Many Greenhouse Growers across North America are facing the same common challenge which affects the sustainability and growth of their operations. Inflation in recent years has driven the cost of most growing inputs to drastically increase, while the selling prices of their production has not increased on par. Production margins are getting tighter, and Growers want to know “how can we produce more, for less?”
At Crop Defenders, we understand how challenging this feels, and how this pressure affects Owners and Management, Growers, and IPM roles differently. There are many ways to approach this problem, yet one of the most effective approaches involves developing strategies to increase the profitability per square meter through sustainable pest management.
In this blog post, we will specifically focus on a pest that causes more direct loss through its feeding damage than others: thrips.
Tiny but devastating, thrips outbreaks can eat away up to hundreds of thousands of dollars of potential profit from a greenhouse. In this blog post, we'll explore actionable strategies to control them at every life stage. By the end, you'll be empowered with insights to that will help you sustainably manage thrips, and keep your crops healthy and thriving.
Understanding Thrips Control: A Lifecycle Approach
Greenhouse Growers in Canada and the United States often struggle with four main thrips species: Western Flower Thrips (Frankliniella occidentalis), Onion Thrips (Thrips tabaci), Poinsettia Thrips (Echinothrips americanus), and more recently Pepper Thrips (Thrips parvispinus). They are all notorious for their rapid reproduction and resistance to many control methods. To effectively manage them, it's crucial to understand their life cycle, which consists of several distinct stages: eggs, larvae, prepupae, pupae, and adults. Each stage presents unique challenges and opportunities for control.
1. Recognizing Thrips Eggs and What to Do for Control
Thrips eggs are tiny, translucent, and often embedded within plant tissues, making them challenging to spot with the naked eye. They are typically laid on the undersides of leaves, in flowers, or within plant stems. The tissue surrounding the eggs provides protection and can prevent eggs from being affected by certain pesticides.
1. Understanding Where Thrips Lay Eggs
Thrips typically insert their eggs into plant tissue, making them challenging to detect. Eggs are often laid on the undersides of leaves, within leaf veins, or in flower buds.
In crops like cucumber, pepper, cannabis, strawberry, and tomato, eggs are usually embedded in leaf tissue or flower structures. In ornamental plants like chrysanthemums, poinsettias, and gerbera, thrips often target young leaves, petals, and flower buds for egg-laying.
2. Using a Hand Lens or Microscope
A high-quality hand lens is essential for detecting thrips eggs. Look closely at areas with fine scarring or small puncture marks on leaves, as these often indicate where eggs have been inserted.
For crops like strawberries and peppers, check new growth and flower clusters, as these areas are prime sites for thrips egg-laying.
3. Monitoring Leaf and Flower Distortions
Early signs of thrips presence can include leaf distortions, silvery streaks, or curled edges. These distortions often occur near where thrips eggs are inserted. In plants like poinsettias and chrysanthemums, distorted young leaves or stunted buds are telltale signs.
In tomatoes and cucumbers, tiny spots of discoloration or scarring near veins and flower buds can signal thrips egg-laying activity.
4. Dissecting Plant Tissue
In crops like cannabis and ornamental plants (gerberas and chrysanthemums), gently peeling back layers of young leaves or flower petals can reveal hidden thrips eggs. Eggs may appear as tiny, pale oval shapes embedded within the tissue.
Dissect flower buds, particularly in strawberries and poinsettias, as thrips often lay eggs deep within tightly closed buds.
5. Control Measures:
Preventive Measures: Use yellow or blue sticky traps to monitor adult thrips populations. High counts can indicate the presence of eggs and prompts early intervention.
Predatory Mites: Introduce predatory mites like Amblyseius cucumeris, or Amblyseius swirskii before eggs start hatching. A common behaviour of predatory mites such as swirskii and cucumeris is to hang out near thrips eggs so they can consume the hatchlings as they come out of the eggs. They’ll consume them one by one and clean up a whole leaf.
2. How to Recognize Thrips Larvae and Control Them
Thrips larvae are small, pale, and lack wings or wing buds. They are usually found feeding on the undersides of leaves, causing silvery streaks and deformed growth.
