Common Varieties of Pests and Diseases on Osmanthus and Their Control Methods
In natural environments, osmanthus trees planted sparsely rarely suffer from serious pests and diseases, so some people mistakenly believe that osmanthus does not require plant protection work. This is an incorrect view. Although the types of pests and diseases that can cause mass death of osmanthus trees are still uncommon, the pests and diseases that affect osmanthus growth and flower yield are gradually increasing. At present, many regions have listed osmanthus as a key economic tree species for development, and the cultivation scale is growing larger and larger. People not only value its ecological benefits in landscaping, but also pay more attention to the economic benefits of its flower yield. Therefore, sufficient attention must be given to the prevention and control of osmanthus pests and diseases.
(I) Diseases and Their Control
1. Osmanthus Brown Spot Disease
This disease is caused by Cercospora osmanthicola. It is distributed in Shanghai, Jiangsu, Zhejiang, Guangdong, Shaanxi and other places.
(1) Symptoms: In the early stage of occurrence, some small yellow spots appear on the leaves, scattered, gradually becoming yellow-brown to gray-brown nearly circular spots, or irregular spots limited by leaf veins, 2-3 mm in diameter, with no obvious edge. The outer edge has a yellow halo. A large number of fine gray-black mold spots are produced on the upper surface of the leaves. The lesions can merge with each other to form large spots, causing the leaves to wither and die.
(2) Control methods: Select disease-free plants as propagation stock, strengthen cultivation management, and enhance tree vigor. Remove diseased insects and reduce infection sources. For seedlings in severely affected areas, when leaving the nursery, spray 1000 times potassium permanganate solution for disinfection. During the disease period, spray either 1:2:200 Bordeaux mixture, or 50% benomyl wettable powder 1000-1500 times solution, or 50% Tuzet wettable powder 1000 times solution, or 65% zineb wettable powder 800 times solution for control.
2. Osmanthus Leaf Spot Disease
This disease is caused by Phyllosticta osmanthicola. It occurs in various osmanthus-producing areas, such as Jiangsu, Zhejiang, Shanghai, Hubei, Guangxi and other provinces and municipalities, where damage symptoms of varying degrees can be seen.
(1) Symptoms: The pathogen mostly invades from the leaf margin or leaf tip. The lesions are initially pale yellow-green, then gradually expand, becoming gray-brown to gray, irregular or nearly circular in shape, with obvious edges. Later, many black dots are produced on the lesions, which are the pathogen's pycnidia. Damage to the lower part of the canopy is often more severe than to the top, and old leaves are more severely affected than new leaves.
(2) Control methods: In winter, remove diseased leaves and burn or bury them, clean the garden, and reduce overwintering sources of the disease. Strengthen cultivation management and increase fertilizer application. During hot and dry weather, water appropriately to strengthen tree vigor and improve disease resistance.
3. Osmanthus Sooty Mold Disease
This disease is caused by various fungi, commonly including Citrus sooty mold, Chaetothyrium spinigerum and Meliola butleri. This disease is extremely widespread, occurring almost everywhere, and not only harms osmanthus but also harms citrus, tea trees and many other plants.
(1) Symptoms: The symptoms of osmanthus sooty mold disease also differ depending on the different pathogenic fungi. For example, the sooty mold of the genus Capnodium is black and thin-paper-like, easily torn off or naturally falling off; the sooty mold of Chaetothyrium spinigerum is black like the soot at the bottom of a pot, and if wiped off with a finger, the leaf surface is still green; the mold layer of Meliola is radial small mold spots, scattered on the upper and lower leaf surfaces. Because its hyphae produce haustoria, it can adhere tightly to the host surface, so it is not easy to fall off. When sooty mold disease is severe, a thick black mold layer covers all mature leaves and branches of the whole tree, hindering leaf photosynthesis, inhibiting new shoot growth, causing diseased leaves to turn yellow and wilt, and causing early leaf drop, reducing ornamental value and flower yield.
(2) Control methods: The key to controlling this disease is to control pests (see the pest section for specific methods). In maintenance and management, appropriate pruning should be carried out, weeds removed, ventilation and light transmission improved, and tree vigor enhanced to reduce the degree of disease occurrence. Chemical control: 2% ferrous sulfate solution or 50% Tuzet 1000-15000 times, 50% carbendazim wettable powder 1000 times solution all have relatively good control effects. For sooty mold disease caused by the genus Meliola, spray 2-3 times copper soap solution (copper sulfate 0.5 kg, rosin mixture 2 kg, water 200 kg) between June and July.
4. Osmanthus Algal Spot Disease
(1) Symptoms: The lesions can appear on both the upper and lower surfaces of the leaves, but mainly on the upper surface. Initially, white to yellow-brown needle-head-sized small round spots are produced on the leaf surface. Sometimes the small round spots are arranged in a cross shape, then expand radially in all directions, forming nearly circular or irregular slightly raised felt-like masses, with a fibrous texture on the surface, irregular notched edges, gray-green or yellow-brown, 1-10 mm in diameter, later darker in color and smooth on the surface. It usually occurs more on the middle and lower parts of the plant, and less on the upper young leaves. After the plant is damaged, photosynthesis is affected, and in severe cases the cortex of the branches may peel off or die.
