September Flower Pest and Disease Bulletin and Edible Mushroom Preservation Methods

As White Dew arrives, the weather in most parts of China gradually turns cooler, and by the Autumn Equinox day and night are balanced, marking the beginning of autumn in the Northern Hemisphere. Some flower species with summer dormancy and semi-dormancy habits will resume growth as temperatures drop, making this another important growing season in the year for various flowers.

This month, due to higher temperatures and low air humidity, some leaf-feeding and sap-sucking pests may still occur widely, such as slug moths, bagworms, spider mites, scale insects, box tree webworms, Atlas moths, wood-boring longhorn beetles, psyllids, and lace bugs; some diseases will also continue to occur and cause damage, such as silk tree wilt, mahonia powdery mildew, osmanthus brown spot, crape myrtle witches' broom, cherry brown spot shot hole, and sunscald, which will continue to occur and cause damage over large areas under high temperature and drought conditions; red spot disease, bacterial shot hole, and gummosis will also occur severely.

Main Diseases Occurring in September and Control Measures

Cherry Brown Spot Shot Hole

It mainly damages ornamental flowering trees such as flowering peach, fruit peach, Japanese apricot, red-leaf plum, and elm-leaved spirea, causing dense holes to appear on the leaves, leading to massive defoliation of diseased leaves and seriously affecting the normal growth of the plants.

This disease occurs throughout the country. Its pathogen is Cercospora circumscissa, belonging to Deuteromycotina, Hyphomycetes, Hyphomycetales. It mainly damages mature leaves and young twigs. In the early stage of diseased leaves, purple-brown dots the size of pinheads appear, which expand into circular spots about 1-4 mm in diameter, with purple to red-purple edges and brown centers with slight concentric rings. Velvety small dots grow on the spots. In the later stage, the spots fall off, forming shot holes. The pathogen overwinters in twigs and fallen leaves. Generally, disease is seen on lower leaves in June, with the peak period from August to September. From late August to late September, large numbers of diseased leaves fall, with only a small amount of leaves remaining on the twigs. The disease is prone to occur and is severe under conditions of dense planting, poor ventilation, and weakened branches.

Control Measures

1. In autumn and winter, promptly clear fallen leaves and burn them in a centralized manner; during the growing season, water promptly;

2. Regularly prune out inner canopy branches, diseased and pest-infested branches, weak branches, and dead branches to ensure good canopy ventilation;

3. Before spring budbreak, disinfect the tree body with 2-3 degrees Baume lime sulfur mixture;

4. In the early stage of disease, spray plants with 50% carbendazim wettable powder at 500 times dilution, or 70% thiophanate-methyl wettable powder at 1000 times dilution, once every half month, for 3-4 consecutive times, which has good control effects.

Witches' Broom

The main ornamental flowering trees affected by witches' broom include: crape myrtle, Chinese rose, rhododendron, oleander, elm, bamboo, small-leaved hackberry, hawthorn, lilac, periwinkle, and banyan.

The main causes of witches' broom are phytoplasmas and fungi. The former is a type of plant pathogenic bacterium that cannot yet be cultured artificially, a prokaryote without cell walls and surrounded only by a triple-layered unit membrane, obligately parasitic in the phloem sieve tube system of plants, causing clustered branches, floral abnormalities, leaf yellowing, tree necrosis, and growth decline and death. From the perspective of symptom development, first the apical growth of branches is inhibited, which stimulates the growth of lateral buds; soon these are also inhibited, causing their own lateral buds to develop prematurely into small branches. As a result of this repeated process, the branches of the affected flowering trees increase in number of small branches and volume over time, and the clustered branches die in the same year or die year by year. From the morphology and anatomy of the clustered branches and leaves, the main branch within the cluster is not obvious, the small branches are thin with shortened internodes, the parenchyma tissue is well developed, and the mechanical tissue is poorly developed, making them fragile and easily broken; the leaves on the branches are small and yellowed, with indistinct differentiation of palisade and spongy tissue. Diseased branches can initially bear small fruits or deformed fruits, but later become flowerless and fruitless, or even stop flowering altogether. Witches' broom caused by phytoplasma is devastating; the disease starts from individual branches and gradually spreads to the whole plant. Phytoplasma-caused witches' broom is mainly transmitted by insects in nature, and under cultivation conditions, it is transmitted through propagation materials such as grafting, cuttings, and division.

