Commercial Disease Controls
The Pennsylvania State University
Cooperative Extension

Lettuce

Seed Treatment

Dust seed with Thiram 65Wp at the rate of 1 level teaspoon per pound of seed (3 ounces per 100 pounds).

Disease Control

Damping-Off and Other Seedling Diseases
Apply the following in a 7-inch band after seeding or transplanting. Use formula given in the "Calibration for Changing from Broadcast to Band Application" section of Calibrating Granular Application Equipment to determine amount of Ridomil Gold or Ultra Flourish needed per acre.

mefenoxam-1-2 pt Ridomil Gold 4E/A or 2-4 pt Ultra Flourish 2E/A

Big-Vein
The disease is favored by cool temperatures(<60oF [<15.6oC]) and high soil moisture conditions. Produce the crop on raised beds and avoid planting in fields having low areas. Soil fumigation is helpful.

Corky Root
This disease is favored by high soil moisture conditions. Cultural practices that reduce soil compaction, such as use of a rye cover crop, use of high beds, limiting irrigation between transplanting or thinning and the rosette stage of growth to encourage a deep root system, should be adopted to reduce disease incidence.

Downy Mildew
An application of mefenoxam (Ridomil Gold 4E or Ultra Flourish 2E) for darnping-off will assist in control of downy mildew. Use one of the following during periods of high moisture and moderate temperatures.

Alternate
Forum--6 oz 4.18SC/A (must be tank-mixed with another fungicide registered on lettuce for downy mildew), or Aliette--3 lb 8OWDG/A (14-day schedule), or
maneb--1.5-2 lb 8OWP/A (7- to 10-day schedule) or OLF, or
Previcur Flex--2.0 pt 6F/A
with
azoxystrobin (Quadris--12.3 - 15.4 oz 2.08F/A or Amistar--4-5 oz 80WDG/A) Tanos--8 oz 50WP/A plus maneb

Leaf Spots
When conditions favor disease development, alternate the following and repeat every 7 to 14 days.

azoxystrobin (Quadris--6.2 - 15.4 oz 2.08F/A or Amistar--2-5 oz 80WDG/A, or
maneb--1.5-2 lb 75 WP/A or OLF

Bottom Rot (Rhizoctonia), Drop (Sclerotinia)
A midsummer application of a soil fumigant will be beneficial for the fall crop. For the spring and fall crop, all fields should receive the following fungicide application one week after transplanting or thinning and 10 to 20 days later.

Endura--8-11 oz 70W/A, or
Rovral--l.5-2 lb 5OWP/A or OLF.

Drop
Preplant: The following biological fungicide has been tested in some states; however, limited information is available on effectiveness in the Mid- Atlantic region. Apply 3 to 4 months prior to the onset of disease to allow the active agent to reduce inoculum levels of sclerotia in the soil. Following application, incorporate to a depth of 1 to 2 inches but do not plow before seeding or transplanting lettuce to avoid untreated sclerotia in lower soil layers from infesting the upper soil layers.

Contans--2-4lb 5.3WG/A

Post seeding or transplanting: Use one of the following beginning one week after transplanting or thinning, and 10 and 20 days later:

Rovral--l.5-2 lb 5OWP/A

Gray Mold (Botrytis)
Most troublesome in plant bed where air drainage is poor. Avoid crowding of plants and watering late in the day. Use one of the following as a foliar spray:

Botran--3 tbsp 75WP/gal, or
Ronilan--l.5 tsp 5ODF/gal or OLF, or
Rovral--2 tbsp 5OWP/gal

Yellows
Control leafhopper vectors with insecticides.

Viruses
Lettuce Mosaic Virus (LMV)
Use virus-free or MT lettuce seed.

Turnip Mosaic Virus (TuMV)
Troublesome in late summer and early fall plantings. Control weed hosts around risers and areas bordering fields.

Tomato Spotted Wilt Virus (TSWV)
TSWV can attack lettuce. The virus is spread from ornamental plants (flowers) to lettuce by thrips. Be sure not to grow any ornamental bedding plants in the same greenhouse as lettuce transplants. Monitor greenhouse thrips and begin an insecticide control program once observed.

Note: Where trade names are used, no discrimination is intended and no endorsement by the Cooperative Extension Service is implied. Information provided is intended for consideration by the user, but is not intended to be a recommendation. Production decisions should be based on consideration of many types of information (scientific, experiential, economic, legal, etc.) available to the user.