There are several diseases that can affect eggplants, especially when the stalks become rotten. Common conditions include bacterial soft rot, black rot, stem rot, sclerotinia, and bacterial blight. In greenhouse settings, two main types of diseases caused by decaying stalks are most prevalent.
**I. Bacterial Soft Rot**
This disease typically enters through wounds caused by activities like picking leaves. Initially, the infected area appears pale brown and begins to soften. As the infection progresses, the outer layer of the stem (epidermis) and inner pith turn brown and decay, leading to dehydration and shrinkage. However, the upper parts of the plant may not show obvious symptoms at first. The vascular system remains unaffected in the early stages. Over time, the upper leaves of the affected stem may wilt and die. A strong, unpleasant odor often accompanies the infected area. This disease tends to be more severe near the entrance of the greenhouse and where condensation from the plastic film drips down.
Bacteria cannot spread effectively without water droplets or plant wounds. Therefore, preventing bacterial diseases should start with reducing humidity inside the greenhouse. Using drip irrigation, covering the greenhouse with a plastic sheet, and watering appropriately can help control moisture levels. After morning ventilation, briefly opening the greenhouse allows high-humidity air to escape, reducing condensation. Improving the structure of the greenhouse, such as using high-quality non-drip films, can also significantly reduce disease occurrence.
If the disease has already developed, you can treat the affected areas by applying 72% agricultural streptomycin diluted 1500 times, or 50% copper carboxylate (DT) at 200 times concentration, or 47% mancozeb at 200 times. Combining these with 72% streptomycin diluted 4000 times and 47% mancozeb at 600 times can enhance effectiveness. Apply this treatment every 7 to 10 days for 2 to 3 consecutive applications.
**II. Black Rot**
Black rot is another common issue caused by decaying stalks. It primarily affects the base of the stem, where the affected area becomes shriveled and sunken, covered with dark brown moldy growth. The interior of the stem turns brown, and cracks may appear at the base. At the onset, small dark brown spots form, irregular in shape, and can spread along the veins. The center of the lesions may appear slightly lighter. Severe cases can lead to leaf death.
To prevent and manage this disease, it’s essential to start with seed disinfection. For example, you can mix 2.5% thiram at 10 ml per 150–200 ml of water, then apply it to 5–10 kg of seeds. Once the disease appears, you can spray 75% chlorothalonil wettable powder at 600 times dilution, or combine 50% carbendazim wettable powder at 600 times with 50% dicloran copper (DT) at 500 times. When spraying, make sure to cover all areas evenly, paying special attention to the base of the stems where the disease is most likely to occur.
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