(2) Control methods: Reasonable fertilization and drainage, appropriate pruning and branch training, clearing garden weeds, and strengthening maintenance management can all reduce the occurrence of this disease to a certain extent. Before the disease occurs in early spring, spraying 75% chlorothalonil wettable powder 800-1000 times has a good preventive effect on this disease. In places where the disease is severe, spraying once in late autumn can have a certain effect on reducing the disease in the following year.
5. Osmanthus Root-Knot Nematode Disease
This disease is caused by the southern root-knot nematode. It usually occurs in osmanthus cutting seedlings, especially in 1-2 year old seedlings, where the disease incidence can sometimes reach more than 90%.
(1) Symptoms: Root-knot nematodes mainly damage the roots, initially forming many root galls of different sizes. The fibrous roots of diseased plants are reduced, and the root tips are swollen. The root galls are initially yellow-white, then gradually turn brown and rot. The aboveground part grows weakly and is prone to withering and dying under drought conditions. Mildly affected plants generally do not show symptoms, but as the cultivation years of the plant increase, the number of nematodes continuously increases. At this time, the plant will show symptoms such as declining growth, yellowing and stunting, similar to the symptoms of fertilizer deficiency and drought, so it is often mistaken for being caused by lack of water and fertilizer.
(2) Control methods: Carry out plant quarantine well, and do not introduce seedlings from affected areas. For suspicious seedbed soil, use 10% cadusafos granules for control, using 400 g of active ingredient per 666.6 sq m. When applying, first scrape away the soil 3-5 cm deep under the canopy, apply the pesticide evenly, and then cover with soil. During the growing period, apply 10% fenamiphos granules 3-5 kg per 666.6 sq m. The pesticide should be applied around the root zone, and can be applied in furrows, holes or by broadcasting. Strengthen cultivation management and increase organic fertilizer application (because actinomycetes in organic fertilizers have certain inhibitory effects on nematode growth). In affected areas, crop rotation of more than three years should be implemented. First using disease-resistant rootstock varieties can often achieve good preventive effects.
6. Osmanthus Violet Root Rot
This disease is caused by Helicobasidium purpureum. The disease is extremely widespread and affects many plant species. In recent years, it has caused devastating disasters in nurseries in some areas of Guizhou, and it is also quite common in osmanthus-producing areas such as Suzhou, Hangzhou and Guilin.
(1) Symptoms: Generally, the disease occurs in April, and damage is severe from May to August. The leaves of diseased trees are pale green, and new shoots are thin and weak. The underground young roots are damaged first, gradually spreading to the thick lateral roots and main roots. At the initial stage of the disease, the root bark loses its luster, then turns yellow-brown, and finally becomes black-brown. In severe cases, the cortex rots, leaving only the separated cork layer and xylem, and purple root-like fungal strands are wrapped around the root surface. In the rainy season, the mycelium can spread to the root crown or stem base, and sometimes even to the soil surface, forming a purple-red mycelial layer.
(2) Control methods: Select well-drained sandy loam soil for seedling raising, and using layered propagation seedlings or cuttings can reduce disease occurrence. Quarantine work should be emphasized when transferring seedlings. For diseased osmanthus trees, the soil should be scraped away in spring to air the roots, completely exposing all soil under the canopy so that the root crown is fully exposed. After 10-15 days of sun exposure, apply 5-7.5 kg of fully fermented "5406" bacterial fertilizer per plant, or pour 2.5% ferrous sulfate solution, then cover with soil, and the original diseased soil should be dug out. In severely affected areas, the soil can be disinfected with fuberidazole or 50% carbendazim (5-10 g per sq m), or 50% Tuzet 250-300 times solution or 5 degrees Baumé lime sulfur mixture can be spread on the roots of diseased plants. Pay attention to drainage, loosening the soil and increasing organic fertilizer application, all of which can reduce the damage of this disease to a certain extent. There are many types of pathogens that cause osmanthus root rot, and their symptoms and disease occurrence environments are often similar to violet root rot, so the control methods can also refer to those for violet root rot.
7. Osmanthus Iron Deficiency Disease
(1) Symptoms: Iron is a trace element. When osmanthus lacks iron, it first affects the formation of chlorophyll, especially the areas between the veins of young leaves are prone to showing chlorosis. When iron deficiency is mild, the area near the veins remains green, while areas farther from the veins begin to turn yellow. In severe cases, both young and old leaves become yellow-white, and some old leaves may also show yellow-brown necrotic spots, and are often attacked by some weakly parasitic fungi, causing early leaf drop. Osmanthus suffering from iron deficiency disease generally cannot bloom.
(2) Control methods: The control of this disease mainly uses chemicals to improve soil properties. During the new shoot growth period, spray 0.2%-0.5% ferrous sulfate solution on the leaves once a month. This method takes effect very quickly. Two to three days after spraying, yellow leaves can turn green, but sometimes the effect is not lasting. Some parks put 0.1 ferrous sulfate solution in a saline bottle, invert it on the trunk, and use an injection needle inserted into the bark for slow drip irrigation (the same method doctors use for saline drips), with relatively good results, but the procedure is troublesome. If chelated urea iron or ferrous sulfate is mixed with acidic organic fertilizer, the method is simple and easy to be effective in soil that is not strongly alkaline. The latest technology is to apply relatively stable chelated iron Fe-EDTA (ethylenediaminetetraacetic acid iron) to the soil, using 20-40 g per plant, with quick and lasting results. In addition, a 0.1% chelated iron solution can also be used for foliar spraying, and leaf color recovery is faster, but it must not be excessive to avoid chemical damage. Improve the soil. During spring drought, pay attention to irrigation to suppress alkalinity. In low-lying areas, salt water should be drained in time to reduce soil salt content. Increasing organic fertilizer application and intercropping green manure under trees can increase humus in the soil and improve soil structure and physical and chemical properties, all of which have certain effects on preventing and reducing the occurrence of this disease.
