conditions (short days, low light intensity) one should use the Dutch method of trellising to ensure maximum light penetration. • Air movement in the tunnel or in the field is also important and planting in the direction of the prevailing wind for field production will also be advantageous in reducing disease incidence. For tunnel production, maintaining a relative humidity of between 65 and 75% with air movement at 0.5m/s will also assist reducing infection • Soil preparation for peppers, as with any crop, is essential in good crop production. It also assists in the control of Powdery Mildew infections. A soil analysis is essential in ensuring that the balance of the nutrients in the soil is correct as this will increase the resistance of the crop. If the sum of the K and Na is greater than 10, there is reduced manganese availability and this will result in increased Powdery Mildew infection. If the calcium balance indicates excessive levels of calcium, an expected reduction of magnesium uptake can occur resulting in a more susceptible plant. • The amount of available carbon in the soil is also essential for
adequate production. 6% available Excessive applications of nitrogen carbon assists in the production have been found to excite Powdery of active roots which helps with Mildew. See attached guidelines on the development of strong healthy fertilization of peppers. It is better to plants with a strong resistance to apply fertilizer according to growth infection. The carbon content can phases than to fertilizer requirement be used to determine the amount or by week as the length of the crop of organic matter or compost that differs from season to season. should be applied to the soil prior to • Oxygen in the root zone is extremely planting. The use of organic matter important, it assists in energy and compost helps aerate the soil. production, produces a healthy root Poor air circulation in the soil can also system (longevity, health and yield), result in the development of Powdery assisted by the incorporation of Mildew infections. organic matter at planting, minimal compaction of the soil and prevention • The control of soil pathogens of over irrigation. Weeding however is also an important part of this has been found to damage the feeder process, particularly with regards to roots just below the surface of the nematodes. It is essential to apply 3 soil, preventing nutrient uptake. applications of nematicides to catch • An integral part of your Powdery all the phases of the growth of the Mildew preventative program is nematodes. The nematodes reduce fungal sprays and spray management. the manganese availability that How effective is your spray? The consequently reduces the resistance ideal spray should of the crop to the Soil preparation for peppers, have a droplet size disease. The use of indicator plants as with any crop, is essential of approximately 400 um or 2984 in the field will in good crop production. It droplets/ml. For also assist in the also assists in the control of systemic sprays, identification of Powdery Mildew infections. 20 – 30 drops/ the presence of A soil analysis is essential cm2, whilst contact nematodes. Open in ensuring that the balance sprays should be field melons will show nematodes of the nutrients in the soil is applied at 502 – 70 drops/cm . within 5 days. Also correct as this will increase Preventative sprays remember to test the resistance of the crop. are really important, your water for start early. Use only the presence of registered products. Bicarbonates nematodes. of sodium or potassium have been • Planting your seedlings correctly is found to be as effective as neem also important. Seedlings should be oil and sulphur burners. Systemic planted only as deep as the top of sprays should be followed by contact the plug. Planting too deep causes sprays. the plants to be more susceptible • Disease resistance, especially against to disease. This is because the plant virus diseases, is essential in the is stimulated into producing lateral production of sweet peppers. The roots. This causes damage to the most important virus threats come stem that in turn allows for an from Tobacco Mosaic Virus (TMV) infection to occur. Also, these lateral and Potato Virus Y strain 0 and roots may be less efficient at taking strain 1 (PVY-0 & PVY-1). The latest up nutrients as the crop matures. development on this front is the Transplanting of younger seedlings resistance to Bacterial Spot (Xv), is better as it allows for better root Tomato Spotted Wilt Virus (TSWV) development. The ideal seedling and Root-knot nematodes (Ma). should have 2 cotyledon leaves and Finally, one should remember that 2 true leaves. Direct seeding should disease resistance is lost as soon as also be considered as it eliminates plants experience stress. It is therefore transplant shock. In Europe, grafting ever important to ensure your of seedlings is also a popular practice greenhouse attendants are observant in helping prevent damage from and diligent in reporting any plant stress nematodes. immediately. Delay in taking action is • Again, the management of irrigation and fertilizer applications are essential directly related to loss in revenue. JS for the control of Powdery Mildew.
