Growers know the despair when a crop has a root disease or a virus infection. Some growers will use a chemical to try to control it, but this approach is often not effective. It may even worsen the situation. As with everything, prevention is better than cure. Prevention starts with understanding what causes root or virus diseases * and what steps can be implemented to avert difficulties in advance.

By Elly Nederhoff & Bert Houter, CropHouse, New Zealand, Elly@ CropHouse. co. nz with supplements added by World Garden Ltd.

Spores in growing system

Recirculation or the re-use of drain water brings the risk of spreading root diseases.

The start of a disease is when a pathogen, like a fungal spore, is released from a source and transmitted by a 'vector' into a crop. A vector is something that helps the spread of a pathogen. For instance, it is not unusual for the irrigation water to be contaminated with fungal spores. Through irrigation, spores are introduced into the growing system. If a fungal spore lands on a plant root, the spore germinates and produces 'mycelium' thread that penetrates the plant root. If the fungus grows inside the plant and establishes itself, the plant is infected. Millions of spores will be produced and released. The infected plant is host to the fungus, and it also becomes a source of fungal spores.

Then a vector, such as water, wind, insects or people spread the spores to other plants. There the spore germinates and infects the plant. Millions of spores spread from here. After some time all the plants are infected and the system is full of spores and fungal growth. Obviously the production will suffer.

There are ways to break this circle, namely by controlling the sources of the pathogen and/or the vectors.

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Rapid spread to all plants

Water is a notorious vector for pathogens such as fungal spores, bacteria, viruses and nematodes. If the raw water or the nutrient solution contains pathogens, the disease will spread rapidly to all plants. If the drain water is re-used for irrigation, the disease will spread even faster. Recirculation is a good thing, because it saves water and fertilizers and avoids the emission of nutrients to the environment. But there is a serious risk of spreading diseases. Filtration is not a solution, because fungal spores, bacteria and viruses are too small to be caught by a simple filter. Proper disinfection is the only option.

WHAT CAN YOU DO?

*Before disinfection can be effective, a thorough cleaning of all systems should be implemented. This must be done before sterilization.  ENZYMES have proven to be the most effective means of aiding the removal of dead matter from inert surfaces. This technology should be used throughout the growing cycle with all watering and operating procedures. The technology has evolved from the cleaning of surgical equipment in hospitals prior to sterilization. The removal of these “bio-fixatives” is an important step to averting the development of anaerobic activity. HYGROZYME is the only known sterilized enzyme with this purpose in mind. The use of HYGROZYME is a highly potent and effective means of inhibiting the development, as well as the spread, of disease in growing systems. Dr. John Vella, the world renowned agricultural scientist from Australia, has witnessed numerous situations in which he has noted the use of HYGROZME as being the deciding factor in the rescue of up to 15,000 plants in one episode alone. Many of these types of problems can be avoided simply by using HYGROZYME from the outset of growing operations and continuing it’s use throughout the growing cycle. Further, it’s use in cleaning tools and equipment should not be overlooked as well as it’s compatibility with hydrogen peroxide in low ppm. It should also be noted that the use of enzymes should be accompanied by a properly oxygenated system.  The use of air stones should be avoided or replaced by a simple tube with holes emitting 2mm bubbles as the air stones, when not changed regularly lend themselves to system failure.

People are an important vector too. Spores cling to people's clothes and are transmitted from one plant to another. Small amounts of soil or droplets of water stick to the workers' feet, hands or clothes, and also to tools, wheels and crates. Even a crumb of soil or a droplet of water can contain millions of spores or other pathogens. A knife used for cutting plants (harvesting, pruning) will have plant sap on it that can be full of viruses. If that knife is then used on another plant, the virus is transmitted. Thus viruses often spread from plant to plant within a row.