Control Measures

1. When propagating flowering trees by cuttings, grafting, division, layering, and other methods, healthy mother plants must be selected;

2. When a small number of witches' brooms are found on potted or field-planted crape myrtle, rhododendron, Chinese elm, Chinese rose, oleander, lilac, or periwinkle plants, the brooms should be pruned off and burned as early as possible, and the pruning tools should be strictly disinfected;

3. Starting from spring shoot emergence and leaf expansion of flowering trees, regularly spray 10% imidacloprid wettable powder at 2000 times dilution, or 40% omethoate emulsifiable concentrate at 1500 times dilution, to kill aphids, thrips, true bugs, scale insects, and other sap-sucking pests, eliminating transmission vectors;

4. For already diseased plants, injecting tetracycline-class drugs has a good therapeutic effect.

Silk Tree Wilt

Silk tree wilt is a devastating disease that can reach epidemic proportions. It can occur from young seedlings to large trees. When severe, it causes large numbers of trees to wither and die. It commonly occurs in Beijing, Nanjing, Jinan, Hefei, and other places in China. After silk tree is infected with wilt, leaves wilt, droop, dry, and shrink, then leaves fall off and branches die. In some cases, one or two branches or several branches show symptoms; in some cases, half the branches die; in severe cases, the whole plant dies. A complete discoloration ring appears on the cross-section of the trunk and branches, and the root cortex of diseased plants turns brown and rots. In summer, the trunk becomes rough, or the trunk exudes black liquid, and lenticels swell. Under humid conditions, cinnamon-colored to white powdery mold layers can be produced from the lenticels of diseased plants.

The pathogen persists in soil, diseased residues, and seeds, directly invading through underground roots or through wounds, causing plant death. In nurseries, some diseased seedlings have intact roots but withered cut ends; after longitudinal cutting, the interior has turned brown. The pathogen can also be isolated from the browned sapwood. The cut end is one of the main routes of pathogen invasion. This disease is a systemic infectious disease and can occur throughout the growing season. Symptoms appear in May, with the peak period from June to August, and the disease can continue until October. High temperature and high humidity favor pathogen proliferation and infection. Heavy rain and irrigation favor pathogen spread, but water deficiency and drought will also promote disease occurrence.

Control Measures

The pathogen source of this disease is widespread, the infection period is long, it spreads through soil, and it is a systemic disease. It is difficult to detect in the early stages, and once symptoms appear it is difficult to save the plant. Therefore, prevention should be the priority, with integrated control.

1. Choose suitable planting sites. Silk tree grows better in relatively loose soil. Street soil is firm and has poor permeability, so it is best not to use silk tree as a street tree, but to plant it in green belts on both sides of roads;

2. Strengthen cultivation management, such as regular loosening of soil to increase soil permeability, and attention to drought prevention and drainage. Prune as little as possible, and apply protective agent to wounds after pruning. Remove severely diseased plants to reduce infection sources;

3. Emphasize chemical control. Before symptoms appear during the growing season, dig holes and irrigate with systemic agents, such as 50% thiophanate at 500 times dilution, 40% carbendazim suspension concentrate at 800 times dilution, etc. When transplanting, dip roots in 1% copper sulfate solution, and apply protective agent to wounds on branches and trunks to prevent pathogen infection.

Powdery Mildew

In September, it continues to occur throughout the country, damaging many flowers, such as crape myrtle, mahonia, photinia, large-leaf boxwood, Chinese rose, cotton rose, scarlet sage, calendula, garden balsam, cineraria, four-o'clock, Chinese peony, and tree peony.

