Image by U.S. Department of Agriculture
By Amy Grant
There are a number of viruses that can infect your lettuce crop, but one of the more common is lettuce mosaic virus or LMV. Lettuce mosaic virus can infect all lettuce types – from crisphead, Boston, Bibb, and leaf to cos, Romaine escarole and less commonly endive.
What is Lettuce Mosaic?
If your greens seem to be afflicted with something and you suspect it might be viral, a couple of good questions to answer are what is lettuce mosaic, and what are the signs of lettuce mosaic?
Lettuce mosaic virus is just that, a virus that is seed borne in all types of lettuce except endive. It is the result of infected seeds, although weed hosts are carriers, and the disease can be vectored by aphids, which spread the virus throughout the crop and into nearby flora. The resulting contagion can be catastrophic, specifically in commercial crops.
Signs of Lettuce Mosaic
The plants infected through seed upon which the aphids are feeding are called seed-borne “mother” plants. These are the source of the infection, acting as virus reservoirs from whence the aphids spread the disease to surrounding healthy vegetation. The “mother” plants show early signs of lettuce mosaic, becoming stunted with underdeveloped heads.
Secondary infected lettuce symptoms appear as mosaic on the foliage and include leaf puckering, stunting of growth and deep serration of leaf margins. The plants infected after the “mother” plant may indeed attain full size, but with older, outer leaves deformed and yellow, or with brown necrotic blotches on the leaves. Endive may be stunted in growth but other symptoms of LMV tend to be minimal.
Treatment of Lettuce Mosaic Virus
Lettuce mosaic control is being attempted in two ways. The number one way is via testing for the virus in seed and then planting the uninfected seeds. Testing is done three different ways: direct reading of lettuce seeds, inoculation of seed with an indexing host or through a serological technique. The goal is to only sell and plant uninfected seed per 30,000 seeds tested. A second lettuce mosaic control method is the incorporation of virus resistance into the seed itself.
Ongoing weed control and immediate plowing in of harvested lettuce are of importance in the control of LMV, as is aphid management. There are currently some LMV resistant lettuce varieties available. You may also choose to grow endive as the green of choice in the home garden as it is much more disease resistant.