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Growing Cannabis
under
Protective Cover or not? When it comes to cultivating cannabis, there are pros and cons of growing in a greenhouse. At the end of the day, what matters most to the producer, is getting as much yield as possible. Higher yield means a greater return on investment.
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herefore, is setting up a greenhouse for cannabis production worth the investment? In this editorial greenhouse yield per square meter comparing growing cannabis indoors and outdoors is discussed.
Growing Cannabis Indoors As there has been a long-standing prohibition on cannabis, much of the weed produced in the last century has been done so ‘behind closed doors’. Growing cannabis under protective cover has given birth to some of the most popular varieties today. That is because the producer can control the elements in which the plants are grown. Therefore, growing under cover, allows you to pinpoint and maintain the ideal environment for all of your plants to produce the highest yield. Growing Cannabis Outdoors While growing under cover is an efficient way to grow weed, it might be not the most cost-efficient. This is especially true if you live in a climate that doesn’t get much below 10° C when the sun goes down. Then your
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best bet is to grow outdoors. Even if you can’t grow as big of a yield, you will still receive a fair yield with sunlight and rain. This will offset the expenses of electricity and water incurred by undercover growing. Some cannabis growers is of meaning you could earn just as much money growing outdoors as you would by investing in greenhouse production over a smaller surface but higher yield per square meter. But let us discuss the advantages of greenhouse production first.
Advantages of Greenhouse Growing Greenhouses can help solve your debate between indoors and outdoors cannabis growing. The most costly aspect of growing undercover is not only the initial construction investment, but the electricity to run climate management, dosing and irrigation systems. Unlike being outside, where plants are susceptible to Mother Nature’s unpredictable events, inside a greenhouse climate control and protection prevail. Harsh winds and rain or light hail and black frost can’t damage leaves on cannabis plants. Another advantage of growing cannabis in a greenhouse is that you control the
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climate to best suit plants at different levels of growth. Furthermore, this also let you grow cannabis all year long. By using propane heat or natural gas, you can increase carbon dioxide levels to promote even more growth. Just be sure to install a carbon monoxide detector in multiple areas of your property. Greenhouse Yield per Square meter Generally, it is difficult to give an exact measurement of what yield to expect as it encompasses the plant and row density, the efficient management of climate and irrigation and sometimes unforeseen circumstances like power outages. The closest average of cannabis produced in a greenhouse, is 4,5 Kg per square meter (from several surveys in SA and foreign sources).
Optimising profits In order to obtain a significant return on investment when it comes to growing cannabis in your greenhouse, the producer needs to invest in technologies pertaining to optimal production. One wants to create a greenhouse system constructed to keep plants growing well and yield optimally. Galvanized steel framing in your structure lasts longer and is sturdier than PVC tubes or other plastic and breakable structure materials and galvanized steel won’t rust. This is an important aspect because growing cannabis creates a lot of humidity. Water vapour corrodes most metals, causing them to 13
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add pollutants into the atmosphere. With your cannabis’ stomata open, the plants can take in heavy metal particles. Choosing the right cover is crucial for optimal greenhouse yield. The cover is critical because it plays an integral role in heat retention. Greenhouses are covered with polycarbonate sheets or polyethylene film. You want to get a cover that has exact UV translucency for your cannabis production. This allows for leaves under the canopies of cannabis plants to get more nutrients from natural sunlight. Seeing you can control the climate inside a greenhouse, you can make the most of your yields by getting a screen that functions automatically according to the plant’s climate requirements. UV rays can destroy some of the compounds of marijuana when the plant has been exposed to the sun’s radiation for too long.
