Integrated Pest Management (IPM): Control Strategies

Last week, we reviewed the four pillars of Integrated Pest Management (IPM): monitoring, identification, control, and evaluation. Among these, control is the most diverse pillar. The techniques a grower chooses will depend on crop type, pest thresholds, historical pest issues, and environmental conditions. While we can’t cover every method, here are the core approaches to pest control in IPM.

 

Setting Action Thresholds

Seeing a single aphid doesn’t mean it’s time to spray the entire greenhouse. But when does a molehill become a mountain? At what point should you act and how?

Defining action thresholds in advance helps you respond in a calm, controlled manner rather than scrambling when a problem appears. Writing them down also ensures other team members can act if you’re away.

Action threshold: the pest density at which economic damage outweighs the cost of control. Thresholds may be based on trap counts, visible crop damage, or other indicators.

Because thresholds vary by crop, pest, region, and even grower, scouting records and past control outcomes are your best tools for setting them. If you’re just starting out, you can:

• Reach out to fellow growers in your network
• Consult your biocontrol supplier (GrowLiv Biologicals)
• Hire an IPM consultant
• Check government-funded extension services in your area

Thresholds also depend on the type of control. Biocontrol agents should be released preventatively or at low pest levels. Chemical controls, on the other hand, can be applied later when pest populations are higher. This creates the need for multi-level thresholds.

Multi-Level Thresholds

Multi-level thresholds include contingency plans based on pest density. For example, in thrips management:

• <10 thrips per yellow sticky card per week → release predatory mites
• >20 thrips per card per week → apply a contact spray

The decision between thresholds may also depend on crop stage or the presence of other pests.

Cultural Control

Cultural controls involve planning cultivation practices to make the environment less favorable for pests. They must often be planned in advance, but they can prevent infestations before they begin.

Examples:

• Selecting pest- and disease-resistant cultivars (higher upfront cost, but highly effective).
• Planting trap crops (e.g., marigolds for thrips).

Managing vegetation around the greenhouse to reduce pest reservoirs or growing beneficial insect–friendly plants nearby.

Definition – Trap crop: a plant highly attractive to pests, used to lure them away from the main crop. Trap crops may be treated with insecticides or sacrificed to reduce pest pressure.

Physical Control

Physical controls involve direct removal of pests or physical barriers to exclude them.

Examples:

• Handpicking (useful only for small infestations of larger pests).
• Traps (e.g., sticky cards to capture flying insects).
• Screens and mesh barriers to exclude pests while allowing airflow.

Biological control 

Biological control is the use of other organisms to help control pest populations. The organisms are also known as natural enemies or, if insects, beneficial insects. Many growers are turning to biological control methods as a replacement for pesticides, especially greenhouse growers that can easily release and maintain natural enemy populations. Biological control agents can be broken up into the following categories: 

Predators 

Predators are insects that hunt and eat the pest insects on your crop. Most predators will hunt multiple types of pests, but others prefer to hunt a specific pest. Persimillis mites, for example, only hunt spider mites and spider mite eggs. 

Parasitoids 

Parasitoids are insects that lay their eggs on or inside of the pest insects, where they hatch and feed on the pest insects, killing them. Almost all parasitoids are specific to certain pest species. Make sure you are ordering the correct one.  

Pathogens 

Bacterial biocontrol agents are bacteria that are added to the soil to control soil-dwelling pests. The most common bacterial biocontrol agent is Bacillus thuringiensis, also known as Bt. There are multiple different strains of Bt, each of which targets a specific type of pest, so make sure you are purchasing the correct strain when ordering. Unlike chemical pesticides, Bt will not harm beneficial insect populations: the proteins secreted by Bt only become toxins when they enter the digestive system of the target pest group (e.g. caterpillars), leaving non-target organisms unharmed. 

Did you know? Some crops have been engineered to actually produce the Bt toxin, which means that insects that eat the plants will be poisoned. 

Nematodes 

While there are nematodes that are detrimental to plant health, here we are discussing entomopathogenic nematodes specifically. 

Nematodes are microorganisms that infect pest insects, sterilizing them. Like bacterial pathogens, they are generally released into the soil and infect pest insect larvae that dwell there. 

IPM and biocontrol are often used interchangeably, but biocontrol is just one type of control within the very many types of control utilized within IPM strategies. 

Did you know? Biocontrol, while one of the more advanced techniques of pest control, was used as early as 324 BCE! There are records of farmers in China introducing ants to trees to help control pest caterpillars and boring insects. 

Chemical control 

In IPM, chemical control is often seen as taking a backseat to other control methods, mostly due to potential incompatibility with biological control methods, resistance development of pests, and undue effects on the environment. That being said, it still has a place in many IPM plans.  

Things to consider when adding chemical control to your IPM strategy: 

• Broad spectrum pesticides generally have a persistence of 2-3 months, which is great for deterring pests, but not helpful for biological control agents if you later decide to use them. 
• Only use selective pesticides and cycle 2-3 different formulations. Pests may evolve resistance to a pesticide, especially if the pesticide is overused. 
• Pesticides can pose a direct hazard to workers and secondary exposure hazards to family, friends, and pets. Double-check that you are following the directions correctly and respecting re-entry limits. 

 

Did you know? Pest populations generally recover more quickly than beneficial insect populations, so using a pesticide on your crop when you’re already using a biological control method can sometimes worsen the issue. 

Overall, there are dozens of different control methods to explore within IPM, so you’re bound to find a couple that work for you. Continue to take thorough scouting notes during and after employing pest control measures so that you can read back through them later and determine which control methods worked and which didn’t seem to make much of a difference. Each grower’s situation will be different, and so the control methods that work best will be different as well.