team-6/backend/storage/plants/diseases.tomato.md

Tomato (Solanum lycopersicum)

1. Early Blight (Alternaria solani)

   • Integrated Management Strategies:
     • Cultural & Preventive: The first line of defense is crucial. Use certified disease-free seeds and resistant cultivars (e.g., 'Mountain Fresh Plus', 'Celebrity'). Practice a crop rotation of at least 3 years, avoiding other susceptible crops like potatoes and eggplants. Ensure proper plant spacing to promote air circulation and stake or cage plants to keep foliage off the ground. Mulch the soil to create a barrier that prevents fungal spores from splashing onto lower leaves. Avoid overhead irrigation; use drip irrigation or soaker hoses to keep foliage dry. Remove and destroy infected lower leaves as they appear and clear all plant debris from the garden at the end of the season.
     • Biological: Biofungicides containing Bacillus subtilis (strain QST 713) or Bacillus amyloliquefaciens can be used preventively to colonize the leaf surface and inhibit fungal spore germination.
     • Chemical: Apply fungicides preventively when conditions are favorable for disease. For organic growers, copper-based fungicides (e.g., copper hydroxide) are effective but must be used judiciously to avoid soil accumulation. Conventional options include protectant fungicides with active ingredients like chlorothalonil or mancozeb.

2. Late Blight (Phytophthora infestans)

   • Integrated Management Strategies:
     • Cultural & Preventive: This is the most critical disease to prevent. Plant late blight-resistant varieties ('Mountain Magic', 'Iron Lady', 'Defiant PhR'). Do not save seed potatoes, as the pathogen can overwinter in them. Maintain a rigorous 3-4 year crop rotation, separating tomatoes and potatoes as far as possible. Ensure excellent air circulation through spacing and pruning. Water only at the base of the plant. Monitor disease forecasting networks (e.g., USAblight.org) to know when conditions are high-risk. Immediately destroy any infected plants by bagging and removing them from the site (do not compost).
     • Biological: Biofungicides containing various strains of Bacillus species can offer some suppression when applied preventively but are generally not effective once an outbreak begins.
     • Chemical: Preventive fungicide applications are essential in high-risk conditions. Copper-based products are the primary organic option. For conventional growers, a preventative program using chlorothalonil or mancozeb is common. If the disease is present, more targeted oomycete-specific fungicides with active ingredients like cyazofamid, mandipropamid, or mefenoxam may be needed. Rotation of chemical classes is critical to prevent resistance.

3. Fusarium Wilt (Fusarium oxysporum f. sp. lycopersici)

   • Integrated Management Strategies:
     • Cultural & Preventive: The best method is to use resistant varieties, indicated by an "F" in the cultivar name (e.g., 'Better Boy VFN'). There are three known races of the fungus, so look for varieties with F1, F2, and F3 resistance. Since the pathogen is soil-borne and very persistent, a long crop rotation (5-7 years) is recommended. Raise the soil pH to between 6.5 and 7.0, as the fungus is less active in neutral to slightly alkaline soils. Improve soil drainage and avoid over-fertilizing with nitrogen.
     • Biological: Soil amendments with compost can introduce beneficial microorganisms that compete with Fusarium. Some commercial biofungicides containing strains of the fungus Trichoderma harzianum or bacteria Streptomyces lydicus have shown suppressive effects on soil-borne pathogens.
     • Chemical: There are no effective chemical fungicides for treating an already infected plant, as the fungus resides within the plant's vascular system. Soil fumigation can be used in commercial fields before planting but is not practical for most gardeners. Prevention is the only effective strategy.

4. Verticillium Wilt (Verticillium dahliae)

   • Integrated Management Strategies:
     • Cultural & Preventive: As with Fusarium wilt, the primary control is planting resistant varieties, designated with a "V" (e.g., 'Celebrity VFN'). The pathogen has a very wide host range and can survive in the soil for many years as microsclerotia, making crop rotation less effective but still beneficial. Good sanitation and removing crop debris are important. Avoid excessive nitrogen fertilization.
     • Biological: Soil solarization (covering moist soil with clear plastic during the hottest months) can reduce the population of microsclerotia in the upper soil layers in hot climates. Biofumigation with mustard cover crops has also shown some efficacy in reducing pathogen inoculum.
     • Chemical: Similar to Fusarium wilt, fungicides are not effective for curing infected plants. Pre-plant soil fumigation is the main chemical tool used in large-scale agriculture.

5. Bacterial Spot (Xanthomonas species)

   • Integrated Management Strategies:
     • Cultural & Preventive: Start with certified disease-free seed and transplants. Practice a 3-year crop rotation, avoiding peppers. Use mulch to prevent bacteria from splashing from the soil onto plants. Avoid working among plants when they are wet. Promote rapid drying of foliage through proper spacing and morning watering at the soil level.
     • Biological: Some studies suggest certain bacteriophage therapies can reduce bacterial populations, but this is not yet a mainstream control method.
     • Chemical: Control is difficult once established. Preventive sprays are most effective. Copper-based bactericides (e.g., copper hydroxide) are the standard treatment, often mixed with mancozeb to improve efficacy and reduce the risk of bacterial resistance. Products containing the antibiotic streptomycin may be used in some areas, but resistance is a major concern.