Pest Management In Hydroponics
By Dr. Tahir Mahmood
After nutrition, there is nothing more important than pest management when growing products in a hydroponic (soilless) medium. Although the same disease and insect avoidance procedures used in soil are practiced in hydroponics, control measures in hydroponics are more important. This is because the hydroponic nutrient solution used for feeding can be an ideal environment for some types of pests. Measures must therefore be taken to keep them out.
In most instances better pest control is based on common sense. Keeping pests out of a crop is better and easier than attempting to control them after they have made their appearance and started creating crop problems. One of the easiest ways of doing this is by making sure that working and growing areas are clean. As the trend today is moving away from chemical pest control (especially on food crops), sanitation is the most important pest control approach that can be adopted. Since most of the pest problems are brought to the crop, preventing their entrances lies at the root of a good pest management program.
Pest control is a highly specialized field that depends on the type of crop, the method of growing, and the environment. Some brief general measures to control pest attacks will be discussed in the following paragraphs. Keep in mind, however, that these general recommendations can go a long way in preventing the occurrence of a pest problem, thereby avoiding the hazard of lost crops and the expense of the continuous use of chemical pesticides.
A two-step procedure should be followed to tackle the pest problem in plants after the attack.
- Identification of the pest problem
- Kind and intensity of the problem
Once the pest attack has occurred, the most important thing to do is identify the pest before taking any corrective action. In certain cases it might be necessary to call an expert to assist in identification and to prescribe pest control measures.
Identification of pest problems is very important because some pest problems occur as a secondary effect. Controlling them by using any chemical will be ineffective until the primary cause is identified and corrected.
For example, a pest problem can gain a foothold if that crop is under any kind of stress. These stresses include nutrient deficiency, water, and temperature stress. They can set up a crop for invasion by some ever-present, but not usually seen pest. Older plant tissues become easy targets for diseases and become a desirable habitat for insects. Any type of pest management will be very inefficient until the grower’s growing system becomes well managed - free of nutrient and environmental stresses. Therefore it is very important to identify and determine the primary cause for a developing pest problem so that the correct action can be taken to control it.
Kind and Intensity of Stress
The kind (disease, insects) and intensity of a pest problem are also very important to know before starting any pest corrective measures. This is because the kind and intensity of pest problems that a grower confronts varies considerably from one place to another. This in turn affects the controls used. It is very critical that a grower be familiar with specific pests and their threshold levels (the degree to which they start doing harm to plants), as well as the corrective measures. Daily monitoring procedures should be developed and routinely practiced. It is very important for the growers to be familiar with the levels of pest incidence. Every grower must be able to recognize at what level a pest can be tolerated without requiring treatment. They can then assess the crop damage and the economical impact.
As mentioned in the beginning, pest management is very important in hydroponic growing compared to open field crops for several reasons. In the following section some pests and their general management strategies will be discussed for effective control.
Types of Pests and General Ways to Tackle Them
Anything that has a negative effect on plant growth falls under the category of pests; it can be through roots, shoots, leaves, etc. Weeds are also a pest in both open field crops and some organic hydroponic vegetable growing operations.
Most Pests Fall Under Three Categories: Diseases, Insects and Weeds.
Diseases
There are different types of diseases with different modes of action. Some attack the plant through the soil (e.g., phythium). The other common pests are various fungi that inhabit plant leaves. They vary in type and occurrence, depending upon plant species and environmental conditions. These diseases are particularly severe when conditions are warm and moist. The best way to control these types of diseases is to keep plant leaves dry and to avoid extreme temperatures with relatively low humidity. Spraying certain fungicides on the foliage can control them and using some preventative measures can also control them. The incidence of these kinds of diseases can also be minimized by creating resistance within the plant.
The classic example of this is the use of a product carrying Chitosan. It can build up resistance in the plant against mildew diseases.
As was mentioned earlier, hydroponic growing is highly prone to pest attacks because the nutrient solution used for irrigation is an ideal environment for the growth of algae and other pests. Minimizing exposure of the nutrient solution to light can prevent the growth of algae, which will clog delivery tubes, pipes, and valves and which will bring spores that can induce disease in plants. To avoid this problem, filter the nutrient solution. Filtering will help keep many disease-causing organisms away from plants. Some pest control chemicals can also be used to disinfect solution, but care should be taken so that its concentration does not become toxic.
There are certain other methods that can help to reduce the chance of disease occurrence in plants. These include:
- Use Sulphur dusting to control/prevent diseases.
- Use a sterilized medium or a medium that has fewer chances of disease incidence, like coco coir.
- Avoid allowing plants to experience any stress (temperature, nutrition, water etc).
- Use natural and synthetic fungicides.
These kinds of diseases can be effectively controlled using resistant cultivars, and by controlling the insects that carry these diseases from one place to another.
Insects
Insects are normally brought to the crop and is usually their offspring that cause damage to plants. Having an idea about the life cycle of insect pests can pinpoint steps to control them at the right time. By knowing that an insect infestation might occur and the conditions that are suitable for this, the grower can use appropriate measures to control them, even if their present population is insufficient to damage the crop. Ideal conditions for pest attacks are:
- Dense plant population
- Low temperature
- High humidity
- Old medium /soil that carries eggs of insect pests
Insect populations can be controlled by several means:
- Insecticides
- Organic and safe products like Neem Oil
- Inorganic insecticides available in the market
- Biological Control. Use of insect predators to get rid of insect pest population
- Yellow Sticky traps (especially for white flies because these flies are attracted by the yellow color and adhere to the sticky board on contact)
As with most diseases, the prevention of insect attacks is more effective than the effort to bring a damaging population under control. There are several ways to prevent insect attacks.
- Keep the plant canopy open by maintaining the plant spacing, pruning and stacking. Provide air movement in crops.
- Reduce the humidity. This will help to create a less ideal situation for these insects.
- Remove old plants and medium where an insect attack has occurred.
- Improve sanitation and better cultural practices.
Dr. Tahir Mahmood
Director Research and Development
Grotek Manufacturing Inc