The Problem: Aphids Love Lettuce

Few pests frustrate lettuce growers more than aphids. These tiny, soft-bodied insects reproduce rapidly, hide deep within lettuce heads, and can quickly turn a healthy crop into an unappetizing harvest. In home greenhouses, where temperatures are favorable and natural predators may be limited, aphid populations can explode in a matter of days.

How Aphids Damage Lettuce

Aphids feed by piercing plant tissue and extracting sap. Damage includes curled leaves, stunted growth, sticky honeydew deposits, and contamination of harvestable heads. They can also transmit plant diseases. The favorable temperatures for Aphids thrive is between 65–80°F on plants with tender new growth.

Best Methods to Get Rid of Aphids

Rank	Method	Effectiveness	Best Use
1	Green Lacewing Larvae	★★★★★	Long-term greenhouse control
2	Insecticidal Soap	★★★★★	Active infestations
3	Water Spray	★★★★☆	Early infestations
4	Remove Infested Leaves	★★★★☆	Localized outbreaks
5	Neem Oil	★★★☆☆	Supplemental control

Recommended Strategy

The most successful greenhouse growers use Integrated Pest Management (IPM), which means combining scouting, sanitation, physical removal, and beneficial insects. No single treatment works forever, but a layered approach is highly effective.

Method #1: Green Lacewing Larvae

Green lacewing larvae are often called 'aphid lions' because they aggressively consume aphids. Unlike ladybugs, lacewing larvae begin feeding immediately and are more likely to remain where released.

Method #2: Insecticidal Soap

Insecticidal soap provides excellent knockdown of aphids. Thorough coverage is essential, particularly on the undersides of leaves. Repeat applications may be necessary every 4–7 days.

Method #3: Water Spray

A strong spray of water can physically remove large numbers of aphids. This is inexpensive, safe, and works well when populations are caught early.

Method #4: Good Air Circulation

Poor air circulation can contribute to aphid outbreaks by creating a sheltered environment where pests thrive and natural controls are less effective. Stagnant air often leads to pockets of warm, humid conditions and encourages soft, lush plant growth that aphids find particularly attractive. Without steady airflow, aphids can settle and reproduce undisturbed on the undersides of leaves, while beneficial insects may be less active and plants become more susceptible to stress. Good air circulation helps create a less favorable environment for aphids, strengthens plant tissues, reduces localized humidity, and makes it easier to spot and manage infestations before populations explode.

Method #5: Screening

A greenhouse with screens covering every opening of windows and vents adds protection. Greenhouses from Sturdi Built are 100% screened in when the door is closed.

Where to Purchase Supplies

•        Arbico Organics – Beneficial insects including lacewing larvae and eggs.
•        DMV Beneficials – Commercial beneficial insects.
•        Local Garden Centers – Insecticidal soaps and neem oil products.
•        Farm Suppliers – Sprayers, monitoring tools, and insect screening.

Greenhouse Prevention Checklist

• Inspect new plants before introducing them.
• Scout lettuce weekly.
• Maintain good airflow.
• Avoid excessive nitrogen fertilizer.
• Control ants that protect aphids.
• Act immediately when aphids are first detected.

Final Thoughts

For most greenhouse lettuce growers, the winning combination is simple: scout regularly, wash plants when needed, use insecticidal soap for outbreaks, and introduce lacewing larvae for long-term biological control. Early intervention is dramatically easier and less expensive than treating a severe infestation.