Shade net structures If you live in an area where 35-40°C is commonplace, then growing under shade net structures is a good option. In turn, it will lower the heat that can burn budding plants. Shade cloth is manufactured according to pre-researched formulations for different applications. Therefore, the shade cloth supplier will be able to recommend the correct colour and translucency of cloth for cannabis plants. It is suggested not to use black shade net because it absorbs heat and could have various negative effects on plants. In fact, it could create a sauna for your cannabis crops. Another issue with a dark, or tight woven shade cloth, is that the plants are not going to get adequate day light time from sunlight during the shorter days of winter. Ventilation Think of a greenhouse as a steamed up vehicle in winter. What do you do to get the windshield un-fogged? Open the window! Make sure that you build your greenhouse with a ridge vent to circulate air. However, go the extra step by getting roll-up side walls. This is a great way to maintain cooling costs. Not to mention, allowing fresh air from the outdoors can be beneficial for the plants. Expand for higher yields Greenhouses have become a growing trend that cannabis producers use to keep production flowing. Seeing there are so many benefits of indoor growing, there is no reason that increased cannabis yields can’t come from a greenhouse with well-managed technologies that are improving annually. In South Africa, cannabis production for medicinal purposes is strongly regulated and it is found that to prevent criminal injustices to this rather new and costly horticultural sector, high security measures are taken to protect cropping sites. Nevertheless, there are local greenhouse construction companies that will be able to furnish local and foreign producers that wish to set up a greenhouse system for cannabis, with apt information and turnkey solutions. JS
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Signposts in vegetable production An understanding of what’s happening in the SA vegetable industry is crucial when making production decisions. We would like to make you attentive of important ‘signposts’ in critical areas of VUP production in SA – and advise you to stop and consider your choices at each. In summarising this article: • Higher yield and pack-out are essential for survival. What do you need to adjust to ensure you achieve this? • Generally profit margins are a lot tighter and are nowadays similar to those in modern agri-business. With this in mind, should one restructure ones whole production enterprise? The signpost; “NO MORE IDEALISM” in VUP in SA Even today, there are still amazing stories of how much money you can supposedly make quickly by growing vegetables under protection, and also of the wonderful lifestyle one may enjoy. Although the “big bucks” is sometimes possible, it is definitely the exception and not the rule. So when you hear someone saying “put up some tunnels, plant tomatoes/cucumbers/peppers, break even in the first year and hit the big time,” then see this in the context of: • A 3 – 5 year financial plan, • A conservative business plan based on reasonable returns, • An accurate market assessment and ready markets, • A cohesive budget linking costs, capital requirements, turnover and nett profits etc. • Lastly, note that many producers only break even after the third year of production! Notice all the buzz words used: financial plan, business plan, returns, market assessment, budget, capital, turnover etc. Not once yet mention was made of any aspect of undercover production (although this is intrinsic to the plan). The point is - that this is about good solid business, and that business just happens to be growing or “manufacturing” vegetables under plastic or shade cloth, and then selling these vegetable products into the markets. We in no way belittles the passion with which we all farm and some of our reasons for doing it; driving arm out the window and experience wind in our face, wide open spaces, working with plants and nature, the sense of order and
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security that comes from viewing rows of well-structured tunnels or shade-houses full of green crops, the sight of “red” gold being packed into crates, punnets or value packs etc.. At the end of the day our passions must be directed into financially profitable businesses, and the business side is more important than our passion for vegetable production and its “supposed lifestyle”. Get back to earth; “NO MORE IDEALISM” in vegetable production in SA! Another big signpost is transport costs When choosing a new farm and what crops to grow, what structures to erect, make sure that the profit margins and volumes supplied can cover transport expenditure. Given current prices of fuel, the grower who is only 50km from his market is far better of than the grower more than 150km away, never mind more than 300 km from the markets. Given similar hectares, yields and pack-out and other input costs, the grower closer to the market will pay about a third of the transport costs per kg than the grower 150km away. Even though the “further away” grower might have cheaper labour costs due to being further away from the city centres – he will be under more pressure to add value to his products so that increased transport costs can be offset by a better price per kg of product. The further than 150km away grower will also have to give far more attention to cold chain logistics, so that trucks are always full to minimise transport costs per kg of product. Thus his/her time spent on quality crop production and other aspects of management could become less. The third signpost is traceability. Everybody is talking about traceability