The pathogen damages leaves, young shoots, and inflorescences. White powdery mold layers form on affected parts, later turning gray-white, often causing leaf shrinkage, discoloration, and failure to unfold normally, branch bending, deformity and shrinkage, inflorescence distortion, and flower bud discoloration, seriously affecting the normal growth and flowering of flowering trees. The pathogen overwinters as mycelium latent in the dormant buds of infected plants. From late March to early April of the following year, as the buds grow and when the climate is suitable, the mycelium begins to expand and spread, forming conidia that are transmitted by wind and rain to the young shoots, new leaves, and inflorescences of new host plants. The conidia can cause repeated reinfection multiple times. Under conditions of poor ventilation and light, and overly dense planting, the disease is particularly severe. Generally, the disease begins in spring each year, with the peak period from June to September, and after late September the disease gradually decreases.

Control Measures

1. Control density, increase ventilation and light, apply more phosphorus and potassium fertilizers, and improve plant disease resistance;

2. For flowering tree species prone to this disease, or when powdery mildew has already occurred nearby, during each sprouting and shoot-emergence period after pruning, spray 1 degree Baume lime sulfur mixture or 27% high-fat film at 500 times dilution on new shoots and young leaves, once every 10 days, for 2-3 consecutive times;

3. Promptly prune off newly diseased shoots and burn them in a centralized manner;

4. In the early stage of disease, alternately spray 15% triadimefon wettable powder at 1000 times dilution, or 15% triazolidone wettable powder at 2500 times dilution for control.

Mosaic Disease

Due to virus invasion, local or whole-plant leaves and young shoots of flowering trees show yellow-green mottling and deformity symptoms. The virus is a non-cellular entity. After invading the plant body, it sometimes presents yellow-green mottling or stripes on leaves, such as in scarlet sage and camellia sasanqua "mosaic disease." On the surface, it looks somewhat similar to yellowing caused by oxygen deficiency, but careful observation of the diseased parts reveals that the chlorosis caused by mosaic disease is uneven, a yellow-green patchwork distributed in blocks or strips on the leaves. Not only is the distribution of diseased leaves on the plant irregular, but the distribution of yellow diseased spots on the leaves is also irregular, often manifesting as leaf shrinkage with no luster, leaves becoming smaller or narrow and elongated in deformity, rarely necrotic, and the whole plant growing poorly. It starts from a few plants and gradually increases from few to many, from mild to severe, with obvious infectivity. Once the virus enters the plant body, it undergoes massive "replication" and reproduction, is very difficult to kill or eliminate, and the plant will carry the virus for life. It is a very troublesome and intractable disease. Unlike fungal diseases, after entering the body it does not fix in a certain part of the plant, but reaches every part of the plant through the plant sap circulation. Its damage to the plant is mainly not killing tissues, but causing the plant's superior traits to gradually degenerate, leading to decreased resistance and weakening, making it susceptible to other pests and diseases and ultimately death.

Flower species prone to "mosaic disease" include: gladiolus, canna, lily, scarlet sage, tulip, orchid, geranium, cyclamen, dahlia, sago palm, camellia, camellia sasanqua, carnation, etc. Piercing-sucking mouthpart insects are the most important virus vectors in nature, such as aphids, scale insects, true bugs, and leafhoppers. When they suck sap on diseased plants, they also take in some virus, and then inject the carried virus into healthy plants by piercing and sucking the sap of other plants. In addition, scions, cuttings, rhizomes, seed bulbs, etc. may all carry viruses, and operations such as pinching and pruning may also spread viruses.

Control Measures

1. Promptly kill piercing-sucking mouthpart pests, prohibit the use of virus-carrying branches or bulbs for propagation, promptly pull out diseased plants and burn them, and strictly disinfect tools used for grafting and cuttings.

2. For mildly affected plants, pesticides such as Kangduji No. 1, Junduqing, Virus A, Zhibingling, and Bingdubike can be used for control.

In September, other relatively serious flowering tree diseases include sooty mold, algal spot, black spot, gummosis, sunscald, and leaf gall, which should continue to be given attention, with timely and effective integrated control measures taken.