At present, the more ideal measure for correcting iron deficiency is to select suitable rootstock varieties, or perform trunk approach grafting or root grafting to change the rootstock variety.
(II) Pests and Their Control
1. Citrus Red Mite
(1) Morphology: The female adult mite body is broadly oval, with a raised back, dark red or purple-red, with tubercles on the back bearing white setae, 4 pairs of legs, claw-like, with well-developed empodia. The male adult mite body is slightly smaller than the female adult mite, with a slightly pointed abdominal end, diamond-shaped, bright red or brown, with relatively long legs, 4 pairs.
(2) Control methods: For adult trees, control should be strengthened in early spring and late autumn; for nurseries and young trees, in addition to spring and autumn, winter control work should also be strengthened. Comprehensive control methods must be adopted for citrus red mite, namely chemical control in the early stage, protection and utilization of natural enemies in the later stage, and strengthening maintenance management throughout the year to enhance tree vigor. In winter, spray 20% chlorobenzilate wettable powder 600-800 times solution, which has good effect. Lime sulfur mixture can be used at 1-2 Baumé degrees in winter and 0.3-0.5 Baumé degrees in spring, and is relatively safe for the predatory mite natural enemy. In early April, spray once a week with 20% dimethoate, or 40% omethoate, or 75% phoxim, or 280% dichlorvos, or 20% amitraz emulsion, for 2-3 consecutive times, effective against adult and young mites. In recent years, 73% propargite emulsifiable concentrate 4000 times solution has been promoted, with efficacy lasting about 24 days and good results. When suitable pesticides are temporarily unavailable, spraying 20-type washing powder (300-500 times solution in summer) sometimes also gives good control. When controlling this mite, pyrethroid pesticides should not be used, because such agents do not have an ideal killing effect on citrus red mite, and pesticides should be rotated or mixed, which can both enhance the mite-killing effect and avoid resistance. Using omethoate applied in the root zone of young plants also gives good results, as it can both kill mites and protect natural enemies.
2. Osmanthus Nymphalid Butterfly
(1) Morphology: Most of the forewings and hindwings are black. Along the outer margin of the forewing there are 3 rows of yellow spots forming bands, and there are 3 yellow markings in the discal cell. The hindwing has the same markings as the forewing. The head, thorax and antennae are all black, the legs and abdomen are yellow-gray, with several black transverse stripes.
(2) Control methods: During the larval and pupal stages, frequently inspect osmanthus plants, and once larvae and pupae are found, remove them promptly. During the larval occurrence period, spray 80% dichlorvos emulsifiable concentrate 1000 times solution, or 90% trichlorfon technical material 800-1000 times solution to kill them.
3. Whitefly
(1) Morphology: Yellow, covered with white wax powder. The wings are semi-transparent and also covered with white wax powder. The compound eyes are red-brown, divided into upper and lower parts, connected by a small eye in the middle.
(2) Control methods: Properly prune branches and improve ventilation and light transmission, which can reduce damage. During the peak adult occurrence period or when larvae hatch in large numbers, choose 40% omethoate emulsifiable concentrate, 50% malathion emulsion, 50% fenitrothion emulsion, 25% phosmet emulsifiable concentrate 1000 times solution, 90% trichlorfon 500-1000 times solution; 80% dichlorvos 1500 times solution, 25% quinalphos emulsifiable concentrate 1000 times solution, 20% amitraz (mitac) emulsifiable concentrate 1500 times solution, 25% buprofezin powder 2000-3000 times solution. Recent reports say that spraying 2-3 times during the peak egg hatching period with 2.5% deltamethrin emulsifiable concentrate diluted 5000 times with water gives the best control effect.
Whitefly adults have a strong tropism to yellow, so yellow wooden boards or plastic boards can be placed beside osmanthus trees, coated with sticky oil on the yellow boards, and the osmanthus branches shaken so that whitefly adults fly about and stick to the yellow boards, playing a trapping and killing role and having a certain effect on controlling their damage. In addition, using a small vacuum cleaner (such as a car vacuum cleaner) and suctioning continuously several times during the adult stage can completely control their damage.
Knowledge on Identification and Control of Major Pests and Diseases in Osmanthus Planting
This article attempts to give a general introduction to the occurrence characteristics, identification methods and control measures of pests and diseases that commonly occur and cause serious damage in osmanthus cultivation.
