Many greenhouse growers no longer rely exclusively on conventional pesticides to control pests. Most have increased their use of mechanical and biological control agent (BCA) methods. While pesticide resistance issues have driven much of this change in management philosophy, many growers are now discovering how well BCAs work and how to easily incorporate them into pest management programs.
Many greenhouse growers have found that BCAs can be used to achieve commercially acceptable levels of control. However, a few remaining growers believe that BCAs are not practical to implement. The barriers that impede adoption of BCAs typically include the perception that they are less effective than their conventional pesticide counterparts and require special skills and knowledge for success.
Performance barriers often can be addressed by implementing preventative use strategies and by fully adopting principles of integrated pest management (IPM) rather than as a direct replacement to conventional pesticides. Development of pest management strategies that marry mechanical, biological and chemical control methods, as well as regular scouting and pest monitoring, will maximize efficiency of BCA.
Developing An IPM Program
The first stage in developing an IPM plan is to establish action, or economic, thresholds. The economic threshold is the pest population that will trigger pest control decisions. Economic thresholds will vary by plant species and growth stage, plant susceptibility and growing conditions, as well as grower management preference.
Once economic thresholds have been established, regular pest monitoring should be performed to accurately identify and quantify pest populations over time. Conventional pesticide use is not typically warranted unless pest population exceeds economic thresholds.
Prevention is the first line of pest control. When feasible, plants cultivars should be selected with resistance to common pests. Cultural practices should be adopted that maximize plant growth and vigor because weak plants typically are more susceptible to pests. Pest proof netting or other physical barriers often are used to prevent insects from moving into or among greenhouses. Preventative and cultural methods that minimize pest populations dramatically increase efficiency of BCAs.
Biological control agents work best under low pest populations and few BCAs provide the rapid and total control afforded by conventional pesticides. Treating pests preventatively with BCAs will maintain a low pest population, making it less likely that pest populations reach economic thresholds. Biological control agents typically should be introduced or applied early in a growing cycle to allow for most effective control.
If pests do reach thresholds, conventional pesticides that are compatible with biological control agents can quickly reduce pest populations to manageable levels. Biorational pesticides like horticultural oils or insect growth regulators often are compatible with many BCAs. Consult BCA suppliers for information regarding pesticide compatibility before making applications. Apply conventional synthetic insecticides responsibly− only treat when necessary and rotate modes of action to limit the potential for targeted pests to develop resistance.
If a conventional pesticide must be used that is not compatible with introduced BCAs, it will be necessary to reintroduce BCAs. Depending on the pesticide, it may take several weeks for residues on treated surfaces to fall to levels low enough not to harm BCAs. Again, consult the BCA supplier for information regarding compatibility and for information on how to safely reintroduce BCAs.
Beneficial nematodes often are one of the first BCAs adopted by growers experimenting with biological control for the first time. Beneficial nematodes have been used effectively in IPM programs for control of a number of greenhouse pests, such as fungus gnats, western flower thrips and shore flies. Beneficial nematodes are not a large departure from most growers’ current program because they can be applied by using conventional application equipment with few modifications, are compatible with several conventional pesticides and cost is consistent with conventional pesticides.
As with other BCAs, applications of beneficial nematodes are most effective when they are introduced early in the growing cycle before pest populations are high. In most instances, regular applications of beneficial nematodes in conjunction with good cultural practices will effectively manage pest populations below economic thresholds.
If, however, environmental conditions are favorable for pest problems and economic thresholds are exceeded, effective conventional insecticides can be applied to quickly and efficiently reduce pest populations. Regular beneficial nematode applications should resume once pest populations have been reduced below economic threshold. An IPM-based program like this maximizes efficiency of pest control while reducing conventional pesticide inputs and the likelihood of pests developing pesticide resistance.
Biological control agents, when utilized properly as a component of an IPM program effectively, can control many greenhouse pests. Most BCAs should be first used preventatively, and continuously for most efficient control. Conventional pesticides should only be used as needed to ensure economically sustainable production − limiting opportunities for development of pesticide resistance.