Hektar

Pustular Spotting of Tomato Fruits – Pseudomonas syringae pv. tomato (Okabe) Alstatt

Disease Symptoms (Key Diagnostic Characteristics)

The Pseudomonas syringae bacterium affects tomatoes in both field and greenhouse environments.

• Leaf Symptoms: Initial signs include small, water-soaked brown spots on the leaves. These spots later darken to blackish-brown, becoming circular and 1-3 mm in diameter. As they mature, they develop a parchment-like texture and are surrounded by a yellowish-green halo.
• Stem Symptoms: Brown lesions with irregular borders appear on the stems.
• Fruit Symptoms: Tomatoes exhibit characteristic superficial, charcoal-black necrotic spots. These are small, slightly raised, well-defined, and scattered across the fruit’s surface.

Favorable Conditions for Disease Development and Spread

• Temperature and Humidity: Ideal conditions include temperatures between 18-28°C and humidity levels over 85%. The presence of water droplets on leaves from fog or sprinkler irrigation encourages infection.
• Ventilation: Poor ventilation in greenhouses, leading to condensation, promotes the bacterium’s growth and spread.
• Precipitation and Wind: Rainfall, especially when accompanied by wind, can disperse the bacterium.
• Host Range: In addition to tomatoes, the bacterium can infect wild flora such as Solanum nigrum and Hyascyamus niger.

Prevention and Control Measures

• Field Management: Grow tomatoes on raised beds if possible, and position crops perpendicular to prevailing winds to limit bacterial spread. Opt for drip irrigation instead of overhead sprinklers, and avoid low-lying areas prone to water accumulation.
• Crop Rotation: Avoid intercropping with peppers or eggplants, as they share common pests and pathogens with tomatoes.
• Foliar Treatments: Apply foliar sprays with products that reach both sides of the leaves, using treatments with:
• Copper-based products: Copper hydroxide (e.g., Funguran 300 SC 0.15%, Champ 77 WG 0.2%) and neutralized copper sulfate (e.g., Bouillie Bordelaise 0.75%).
• Mancozeb-based products: Such as Dithane M45 0.2%, Dithane 75 WG Neotec 0.2%, Manzate 0.2%, and Novozir MN 80 0.2%.
• Combination Products: Iprovalicarb with copper oxychloride (e.g., Melody Compact 49 WG 0.2%).
• Alternative Organic Approach: Use ecological fortifiers like Copfort, applied as a foliar spray at concentrations of 0.15-0.30%. This product penetrates the cuticle and stimulates the plant to produce phytoalexins, which inhibit bacterial multiplication.