I. Identification and Control of Major Osmanthus Diseases The main types of osmanthus diseases include Aucuba japonica anthracnose, hibiscus anthracnose, orchid anthracnose, osmanthus anthracnose (Hefei, Chuzhou, Huangshan), Daphne odora sooty mold, gardenia sooty mold, camellia algal spot disease (Hefei), osmanthus leaf blight, osmanthus Pseudocercospora brown spot disease (Hefei, Chuzhou, Wuhu, Huangshan), osmanthus red spot disease (Hefei, Wuhu, Chuzhou, Huangshan), osmanthus Septoria leaf spot disease, osmanthus Ascochyta leaf spot disease (Huangshan), osmanthus Pestalotiopsis gray spot disease (Huangshan), osmanthus Monochaetia brown spot disease, osmanthus Phoma disease (Huangshan), osmanthus Macrophoma brown spot disease, osmanthus Alternaria leaf spot disease (Huangshan), sunscald, root-knot nematode disease, canker disease, etc. Among them, brown spot disease and leaf blight are the most severe and widespread.
1. Leaf Spot Disease
The lesions occur on both sides of the leaves. In the early stage of the disease, only some scattered brown spots appear on the leaf surface. Later, the center of the lesion on the leaf surface is gray-white to light brown, nearly circular or irregular in shape, and in severe cases several lesions combine together; the lesion edge is red-brown to dark brown, with a light brown halo outside, and a large number of fine gray-black mold spots are scattered on the upper leaf surface. These are the pathogen's conidiomata and conidia; the lesions on the lower leaf surface are brown; because the lesions gradually expand and merge into large patches, they often cause a large number of leaves to wither and fall off, seriously affecting the normal growth and flowering of the plant.
The pathogen of this disease overwinters as mycelial masses on diseased plants and fallen leaves. When the temperature rises from April to June of the following year, new conidia are produced and spread by airflow and rainwater for infection and damage, and then new conidia are produced for reinfection. This disease can occur from April to October; on the plant, old leaves are more severely affected than young leaves. The Jingu osmanthus variety is most susceptible, the Yingui variety is next, and the Dangui variety is not susceptible; plants with weak growth or transplanted in the same year are prone to the disease; under conditions of compacted, heavy and sticky soil and insufficient fertility, the disease is likely to occur; in the hot and humid season from July to August, the disease can spread rapidly.
Control methods: Strengthen water and fertilizer management, loosen the soil frequently, avoid soil waterlogging, promote robust plant growth, and improve the plant's disease resistance; thoroughly remove diseased leaves in winter and burn them in a centralized manner to reduce overwintering pathogens, which can significantly inhibit the occurrence of the disease in the coming year; from bud break and leaf emergence to leaf hardening in spring, spray 1:2:100 lime double Bordeaux mixture once every half month to prevent the occurrence of the disease; in the early stage of the disease, spray 50% sulfur-carbendazim suspension 800 times solution, or spray 50% carbendazim plus 75% chlorothalonil wettable powder 500 times solution, or spray 50% zineb wettable powder 800 times solution; 25% propiconazole emulsifiable concentrate 5000 times solution can also be sprayed, with an interval of 48 days. When seedlings from severely affected areas leave the nursery, spray 0.1% potassium permanganate solution for sterilization.
2. Leaf Blight
Also called leaf spot disease, it is an important disease of osmanthus.
It mainly damages leaves. The lesions mostly start at the leaf tip or leaf margin, initially yellow-green or light brown small spots, then gradually expand, becoming red-brown to gray-brown, nearly circular or irregular in shape; the color on the back of the lesion is lighter, and the edge is dark brown; the lesions sometimes curl and crack brittlely, and several lesions can merge with each other to reach 1/2-1/3 of the leaf, or form irregular large patches; later, many black small granular dots are scattered on the lesions, which are the pathogen's pycnidia. This disease can occur throughout the year, causing large areas of leaves to dry up and leading to early leaf drop; leaves in the middle and lower part of the canopy are more severely damaged than those at the top, and old leaves are more severely affected than new leaves.
Its pathogen overwinters as mycelium and pycnidia on diseased leaves. In spring, when temperature and humidity are suitable, conidia infect and cause disease, spread by wind and rain, especially most severe from July to November; when the temperature is 20-27°C, with more rain or high humidity, poor ventilation, insufficient fertilizer, weak tree vigor, or freezing damage and mechanical injury, the disease is likely to occur; when the climate is hot and dry and watering is not timely, the condition worsens.
Control methods: In late autumn and early winter, thoroughly remove diseased leaves and burn or deeply bury them in a centralized manner to reduce overwintering pathogens, which can effectively inhibit the occurrence of the disease in the coming year; for transplanted seedlings or introduced seedlings, remove diseased leaves and burn them in a centralized manner. If necessary, before leaving the nursery, spray the seedlings with 50% carbendazim wettable powder 500 times solution or 0.1% potassium permanganate solution for sterilization and disinfection; strengthen management, increase phosphorus and potassium fertilizer application, loosen soil and remove weeds frequently, prevent soil compaction or waterlogging, and water and spray in time during hot and dry weather to increase the disease resistance of osmanthus plants; in areas with severe disease, starting from late June, spray once every half month with 70% mancozeb wettable powder 500 times solution, or 75% chlorothalonil wettable powder 800 times solution, or 1:2:100 lime double Bordeaux mixture, for 3-4 consecutive times, with good control effect; 25% propiconazole emulsifiable concentrate 5000 times solution can also be sprayed, with an interval of 48 days.
3. Sooty Mold Disease
It mainly appears as a layer of gray-black powdery material of varying shades covering the leaf surface and branches, sometimes even forming a black film. The reason is that when insects such as aphids, scale insects and whiteflies suck and damage osmanthus, the excretions they secrete cause parasitism by various fungi, thereby inducing the dark, gray sooty mold disease.
