Summary: Strawberries are an important economic fruit in the United States and the UK, but fruit quality and yield are threatened by a variety of pests and diseases. Biological control methods like nematodes and mineral oil sprays help to protect strawberries from pests and improve yields.
Overview:
What pests affect strawberry plants?
Garden Slugs
Western flower thrips
Two-spotted spider mite
Western tarnished plant bug
Strawberry sap beetle
Red stele root rot
How do I manage strawberry pests?
FAQ
Summary
Strawberries are an important crop in many economies, including the United States and the UK. The United States is the world’s second-largest strawberry producer, harvesting around 1.3 million tonnes each year. In the UK, annual strawberry production is valued at about £389 million (US $518.9 million). Western flower thrips alone cause an estimated £15 million in annual losses in the UK, while in the US, the spotted wing drosophila inflicts roughly $700 million in economic damage each year across fruit crops, including strawberries. This article will focus on identifying and controlling common strawberry insect pests and diseases, and explore the use of biological methods to reduce their impact.
What pests affect strawberry plants?
Strawberry plants are vulnerable to attack by a variety of pests, including beetles, slugs, mites, flies, and microbial pathogens. Some pests are more damaging than others, and their impact varies by climate and geographical location.
Garden Slug (Arion hortensis)
Slugs belong to a group of animals called molluscs and cause damage to strawberry plants by feeding on ripe fruit. Adult garden slugs are grey-brown and grow to about 2.54 to 3.8 cm. Slug damage typically appears as small, deep holes in the fruit, often near the stem. Slugs are most active at night and in damp conditions. Dried slime trails are a sign of slug infestations. Slug feeding can lead to further damage by insect pests. Slugs are relatively large compared to other pests and are easier to spot on strawberry plants.
Western flower thrips (Frankliniella occidentalis)
This insect pest causes damage to strawberry plants by feeding on flowers and causing premature wilting. Adult western flower thrips appear in shades of yellow and brown and grow up to 0.8 mm. Their wings have a feathery appearance, and the developmental stages of this pest (nymphs) typically appear as yellow or white. Thrips damage may cause discolouration near the stem of the fruit. However, this usually does not significantly affect the strawberries’ marketability.
Two-spotted spider mite (Tetranychus urticae)
This pest causes damage to strawberry plants by piercing leaves and feeding on plant fluids. Adult two-spotted spider mites have a diameter of around 0.5 mm and have a characteristic spot on each flank. Symptoms of damage include leaf yellowing and stippling, and extensive silk webbing may be present with larger infestations. Damage can stunt plant growth and reduce yields. Large infestations may be visible on the underside of leaves where this pest tends to feed and lay eggs.
Western tarnished plant bug (Lygus hesperus)
This pest, also known as the lygus bug, causes damage to strawberry plants by feeding on individual seeds, which prevents or slows the development of surrounding fruit. Adults have an oval, flat shape and reach 6 mm in length. Their bodies are typically green-brown, and their wings have red-brown markings. Damage appears as “cat-facing,” where feeding by western tarnished plant bugs causes distorted, misshapen areas on the fruit, leading to uneven ripening.
Strawberry sap beetle (Stelidota geminata)
This pest causes damage to strawberry plants by feeding on overripe fruit. Adults are typically dark brown and measure about 3.2 to 6.3 mm in length, while the white larvae grow to around 2.5 mm. Damage appears as wounds in rotten or overripe fruit, though this pest can also feed on ripe fruit. Feeding promotes microbial growth on the fruit, leading to additional damage. These beetles often lay their eggs directly in the fruit they are consuming.
Spotted wing drosophila (Drosophila suzukii)
This pest is a species of small fly which damages strawberry plants by feeding on both ripening and rotting fruit. Adults have brown bodies, red eyes and grow to 2-3 mm in length. Males have characteristic dark spots on the tips of their wings. Larvae may also be seen feeding on fruit and grow to 3.5 mm long. Damage appears as brown or rotting fruit, and spotted wing drosophila feeding encourages microbial growth.
Strawberry aphid (Chaetosiphon fragaefolii)
This small pest damages strawberry plants by feeding directly on plant fluids. Adults appear in shades of light yellow and green and grow to about 2 mm in length. Both adults and nymphs have characteristic horizontal stripes on their bodies. Damage appears as leaf discolouration and curling, and stunted plant growth. Aphids secrete sticky honeydew, which encourages the growth of sooty mould and may cause increased ant activity in the area.
Red stele root rot (Phytophthora fragariae)
This disease is caused by a species of water mould that infects strawberry plants, typically leading to wilting and dieback of tissues near the roots. As infections become more severe, strawberry plants can collapse. Symptoms include black lesions on the surface of roots, a red “rat-tail” appearance on primary roots, in addition to leaf discolouration. This pathogen spreads in the soil and is particularly problematic in wet conditions, especially when growing areas are saturated.