The first larval instar stage hatches from the egg. After molting (shedding their skin), the first larval instar becomes a slightly larger second larval instar. Both stages are very tiny (1st 0.2-0.3mm; 2nd 0.4-0.5mm) and are preferred by predatory mites for feeding. Larval stages are primarily found in flowers as they love to consume pollen. Young larvae can also be found on leaves and fruit.
Control Measures:
Biological Control Agents: Introduce predatory mites like Amblyseius cucumeris, or Amblyseius swirskii, both of these feed on the larval stages.
3. How to Recognize Thrips Pre-Pupae and Pupae and Control Them
Thrips pre-pupae and pupae are transitional stages where thrips develop into adults. For Western Flower Thrips (Frankliniella occidentalis), Onion Thrips (Thrips tabaci), and Pepper Thrips (Thrips parvispinus), these stages typically occur in the soil or within plant debris, making them less visible. For Poinsettia Thrips (Echinothrips americanus), these stages can be found on the plant.
Pre-pupae are slightly larger than 2nd instar larvae, they are 1-1.2mm in length. Thrips pupae are 1.2-1.5mm in length and look more like an immature thrips adult. Wing buds are present on both the pre-pupae and pupae.
Control Measures:
Soil Treatments: Apply beneficial nematodes like Steinernema feltiae to the soil. These microscopic worms infect and kill thrips prepupae and pupae.
Predators:
Dalotia coriaria (Atheta) is another available soil dwelling predator. Atheta larvae and adults feed on thrips prepupae and pupae. The additional benefit of having Atheta is their ability to distribute themselves by flying and searching for thrips.
Stratiolaelapes scimitus (Hypoaspis) is a soil dwelling mite and will feed on thrips pre-pupae and pupae.
Orius insidiosus can be used to target Echinothrips americanus pre-pupae and pupae on foliage.
Sanitation: Regularly remove plant debris and fallen leaves from the greenhouse floor to eliminate potential pupation sites. Investing in labor practices to remove floor debris can significantly reduce the risk of having newly developed thrips adults attack your crop.
4. How to Recognize Thrips Adults and Control Them
Thrips adults are slender, winged insects that can range in color from yellow to dark brown. They are often found on flowers, leaves, and new growth, where they feed and reproduce.
Control Measures:
Predatory Insects: Introduce predatory insects like Orius insidiosus which actively hunt and consume adult thrips, as well as most other life stages.
Trap Plants: Use plants which are more attractive to thrips than your commercial crops. Effective options include potted bush bean plants, yellow flowering chrysanthemum, gerbera, or marigold, as well as cuban oregano. Pair trap plants with yellow sticky cards placed in holders to increase attraction. Monitor infestation levels, and bag infested plants and replace them when necessary.
Biological Insecticides: Apply biological insecticides such as Metarhizium anisopliae or Metarhizium robertsii; these are fungal pathogens that infect and kill all thrips stages. Ensure thorough coverage and repeat applications as needed.
5. Why It Is Important to Target Each of These Life Stages
Thrips control requires a comprehensive approach that targets all life stages. Neglecting any stage can lead to population surges, and the ultimate consequence is economic loss. Having thrips in your crops is inevitable, but costly outbreaks can be prevented. By addressing each stage - eggs, larvae, prepupae, pupae, and adults - you can get:
Reduced Stress: Effective control at all stages means fewer thrips-related issues and less stress for you as a Grower.
Lower Thrips Populations: A multi-faceted approach keeps thrips populations at manageable levels, reducing the risk of outbreaks.
Higher Yields: Healthy plants free from thrips damage produce more high-quality yields.
You Can Prevent:
Population Surges: Gaps in control measures allow thrips to reproduce unchecked, leading to rapid population growth.
Increased Costs: Ineffective control results in more resources spent on emergency measures, often involving chemical pesticides that harm beneficial organisms.
Crop Damage: Thrips damage reduces plant vigor, affects yields, and compromises the quality of your vegetables, soft fruits, and flowers.
Take Action! Schedule a Consultation for Customized Greenhouse Solutions
Ready to defend your greenhouse production against thrips outbreaks? Don't wait until it's too late! Schedule a call with our Specialists to receive personalized advice, tailored to your specific needs. Our team will help you develop a customized strategy to prevent thrips outbreaks ecologically and economically.
Let's work together to keep your production thriving!
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