greenhouses I shade net I hydroponics I aquaponics
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?
A
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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September/October 2020
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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