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and admin and records and systems and so on…. It can be quite off-putting. Match your level of traceability with your customer requirements! Most traceability issues currently relevant revolve around safety and chemical use. The choices can be seen from a couple of business angles. 1. Your customers do not require traceability therefore you simply do not introduce any system to trace products or production. You only tackle this if and when required. This typically applies to many products delivered to the fresh produce markets or outside main chain stores. 2. Your customers do not require traceability but you put the basics in place so that you comply when eventually required, or you use your traceability systems to canvas new business. 3. Your customers require Europgap and traceability. You can either go the whole way or give them the bare minimum. This is typical of most production going into retail networks or export. For various reasons most vegetable growing enterprises tend to only supply that which is required and only put in place systems and processes to supply that only which is requested. Whatever one decides to do – the question must be asked and answered! To wrap this up – face these three signposts and ask yourself the questions. • Do I grow vegetables because I really enjoy the lifestyle and can make a lot of money one day, or is my vegetable enterprise based on solid business principles which are applied and monitored? • How am I positioned regarding transport issues and related costing with respect to my products, markets and profit margin? What has to change? • How do I need to position my vegetable business on matters of traceability? Answer these or seek information to make your fresh produce enterprise profitable and secure in the market you aim for. By: Derek in Forum Articles
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Eskom’s recently tabled tariff restructure programme, which proposes changes such as charging consumers a fixed connection fee, may indeed improve the landscape for renewable energy in South Africa.
Eskom changes mind about
Renewable Energy Power
T
ygue Theron, Head of Business Lifting the generation cap Development at Energy Partners Intelligence – a Theron explains that Eskom is in fact division of Energy Partners and coming out in support of greater part of the PSG group of companies renewable energy adoption in the – says that while there has been a fair country, while also acknowledging that amount of criticism levelled against the this will expose the utility to additional state-owned utility’s proposed plan (as costs. “I believe one of the biggest well as its recent request for a 10.95% developments for renewable energy increase in tariffs), there is another way adoption locally, was when Eskom CEO, to look at the situation. André De Ruyter, joined the call for lifting the generation cap on renewable “One of the biggest points of contention systems. is the proposal that users are charged a At the same time, we “One of the biggest points split tariff, consisting of contention is the proposal have to recognise that of a volumetric surplus renewable that users are charged a usage cost, and energy will have to split tariff, consisting of a a fixed daily be stored and connection cost. volumetric usage cost, and a distributed through While consumers fixed daily connection cost. the national grid, who rely on solar “ Tygue Theron, Head of Business and that Eskom’s power are saying coal-fired generation Development at Energy Partners that this would facilities still have to Intelligence, Eskom make it longer be able to provide before they get power during the a return on their investment (thus early morning and evening hours. lowering the feasibility of investing in a These are maintenance and operational solar energy system), it could actually costs that the utility would not be better for renewable energy in SA in be able recover under the current tariff the long-run.” model.”
Greater stability? Ultimately, Theron points out that the proposed tariff restructure could indeed lead to greater stability for South Africa’s power grid. “We have run quite a few models so far, and we have found that this change, as well as the other proposed tariff changes, will not have too much of an effect on businesses. While it may increase costs for home users, it would help us get closer to our renewable energy goals while relieving some pressure on businesses in the country.” Tygue Theron, Head of Business Development at Energy Partners Intelligence is available for interviews and is keen to discuss the following points: • How the proposed tariff restructure programme can benefit renewable energy growth and more affordable energy generation; • A breakdown of the possible 10.95% tariff increase for the 2021/22 financial year; • The energy options for businesses and consumers going forward. Source: Eskom PR
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Delayed management of media pH commonly results in poor growth and reduced plant quality in greenhouses and nurseries. The pH or soil reaction has a primary influence on the solubility and availability of plant nutrients.
