It is already known that hydroponics, compared to the conventional system, is less susceptible to pests and diseases, but one of the most common problems (mainly in lettuce cultivars) is root rot, that is, the rot of the plant’s roots, an effect caused by species of fungus Pythium ssp.
In several states where hydroponics is practiced, root rot is diagnosed as the main cause of losses by producers, as the roots can be contaminated in all periods of development.
These fungi have an efficient mechanism of dissemination in NFT systems, through spores of asexual origin, endowed with flagella, called zoospores. These spores are carried by the nutrient solution that circulates in the system, that is, it is able to contaminate the roots of all plants present in the cultivation channels.
Identifying the problem
In summer months there is a higher incidence and severity of the problem, the high temperature of the nutrient solution (which decreases its oxygenation) an important factor for the development of the fungus (since Pythium is an opportunistic fungus), causing stresses in plants and contributing to the decrease of their natural resistance.
At first, it is possible to notice that the infected root tips have a certain brownish darkening, softened appearance and release a foul-smelling liquid. Subsequently, the root rots, causing necrosis of the entire root system, leading the plant to death.
It is also possible that Pythium spp causes sub-clinical infections. These infections reduce production, but do not exhibit the classic symptoms of the disease, causing the producer not to detect the problem at the beginning. Plants that are able to grow are smaller in size and generally become hot withered.
The best form of control is preventive, preventing the entry of the pathogen into the system, mainly through water. For this it is necessary to use good quality water and healthy seedlings. In the areas where the presence of the fungus was found, it is necessary to clean the materials, from benches and profiles to the irrigation system.
The most important preventive action is the choice of a technical and adequate structure in the assembly of the hydroponic system, that is:
- Suitable profiles in double plastic layer, white on the outside and graphite on the inside (reflecting heat);
- Short benches (see the HPM System ) that allow the nutrient solution to quickly travel back to the reservoir so that the solution does not heat up;
- Optimal oxygenation in the nutrient solution reservoir;
- Ideal assembly of the engine room (where the reservoirs are located);
- Ideal working temperature inside agricultural greenhouses;
- Use of suitable screens and films, in addition to other factors.
Another alternative to combat this problem is biological control. It can be one of the most promising and efficient methods to control the disease, as it has the advantage that biocontrol agents act directly in the infection zone. Bacteria of the bacillus genera are the most promising.