Lettuce Disease Management
Lettuce is easy to grow and does well as a cool-season crop in Florida. However, growing lettuce involves pest management and, more importantly, disease management. The state’s warm and moist climate provides the perfect environment for diseases to develop. These diseases range from serious ones such as downy mildew to minor diseases such as bottom rot.
Downy mildew is a fungus that can affect up to 80 percent of acreage once established. Mature leaves are often most affected by this disease. Lettuce develops a yellow area on the upper side of the leaves and a white or gray fluff on the underside.
This disease comes from weeds and typically affects less than five percent of acreage. Because of the warm weather, leaf spot is commonly a fall disease.
Lettuce Mosaic Virus
Wrapper leaves affected by lettuce mosaic virus may appear dull, are folded backward, and may have more marginal serration. Romaine lettuce leaves typically show the same symptoms in addition to leaf blistering. Butter head lettuce experiences stunting and severe chlorosis.
Tomato Spotted Wilt Virus
Transported by thrips, this virus was first spotted in 2004 and will probably increase in the coming years.
Bottom rot generally affects iceberg, Boston, and Bibb varieties of lettuce and can be observed during warm weather. Although loss from this disease is typically less than five percent of acreage, it can affect up to 100 percent in rare cases. Lettuce suffering from bottom rot usually loses a couple of wrapper leaves.
Drop generally affects between one to two percent of acreage yearly, but in general it only becomes an issue when the land is unable to be flooded in the summer. The disease first attacks older leaves, which experience a progressive wilt, and then younger and outer leaves collapse around the plant.
These diseases include bacterial corky root rot, bacterial soft rot, and a number of diseases that can affect roots, leaves, and even the entire plant.
Maneb is a fungicide primarily used to manage downy mildew and is applied every seven to 10 days. Florida lettuce growers also use copper (hydroxide or sulfate) to manage downy mildew as well as bacterial diseases. Growers can also use sulfur to control several lettuce diseases.
Scouting is the main cultural practice used by lettuce growers. Growers also plow in residue, remove perimeter and field vegetation, and use mulches. Flooding can also be used if water management districts allow the practice.
Phage use has become increasingly successful at reducing bacterial diseases. While this is an active area of disease management, more research has to be done to determine the best environmental condition for phage and the best time to apply it during the disease cycle.
For more information on growing crops in the state, please view the 2012-2013 Vegetable Production Handbook for Florida, which includes the chapter Lettuce, Endive, Escarole Production in Florida.
Adapted and excerpted from:
M. Moslem and E. Dunn, Florida Crop/Pest Management Profile: Lettuce (CIR1460), UF/IFAS Agronomy Department (rev. 07/2011).
R. Truck, “Grow A Salad This Winter; Lettuce Easy To Grow, Delicious,” Gardening In The Panhandle (01/2013).
Related Sites & Articles
- Florida Crop/Pest Management Profile: Lettuce
- Insect Management for Leafy Vegetables (Lettuce, Endive, and Escarole)
- Weed Control in Leafy Vegetables (Lettuce, Endive, Escarole and Spinach)
- Cole Crop Production in Florida
- Plant Pathology Department