Chestnut Pest and Disease Prevention and Control Methods and Technical Key Points
In Anhui Province, chestnuts are mainly distributed in the mountainous areas of southeastern and western Anhui. Since the 1990s, they have also been developed on a large scale in the Jianghuai hilly region. The main chestnut-producing counties (cities) include Jinzhai, Huoshan, Shucheng, Yuexi, Guangde, Ningguo, Taihu, and others. There are about 150 species of pests and diseases harming chestnuts in our province, with common and severe occurrences affecting chestnuts...
1. Young buds After the young buds become diseased, brown lesions about 2 mm in diameter appear on the hypocotyl, followed by small dark brown spots 1 mm in diameter on the cotyledons.2. Leaves When leaves are infected, grayish-brown or dark brown raised small spots first appear, then expand into dark brown circular lesions 2 to 6 mm in diameter, with obvious concentric rings and a yellow-white halo around the periphery. When the air is humid, black mold-like growth appears on the lesions, which can cause the leaves to wither and die.
3. Stems When petioles, stems, and fruit stalks are infected, the lesions are elliptical to spindle-shaped, dark brown with concentric rings. When they encircle the side branches and main stem, the side branches or the entire plant wither and die.
4. Pods The lesions on pods are basically similar to those on leaves. In severe cases, the seeds stop growing and form red seeds, and the pods tend to split before harvest. When humidity is high, mycelium can grow inside the pods.
Infection cycle
The pathogen overwinters or oversummers as mycelium or spores in diseased plant residues and inside and on the surface of seeds. In the south, the disease can occur year-round, causing damage in successive cycles, with no obvious overwintering period. After oversummering and overwintering, the mycelium forms conidia under high humidity conditions, which spread with the wind and cause primary infection. Sowing infected seeds can cause seed rot and seedling death. New conidia produced on diseased plants can spread with the wind and cause multiple secondary infections.
Occurrence characteristics
Brassica rapa (pak choi type) is the most susceptible, while Brassica napus (cabbage type) is relatively resistant. High temperature and high humidity favor disease development. If high temperature and rainy weather occur during the flowering period of rapeseed, the incubation period is short and the disease develops easily. Rainy weather during pod development is extremely favorable for spore spread and infection. In low-lying fields with continuous cropping, and with biased or excessive application of nitrogen fertilizer, the disease is severe.
Prevention and control methods
1. Agricultural control Use disease-resistant varieties or disease-free seeds, and select seeds from disease-free plants before harvest. Rotate with non-cruciferous crops. Avoid biased or excessive application of nitrogen fertilizer, and pay attention to increasing potassium fertilizer. Water at the right time and in the right amount. Clean up diseased plant residues in the field in a timely manner.
2. Seed treatment Soak seeds in warm water at 50°C for 20 to 30 minutes. You can also dress seeds with 0.4% of seed weight of 50% thiram or 0.25% of 50% iprodione. Alternatively, soak seeds in 100-fold dilution of 40% formalin for 25 minutes, wash clean, air-dry, and then sow.
3. Field spraying Spray promptly for control at the early stage of disease occurrence in the field, once every 7 days, and spray 2 to 3 times consecutively depending on disease severity. Optional agents include 1500-fold dilution of 50% iprodione, or 600-fold dilution of 75% chlorothalonil, or 500-fold dilution of 64% oxadixyl-mancozeb, or 800-fold dilution of 80% mancozeb, or 600-fold dilution of 12% copper green emulsifiable concentrate, or 500-fold dilution of 70% mancozeb.