8MP Fixed IR Turret Camera,8MP Fixed IR Bullet Camera,8MP Motorized IR Bullet Camera,8MP Motorized IR Turret Camera Tiandy Technologies CO.,LTD , https://en.tiandy.com
Onion blight
Onion diseases can cause significant damage to crops, leading to reduced yield and quality. One common issue is a fungal infection that primarily affects the leaves and stems of onions, including green onions and shallots. Initially, there may be no visible symptoms on the green or white parts of the plant. However, as the disease progresses, grayish-white spots appear and gradually expand. These spots lead to the wilting of the leaves from the top down, resulting in what farmers call a "dry tip" condition.
In humid conditions, a thin layer of white mold may develop on the infected areas, while in dry weather, this mold disappears. Upon cutting open the inner walls of the conical leaves, white mycelium can be observed, which helps distinguish this disease from physiological "dry tip," a non-infectious condition.
The pathogen responsible for this disease is *Phytophthora allii* (Saw.), which is also classified as *P. nicotianae* var. *parasitica* (Dast.) Waterhouse. The disease cycle involves the survival of mycelium, spores, oospores, and chlamydospores within infected plant tissues. In southern regions, zoospores are the main agents of initial and secondary infections, spreading through rain splash or irrigation water into the plant via stomata.
Wet and warm weather, low-lying fields, poor drainage, and excessive nitrogen fertilizer application all contribute to the development of this disease. Currently, there is limited research on the resistance of different onion varieties. Some varieties known for strong resistance to purple spot disease also show resistance to this pathogen, but more field testing is needed to confirm their effectiveness in various growing conditions.
To manage the disease, it's essential to select resistant onion varieties. Farmers should implement deep furrow cultivation, ensure proper drainage, and remove excess water after rainfall. Balanced fertilization and foliar nutrient applications can help prevent excessive vegetative growth, thereby improving plant health and reducing disease susceptibility.
When weather conditions favor disease development, timely fungicide applications are recommended. Effective options include 25% metalaxyl wettable powder, 64% mancozeb at 600 times dilution, 66.5% propamocarb hydrochloride at 800 times, 72% cymoxanil wettable powder at 600–800 times, or a combination of 69% azoxystrobin + 75% chlorothalonil (1:1) diluted 1000 times. Apply 2–3 times, with intervals of 7–10 days, alternating between different products to prevent resistance.