It usually occurs in hot and humid seasons and in stuffy, humid, shaded and poorly ventilated environments. The gray-black sooty mold layer not only affects the ornamental value of osmanthus plants, but also affects leaf photosynthesis, causing poor plant growth and causing infected leaves to turn yellow, wilt and fall off early.
Control methods: Strengthen shaping and pruning of osmanthus plants to ensure ventilation and light transmission inside the canopy and promote good plant growth; when insects such as aphids, scale insects and whiteflies are found sucking and damaging osmanthus, carry out effective control in time to kill them; for potted plants, frequently spray water to wash the leaf surface; in the early stage of the disease, spray 50% sulfur-carbendazim suspension 500 times solution, or 50% carbendazim wettable powder 800 times solution, or 75% chlorothalonil wettable powder 500 times solution on branches and leaves, with relatively good control effect.
4. Yellowing Disease
That is, iron deficiency chlorosis. If iron deficiency is mild, it appears as chlorosis and yellowing between the veins of young leaves, while the vein tissue remains green; if iron deficiency is severe, it appears as yellowing of all new and old leaves, young leaves slowly stop growing, some old leaves show yellow-brown spots, and the plant cannot grow and bloom normally, seriously affecting ornamental effect and flower harvest.
The reasons are as follows:
First, field-planted plants are affected because the soil is somewhat alkaline;
Second, potted plants are affected because the formula ratio was improper when preparing the potting soil, causing pH imbalance;
Third, osmanthus planted after urban and rural demolition of illegal structures is affected because building residue was not thoroughly cleaned up;
Fourth, management errors, such as irrigation water with a relatively high pH value; thereby causing the iron element in the soil to exist in the form of sparingly soluble ferric hydroxide, which cannot be absorbed by the osmanthus root system.
Control methods: For mild iron deficiency, apply 0.5% ferrous sulfate solution to the roots and spray 0.2% ferrous sulfate solution on the leaves; when iron deficiency is severe, apply 20-40 g of chelated iron [Fe-EDTA (ethylenediaminetetraacetic acid iron)] to the soil around the root zone of each osmanthus plant (including potted osmanthus), and at the same time spray 0.1% chelated iron solution on the leaves; during the spring new shoot growth season, spray 0.2% ferrous sulfate solution on the leaves once every half month; when preparing potting soil, use 0.5% ferrous sulfate solution to adjust its pH value to below 6.5.
5. Dry Rot
It mainly occurs on relatively large newly transplanted osmanthus plants.
In landscaping or large osmanthus transplanting, due to bruising during digging, scratching during long-distance transport, binding injury during lifting and planting, accidental impact injury and other reasons, the bark of the trunk or large branches of osmanthus plants is severely damaged, or large pieces of trunk bark are lifted off, and if not properly protected in time, rain and sewage infect the wounds, inducing large-scale invasion and parasitism by fungi (such as wood-rotting fungi) and bacteria (such as soil Agrobacterium), causing the wounds to rot, xylem exposure or canker formation, resulting in poor plant growth, massive leaf drop, large branch death, and in severe cases the death of the entire osmanthus plant.
Control methods: For small wounds on the trunk or large branches, apply wound healing agent in time; for smaller wounds with local or small amounts of rot, clean the wound locally until fresh xylem and phloem are exposed, then apply wound healing agent on the fresh wound, which can promote rapid healing; for old large wounds on the trunk where the phloem has long been destroyed and the xylem has been exposed for many years, clean the rotted exposed xylem, and regularly apply lime sulfur mixture each year for antisepsis, or use two-component "Yunshi glue" after color mixing and quickly apply it to the fresh wound, for better protection; for thick osmanthus plants whose trunks have formed cavities, first thoroughly remove the rotted part, being careful not to destroy the isolation layer between the rotted xylem and the unrotted xylem, and fill the cavity with polyurethane foam.
II. Identification and Control of Major Osmanthus Pests The main types of osmanthus pests include slug moths, mites, scale insects, whiteflies, Psilogramma menephron, bagworms, lanternflies, Atractomorpha sinensis and others, among which mites, scale insects and whiteflies are the most severe and widespread.
1. Carmine Spider Mite
The mites damaging osmanthus are mainly citrus red mite and carmine spider mite, and their occurrence has been very severe in all parts of the province in recent years. The adult carmine spider mite is 0.5-0.6 mm long. The female mite is oval, vermilion to rust-red, or dark brown to black-brown; the male mite is slightly diamond-shaped, light yellow, slightly smaller, 0.3-0.4 mm long.
Eggs are round, light red to pink. Young mites are nearly round when newly hatched, semi-transparent, and the body becomes dark green after feeding. Nymphs are oval and darker in color. It can occur 10-15 generations a year. In the south, adult mites, nymphs and eggs overwinter on host plants and weeds; in the following spring, when the average temperature reaches above 7°C, they begin activity, feeding and reproduction damage. Adult mites, young mites and nymphs all like to gather on the underside of leaves to feed, and eggs are mostly laid on both sides of the veins on the underside of leaves or under dense fine silk webs. Each female mite can lay 50-500 eggs in her lifetime. Hot and dry seasons are most conducive to their outbreak, causing the leaves of an entire plant or an entire osmanthus grove to become gray-yellow, seriously affecting the growth, flowering and display appreciation of osmanthus.