pH Management Crucial for Success
M
any crops have a narrow range the solution becomes. The greater the of pH tolerance. If the pH of ratio of OH- ions to H+, the more basic the soil medium falls above or the solution becomes. PH is measured below this tolerance zone, they on a scale of 1-14. A pH of 7 indicates may not grow properly due to nutrient that the H+ and OH- ions are in balance. deficiency or toxicity. A reading below 7 means that there are more H+ ions and a reading above 7 In general greenhouse production a pH of 6.2-6.8 is considered ideal for mineral soils, indicates more OH- ions. and 5.8-6.2 is recommended for peat or In horticulture traditionally a pH reading bark media. But, this largely depends upon is taken to make amendments to growing the crops grown. Poinsettias are tolerant media and irrigation water. But while of variable pH, while seed geraniums are pH is a good indicator of the availability very particular, since pH 5.7 or below can of dissolved fertilizers in the root zone, result in iron toxicity problems. it is not at all good at predicting the effect that a given irrigation source will Except for nitrates, have on the media potassium, and total Alkalinity levels indicate pH. Therefor you soluble salts, the the relative ability of the must also know the availability of most buffering capacity or media to resist or neutralize fertilizer elements alkalinity of the media is affected to some the effects of acids. The and the irrigation extent by the media higher the alkalinity level, source. Alkalinity pH. Calcium and the greater the amount levels indicate the magnesium become of acidification that will relative ability of the more available as the media to resist or be required to produce a pH increases, but neutralize the effects desired pH drop. the opposite is true of acids. The higher for iron, manganese the alkalinity level, the and phosphorus. A one unit pH drop can greater the amount of acidification that will increase the solubility of manganese by as be required to produce a desired pH drop. much as 100 times and the solubility of iron by as much as 1000 times. Lime But what is pH? Many horticultural soils require the addition of lime to correct pH and to pH measures the relative concentration supply calcium and magnesium. Lime of hydrogen ions (H+) to hydroxide ions directly affects the alkalinity of the soil (OH-). The greater the number of H+ medium. The amount of lime needed ions in relation to OH- the more acidic
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depends upon these factors: the type of lime, the fineness of the lime particles and the pH, acid content, and buffering capacity of the media. Most potting soils today are amended with dolomitic limestone to supply adequate calcium and magnesium and to buffer the acid content of peat, a prime constituent of many potting soils. Other types of limestone include calcium carbonate, which supplies only calcium, and hydrated lime, which reacts very fast, but is not as long lasting. Hydrated lime is seldom used alone since it is very quick acting and short lived. It is sometimes used in emergencies to raise pH after the plants have been potted, or as a partial component of the lime additives. For greenhouse and nursery soils, the calcium carbonate or dolomite lime used should be rated as 65 mesh or better, which means that 65% of the particles are small enough to pass through a 100 mesh screen. This is often called pulverized lime. Calcium sulfate or gypsum has a neutral effect upon pH and can be used as a calcium source when no pH effect is required. The amount of lime to use depends upon the peat source. If the peat is highly buffered (acidic), then more lime is needed to have the same effect. Perlite, vermiculite and most other aerating materials have little effect on pH, but since their addition decreases the 17
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volume of peat, proportionately less lime is needed. For example, if a cubic meter of pure peat required 7 kg. of lime to raise the pH to 6.0, then a 50% peat, 50% perlite mixture would require only half as much.
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Several factors come into play when attempting pH alterations. Variables that can influence the rate of pH change and the amount of modifying action needed are: soil temperature, root volume, leaching fraction, the buffering capacity of both the soil medium, and the irrigation source. It is always best to catch pH problems early, before drastic steps are needed. When it becomes necessary to raise or lower the pH in the crop, it is wise to start conservatively to avoid overshooting the tolerance range in the other direction. Wild pH swings can be worse than the original problem.