How do I manage strawberry pests?
Fortunately, there are many methods available for protecting crops from the strawberry plant pests listed above. Effective strategies include a combination of Integrated Pest Management (IPM) practices and biological control methods.
Monitoring
Watch for the symptoms described above. The most common signs of pest or disease damage in strawberries are leaf discolouration, fruit rot, and misshapen berries. Reduced plant growth is another common symptom. Some pests, including slugs and strawberry sap beetles, may be seen feeding directly on fruits. Other pests like the two-spotted spider mite and strawberry aphids may only be visible when infections are more severe. Specific symptoms can help identify the pest responsible. For example, “cat-facing” is caused by the western tarnished plant bug but not by slugs or western flower thrips.
Cultural Control
Cultural control involves using specific farming or garden practices to lower the risk of pest infestations. This method of crop management depends on correctly identifying the pest causing the issue. Inspecting transplants carefully before planting helps prevent pests from entering the growing area. Many pests, such as slugs and the western tarnished plant bug, can hide in weeds or fallen plant material, so it’s important to keep fields clean and manage weeds both within and around strawberry beds. Quickly removing rotten or fallen fruit helps stop pests like spotted wing drosophila and strawberry sap beetles from growing in number, as they lay eggs in fruit. Good drainage helps prevent the growth and spread of the disease that causes red stele root rot.
Biological Control
- Natural Substances: These are typically derived from plants and can be used to spray plants to repel or kill pests. For example, many plant oils like cottonseed, peppermint, and rosemary oil can combat western tarnished plant bugs by preventing them from feeding or laying eggs on plants.
- Semiochemicals: These are messaging compounds that can be used to disrupt pest behaviour. For example, pheromones can be used to trap and disrupt the mating of moth species like the light brown apple moth, which can attack strawberries.
- Microbials: These are microorganisms like bacteria, fungi, and viruses that harm pests and disease-causing microbes but do not harm crops. For example, the fungal species Lecanicillium muscarium causes a fatal infection in many pests, including the developmental stages of two-spotted spider mites.
- Macrobials: These are larger animals, like certain beneficial insects, that feed on or parasitise pests. For example, parasitic nematodes (tiny worms) feed directly on slugs and snails and help to control their numbers.
Chemical Pesticides
As a world leader in nature-based pest management knowledge implementation, CABI encourages IPM as the preferred, ecologically-based approach to producing healthy crops, which allows for chemical pesticide use only as needed, and when adhering to measures that limit the exposure of people and the environment to them (see FAO, International Code of Conduct on Pesticide Management).
Before considering the use of chemical pesticides, farmers should explore all available non-chemical solutions to control bean bugs, including the ones listed above. For tailored pest management advice, visit the CABI BioProtection Portal, where you can enter your location and pest problem to explore customised solutions.
In case chemical pesticides are considered for use, farmers should look to select lower-risk chemical pesticides which, when used as part of an IPM strategy, help manage pest problems while minimising harmful effects on human health and the environment. Agricultural advisory service providers can provide information on lower-risk chemical pesticides that are locally available and are compatible within an IPM strategy. These experts can also advise on the required personal protective equipment.
FAQ
What is the most common pest for strawberries?
Strawberries are vulnerable to attack from a variety of pests, but the most common pest type varies by region. For instance, the western flower thrips is native to the United States and is more common there, while garden slugs are common across the UK but only in certain regions of the US.
How do I stop bugs from eating my strawberries?
You can take several steps to stop bugs from eating your strawberries. Many pests hide in weeds, fallen leaves, or rotting fruit. Keep the area clean and free of debris to reduce pest damage. The best control methods depend on the type of pest.
What to spray on strawberries?
The type of spray to use on strawberries depends on which pest is causing the problem. Many insects are harmless and don’t need control. Mineral oil sprays can help prevent damage from western tarnished plant bugs.
How to get rid of strawberry beetles?
Traps containing fermenting plant juices can help to combat strawberry sap beetles. Pesticide sprays are not considered effective against this pest and are not recommended.
Summary
Strawberries are key crops in the United States and the UK, but pests like slugs, thrips, mites, and aphids threaten yields and quality. IPM and biological control, using beneficial nematodes, plant oils, and microbial agents, offer sustainable solutions. Adopting eco-friendly pest control practices promotes long-term sustainability in strawberry production while supporting both environmental and economic resilience for growers.
Explore our detailed pest management guides on controlling fungal diseases like Botrytis cinerea and powdery mildew.
