How To Use This Problems Section
The chart is organized to give you a quick and dirty summary of the possible symptoms that you may encounter. Those problem causes for which we have full files will be linked to those files. Those causes with no link will have a paragraph below the chart helping you deal with that particular problem.
| Problems Found On Lettuce | |
|---|---|
| Symptoms | Probable Causes |
| Plants “Bolt”; Go to Seed | Hot Weather |
| Foliage Curls; Puckers, and Turns Yellow | Aphids |
| Seedling Stems Severed | Cutworms |
| Seedlings are Chewed or Eaten Entirely | Rabbits |
| Large Ragged Holes in Leaves | Slugs |
| Rust-Colored Spots on Leaves | Bottom Rot |
| Seedlings Rot and Die | Damping-Off |
| Pale Areas on Upper Leaves | Downy Mildew – a fungal disease |
Rust-Colored Spots on Leaves Caused By Bottom Rot
Lettuce infected with bottom rot develops rust-colored spots on the lower leaves, that spread until the whole plant is rotted. There is no cure for this problem. Harvest the infected plants and destroy them to prevent infection of nearby plants. Clean up the garden at the end of the season to prevent the disease from overwintering. Next year plant other crops where the infected lettuce was. Varieties resistant to bottom rot include ‘Canasta’, ‘King Crown’, and ‘Nancy.’
Seedlings Rot and Die from Damping-Off
Seedlings that have damping-off disease simply topple over, exposing a watery soft rot on the stem at the soil line. There is no cure for this fungal disease. Remove and destroy infected garden plants. When starting seeds indoors, use sterile potting mix--a soilless mix is best. Provide soil with adequate drainage and improve air circulation with a fan. For seeding directly into the garden bed, make sure soil is well drained and warm. Where damping-off has been a problem, try spreading sterile soilless mix, washed builder’s sand, or vermiculite in planting beds and then plant the seeds.
Plants “Bolt”; Go To Seed Because Of Hot Weather
Lettuce is composed primarily of water. When the weather is hot and dry, lettuce loses moisture rapidly, which causes moisture stress and heat stress. Plants respond by rapidly sending up a flower stalk and setting seed, a process called “bolting.” Bolting causes a chemical change in a plant’s sap that leads to a bitter flavor. This "bolting" to seed indicates that it is time to pull up and discard the plant. Proper spacing and mulching delays the bolting process by cooling the microclimate around the plants and slowing water loss. Planting lettuce in a shady spot also helps. Covering plants with shade cloth or garden fleece filters the sunlight and reduces temperature to retard moisture loss and provides some wind protection. Lettuce varieties that resist bolting include the looseleaf types ‘Oak Leaf’, ‘Royal Oak Leaf’, ‘Salad Bowl’ and ‘Slo-Bolt’; a head type ‘Great Lakes 659;’ and butterhead types ‘Augusta’ ‘Buttercrunch’, ‘Butter King’, ‘Green Lake’, and ‘Hot Weather’.
