Last week, we talked about integrated pest management (IPM) and the four major pillars: monitoring, identification, control, and evaluation. Control is arguably the most diverse pillar, as pest control and pest management techniques used by a grower will depend on dozens of different factors, including crop type, pest type, severity of infestation, growing environment, budget, and environmental conditions. We can’t cover everything, but here are the broad strokes of pest control in IPM.
Setting action thresholds
Seeing a single aphid while scouting doesn’t necessitate dousing the entire greenhouse in pesticides. But when does a molehill become a mountain? At what point should you act? And what type of action should be taken? If we want to talk about pest control, we need to talk about deciding when and how to utilize control methods. Answering the above questions in advance of a pest problem will help you resolve the issue in a calm, controlled fashion. Planning and writing it down will also mean that you’re not the only one who can take action if a problem arises while you are away. One of the recommended ways to plan is to define your action thresholds.
The point at which the grower is losing money by not treating the pest problem; the cost of pest control is less than the cost of crop damage by pests. Generally defined by how severe an infestation is, which can be measured by number of insects in traps, amount of damage to crop, etc.
Action thresholds will differ for every grower, crop, pest and even region. Your scouting notes and information about the outcomes of previous control strategies will be the most helpful in determining what a good threshold might be.
However, if you’re just starting out or don’t have very thorough records of past scouting data there are other options.
- Reach out to growers in your network
- Utilize online resources such as GPN Magazine to research established thresholds for different pests and crops.
- Talk to your biocontrol supplier GrowLiv Biologicals
- Hire an IPM consultant
- Check if there’s a government funded extension service for farmers in your area.
Thresholds will also be influenced by what type of control you want to use: if you want to use natural enemies (biocontrol), for example, you will have to start releasing beneficial insects preventatively or when pest populations are relatively low. If you plan on using a chemical control method, then you can wait until the pest population is a bit higher before spraying plants. In the same vein, if you don’t notice an infestation right away, you may be limited to more quick-acting control methods since the pest population may already be quite established. This can lead to multi-level thresholds.
These are action thresholds that have more than one contingency. For example, a growing facility might have a two-part threshold for thrips: if less than 10 thrips are counted on each yellow sticky card per week, then predatory mites may be used. If more than 20 thrips are counted on each yellow sticky card per week, then a contact spray may be a better option. Between these two thresholds, the management strategy chosen will depend on the stage of development of the crop, other potential pests, etc.
Cultural controls are those that involve planning your planting, cultivation and management practices in ways that make the environment less favorable for the establishment, dispersal, and development of pests. While cultural control techniques generally must be planned in advance, they are helpful in stopping infestations before they start and can be used against many kinds of pests, making them a worthwhile investment of time and planning.
Examples of cultural control
- Choosing disease- and pest-resistant cultivars when possible. The upfront cost is higher for resistant varieties but they are usually very effective at managing pest and disease pressure.
- Trap crops. A common trap crop for thrips, for example, is the yellow marigold.
- Managing the conditions outside the greenhouse. By reducing the amount of plant life surrounding your production area, you also reduce the number of pests nearby. If you can’t bear to get rid of your garden, consider growing plants that are attractive to beneficial insects.
Definition Trap crop - A crop that is very attractive to certain pests. Growers may treat them with insecticides and place them around the greenhouse in order to lure in and kill pest insects. Also known as sacrificial crops.
Physical control is about taking a hands-on approach and physically removing pests from the crop or utilizing physical barriers.
Examples of physical control
- Handpicking: Since it is so time-consuming, this control method is not used as often as others but may work for very localized infestations and larger pests.
- Traps: There are many kinds of traps, including sticky card traps, to catch and incapacitate pests.
- Physical barriers: This can include screens, which allow for ventilation without providing an entry point for pests.
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 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 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.
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.
While there exist 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.
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.
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