Disease Control

NOTE:  For the products for disease control listed below, one product trade name and formulation is provided for each active ingredient (common name) as an example of rates, days to harvest (dh), REI, and special instructions. In many cases there are other products available with the same active ingredient. Please see Table 22 and Alphabetical Listing by Trade Name for more information on products with the same active ingredients.

Gray Mold (Botrytis)

Avoid close planting and orient rows in the direction of prevailing winds. Do not plant in poorly drained areas. Plant on raised beds. Minimize damage to lettuce by cultural practices or other pathogens and pests. Avoid overhead irrigation. Do not plant where excessive plant residues are present. Transplanting mature plants results in more breakage. Direct seed Romaine lettuce as transplants are especially susceptible.

boscalid (Endura): 8.0-11.0 oz/A (14 dh, REI 12h, Group 7). Apply ar seeding or transplant. A protective fungicide barrier is needed to maximize control.

dichloran (Botran 5F): 1.8-3.2 qt/A. (14 dh, REI 12h, Group 14). Apply as a basal drench. Do not disturb soil around plants.

iprodione (Rovral 4F): 1.5-2.0 pt/A. (14 dh, REI 24h, Group 2). Do not cultivate after application.

Bottom Rot (Rhizoctonia solani)

Rotate crops with non-hosts. Do not plant into fields having significant undecomposed crop residues. Plant in well-drained sites and avoid over-irrigation. Practice careful cultivar selection as more upright plants are less susecptible.

azoxystrobin (Quadris): 6.0 -15.5 fl oz/A. (0 dh, REI 4h, Group 11). Do not apply more than one sequential application before switching to a material with different mode of action.

iprodione (Rovral 4 F): 1.5 to 2 pt/A (14 dh, REI 24h, Group 2). Lettuce only. Make first application between the three-leaf stage to just after thinning. Direct application to soil and plant base. If necessary, apply two more applications, 10 days apart. Do not irrigate for 24 hours after application.

Drop, White Mold (Sclerotinia minor)

Do not plant seed contaminated with sclerotia (survival structures). Avoid planting into severely infested fields. Rotate with non-host crops like grasses. Avoid excessive nitrogen fertilization and irrigate in the morning or with sub-surface drip irrigation to provide dry soil. Deep plow after harvest to bury sclerotia. Soil sterilization with chemicals, steam or heat (solarization) treatments can significantly reduce inoculum levels. Incorporation of crop residues from Brassica crops may provide a suppressive efffect.

boscalid (Endura): 8.0-11.0 oz/A (14 dh, REI 12h, Group 7). Apply ar seeding or transplant. A protective fungicide barrier is needed to maximize control.

Coniothyrium mintans (Contans WG): Apply 1 to 4 lb/A in 20 to 50 gal water (REI 4h, Group not applicable). Spray on the soil surface and incorporate into the top 2” of soil. Fall application is best or 3 to 4 months before planting to allow for the biocontrol agent to infect the sclerotia of Sclerotinia.

dichloran (Botran 5F): 1.8-3.2 qt/A. (14 dh, REI 12h, Group 14). Apply as a basal drench. Do not disturb soil around plants.

iprodione (Rovral 4F): 2 pt/A (14 dh, REI 24h, Group 2). Lettuce only. Direct application to lower stems and branches and adjacent soil surface. Apply just prior to row closing, or at early first sign of disease, and repeat at 14- to 21-day intervals if necessary. Do not irrigate for 24 hr after application.

Septoria Leaf Spot (Septoria petroselini)

Septoria is a seed-borne fungus but may overwinter on plant debris. The species that attacks lettuce does not attack other vegetable crops and vice versa. Plow under plant debris at the end of the season. Rotate away from lettuce for at least a year.

azoxystrobin (Quadris): 6.0 to 15.5 oz/A (0 dh, REI 4h, Group 11). Apply at first sign of disease. Do not mix with Warrior, Pounce or Aliette. To avoid resistance development, do not apply more than twice.

maneb (Maneb WP): 1.5-2.0 lb/A. (10 dh, REI 24h, Group M3).

Downy Mildew (Bremia lactucae)

Downy mildew is favored by cool, rainy weather. Night temperatures of 43°F to 50°F and day temperatures of 55°F to 70°F with 100% humidity are ideal for disease development. As temperatures increase, the disease disappears. Plant resistant cultivars. Use irrigation practices that reduce leaf wetness and humidity. Protect greenhouse grown transplants with fungicides so that the disease is not introduced into the field.

azoxystrobin (Quadris): 12.0 to 15.5 fl oz/A (0 dh, REI 4h, Group 11). Apply at the first sign of disease and rotate with fosety-Al after 5 to 7 days if necessary. Do not rotate with other strobilurins.

dimethomorph (Forum):  6 oz/A. (0 dh, REI 12h, Group 15). Must be applied as tank mix with another fungicide with a different mode of action.

famoxadone & cymoxanil (Tanos): 8 oz/A (3 dh, REI 12h, Groups 11 & 27). Head lettuce only. Apply prior to disease development. Tank mix with appropriate contact fungicide with a different mode of action.

fenamidone (Reason 500 SC): 5.5 fl oz/A. (7 dh, REI 12h, Group 11). Do not alternate with Quadris.

fosetyl-Al (Aliette WDG): 2 to 5 lb/A (3 dh, REI 12h, Group 33). Apply when conditions for disease are favorable. Use the high rate when disease is active. Reapply every 7 to 21 days.

mandipropamid (Revus): 8.0 fl oz/A. (1 dh, REI 12h, Group 40). Addition of a spreading/penetrating adjuvant is recommended.

maneb (Maneb WP): 1.5-2.0 lb/A. (10 dh, REI 24h, Group M3). 

propamocarb HCl (Previcur Flex): 2.0 pt/A. (2 dh, REI 12h, Group28).

Mosaic (Lettuce and Cucumber Mosaic Viruses)

Plant mosaic-indexed seed away from old lettuce fields.

Seed Decay

Use treated seed. Do not use treated seed for food, feed or oil purposes.

Tip Burn

This is a physiological condition caused by the plant’s inabilty to obtain sufficient calcium due to rapid plant growth, excessive fertilization rates, or uneven water availability. Plant varieties resistant to this physiological disorder such as Ithaca and Mesa 659. Avoid excess fertilization. Irrigate with drip irrigation systems. Foliar calcium supplements may have some benefit.

Yellows

Do not plant lettuce or other senstive crops in fields or areas having a history of this disease. Control alternate weed hosts. Control leafhoppers, which carry the disease-causing organism (phytoplasm). See Insect Control.