Trolleys and other vehicles, crates and boxes, as well as tools and equipment can transmit pathogens. People's working shoes carry soil-borne pathogens too. Growers should be aware of visitors, especially those who visit various greenhouses one after the other. They can bring an infection from another place into your greenhouse. The spread of pathogens can be reduced by strict hygienic practices, such as disinfecting shoes, wearing special overalls (a different one in each compartment), disinfecting wheels, tools, avoiding moving from one compartment to another, cleaning the knife after every plant.

Possible sources (or hosts) of root pathogens

· seeds & seedlings
· growing media (substrates)
· irrigation water
· plant sap on tools
· soil in greenhouse or outside
· dust blown in
· natural vegetation & weeds
· greenhouses nearby
· compost heaps
· drainage system
· reticulating nutrient solution

Possible vectors (transmitters) of pathogens

· people (workers, visitors)
· boots, wheels
· tools, crates
· hands, clothes
· knives with plant sap (can contain viruses)
· insects, mites, nematodes, fungi etc.
· birds, mice and other animals
· irrigation water
· drain water
· water splashing up from the ground

Heat treatment is one of the various treatments available for disinfecting the irrigation water and the drain water.

Viruses are often transmitted via plant sap or dead or alive plant tissue. After a virus infection, it is important to remove all old dead plant material from the greenhouse before planting. *Use enzymes –HYGROZYME- to help reduce the effects of dead matter in the growing medium as it cn be used in conjunction with hydrogen peroxide in low ppm with effective results. 

{mospagebreak title=Spores in growing system}

Spores in growing system

Recirculation or the re-use of drain water brings the risk of spreading root diseases.

The start of a disease is when a pathogen, like a fungal spore, is released from a source and transmitted by a 'vector' into a crop. A vector is something that helps the spread of a pathogen. For instance, it is not unusual for the irrigation water to be contaminated with fungal spores. Through irrigation, spores are introduced into the growing system. If a fungal spore lands on a plant root, the spore germinates and produces 'mycelium' thread that penetrates the plant root. If the fungus grows inside the plant and establishes itself, the plant is infected. Millions of spores will be produced and released. The infected plant is host to the fungus, and it also becomes a source of fungal spores.

Then a vector, such as water, wind, insects or people spread the spores to other plants. There the spore germinates and infects the plant. Millions of spores spread from here. After some time all the plants are infected and the system is full of spores and fungal growth. Obviously the production will suffer.

There are ways to break this circle, namely by controlling the sources of the pathogen and/or the vectors.

{mospagebreak title=Root diseases from birds}

Root diseases from birds

Animals, including mammals, birds, amphibians, insects and mites can carry pathogens, like fungal spores, on the outside of their body or in their digestive tract. Nematodes and fungi can also spread viruses and bacteria. Birds may not seem logical vectors for root diseases, but they can carry soil with pathogens in it. Insects such as aphids, whitefly, thrips, beetles and leafhoppers are well-known vectors of viruses. Most insects transfer viruses by feeding on virus-infected plants (which can be weeds) and subsequently feeding on horticultural crops. Plant diseases can be prevented by several actions. One is controlling the vector. This can be controlling the insects that transmit the virus, or even controlling the weeds that host the insects that transmit the virus.

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Compensate the dead roots and *dead protein matter

The condition of the plants is an important factor in preventing diseases. Fast growing plants are able to withstand or overcome an infection. For example, infected plants suffer root death. But if the plant grows fast enough, it can compensate the dead roots by quickly forming new roots. A healthy plant can outgrow an infection, and the grower won't even notice that a pathogen is active. In contrast, if plants grow slower than the fungus progresses, the plant will be killed.

Also, plants growing in stressful conditions are weaker and more susceptible to diseases. For instance, some fungi cannot penetrate a healthy root, but they can enter old roots and wounds. As an example we look at the fungus Pythium. Pythium is known for attacking plants that are weakened by poor growing conditions or that have damaged roots. For instance plants that are just transplanted often have damaged roots, and are therefore very vulnerable to root diseases. Plant diseases can be minimized by avoiding stress on plants.

