### Lettuce (*Lactuca sativa*)

1.  **Downy Mildew** (*Bremia lactucae*)
    *   **Integrated Management Strategies:**
        *   **Cultural & Preventive:** Planting resistant cultivars is the most effective method; however, the pathogen has many races, so resistance can be overcome. Maximize spacing between plants for air circulation. Use drip irrigation. In greenhouses, vent to reduce humidity, especially at night. Remove crop residue and control wild lettuce weeds.
        *   **Biological:** Limited efficacy, but some *Bacillus* strains may offer preventative suppression.
        *   **Chemical:** Preventive fungicide programs are key. Organic options include copper-based products. Conventional, oomycete-specific fungicides are highly effective, including products with active ingredients like mandipropamid, cyazofamid, and phosphorous acid. Rotating chemistries is vital.

2.  **Sclerotinia Drop** (*Sclerotinia sclerotiorum* & *S. minor*)
    *   **Integrated Management Strategies:**
        *   **Cultural & Preventive:** This is a soil-borne disease. A long crop rotation (4+ years) with non-host crops (like corn or onions) is important. Improve soil drainage and avoid excessive irrigation. Deep plowing can bury the sclerotia. Some cultivars show partial resistance or have an upright architecture that reduces leaf-soil contact.
        *   **Biological:** The fungus *Coniothyrium minitans* is a parasite of *Sclerotinia* sclerotia and is available as a commercial biofungicide (e.g., Contans®) that is applied to the soil to reduce inoculum over time.
        *   **Chemical:** Soil-applied fungicides at the time of planting or thinning can be effective. Active ingredients include iprodione, boscalid, and fluazinam.

3.  **Bottom Rot** (*Rhizoctonia solani*)
    *   **Integrated Management Strategies:**
        *   **Cultural & Preventive:** Manage soil moisture to avoid prolonged wetness. Crop rotation with non-susceptible crops is beneficial. Plant on raised beds to promote drainage and reduce soil contact with lower leaves. Some cultivars are less susceptible than others.
        *   **Biological:** Soil applications of *Trichoderma* or *Bacillus*-based biofungicides may help suppress the pathogen.
        *   **Chemical:** Fungicides applied as a directed spray to the base of the plant and soil surface are most effective. Active ingredients include iprodione, azoxystrobin, and fluazinam.

4.  **Powdery Mildew** (*Erysiphe cichoracearum*)
    *   **Integrated Management Strategies:**
        *   **Cultural & Preventive:** Plant resistant varieties if available. Provide good air circulation through proper spacing. Manage weeds.
        *   **Biological:** *Bacillus subtilis*-based products can be effective as preventatives.
        *   **Chemical:** Organic options include sulfur, horticultural oils, neem oil, and potassium bicarbonate. Conventional systemic fungicides (e.g., myclobutanil) are also very effective.

5.  **Bacterial Leaf Spot** (*Xanthomonas campestris* pv. *vitians*)
    *   **Integrated Management Strategies:**
        *   **Cultural & Preventive:** Use certified disease-free seed. Practice a 3-year rotation away from lettuce. Avoid overhead irrigation to prevent bacterial splash. Control weeds in and around the field. Remove crop debris promptly after harvest.
        *   **Biological:** No effective biological controls are commercially available.
        *   **Chemical:** Copper-based bactericides are the primary chemical control. They provide protective, not curative, action and must be applied before symptoms are widespread. Resistance to copper is a concern.