Cultivation problems

Insects

Many insects are attracted to lettuce, including:

• Cutworms which cut seedlings off at the soil line
• Wireworms and nematodes which cause yellow, stunted plants
• Aphids which cause yellow, distorted leaves
• Thrips which turn leaves grey-green or silver
• Leafhoppers are piercing and sucking insects that attack most leafy vegetables. In lettuce, yellowing, stunting and twisting of leaves characterize it.
• Leafminers which create tunnels within the leaves
• Flea beetles which cut small holes in leaves;
• Slugs and snails which cut large holes in leaves

However, lettuce contains several defensive compounds, including sesquiterpene lactones and other natural phenolics such as flavonol and glycosides, which help to protect it against pests.

Certain varieties contain more than others, and some selective breeding and genetic modification studies have focused on using this trait to identify and produce commercial varieties with increased pest resistance.

Viral diseases

Lettuce also suffers from several viral diseases, including:

• Big vein which causes yellow, distorted leaves
• Mosaic virus is spread by aphids and causes stunted plant growth and deformed leaves.

Bacteria

Aster yellows are disease-causing bacteria carried by leafhoppers, which causes deformed leaves.

Fungal diseases include:

• Powdery mildew and Downey mildew cause leaves to mould and die
• Bottom rot, lettuce drop, and grey mould cause entire plants to rot and collapse.

Soil nutrient deficiencies:

Can cause various plant problem ranging from malformed plants to a lack of head growth.