Greenhouses are ideal for cultivating plants, but they can also attract a variety of insect pests. Even with the right conditions, poor housekeeping and soggy soil can create an environment that encourages pests to breed and spread, affecting your crops one by one.

Effectively managing these pests is essential for maintaining healthy greenhouse plants and preventing economic loss. Here are 14 common greenhouse pests, along with why they appear and pest management strategies using biological control agents, cultural practices, and other effective methods. 

 

1. Aphids

Description: Aphids are small insects with piercing-sucking mouthparts that feed on plant sap, causing aphid infestations. These soft-bodied insects are visible to the naked eye and excrete a sticky substance called honeydew, which attracts sooty mold and inhibits plant growth.

Why They Appear: Aphids are drawn to tender new plants and lush plant growth, especially in humid conditions and over-fertilizing with nitrogen-rich fertilizers exacerbates the issue.

Management: Beneficial insects like ladybugs and lacewings reduce pest populations as well as washing plants with water to dislodge aphids from the underside of leaves and applying organic insecticidal soaps or neem oil.

2. Whiteflies

Description: The greenhouse whitefly, or bemisia tabaci, is a tiny insect that feeds on plant sap, causing yellowing, wilting, and the spread of viral diseases.

Why They Appear: Whiteflies thrive in warm, sheltered greenhouse environments with ornamental plants and host plants like tomatoes and cucumbers.

Management: To manage an infestation, introduce natural enemies like Encarsia formosa (parasitic wasps), use horticultural oils for pest control, or place yellow sticky cards to monitor pest populations.

3. Spider Mites (Two-Spotted and Red Spider Mites)

Description: Spider mites, including two-spotted spider mites, are tiny insects that create fine webbing on the undersides of leaves, causing speckling, yellowing, and weakened plant tissue.

Why They Appear: They thrive in dry conditions and high temperatures with poor air circulation.

Management: Introduce phytoseiulus persimilis or amblyseius swirskii, both predatory mites, increase humidity levels to deter spider mites and use neem oil to disrupt their life cycle

4. Thrips (Western Flower Thrips)

Description: Thrips, including western flower thrips, feed on plant sap, leaving behind clear spots on the leaf surface and spreading diseases like powdery mildew.

Why They Appear: Thrips are drawn to blooming greenhouse plants and thrive in warm, humid conditions.

Management: Use blue sticky traps for monitoring the amoun growing and introduce minute pirate bugs or natural predators.

5. Fungus Gnats

Description: Adult fungus gnats are black flies with long legs, while their larvae feed on plant roots, damaging young plants.

Why They Appear: Fungus gnats are attracted to moist soil, decaying organic matter, and poor drainage on the soil surface.

Management: Use beneficial nematodes like hypoaspis miles to target larvae, also allow the soil to dry between watering and use yellow sticky traps to catch adults.

6. Mealybugs

Description: Mealybugs are soft-bodied insects covered in a waxy, white substance that feed on plant sap, causing stunted growth and outbreaks.

Why They Appear: They favor high humidity and stressed greenhouse plants.

Management: Wipe pests off with alcohol-soaked cotton swabs also use neem oil or insecticidal soaps in spray and introduce beneficial organisms like rove beetles to defend the plants.

7. Scale Insects

Description: Scale insects, including adult females, have a hard, waxy shell that sucks sap and excretes honeydew, leading to fungal spores like sooty mold.

Why They Appear: They are attracted to weakened greenhouse plants and spread via infested plant material.

Management: To get rid of scale insects, remove and dispose of infected plant parts. Use horticultural oils, such as neem oil, to smother scales, and apply contact insecticides containing safe active ingredients to maintain an organic ecosystem in your raised garden beds in the greenhouse.

8. Caterpillars

Description: These larvae chew holes in leaves and plant tissue, leaving dark spots and weakening plants.

Why They Appear: Adult moths lay eggs on new plants, especially during the growing season.

Management: The easiest things to do are hand-pick caterpillars when visible, use diatomaceous earth on the soil surface, and apply Bacillus thuringiensis (Bt) for targeted pest control.

9. Slugs and Snails

Description: Slugs and snails leave slimy trails and chew holes in plant parts.

Why They Appear: They thrive in damp areas with decaying plant debris.

Management: Remove plant debris and weeds, use barriers like copper tape or diatomaceous earth and hand-pick during nighttime.

10. Leaf Miners

Description: Leaf miners burrow through leaves, leaving winding trails on the leaf surface.

Why They Appear: Infestations often begin in the early spring when adult females lay eggs on leaves.

Management: Remove and destroy infested leaves, use neem oil to target their life cycle and introduce parasitic beneficial wasps.

11. Broad Mites and Cyclamen Mites

Description: Cyclamen mites and broad mites are microscopic pests that stunt plant growth and distort leaves they are hard to detect but not impossible. 

Why They Appear: They are often introduced through infested plant material or poor sanitation.

Management: Immediately quarantine any new plants to prevent the introduction of pests into your greenhouse. Use sulfur sprays or horticultural oils to manage infestations and create an unfavorable environment for mites. Regularly inspect plants using a magnifying hand lens to detect pests early, focusing on the undersides of leaves and areas where pests are likely to hide.

12. Shore Flies

Description: Shore flies resemble fungus gnats but are harmless to plants. However, they spread fungal spores.

Why They Appear: They breed in standing water or algae.

Management: Eliminate standing water and improve ventilation in the greenhouse.

13. Cucumber Beetles

Description: These beetles chew on leaves, flowers, and fruits, causing physical damage to plants and reducing yield. Additionally, they spread diseases like powdery mildew and bacterial wilt, which can severely affect plant health.

Why They Appear: They are attracted to cucumbers and similar plants.

Management: To reduce hiding and breeding spots, remove weeds and plant debris near the greenhouse. Introduce natural predators, such as beneficial insects like lady beetles, to help control beetle populations. Use floating row covers as a physical barrier to prevent beetles from accessing plants, and set up yellow sticky traps to monitor and capture adult beetles.

14. Root-Knot Nematodes

Description: Root-knot nematodes are microscopic worms that infect plant roots, causing the formation of galls, which are swollen, distorted areas on the roots. These galls interfere with the plant's ability to take up water and nutrients, resulting in stunted growth, yellowing of leaves, and a general decline in plant health.

Why They Appear: Root-knot nematodes are often introduced into the greenhouse or garden via contaminated soil or plant debris. They can be carried on plant material or tools, and even on the surface of containers.

Management: To manage root-knot nematodes, solarize the soil by covering it with clear plastic during the hottest months to raise the soil temperature to levels that will kill the nematodes. Another effective strategy is to apply beneficial nematodes, which are natural predators of the harmful nematodes.

Final Thoughts

Familiarizing yourself with these pests will help you take proactive steps to keep them under control. Early detection and effective pest management can significantly reduce pest populations. Using natural predators keeps your raised garden beds organic, while maintaining cleanliness and good housekeeping allows you to spot infestations early and prevent the conditions that enable pests to thrive.