Lettuce is one of the top ten vegetables consumed by Canadians. About 60 percent of lettuce grown in the country is head lettuce, while the remaining 40 percent is leaf lettuce. It is produced either in the field or in greenhouses. Greenhouse lettuce is grown year-round, with most of the production in Quebec and Ontario, close to major markets. Lettuce is consecutively planted throughout its 50-75 day growing season, so growers need to stay on top of pest management for a successful crop throughout the season.
Manage disease inside and out
Botrytis stem rot is the most prevalent disease in lettuce, and can cause grey-green shrivelled leaves. For best control, a fungicide should be applied preventatively. Sclerotinia, or white mould, is primarily an issue for head lettuce. It’s a growing concern as the spores that cause the disease can overwinter in the soil for many years. Downey mildew is more severe in greenhouse lettuce, but it does attack field lettuce as well especially when humid conditions persist.
Start out weed-free
Lettuce can be sensitive to herbicides, so much of the weed control work is done upfront. A pre-seed clean up is often done to make sure the soil is weed free. Plastic coverings are used to control weed growth. Tilling between the rows can also help stop the spread of weeds.
Insect control difficult on large-surface lettuce leaves
Controlling insects on lettuce can prove challenging because there is such a large plant area to protect. Insects are therefore a major threat for lettuce growers. Lettuce aphids can cause stunted, discoloured foliage on the plant. Researchers are looking at how biologic controls can work alongside chemical controls to eliminate aphid concerns. Leafhoppers are dangerous because they carry the aster yellow disease. When aster yellows are high, growers can see anywhere from a 15-50% reduction in yield.