Occurrence Patterns and Control Methods of Major Pests and Diseases of Osmanthus
Osmanthus, also known as muxi (Osmanthus fragrans), is a precious aromatic plant native to China. Xianning is located in southern Hubei and has long been known as the "home of osmanthus." In recent years, damage from osmanthus pests and diseases has increased, reducing its ornamental value. Common ones include: anthracnose, leaf spot disease, rot disease, jewel beetles, psyllids, whiteflies, scale insects, stinging moths, leaf-rolling moths, bagworms and inchworms. Based on control practices in recent years, their occurrence characteristics and control experience are briefly described below.
(1) Anthracnose: It occurs easily under high temperature and high humidity conditions, producing nearly circular purplish-brown spots on leaves and stems, with small black dots on them. When damage is severe, the leaves wither.
Starting from June to July, spray zineb at 500-600 times dilution for prevention; pay attention to ventilation and light penetration, and water and fertilize reasonably. Remove and destroy diseased leaves promptly when found, and spray 50% amobam at 800-1000 times dilution for control. Alternatively, thoroughly clear dead branches, fallen leaves and weeds from the field in winter.
(2) Leaf spot disease: It occurs easily under high temperature and high humidity conditions, causing irregular black spots on the leaf surface, with black mold growing on them, leading to early leaf drop. Starting from June to July, spray 140 times equal-amount Bordeaux mixture for prevention; after onset, spray 70% thiophanate-methyl at 800-1000 times dilution; water and fertilize reasonably; pay attention to ventilation and light penetration; clear dead branches and fallen leaves and burn them in a centralized manner to reduce sources of infection.
(3) Rot disease: It mostly occurs at the root collar. The affected part becomes water-soaked, and after the lesions gradually expand, the plant grows weak and may even die. It occurs severely in summer during the rainy season. In early spring, spread a small amount of sulfur powder around the plant; for severely affected areas, apply asomate and kerosene preparation.
(4) Jewel beetle: Adults bite and feed on young leaves, causing notches, but the main damage is caused by larvae tunneling and feeding within the bark of branches and trunks. The damaged bark has protruding cracks and exudes oily brown gum. When damage is severe, the bark splits open, and the main branches or the entire plant die.
Manual capture: During the adult emergence period, take advantage of their death-feigning behavior by shaking branches and trunks in the early morning before the dew dries, then capture and kill them after they fall to the ground.
Painting trunks and branches: From adult occurrence to larval damage period, paint the trunks and branches with 20-30 times dichlorvos emulsifiable concentrate, omethoate emulsifiable concentrate or monocrotophos emulsifiable concentrate, repeating 3-4 times (at intervals of 7-10 d); use 80% dichlorvos emulsifiable concentrate and 10-20 times clay, add an appropriate amount of water to make a paste, and paint it on the damaged parts of branches and trunks, so that when adults emerge and bite through the bark to exit, they are poisoned and die.
Adult control: Spray the canopy with 90% trichlorfon at 1000 times dilution 2-3 times (at intervals of about 7 d); killing larvae: during the peak hatching period of larvae, scrape off the bark and apply 80% dichlorvos emulsifiable concentrate at 20 times dilution.
(5) Psyllid: Adults and nymphs suck sap from buds, leaves and tender shoots. Affected leaves develop brown necrotic spots, and in severe cases the entire leaf turns brown, causing early leaf drop. Nymphs secrete large amounts of honeydew on the leaves, inducing sooty mold. During the peak occurrence of nymphs, spray 25% carbaryl wettable powder at 200-300 times dilution, or 50% monocrotophos at 2000-3000 times dilution.
(6) Whitefly: Adults and larvae gather on the underside of leaves to suck sap, causing leaves to turn yellow, wilt and even die. This insect secretes large amounts of excrement, contaminating the leaves and causing sooty mold. Seize the young larval stage for spraying, and choose 40% methidathion at 1500 times dilution, or 2.5% deltamethrin 40 ml, or 40% phosmet 150 ml per mu, etc.
Occurrence and Control of Common Pests and Diseases of Osmanthus
1. Leaf spot disease.It mainly damages the leaves. Initially, small brown spots appear, and the lesions become circular or irregular. Later, the center is gray to grayish-white, and the margin is reddish-brown, with blackish-gray moldy growth on the lesions. High temperature and high humidity are often the triggers for onset. It spreads through wind and rain and causes infection. After October, the disease subsides. Control: (1) In winter, prune to remove diseased leaves and clear diseased fallen leaves, and burn them in a centralized manner; (2) In early May, spray 1:2:100-200 Bordeaux mixture, after which 50% benomyl at 1000-1500 times dilution, or pyrazophos at 500 times dilution, or 70% thiophanate-methyl at 1000 times dilution may be sprayed.
2. Blight spot disease.Leaf damage mostly starts from the leaf tip and leaf margin. Small spots are light brown, then expand into circular or irregular shapes. Lesions may connect with each other and reach 1/3 to 1/2 of the leaf, are grayish-brown, with green margins, and later small black dots appear on the lesions. When temperature and humidity are high, ventilation is poor, and plant growth is weak, the disease is more severe. It generally occurs from July to November and spreads through wind and rain. Control: (1) In the early stage of disease, spray 65% zineb at 500 times dilution or 1:2:200 Bordeaux mixture; (2) Afterwards, spray 50% carbendazim wettable powder at 800-1000 times dilution or 50% benomyl wettable powder at 1000-1500 times dilution.