* Independent tests have shown the use of HYGROZYME with all watering procedures or in conjunction with fertilizers, accelerates the breakdown of dead matter present on media and within the growing system. This dramatically reduces the potential sites for anaerobic activity. It further fosters the release of complexed  nutrients and  inhibits the development of competitors such as disease or algae. Such an environment , has been shown to reduce plant stress and encourage rapid growth and  balance within the system.

Plants on cold wet places are first to be infected. Typical winter conditions consisting of low light, low temperatures and high humidity reduce the transpiration and water uptake of plants. This increases the chance of over-watering and water logging. Plants on cold wet places are the first to be affected by Pythium root rot. (Pythium fungus has many species, some thrive at low temperatures). Pythium root rot can be reduced by improving the growing conditions. Avoid excessive watering in dull periods, and ensure adequate drainage. Polystyrene placed under the bags or plastic gullies keep the temperature up. It also supports the bags or gullies, thus avoiding low places where water logging can occur. The most effective method of avoiding cold-stress is by heating during winter, especially heating the root-zone.

Stress from heat

Temperatures that are too high are very stressful for plants and can make them an easy target for diseases. Water that comes back from black plastic irrigation lines can be extremely hot due to sunshine, and can cause direct damage to the roots. The so-called 'tropical Pythium' species thrive in high temperatures. The combination of high temperatures, stressed and damaged plants and the presence of tropical Pythium is a recipe for  root rot. In this case the root rot problem can be avoided by keeping the root-zone at a moderate temperature, for instance by keeping the gullies and irrigation lines shaded.
 * Oxygenation or the implementation of aeration procedures, discourages anaerobic activity.  Enzymes can be used to ward off potential attacks on plants in warmer environments,  but this type of exposure is not conducive to a balanced growing environment. A  balanced system can be the answer to many ills. As such,  Enzymes can play a vital roll in maintaining that balance.

Taking advantage of weakness

Plants that suffer from any insect, fungus, virus or nematode grow slower than normal. Soil-borne fungi like Pythium take advantage of the weakness of the plants. Quite often Pythium is found on the roots together with another root disease. It is likely that the other root disease conquered the plant first, and that Pythium entered the plant afterwards. Plants can also be weakened by the chemical situation in the root-zone, for instance the presence of agrichemicals (pesticides), oxidants (sterilizing agents), high salinity (high CF), high acidity (low pH) and low oxygen content. Moreover, the chemical condition changes the biological environment and may kill the beneficial microbes. The remedy of course is to remove or reduce the stress factor. * A balanced growing medium is what should be established where ever possible. Enzymes will aid by increasing a plants tolerance to adverse conditions.  Their presence, will help in reestablishing balance and aid in restoring the natural protection plants inherently gain through health.

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ADVICE

Keep plants strong and be strict on hygiene

The best way to minimize root diseases and virus diseases is by very strict hygiene and by creating strong plants. Strict hygiene reduces the sources (the presence of pathogens) and the vectors (that transmit the pathogens). After there has been a virus infection, it is important to remove all old dead plant material from the greenhouse before planting.

Creating strong plants enables the plants to defend themselves against attacks and to outgrow any damage caused by a disease. Therefore it is important to avoid quick changes in conditions and to avoid extremes: too wet, too cold, etc. Essential factors are light, temperature, irrigation, pests, root-zone temperature, salinity (CF), acidity (pH), dissolved oxygen and composition of the nutrient solution.

*USE ENZYMES –THE  PREVENTION MAY BE THE CURE

The use of ENZYMES in conjunction with the aforementioned procedures will greatly reduce stress in the growing environment. Environments that are balanced foster healthy plant growth.

Heathly plants grow Bigger, Stronger, Faster …the secret is HYGROZYME.

*supplements submitted by World Garden Ltd.