5 Common Soil-borne Pathogens
By Hugo Alix, agr., M. Sc.
The production of high value-added crops pushes growers to maintain more precise control over their environments, which is even more relevant in a context where the aim is to combine local production with increased productivity per unit of area. Today’s technologies allow us to produce more on a smaller area, but the downside is that when a problem arises, it can have a major impact much greater than on more extensive production. The goal of this guide is to provide you with some tools to better prevent the emergence of soil diseases.
Factors influencing the development of diseases
Fertilization, pH, salinity of the substrate and water quality
The concentration of soluble salts, measured by the electrical conductivity (E.C.), and the pH of a substrate depend on the quantity, quality and type of fertilizer, water and substrate used. E.C. and pH are the two chemical parameters that you must absolutely monitor since they allow you to detect possible anomalies related to the fertilizers or the water source used (e.g., collective water, rainwater, wells, recycling, etc.).
These two parameters must be adjusted according to the species cultivated in order to have optimal growth and a healthy plant. A plant with all the nutrients needed at a proper time will be a vigorous plant and more resistant against pathogens attacks.
Light is an essential parameter that you must control in your greenhouse. Because of weather variations and climate changes (seasonal or one-time events), it is essential to adjust the amount of light reaching the plants. Shading systems must be successfully adjusted to use natural light to its full potential, without causing damage to plants due to excess light. Spring and fall are two periods when frequent adjustments are necessary. Light-related damage will not directly affect the development of soil diseases, but it could weaken the plants, thereby opening the doors to diseases.
Temperature and humidity
Temperature and humidity are two other climatic factors that you need to control in order to achieve optimal plant development. These two parameters can play a major role in the development of soil diseases. A cool and humid environment provides ideal conditions for the development of many pathogens. It is therefore important to maintain an optimal temperature and humidity to avoid excessive temperature gradients, non-homogeneous air circulation, condensation, etc.
Winter is a season when you need to pay special attention to the temperature at night. If you hope to reduce your heating bill by lowering the temperature by a few degrees, you may observe the development of diseases or cold-damaged plants (chilling injury) (Pennisi and Thomas 2015). Also, a poorly maintained heating system, especially if it runs on diesel or gasoline, can produce gases that are harmful to plants. Ethylene is one of them. As a precaution, you may want to keep a few tomato plants as an indicator since they are very sensitive to ethylene, even at low concentrations.
Your irrigation practices can have a big influence on the spread of disease in your greenhouse. If you manually water your plants from the top, splashes can spread disease. Combined with wet foliage this creates an ideal environment for their growth. Capillary mats, an Ebb and Flow system, and drip irrigation are irrigation techniques that reduce the risk of disease propagation.
The volume, frequency and timing of irrigation are also important and greatly influence the occurrence of soil diseases. Watering with too much water, even at a low frequency, can lead to asphyxiation of the roots. The opposite is also true: watering your plants too frequently, even with small amounts of water, can also asphyxiate the roots of your plants. Similarly, if you bring too much water at the end of the day, the substrate may not have time to drain sufficiently, especially in winter when temperatures drop a lot at night as humidity rises. A substrate that is too wet for too long is not recommended at all and greatly increases the risk of disease outbreaks. It is necessary to have long enough intervals between irrigation episodes to allow the substrate to dry sufficiently.
The source of your irrigation water can also have a direct impact on soil diseases. Surface well should be tested for pathogens such as Pythium spp., Phytophthora spp. or Erwinia spp. Many soil pathogens are transmitted through irrigation water. This is also the case when you recycle your water, it is important to make sure that it is not contaminated before re-injecting it into your system.
When choosing your cultivars, it is important to identify their susceptibilities to different diseases. The goal is not to have the cultivar that is resistant to the greatest number of diseases, but to have the cultivar that is resistant to the diseases that you often face or for which there is strong environmental pressure. Not all plant species have cultivars specifically identified as resistant to diseases, so it is important to use other factors, such as the length of the production cycle, light and humidity requirements, etc., to ensure that it fits perfectly with your geographical area and/or the different climate control options offered by your facilities.
Cleaning and disinfection
The last point, but finally the first one we should all pay attention to: greenhouse sanitation.
Whether it is during the purchase or production of your seeds, cuttings or plants, it is imperative to take all necessary measures to reduce the risk of contamination. If you deal with propagators, verify that their products are certified. Regardless of if they are certified or not, place them in quarantine in an isolated area and if you have the opportunity, take samples and have them analyzed to ensure their safety. Also, ensure that the equipment used has been disinfected and that your employees have been trained on how to limit contamination.
Learn more about these 5 soil-borne pathogens in the complete TRAINING GUIDE.