A pathogen, a host, and the right environment: these are the ingredients needed to spark plant disease. A simple recipe, which can have some very complicated results for a grower: infamous diseases including botrytis (gray mold), powdery mildew, late blight, and downy mildew are known to hurt crops as well as the pocket.
This threesome is known as the plant disease triangle:
· A pathogen is a disease-causing organism, for example, a parasitic fungus or bacteria.
· The host is the plant, and if it susceptible to this pathogen, it is capable of being infected and getting sick.
· A favorable environment means that appropriate conditions exist for the pathogen attack on the host to occur, for example, temperature and humidity levels.
If all three of these conditions exist simultaneously and for the appropriate amount of time, the result will be the development of plant disease.
Greenhouse crops can be especially at risk for the formation of crop diseases. This is due to the unique characteristics created in the greenhouse environment including:
- Moderate temperatures –The greenhouse is set up to create temperatures that the host plants prefer. Often, the pathogens will favor similar temperatures to those that their hosts prefer.
- High humidity – Humidity can lead to the formation of water droplets on plant surfaces. This surface water is one of the conditions that enable many fungal and bacterial diseases to infect plants.
- Air movement – Ventilation systems for producing air circulation are common in most greenhouses. Many pathogens move throughout the greenhouse and are dispersed from plant to plant by air currents. Given the right combination of environmental conditions, these pathogens can infect the new plants that they reach.
- Uniformity- Uniformity can be for the good or the bad – if the conditions are uniformly suitable to plant disease growth then it won’t be limited to a spot, it will attack the whole greenhouse. If the whole greenhouse is kept at uniform optimum conditions, then the grower benefits from large scale disease prevention.
- Dense plant spacing – Plants that touch or are in close proximity to one another act as potential sources of disease transfer to their neighbors.
- Rapid, lush growth – Overgrown plants can have a dense canopy that makes them prone to the production of humid microclimates and spaces that are hard to reach with disease-restricting pesticides.
- Frequent handling – Constant handling by workers or equipment can aid in disease transfer between plants or inflict wounds on plants that act as points of entrance for pathogens into the host.
Conditions like these make a greenhouse a very comfortable spot for pathogens to settle in and inflict disease, and indeed many greenhouses have been hit with disease epidemics. The impact of these epidemics leads to yield quantity and quality loss, pesticide use, additional expenses, and extra worry.
However, if properly managed, the greenhouse actually offers ways to prevent diseases. Greenhouses by definition create an internal environment of their own, and greenhouse growers have the unique ability to manipulate the conditions within the facility to their advantage. Herein lies the key to preventing the potentially devastating effects of plant disease. By taking down a leg of the triangle, the grower can bring the whole thing down.
This can be done in a number of ways. The isolation a greenhouse creates from the outdoor environment can help to restrict the introduction of pathogens to the plants. Sanitation measures such as disinfecting growing mediums and equipment can also prevent exposure and spread of disease in the greenhouse. Temperatures can be adjusted to levels that are outside of the ranges favorable to disease development.
A critical factor in preventing greenhouse disease is proper management of humidity levels. Many pathogens require high humidity levels and the resulting water on the surfaces of the plant in order to attack plants. Keeping humidity levels in the greenhouse low is a crucial tool growers have for preventing disease outbreaks.
DryGair offers dehumidification solutions for greenhouse conditions. This system extracts excess humidity from the greenhouse air, circulates the air uniformly throughout the greenhouse to prevents the formation of wet microclimates, and provides the optimum conditions to prevent humidity diseases and the consequences they entail. This is an energy efficient solution targeted at preventing disease before it can even get started.
Greenhouse growers have the power to create the environment that they want within their facility. A knowledge of the pathogen biology, interactions between the pathogen-host-and environment, and the tools available at hand give the grower an upper advantage when it comes to disease management. Breaking the triangle is the key to preventing disease, and producing healthy, high-quality crops.