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Lotus common pests and their control
Liaocheng Botanical Garden is a modern ecological and sightseeing agricultural park, primarily focused on aquatic plants. It showcases over 200 varieties of renowned lotus species. Through careful observation, it has been identified that several pests and diseases significantly affect the growth and health of the lotus in the garden.
First, the main diseases affecting the lotus include:
1. **Black Spot Disease**: This fungal disease mainly affects the leaves. Initially, yellowish chlorotic spots appear, which later develop into brown, ringed lesions with a yellow-green halo. A black mold layer may form on the upper surface of the leaves. The disease becomes severe during rainy seasons and under conditions of excessive nitrogen fertilizer or high summer water temperatures. To manage this, remove infected leaves promptly, replace soil for severely affected plants, and avoid using nitrogen-rich fertilizers. Spraying 75% chlorothalonil diluted 600–800 times can help control the disease.
2. **Brown Spot Disease**: This disease causes round, light brown to yellowish-brown spots on the leaves, with darker edges. In advanced stages, black mold appears on the lesions. It is more prevalent in autumn and during rainy periods. The pathogen overwinters in plant debris. Control measures include removing old leaves, reducing disease sources, and spraying 50% carbendazim at 500 times dilution or 80% dexamethasone at 500–800 times.
3. **Rot Disease**: This disease affects the leaves, petioles, and roots. Early symptoms include green or blue spots along the leaf edges, which eventually cause the entire leaf to turn brown and necrotic. Petiole infections lead to browning and drooping, while root rot causes discoloration and vertical necrosis. Overuse of land, poor soil quality, and prolonged water exposure increase the risk. Management includes proper fertilization, avoiding waterlogging, and removing diseased leaves. Spraying 50% carbendazim or 50% Phytophthora net at 500 times dilution helps control the disease.
Second, the major pests include:
1. **Locusts**: These insects feed on young leaves and buds in early May, causing damage to both the front and back of the leaves. Adults and larvae suck sap, posing a threat from spring to autumn. Control involves spraying 20% cypermethrin at 2000 times dilution.
2. **Cockroach Moth**: These moths feed on lotus leaves, sometimes leaving up to 20–30 eggs on the underside. Severe infestations can defoliate the plants completely. Control methods include manually removing larvae, cleaning up diseased leaves, and applying 90% trichlorfon at 1500–2000 times dilution mixed with spores. Removing weeds and disinfecting the area is also important.
3. **Prickly Pear Moth and Brown Moth (larvae)**: These larvae damage the leaves, typically from mid-June to September. Control involves burning infested leaves and using 90% trichlorfon at 800–1000 times or 2.5% emulsifiable concentrate at 3000 times.
4. **Hydra (Grass)**: These pests feed on the stems and roots of lotus plants, causing yellowing of the leaves. A common control method is to apply lime at 10–15 kg per mu, but care must be taken not to over-apply.
5. **Lotus Root Aphid**: This pest attacks lotus, water lilies, and Typha, leading to stunted growth and poor flowering. Control includes using 50% extermination of loquat EC at 1000 times or 50% disulfuron EC at 2000 times. Special attention should be given to pesticide use due to their potential toxicity to fish.
6. **Spodoptera litura (Lotus Moth)**: The larvae initially feed on the upper surface of the leaves, leaving only the veins and epidermis. As they grow, they cause extensive leaf damage and even eat young stalks. They can migrate to neighboring fields when resources are depleted. Control methods include using Bt emulsion or insecticidal liquid No.6 at 500–800 times, or phoxim 50% EC at 1000 times, deltamethrin 2.5% EC at 3000 times, or 21% killing emulsion at 4000 times.