Hektar

Alternaria in Cucurbitaceae - Alternaria cucumerina

Symptoms of the disease (characteristics for the diagnosis of the disease)

• The disease affects cucumber, melon, watermelon, and pumpkin crops, appearing on all above-ground parts of the plants. On the leaves, it first shows up as circular spots, 1-2 mm in diameter and yellowish in color. These spots gradually enlarge to 3-7 mm, becoming yellowish-brown with a watery, translucent appearance.

• Under favorable conditions, the spots enlarge, developing concentric rings and taking on a dark brown color. Dinescu (1964) observed that, in cucumbers, these spots later turn grayish-white with a pale border. Adjacent to the spots, a blackish-brown fuzz appears, which consists of the fungus’s conidiophores and conidia.

• Similar symptoms appear on the stems as on the leaves. On fruits, infections are less frequent and show as shallow, circular, yellowish-white spots. The surrounding tissue softens and begins to rot. In wet conditions, the fungus produces fruiting bodies on the surface of these spots, forming a black, velvety layer.

Factors favoring the occurrence and evolution of the disease, its transmission and spread

• Transmission of the pathogen is through seeds, and spread is through precipitation, wind, tools, etc.
• Alternaria is favored by warm weather (temperature around 27º C, high atmospheric humidity of 85-90%).

Prevention and control measures

When the attack is reported, alternative foliar treatments with fungicides based on :

• Difenoconazole + Ciflufenamide (Cidely Top 0.1%)
• Chlorothalonil (Bravo 500 SC 0.2%)
• Mancozeb (Dithane M 45 0.2%; Dithane 75 WG Neotec 0.2%; Manzate 0.2%)
• Triadimenol + Folpet (Shavit F 72 WDG 0.2%)

Foliar-applied ecological products : Garex B 0.1 – 0.2%, Copfort 0.15 – 0.3%, provide good protection to cucumber and melon crops against this pathogen.