The optimum temperature for the occurrence of this pest is 25°C-30°C, and the optimum relative air humidity is 35%-55%. Strong winds and rainstorms can wash away the mites and reduce population density.
Control methods: Protect natural enemies, such as Stethorus punctillum, Orius minutus, Scolothrips takahashii, Chrysopa sinica and Chrysopa septempunctata; in winter, remove weeds under the trees and burn them, and use 0.3-0.5 Baumé degrees lime sulfur mixture to kill overwintering adult mites, nymphs and eggs; in the early stage of occurrence, spray 25% fenbutatin oxide (main ingredient azocyclotin) 1500 times solution; or spray 1% abamectin emulsifiable concentrate (main ingredient abamectin) 2000 times solution; in addition, pesticides such as hexythiazox, fenpropathrin and fenazaquin can also be sprayed.
2. Cottony Cushion Scale
The scale insects damaging osmanthus include Aonidiella aurantii, Aspidiotus destructor, Ceroplastes rubens, Coccus hesperidum, Icerya purchasi, Parlatoria pergandii, Pseudaulacaspis cockerelli, Chrysomphalus aonidum, Unaspis yanonensis, Lopholeucaspis japonica, Pulvinaria aurantii, Pseudaulacaspis pentagona, Chrysomphalus ficus, Lepidosaphes gloverii, Aspidiotus cyrtus and others. Among them, cottony cushion scale, Parlatoria pergandii, Lopholeucaspis japonica and Pulvinaria aurantii are especially widespread.
Cottony cushion scale: adult body length 5-7 mm. The female is oval, orange-red, flat on the ventral side, raised on the back, and before oviposition secretes a white egg sac behind the abdomen, with 14-16 longitudinal lines on it; the male body is slender and small throughout, about 3 mm long, with a black thorax, orange-red abdomen, narrow and long black forewings, and hindwings degenerated into hooks. Eggs are oval, 0.7 mm long, orange-red, densely packed in the female's egg sac.
Nymphs are oval, orange-red, with the dorsum covered with pale yellow wax powder. Pupae are 3.5 mm long, orange-red, sparsely covered with pale yellow-brown fine hairs and covered with a thin white waxy powder. Cocoons are long oval, white, composed of loose wax filaments, and coated with white wax powder outside.
This pest occurs 2-3 generations a year, with overlapping generations; most female adults gather and fix in one place, secrete a white waxy egg sac at the end of the abdomen, and lay eggs while secreting wax. The oviposition period lasts more than 30 days, and each female can lay hundreds to 2000 eggs; males are few, and reproduction is mostly parthenogenetic; after hatching, larvae disperse and later move from young shoots and the underside of leaves to branches and trunks where they live in groups, suck tree sap and excrete honeydew, inducing sooty mold disease. Because pests and diseases damage the plant together, they often cause osmanthus leaves to turn yellow and shoots to wither.
Control methods: Usually use fewer pesticides and protect natural enemies well; when a small number of pests are found, wipe them off and crush them in time; in winter, spray 0.3-0.5 Baumé degrees lime sulfur mixture to kill overwintering pests; during the peak egg hatching period, spray 15% buprofezin wettable powder 2000 times solution, or spray 40% dimethoate emulsifiable concentrate 1500 times solution, or spray 40% methidathion emulsifiable concentrate 3000 times solution.
3. Tea Bagworm
Bagworms, also called "hanging ghosts." The bagworm pests damaging osmanthus include tea bagworm, large bagworm, small bagworm and others.
Their common feature is that the insect body hides in a bag, and larvae and female adults gnaw leaves and tender branches. In severe cases, they can eat all the leaves of the whole plant, and the damage is more severe when high temperature and drought last for a long time.
Tea bagworm: adults are dioecious. The female adult is wingless, 12-16 mm long, maggot-shaped, plump, with a small head and a pair of spines; the male is 11-15 mm long, with a wingspan of 22-30 mm, and both body and wings are dark brown. There is a transparent rectangular spot near the tip of the forewing and near the center of the outer margin; eggs are oval, milky yellow-white, about 0.8 mm long; mature larvae are 10-26 mm long, with brown longitudinal bands on the subspiracular line of each thoracic segment and the upper spiracular line of the mesothorax and metathorax, and jade-white between the bands; pupae: female pupa is hammer-shaped, dark brown, with a small head, curved thorax and body length 14-18 mm; male pupa is brown, 11-13 mm long, with the abdomen curved into a hook shape and a pair of cremasters each; the protective case is olive-shaped, black-brown, silky, up to 25-30 mm long, with fragments of branch bark and cut short twigs attached outside, arranged in neat parallel longitudinal cracks.
This pest occurs 2-3 generations a year and overwinters as mature larvae; adult emergence often occurs in the afternoon, and mating occurs the next evening; after emergence, the female remains in the bag, while the male flies near the female's bag to mate; eggs are laid in the bag, about 500 eggs per female; after hatching, larvae crawl from the excretion hole of the protective case to branches and leaves, spin silk and hang down, spread with the wind to surrounding hosts to feed, and use silk to bind leaves and small branches into a protective case; when larvae crawl and feed, the head and thorax are exposed outside the case, and the protective case hangs from the abdomen; feeding time is mostly in the early morning, evening or cloudy days, and they rarely feed at noon on sunny days; in the early stage they feed on leaf mesophyll, leaving the epidermis as transparent spots. As the larval instar increases, they eat leaves into holes and notches. When there are many insects, they can eat all the leaves of the whole plant and gnaw bark, flowers and fruits.
