Lettuce mosaic

About

Lettuce mosaic is a seed-borne virus that stunts lettuce and can keep heads from forming. Aphids then spread it from plant to plant and from weeds. There's no cure, so tested seed is the best defense.

Also called lettuce mosaic virus, LMV

How to recognize it

Symptoms

Seedling leaves roll lengthwise, and the first true leaves are lopsided or lobed. Young leaves show a light and dark green mottle, pale or bronze veins, and small brown specks. Plants infected early stay small and dull yellow-green, and head lettuce doesn't form a head. Plants infected later reach full size, but outer leaves yellow and twist, and wrapper leaves curl away from the head.

Often confused with

Other viruses, such as turnip mosaic, cause similar mottling and stunting. A lab test is needed to be sure.

Worse when

Infected seed, wild lettuce and other weeds nearby, active aphids, and old lettuce left standing near new plantings.

How it spreads

The virus comes in on infected seed; a few percent of the seed from a sick plant carries it. Aphids then move it between plants during brief feeding and bring it in from infected weeds and crops.

When

Any time lettuce is growing, from the seedling stage on.

What to do, gentlest first

Prevention works best; most sprays only protect healthy leaves and can't cure infected ones. Always read and follow the product label.

1. Use virus-tested seed Prevent

   Buy seed from companies that test it for lettuce mosaic. Commercial lettuce seed in Florida and parts of California must test with zero infected seeds in 30,000.

   Don't save seed from plants that looked sick.

2. Grow resistant varieties Prevent

   Resistant lettuce varieties exist; UF/IFAS lists 'Everglades' and 'Floribibb'. Check seed catalogs for LMV resistance.

3. Control weeds and old lettuce Prevent

   Keep wild and prickly lettuce, shepherd's purse, lambsquarters and chickweed out of the area. Pull or turn under old lettuce soon after harvest so it can't pass virus to new plantings.

4. Pull infected plants By hand

   Pull plants with symptoms as soon as you see them, since they won't recover.

5. Aphid control has limited value Organic spray

   Keeping aphids down may slow spread a little, but aphids pass the virus in a quick probe, before a spray can work.

   No spray cures an infected plant. Follow the label.

Plants it affects

Chickpea, Endive and escarole, Lettuce, Marigold, Peas, Spinach, Sweet pea, Zinnia