Alkalinity Other than pH, alkalinity is a measure of a solution’s ability to neutralize acids. It is the alkalinity level that determines how your irrigation water will influence the pH of the growing media. Most people who are familiar with pH would expect that high pH irrigation water would tend to raise the media pH over time. Increasing pH However, if the water has very low Heavy leaching tends to reduce salts alkalinity, it may not have a significant and raise pH provided the water pH is effect on media pH despite its high initial higher than the soil. This also will help pH. By contrast, if one used irrigation to remove any pH-related toxic levels of water with a high alkalinity level, say 200 minor elements such as manganese or ppm bicarbonate a greater effect on media iron. Hydrated lime has been used to raise pH can be expected. pH in existing crops by dissolving 1 kg. The higher the alkalinity of the irrigation per 100 liters fresh water. After leaving water, the faster the root media pH will the mixture overnight, the clear solution change. Rain water sources of irrigation is drenched onto the crop. This method water normally contain little or no does not work very well with hard water bicarbonate. Well water sources often sources. range from 50-150ppm. Although some Potassium bicarbonate bicarbonate alkalinity dissolved at 1 kg. The effects of both pH and is good, higher levels per 100 liters will can be toxic to some alkalinity are important to add about 600 plants and in these the nutrition and root health ppm bicarbonate cases, well water to water plus 400 of crops. Understanding must be mixed with ppm potassium. these principles will help to rainwater to bring take some of the guesswork However, it is best the bicarbonate not to raise the pH out of managing media and too quickly due to the into the desired range. If insufficient solution pH. possibility of ammonia bicarbonate is release. Lower rates available naturally, of bicarbonate (60-180 ppm or 1-3 kg then potassium bicarbonate can be added. per 1000 liters) with each watering are Both limestone and bicarbonate raise pH effective at raising pH over time. by the production of carbonate. Over Decreasing pH time, high alkalinity water sources will tend Iron sulfate dissolved at 1-4 kg. per to increase pH, while low alkalinity sources 100 liters has been used where pH is will decrease it, depending on the rate of too high. The solution should be acidified leaching and fertilization and the nature enough to dissolve all sulfate. Ammonium of the fertilizers used. Growers with very sulfate will lower pH slowly but very low alkalinity levels have sometimes found effectively due to the action of nitrifying it useful to provide a modest background bacteria. The crops treated should be level of bicarbonate of (60-100) ppm. By ammonium tolerant, the pH should not be then adding small additions of acids to less than 6.2, and the temperature should achieve the desired pH, they can dose be above 15°C. nutrient solutions with sufficient buffering Fine ground elemental sulfur at 5 g per capacity to change or stabilize the pH of 15 cm pot or 15 g per 2-3 gallon container the root media. is recommended by some sources as a Changing Media pH gradual way of bringing down pH. It is the action of certain soil bacteria that create By understanding the relationship of the change, usually in about 10-15 days. alkalinity to pH makes it easier to change Acid additions are the most common the media pH when needed. Regular pH method of reducing pH. They work best testing of the root media is necessary to if used as a regular component of the monitor the condition of the root media feed solution to prevent the media from and to identify the need for amendment.
becoming too basic. Reducing the feed solution to around pH 4, depending on the alkalinity, can be effective for producing a more rapid change, but some nutrients may be tied up. Most growers use a laboratory analysis or a trial and error method to calculate how much acid to add to a solution to get a desired pH.
Residues Wherever chemicals are used to raise or lower pH in irrigation water they may leave deposits on leaves, particularly when used in misting systems. Precipitates caused by sulfuric and phosphoric acids are more of a problem than nitric acid, but nitric acid is more hazardous to handle and can elevate EC levels at high injection rates. Testing of pH All commercial horticultural businesses, regardless of size, should have a reliable pH meter. Follow the instructions included to preserve the accuracy and life of your instrument. Solution samples can be read directly, or after a few hours of settling time. Dissolved CO2 in water supplies can cause slightly lower readings until the sample has come to equilibrium with the air. Freshly mixed samples of media should be watered and allowed to stand for 24 hours before a reading is taken to release some of the lime and fertilizers. The preferred method for testing media pH is to obtain several representative samples of a crop and to measure each separately. Multiple measurements will give greater accuracy in reading, and will show the degree of variability of pH from pot to pot. A saturated media extract or a 1:1 soil to distilled water ratio is fine for measuring pH. Testing Alkalinity If you have regular solution analysis performed you can usually request an alkalinity or bicarbonate test as well. Do-ityourself alkalinity test kits are also available at low cost from scientific companies. The effects of both pH and alkalinity are important to the nutrition and root health of crops. Understanding these principles will help to take some of the guesswork out of managing media and solution pH. JS
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greenhouses I shade net I hydroponics I aquaponics Polycarbonate walls look neat and are stronger against normal weather onslaughts. The roofs are covered with polyethylene to ensure proper translucency.