Control methods: Manually remove the protective cases and kill the larvae; protect natural enemies well; use black light lamps and frequency vibration lamps to trap and kill adults; spray 2 billion/g Helicoverpa armigera nucleopolyhedrovirus suspension 1000 times solution at the peak oviposition period; during the peak period of second-instar larvae, spray 90% trichlorfon crystals 1000 times solution, 40% dimethoate emulsifiable concentrate 1000 times solution, 1.2% nicotine-matrine 1000 times solution, or diflubenzuron No. 3 1000-2000 times solution for control.
3. Psilogramma menephron
Adult body length 45-50 mm, body and wings dark gray, mixed with frost-like white powder; wingspan 90-130 mm, the thoracic notum has brownish semicircular stripes, the middle of the forewing has two brownish wavy transverse lines, below the discal cell there are two black longitudinal lines, and there is a black curved line at the wing apex; the hindwing is brownish, and the outer margins of both forewings and hindwings are formed by alternating black and white small square spots.
Eggs are spherical, green when first laid, later turning yellow. Larvae are green, 75-96 mm long, with a pale green head, green thorax, and 8-9 transverse rows of granules on the back; the abdomen is yellow-green, with 7 white oblique bands on the sides; the tail horn is brown-green, with purple-brown granules on it, 12-13 mm long; spiracles are brown, thoracic legs yellow-brown, abdominal legs green.
Pupae are red-brown, 50-60 mm long. This pest occurs 3 generations a year in the Yangtze River basin, overwintering as pupae in the soil. The overwintering generation moth period is from early to mid-April to late July, the first generation from mid-to-late July to early-to-mid September, and the second generation from mid-to-late September to early October. Adults rest during the day in hidden places among trees, branches and leaves, weeds, crops and buildings, and fly out at dusk to become active. Mating and oviposition both occur at night. They have strong flying ability and strong phototaxis; adults mostly lay eggs on the underside of leaves. Newly hatched larvae feed on the leaf surface, and slightly larger ones gnaw leaves into notches and holes, even eating all the leaves. Mature larvae enter the soil to pupate.
Control methods: Turn over the soil in winter to kill overwintering pupae; use black light lamps to trap and kill adults; if Psilogramma menephron larvae appear on a small number of individual osmanthus plants, they can be manually captured and killed; before the third-instar larvae, spray 90% trichlorfon crystals 1000 times solution, 40% dimethoate emulsifiable concentrate 1000 times solution, or 100 billion/g Bacillus thuringiensis spore powder 500 times solution.
4. Latoia lepida
Slug moths, also called "stinging caterpillars." The slug moths damaging osmanthus include Thosea sinensis, Latoia lepida, Setora postornata, Thosea loesa, Latoia pastoralis and others. Their larvae can sometimes eat all the leaves of osmanthus and other plants, causing damaged branches to wither, hindering osmanthus growth and reducing the ornamental and economic value of the flowers and trees. Latoia lepida adult: body length 16-18 mm, emerald green, with a quadrilateral dark brown spot at the wing base, and the hindwing light brown.
Eggs are oval, 0.9-1 mm, yellow-green. Mature larvae are about 24 mm long, emerald green, with a red-brown head, 3 blue-purple and dark green line bands on the center of the back, blue patches and stinging branches on the back, a pair of orange-red stinging spines on the dorsum of the first abdominal segment, and a black pom-pom-like hair tuft at the end of the abdomen. Pupae are oval, 14-17 mm long, yellow-brown; cocoons are black-brown, flat, covered with white silky material, oval, 14-17 mm long. This pest occurs 2-3 generations a year in the Yangtze River basin, overwintering as mature larvae in cocoons on branches and trunks; it pupates from April to May of the following year, and the emergence and oviposition periods of the first and second generation adults are from mid-May to early June and from early August to mid-September.
Adults have strong phototaxis and can mate on the night of emergence, beginning oviposition the next day. A single female can lay 600-900 eggs. Eggs are laid in numbers from several to more than a hundred, mostly 30-40, concentrated on the underside of young leaves in a fish-scale arrangement. Newly hatched larvae only feed on leaf mesophyll and the lower epidermis, leaving the upper epidermis. After the third instar they bite through the epidermis, and after the fifth instar they feed on the entire leaf.
Larvae have 7 instars in total and like to gather; after the fifth instar they gradually disperse. Mature larvae form cocoons in bark crevices, at the base of the trunk and other places, and some first-generation larvae form cocoons on the underside of leaves. Control methods: Inspect osmanthus plants promptly for white to semi-transparent damaged leaves, and for leaves with large numbers of larvae, wear gloves and remove them promptly to kill them, to prevent being stung by their poisonous hairs; manually scrape off overwintering cocoons on branches and trunks, which can reduce the overwintering population and prevent severe occurrence in the coming year; use black light lamps to trap and kill emerged adults, reducing the number of next-generation larvae; during the larval stage, use biological pesticides such as Bacillus thuringiensis and Bacillus thuringiensis for control;
During the larval occurrence period, spray 90% trichlorfon crystals 1000 times solution, 0.3% azadirachtin emulsifiable concentrate 600 times solution, 1.25% nicotine-matrine 1000 times solution, or 1.2% diflubenzuron 8000 times solution to kill larvae.