3. Stinging moth.Green or yellowish-green, with a white dorsal line, it most easily occurs on the underside of leaves, feeding on leaf mesophyll and leaving the epidermal layer. Before larvae descend from the tree to spin cocoons, loosen the soil around the trunk to attract larvae to gather and spin cocoons, then collect and destroy them. Alternatively, spray Bt emulsion with a spore content of more than 10 billion/ml at 500-800 times dilution. In addition, 2.5% deltamethrin emulsifiable concentrate or 20% fenvalerate emulsifiable concentrate at 3000 times dilution can also be sprayed.
4. Scale insect.In the Yangtze River basin, 2 to 3 generations can occur. The most severe damage occurs from May to June and from August to September. They prefer to gather on the shaded side of main shoots and at branch forks, or on branches and leaves. Both adults and nymphs secrete honeydew, leading to sooty mold in ornamental plants. High temperature and high humidity favor occurrence. When only a small number occur, they can be gently brushed off with a soft-bristled brush, with good results. In summer, spraying 0.3 to 0.5 degrees Baume lime sulfur mixture is most beneficial, or 50% monocrotophos emulsifiable concentrate at 1500 times dilution, used alone or in combination, spraying once every 7 to 10 days, for 2 to 3 consecutive sprays.
5. Red spider mite.It often occurs under high temperature and drought conditions. Control methods: During dry weather, attention should be paid to irrigation combined with fertilization to promote vigorous plant growth and enhance insect resistance. When applying chemical pesticides, attention should be paid to frequent rotation, because after the application of certain highly toxic pesticides, resistance may develop. Spraying 40% fenpropathrin emulsifiable concentrate at 2000-3000 times dilution or 40% dimethoate emulsifiable concentrate at 1500 times dilution gives good control results.
Occurrence and Control of Pests and Diseases of Osmanthus
1. Leaf spot disease. It mainly damages the leaves. Initially, small brown spots appear, and the lesions become circular or irregular. Later, the center is gray to grayish-white, and the margin is reddish-brown, with blackish-gray moldy growth on the lesions. High temperature and high humidity are often the triggers for onset. It spreads through wind and rain and causes infection. After October, the disease subsides. Control: (1) In winter, prune to remove diseased leaves and clear diseased fallen leaves, and burn them in a centralized manner; (2) In early May, spray 1:2:100-200 Bordeaux mixture, after which 50% benomyl at 1000-1500 times dilution, or pyrazophos at 500 times dilution, or 70% thiophanate-methyl at 1000 times dilution may be sprayed.2. Blight spot disease. Leaf damage mostly starts from the leaf tip and leaf margin. Small spots are light brown, then expand into circular or irregular shapes. Lesions may connect with each other and reach 1/3 to 1/2 of the leaf, are grayish-brown, with green margins, and later small black dots appear on the lesions. When temperature and humidity are high, ventilation is poor, and plant growth is weak, the disease is more severe. It generally occurs from July to November and spreads through wind and rain. Control: (1) In the early stage of disease, spray 65% zineb at 500 times dilution or 1:2:200 Bordeaux mixture; (2) Afterwards, spray 50% carbendazim wettable powder at 800-1000 times dilution or 50% benomyl wettable powder at 1000-1500 times dilution.
3. Stinging moth. Green or yellowish-green, with a white dorsal line, it most easily occurs on the underside of leaves, feeding on leaf mesophyll and leaving the epidermal layer. Before larvae descend from the tree to spin cocoons, loosen the soil around the trunk to attract larvae to gather and spin cocoons, then collect and destroy them. Alternatively, spray Bt emulsion with a spore content of more than 10 billion/ml at 500-800 times dilution. In addition, 2.5% deltamethrin emulsifiable concentrate or 20% fenvalerate emulsifiable concentrate at 3000 times dilution can also be sprayed.
4. Scale insect. In the Yangtze River basin, 2 to 3 generations can occur. The most severe damage occurs from May to June and from August to September. They prefer to gather on the shaded side of main shoots and at branch forks, or on branches and leaves. Both adults and nymphs secrete honeydew, leading to sooty mold in ornamental plants. High temperature and high humidity favor occurrence. When only a small number occur, they can be gently brushed off with a soft-bristled brush, with good results. In summer, spraying 0.3 to 0.5 degrees Baume lime sulfur mixture is most beneficial, or 50% monocrotophos emulsifiable concentrate at 1500 times dilution, used alone or in combination, spraying once every 7 to 10 days, for 2 to 3 consecutive sprays.
5. Red spider mite. It often occurs under high temperature and drought conditions. Control methods: During dry weather, attention should be paid to irrigation combined with fertilization to promote vigorous plant growth and enhance insect resistance. When applying chemical pesticides, attention should be paid to frequent rotation, because after the application of certain highly toxic pesticides, resistance may develop. Spraying 40% fenpropathrin emulsifiable concentrate at 2000-3000 times dilution or 40% dimethoate emulsifiable concentrate at 1500 times dilution gives good control results.