Leeks are commonly affected by several diseases that lead to leaf death, which can significantly impact their growth and yield. The first of these is a fungal disease characterized by water-soaked lesions on the leaves and the base of the plant. The affected areas appear dark green, while the roots and bulbs turn light brown without clear boundaries. When humidity is high, a sparse white mold develops, and under dry conditions, the leaves turn yellow. Infected roots and stems lose their ability to absorb water and nutrients, leading to wilting or drying of the above-ground parts. To manage this disease, it's important to improve drainage and practice crop rotation. In the early stages, you can apply 25% iprodione at 600 times dilution, 58% metalaxyl-manganese zinc at 500 times, or 40% aluminum phosphite at 200–300 times. Apply about 40–50 kg per acre, and repeat every 7–10 days.
Another common issue is gray mold, which typically starts from the tip of the leaf and spreads downward. Initially, small white or light brown spots appear on both sides of the blade. As the disease progresses, the lesions become elongated or oval in shape, eventually turning into large patches and causing the leaves to dry out. Under wet conditions, a dense layer of gray or gray-green mold forms. Prevention involves good drainage and proper watering. For treatment, use 50% carbendazim at 1000–1500 times dilution, spraying once every 20 days. Alternatively, 20% triadimefon at 800–1000 times or 50% carbendazim at 600 times can be applied. After harvesting, when the new shoots reach 5–8 cm in height, two sprays are recommended.
Root damage caused by root aphids is another significant problem. These pests bore into the bulb, creating empty cavities that lead to decay, yellowing, and eventual death of the plant. Control measures include applying wood ash or mixing 5% phoxim granules (2 kg per acre) with fine soil and placing it around the roots before covering with earth. If larvae are detected, and the leaf tips begin to yellow and droop, a solution of 75% phoxim EC diluted 500 times can be poured directly onto the roots after loosening the topsoil. This should be done carefully and repeated up to 10 times for best results. During the adult emergence period—mid to late April, mid-June, late July, and mid-October—spray 10% chlorpyrifos at 2000–2500 times, 75% phoxim at 1000 times, or 2.5% cypermethrin at 3000 times. Spraying between 9–10 am is most effective. These pests prefer moist, shaded, and humus-rich environments, so improving air circulation around the plants can help reduce infestation.
In addition to these biological causes, physiological issues such as tip burn, leaf blight, and overall plant death can also occur. These may be linked to factors like soil acidification, ammonia toxicity, extreme temperatures (above 35°C or below freezing), or nutrient deficiencies in calcium, boron, or manganese. Addressing these underlying issues through soil testing and balanced fertilization can help prevent such problems. By taking proactive steps, leek growers can maintain healthy crops and minimize losses due to disease and environmental stress.
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