Identifying and Controlling Disease Organisms and Insects: How Well Are You Prepared?
Selecting disease- and insect-resistant plants is a primary example of passive procedures for maintaining a garden free of disease organisms and insect infestations. However, sometimes passive is not an option.
In most cropping systems, disease organisms and insects are always present, waiting for those conditions favoring their multiplication that can lead to plant invasion. One of the major means of preventing an infestation is to control those conditions favoring multiplication and establishing a barrier that will prevent invasion.
For those growing in enclosed environments, the first priority is to effectively sterilize the enclosure, and then to maintain that sterile integrity by keeping disease organisms and insects out. Screening and sanitizing entrances is a means for keeping disease organisms and insects out of a growing chamber.
Also, since clothing and shoes can be a means of carrying disease organisms and insects from place to place and into an enclosed chamber, they too need to be kept clean or be sterilized. Equally important is to establish and maintain those conditions within the enclosure that will prevent insect and disease growth just in case either does enter.
Also, be prepared to combat an infestation if it occurs by being aware of what diseases and insects are in the area and associated with the plant species you’re growing. As such, periodically scouting the growing crop (possibly by someone who does this as a profession, such as a trained and experienced plant pathologist or entomologist) is essential.
If infestations do occur, there are two important requirements needed to effectively control them. First is proper identification of the invader (this might require prompt professional assistance as even the most experienced grower can easily make mistakes). Second, as mentioned above, is being prepared to quickly and effectively deal with the invasion.
For disease control, keeping the plant in a “healthy” state—including maintaining nutrient elements at sufficient levels—is an effective means of control. For example, if plants become too high in nitrogen (N) or have succulent foliage are easily susceptible to disease and insect invasion.
Also, high silicon (Si) content in plant foliage has been found to reduce the ability of hypha to penetrate plant cells (for those growing plants hydroponically, including a soluble source of silicon in the applied nutrient solution formulation is essential in order to utilize this capability).
Keep in mind, however, that a nutrient solution is an ideal matrix for disease organisms—the species and numbers of which depending on temperature, degree of aeration, and biological and elemental content.
For example, those who choose to use nutrient solution formulations containing biological substances are more likely to have root disease infestations than nutrient solutions without added biologicals, as some of these substances can be a potential food source for fungi and bacteria.
As such, recovered nutrient solution requires filtering to remove suspended organic materials, and then sterilized before being re-circulated. Sterilization can be by heating, ultra-violent radiation exposure, or treatment with ozone (O3).
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The method of disease control is determined by the type of organism (whether a virus, fungus or bacteria). Viruses are best controlled by the use of resistant plants or by control of the delivery vector, which is frequently an insect.
For the control of fungi and bacteria, most growers prefer the use of non-chemical means. There are a number of effective natural foliage-applied products whose effectiveness are determined by method, frequency of application and plant leaf characteristics.
However, not all diseases can be effectively controlled using such biological materials; therefore, some plants requiring the use of foliar-applied inorganic chemicals or fogging the surrounding environment with a control chemical.
Then there are some diseases that suddenly “appear” when the plant reaches a certain growth stage. Plants seem more venerable to attack when under stress, be it due to improper nutrition, low or high light radiation conditions, moisture stress or fruit setting. For example: powdery mildew can materialize on cucumber leaves when the plants began to set fruit. This same disease sometimes appears when the plants are magnesium (Mg) deficient.
For insect control, the use of predator insects—referred to by some as beneficials—can be an effective control procedure. This method requires the predator to be in place prior to invasion with an adequate food supply in order to survive in sufficient numbers to be effective. However, not all insects have a corresponding predator. In this case, chemical or biological control procedures applied at the most venerable stage of their life cycle is effective.
There might be times when the cost and effectiveness of a control treatment might not be justified. It all depends on the extent of damage to the plant in terms of appearance and reduced product yield in comparison to the cost for the chemical, the equipment required for application and the time and salary paid to the applicator.
For those with concerns regarding ecological balance, some diseases and insects can be a factor in the unbalancing of an eco-system since they create a condition more damaging to the plant and its surrounding environment if left untreated. Also, some control treatments are based on the Integrated Pest Management (IPM) system of pest control, which defines what cultural, chemical and non-chemical procedures are acceptable within the Best Management Practice (BMP) concepts.
IPM programs have been implemented for application to a number of cropping systems, both in the field and greenhouse, by setting action thresholds, monitoring and identifying pests, preventing pests from becoming a threat and evaluating the proper control method for both effectiveness and risk.