5. Whiteflies
The whitefly pests damaging osmanthus mainly include whitefly, orange-yellow whitefly, orange spiny whitefly, orange-green whitefly and osmanthus whitefly (Hefei, Chuzhou, Wuhu).
They mainly use the mouthparts of adults and larvae to pierce into the leaf mesophyll on the underside of leaves and suck sap, causing osmanthus leaves to curl, lose green and turn yellow, and even dry up; the large amount of honeydew they excrete seriously contaminates osmanthus branches and leaves, and can induce sooty mold disease, causing poor osmanthus growth, thereby affecting normal flowering and display appreciation of the plant.
Control methods: Protect natural enemies well, such as Encarsia smithi, Prospaltella longifuniculata, Amitus spiniferus, yellow Encyrtidae, green lacewings, lady beetles, small wasps and predatory mites; whitefly adults can be trapped and killed with yellow sticky traps; whiteflies have strong pesticide resistance, so when selecting pesticides for control, attention should be paid to adhering to the principle of alternating and mixed use, for example, 10% buprofezin emulsifiable concentrate 1000 times solution, 10% imidacloprid wettable powder 2000 times solution, 40% omethoate emulsifiable concentrate 1500 times solution, 25% buprofezin wettable powder 2000 times solution, 20% fenvalerate 2000 times solution and others can be used alternately.
Detailed Explanation of Control Methods for Osmanthus Leaf Spot Disease What are the control measures and causes of osmanthus leaf spot disease?
When it comes to osmanthus, everyone is probably familiar with it. Although the petals of osmanthus are small, their fragrance is charming and deeply loved by many flower lovers. In the process of growing osmanthus, osmanthus leaf spot disease is a common disease. So, do you know how to control osmanthus leaf spot disease? Let's learn together with the editor.
Osmanthus leaf spot disease is a general term for various spot diseases on osmanthus leaves, such as brown spot disease, blight spot disease and anthracnose. It causes early leaf drop, weakens plant growth vigor, affects ornamental value, and at the same time reduces osmanthus yield, causing economic losses.
Symptoms of Osmanthus Brown Spot Disease
Damaged leaves initially show chlorotic small yellow spots, which gradually expand into nearly circular lesions, or form irregular lesions due to restriction by leaf veins. The lesions are yellow-brown to gray-brown, with a yellow halo on the outside, 2-10 mm in diameter. Later, black moldy material grows on the diseased part, namely the pathogen's conidia and conidiophores. The pathogen of osmanthus brown spot disease belongs to Deuteromycotina, Hyphomycetes, Moniliales, Cercospora. The stroma is brown, nearly circular; conidiophores are borne in bundles on it, pale olive-colored, unbranched, with few septa; conidia are obclavate, nearly colorless to pale olive, straight or slightly curved, size 15-58 x 2.8-3.7 μm. The disease occurs from April to October, and old leaves are more severely affected than young leaves. The pathogen overwinters as mycelium on diseased leaves and is the primary infection source for the following year. Under suitable temperature and humidity conditions, conidia are produced on the diseased part and spread with airflow and water droplets to healthy leaves, causing infection.
Symptoms of Osmanthus Blight Spot Disease
The pathogen mostly invades from the leaf tip and leaf margin. At first there are light brown small spots, which later gradually expand into circular or irregular large lesions. In severe cases, several lesions connect with each other to form large blight spots, causing 1/3-1/2 of the entire leaf to dry up. The lesions are gray-brown to red-brown, with a distinct red-brown edge, and sometimes curl and crack brittlely. Later, many black small granular dots are produced on the diseased part, namely the pathogen's pycnidia. The pathogen of osmanthus blight spot disease belongs to Deuteromycotina, Coelomycetes, Sphaeropsidales, Phyllosticta. Pycnidia are nearly spherical, with an ostiole, 100-150 μm in diameter; conidia are oblong to nearly fusiform, colorless, single-celled, size 6.0-9.5 x 1.8-2.5 μm. The pathogen development temperature is 10-33°C, with the optimum at 27°C. The disease mostly occurs from July to November. The pathogen overwinters as pycnidia on diseased leaves, and conidia are spread by wind and rain. When temperature and humidity are high, ventilation is poor, and plant growth is weak, the disease is severe.
Symptoms of Osmanthus Anthracnose
On affected leaves, small chlorotic spots appear at first, then gradually expand to form round, semicircular or oblong lesions. The lesions are light brown to greyish white, with a reddish-brown ring around the edge. In the later stage, many small black dots, the acervuli of the pathogen, form on the diseased tissue, and in humid conditions pale peach-pink sticky spore masses appear on the diseased area. The pathogen of osmanthus anthracnose belongs to the Deuteromycotina, Coelomycetes, Melanconiales, Colletotrichum. The acervuli are brown or black, 100-300 μm in diameter, and bear several setae; the conidiophores are cylindrical, measuring 12-21×4-51 μm; the conidia are cylindrical, formed beneath the leaf epidermis and breaking through the epidermis when mature, measuring 11-18×4-6 μm. The disease is more severe from April to June, and the pathogen overwinters as acervuli on diseased leaves and is spread by wind and rain.
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