Greenhouse biological control 101: Part I

What greenhouse owners and operators should understand about biological control.

Biological control is the use of one species of a living organism to suppress the population of another. In a greenhouse, there are key insect pests that cause plant damage, vector viruses and reduce aesthetic value. There are biological control agents that can be released to make an impact on the population of most greenhouse pests. Some of the most commonly used biological control agents are: Hypoaspis miles and Steinernema feltiae for gungus gnat; Aphidius colemani and A. ervi for aphids; and Amblyseirs cucumeris, A. swirskii and Orius insidioosus for thrips. There is more to the use of biological control agents than just buying the agents and letting them go and poof – pests are gone forever.

Understanding the relationship between the pests and the biological control agents in the case of parasitoids or predators is critical. Predators eat the pest while parasitoids attach or live within the pest. There are searching mechanisms that aid in these biological control agents finding their host (the pest). They then decide to consume or parasitize that host by laying eggs inside or on it. There are pitfalls that can occur. Some of the most common issues that can cause a biological control system to fail are releasing the biological control agents too early or late, grower’s impatience on efficacy, lack of adequate pest suppression, and chemical use or residue that adversely affects the natural enemy.

In an indoor controlled environment, like a greenhouse, the predictability of pest populations is understandable. Computer systems manage the temperature and light requirements, allowing us to predict pest lifecycles and reproduction rates. We lack external elements like wind and rain that can aid in either reducing or increasing pest populations and the natural enemies that already exist in the environment.

The correlation of pest population and natural enemy population plays an extremely important factor in the success of any biological control system. For a greenhouse biological control system to work effectively, augmentation biological control is used. In an augmentation system, biological control agents are supplemented and released. The biological control agents are then continually released to build the population throughout the production area. Most successful systems occur when the releases are made early in your cropping system and continued through the cropping cycle based on the pest you are managing. An example would be releasing Hypoaspis miles only in the propagation house where your problem exists due to the high levels of moisture and humidity. Once the plants are transplanted and moved to the finishing area, the ideal environment for fungus gnat population is diminished and the Hypoaspis mile release is stopped.

A good way to determine release times is by identifying your past year’s pest problems and then developing a release schedule based on your historical data. From that point forward, the other best tool is to coordinate releases based on your weekly production scheduling for propagation or transplanting.

The most important factor is to understand the relationship between pests and biological control agents to determine if management goals are being reached. In-depth scouting must be performed at a minimum of once a week that includes detailed scouting records. This action is critical to follow the organism’s populations.

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