Historically, greenhouse floriculture has relied on synthetic insecticides to meet its pest control needs. However, growers are increasingly faced with the loss or failure of pest control products, declining access to new chemistries, stricter environmental/health and safety regulations, and the need to produce plants and vegetables in a manner that meets the demands of a retail/consumer driven market. In Canada, the failure of Spinosad (Success) for thrips within 6 to 12 months of its registration prompted a sea of change in pest management philosophy and approach.
Faced with a lack of registered chemical alternatives, growers turned to biological control out of necessity. Necessity led to success. Today biological control forms the foundation for pest management programs in Canadian greenhouses. More than 70% of growers use some form of biocontrol and certain crops are grown from start to finish without pesticide interventions. It has been a steep learning curve requiring a whole new approach and a shift from enactment of reactive ‘control strategies’ to implementation of preventative ‘management strategies.’
Considerations That Lead to Success
A series of drivers has created opportunities for broader integration of natural enemies and new biological products into integrated pest management (IPM) programs, but in turn, these programs are shaped by the bioproducts in which they are used. The diversity of floriculture crops grown and the variety of locations in which they are grown prevent a one-size-fits-all approach to biocontrol, and IPM systems need to be adapted to suit local conditions. There are some basic principles that transcend crops and location, and considerations of these help guide the development of a successful, biologically based, integrated crop management system.
Let’s consider a crop system. Many interactive variables affect the growth of greenhouse crops, the incidence and impact of pests and diseases, and the performance of biological and chemical controls. These include:
■ The type of crop and crop growth stage
■ Production practices and inputs
■ External environmental conditions (temperature, humidity, light).
Understanding how these factors interact with and affect the plant, pests and their control agents, is essential. Biological control agents are living organisms, and all of these variable factors directly affect them. Knowing the conditions under which they perform best helps guide the selection of natural enemies suited to the crop and growing environment. An understanding of issues that can impede or promote their activity then helps to refine and shape the IPM system.
IPM From Start to Finish
The efficient use of biocontrols requires different assumptions and timing of actions than for chemicals. Methods developed to guide the timing of pesticide sprays — action thresholds, for example — are effectively redundant in a biological control program. Why? Because if you wait until thresholds are reached before initiating a biocontrol strategy, it will be too late; pest populations will be too large to be brought under control using a biological agent. Biocontrol strategies function most efficiently when pest numbers are low, as they prevent damaging populations from developing. Insecticides are reactive tools developed, by-and-large, to quickly kill large numbers of pests from a single application. To be successful in biocontrol, take measures early, before pests are readily detected in a crop, and sustain them to suppress pest populations (or disease incidence). Biocontrol agents work best when deployed within a system that supports their success, where a range of components within that system function together to provide the desired level of suppression. While a grower must conceive and implement an IPM program for the entire production period, he or she may consider different approaches for different phases in the crop cycle.
Prevention and Early Intervention
Prevention starts with good sanitation practices, ensuring young plants are brought into a clean production environment and pests are excluded wherever possible. No residues should remain from previous crops, benches and floors should be disinfected, weeds under benches removed, and algae cleaned from the floor. Ensuring that the greenhouse is clean from the get-go and preventing the entry of pests into the greenhouse helps on so many levels.
Experience counts. Being aware of potential threats and using this knowledge to put processes in place to facilitate early detection and/or early action to mitigate pests will get a biocontrol program started successfully. This includes the use of cultural practices that minimize pest build-up. For example, the use of production practices that optimize nutrient and water inputs to grow healthy plants. For some crops, there is a link between fertilizer rate (especially high nitrogen) and population growth of pests like thrips and aphids. Use of best practices will help create a more resilient productive crop that is less prone to pests and diseases.
Many crops are grown from propagative material produced in-house or imported from offshore. In spite of propagators’ best efforts, cuttings frequently carry low numbers of pests. Detection of these insects, which are often cryptic in nature, is next to impossible, and for pests like thrips, the problem is worse because their eggs are laid in plant tissue. Many growers now assume that incoming cuttings will carry some pests. The decision then, is to introduce biocontrols immediately without waiting for sticky card catches to reach a certain threshold. Remember, for highly successful pests (thrips, whiteflies, spider mites, aphids), which have rapid life cycles and a high reproductive potential, early intervention is critical to success of a bio-based IPM program. A strategy often used in the early stages of production is to front-load a biocontrol program to mitigate problems early by overwhelming pests with an army of biologicals. Predatory mites are often used as front-line troops; selection of species depends on the time of year and the pests anticipated.
Another way to alleviate pests on cuttings is by dipping. Immersing cuttings in biopesticides such as insecticidal soap, horticultural oil, or BotaniGard reduces hitchhiking Bemisia whiteflies. Dipping provides thorough coverage, is quick and effective, uses relatively little product, and is readily integrated into the workflow. Risks of disease transfer appear to be low, and can be mitigated through good sanitation practices and regular changes of the dip solution/suspension. The rates for soaps and oils typically have to be reduced from those used when spraying, owing to increased risks of phytotoxicity. Check the labels for guidance.
Strengthening Your Bio Program
In spite of the increasing sophistication of biocontrol programs in floriculture crops, pests can sometimes get ahead of the biologicals. While there are many reasons why this can occur, it means growers need to take steps to bring pest numbers down to levels where the biologicals can catch up. Pesticides can do this, but there are inherent disadvantages to using many chemicals. Choose pesticides with care to ensure they are compatible with the biologicals being used. Consider the whole program when deciding which product to select; materials used to regulate the target pest may have unintended effects on beneficials being used against another.
This is where biopesticides can play an effective supporting role. Within an integrated system, they can selectively control several challenging pests (and diseases) in a manner that is functionally compatible with other natural enemies. Their integration strengthens a biologically based IPM program, resulting in a more robust and (generally) more efficacious system. Several microbial biocontrol agents are registered for pest and disease management in greenhouse crops. Others based on biologically derived materials are also increasingly available.
IPM and biologicals: the way forward
The actions of the past have created the path to the future. Biological control still has a way to go before it totally displaces traditional chemistries, but used as part of an IPM program, it can get us a long way down that path.