Deciding on the
Cover of a Greenhouse The question of what the ideal greenhouse plastic is to cover a greenhouse often surfaces. On the market, there are many types of greenhouse plastic from which to choose. The main decision relies with the available budget, understanding the local environmental conditions and the production objectives before investing in an important component of the production system.
D
Polyethylene uring the early 1960’s, 6 mm polyethylene sheeting came on the scene for hoop house style greenhouses. Then and even today its greatest asset is its price, as 6 mm plastic is economical. Since 1970 technology on greenhouse
covering increased and then UV inhibitors were added to give the plastic a longer lifespan. It was clear that, although 6 mm plastic could survive the sun for up to 3 years, a longer lifespan was needed to decrease input costs to the system. But, half a century later 6 mm poly is still used by some budget conscious growers.
This film lasts according to the manufacturers’ specifications, but growers do stretch the limits to avoid costs – many times to their own peril. The downside to 6 mm is poor weather (excessive wind, or hail), and our South African sun. A bad storm may damage the cover and recovering might be necessary. Over and above, crops may be damaged or lost in a strom. Thus, the 6 mm polyethylene When recovering a greenhouse, the labour cost and production downtime must be brought into consideration; and therefor also perfectly managed to resume production covering will last potentially for as early as possible. four years and pay the farmer the cost of its purchase, but one must take into account the labour and time to recover every 3-4 years or possibly sooner in case of loss through adverse conditions.
Polycarbonate Polycarbonate for walls is an extruded polymer product. This is impact resistant and offers thermally insulation. It is attractive, will not yellow and is fairly easy to install. The down side is how easily damaged it can get from wind, storms, and severe hail. It could attract
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greenhouses I shade net I hydroponics I aquaponics Polyethylene covered hoop houses over a strawberry project. Being in the Western Cape with low levels of hail and less wind in this particular area, the cover could last as much as six to eight years with proper management.
Cover of a Greenhouse
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dust and dirt in areas where open land farming or dusty winds prevail. This may reduce the amount of light entering the greenhouse. It is important to clean polycarbonate to abate algae on the inside and outside of the greenhouse. Also, it is advisable to have lawn grass around the greenhouses. Polycarbonate sheets are more expensive than 6 mm poly, but not as expensive as glass covering (which is very seldom used in SA!). The hoop roof construction is covered with polyethylene. How do you define “Best Greenhouse Film” and which do you think is best? The following are some practical areas of consideration. • What price? If a low cost film is what you are looking for, then 6 mm plastic films will be the better option greenhouse film due to its relatively low initial cost. What you save in the initial film investment you will lose to
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labour cost. 6 mm greenhouse film will not last very longer than four years, and may not come with much if any of a guarantee. You will be replacing that film due to aging from the sun, or a storm ripping a hole in the film. • The Energy Considerations: The price of heating and cooling your greenhouse is the second biggest expense beside the labour of constructing and covering your greenhouse. Which covering offers the best heating and cooling R-value? Obtain at least four quotations. • Estimated UV Lifespan: For the plastic films, how much do you value having a UV guarantee. Some companies offer a 10 year full warranty. Does your plastic films supplier offer this warranty? The big secret is to purchase a film with a proven track record elsewhere in the world. • Adverse conditions: What is the best
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HYGIENE
DISEASES
SCoUTING
CUCUmBER
Hygiene in the fresh produce packhouse Page 4
Pythium disease on greenhouse crops Page 11
Scouting for pests and diseases Page 14
Improving cucumber yield Page 18
greenhouse covering when it comes to wind, hail and snow load? If this is important to you, compare the various suppliers’ warranty records. • How cover replacement labour influence you: Should your greenhouse cover be damaged by a hail storm or excessive wind, tearing the cover; which greenhouse cover is the best in offering you a cost saving when repair or replacement is required? Most greenhouse films will require you to recover the entire structure. Some suppliers offer strips, so in the unlikely event there is damage to the cover, you will only be replacing a single or two sections and not the whole structure. Basically; the above considerations and more are to be made when deciding to select a greenhouse cover for your structure to obtain optimum production and longevity in structure cover. JS
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