Main Pests Occurring in September and Control Measures

Elm Autumn Four-Veined Aphid

It occurs throughout the country, mainly damaging bonsai plants and landscaping trees of elm species such as Chinese elm, Siberian elm, white elm, Zuiweng elm, and Langya elm. Because it is a host-alternating parasitic insect, it also damages various grass-family ornamental plants. Its overwintering hosts are mainly elm species, and its alternate hosts are mainly grass-family plants. It occurs for more than 10 generations per year, overwintering as eggs in bark cracks of Chinese elm, Zuiweng elm, and other trees. In April of the following year, overwintering eggs hatch, damaging leaves and forming galls. After developing into adult aphids, they produce migratory aphids, which fly to grass-family plant roots from May to early June to cause damage. From September to October, they develop into adult aphids, producing sexual aphids on elm trees. After mating, they lay eggs in cracks on the sunny, leeward side of main trunks of elm trees more than 4 years old, overwintering as eggs. Because in late spring and early summer they form sparse or dense granular galls on the leaves of elm species, they not only affect ornamental value but also harm the normal growth of plants.

Control Measures

Around the placement and display of Chinese elm stump bonsai, or near nursery sites where elm seedlings are cultivated, especially from May to June, thoroughly clear grass-family weeds to eliminate the alternate hosts of the elm autumn four-veined aphid. During the overwintering egg hatching stage and after aphids migrate back to elm trees from September to October, spray 10% imidacloprid wettable powder at 2000 times dilution to kill them. In autumn and winter, spraying 3-5 degrees Baume lime sulfur mixture on the main trunks of elm stumps or thick Chinese elm and other elm trees can effectively kill overwintering eggs. If a small number of light red elm autumn four-veined aphid galls appear on bonsai plants, promptly removing them is sufficient.

Gardenia Clearwing Moth

It mainly damages gardenia, large-leaf boxwood, coffee, and other flowering trees. Young larvae feed on young leaves and shoots, causing more notches or holes in the middle and upper canopy of potted or field-planted gardenia and other flowering trees, reducing their ornamental value. When larvae occur in large numbers, they can completely defoliate whole plants or patches of gardenia. It is the most important leaf-feeding pest damaging gardenia.

In the Yangtze River basin, it has 4-5 generations per year, overwintering as pupae in soil at a depth of 3-5 cm, emerging in late April of the following year. Adults of generations 2-4 appear in June, August, and October respectively. Adults mate and lay eggs about 10 hours after emergence. Eggs are mostly laid on hidden young leaves, new shoots, flower buds, and petals, with 1-2 eggs per site. Female adults can lay about 200 eggs, and the egg stage is 3-5 days. Newly hatched larvae first eat the eggshell, then feed on young leaves. After the 4th instar, food intake increases, and the larval stage is about 45 days.

Control Measures

1. During the larval occurrence period, frequently inspect gardenia and other host flowering trees, and manually capture and kill larvae;

2. In late autumn and early winter, plow the soil around flowering tree plants to kill overwintering pupae;

3. If occurrence is over a large area, spray plants with 90% trichlorfon crystal at 800 times dilution, which can quickly kill the larvae.

Atlas Moth

Also known as the Chinese tallow Atlas moth, it is distributed in Liaoning, Shandong, Anhui, Jiangsu, Zhejiang, Shanghai, Jiangxi, Sichuan, and other provinces. It mainly damages ornamental plants such as camphor tree, Chinese tallow, tree of heaven, Elaeocarpus, plane tree, Chinese wingnut, Michelia figo, holly, silk tree, citrus, black locust, and Paulownia. This insect has 2 generations per year, overwintering as pupae in cocoons. First-generation larvae hatch in late May, and the damage period of second-generation larvae is from September to late October. Newly hatched larvae are gregarious, dispersing to cause damage after the 3rd-4th instar; mature larvae weave leaves together on trees to form cocoons, and the overwintering generation mostly forms cocoons on miscellaneous shrubs.

Control Measures

At the end of August, taking advantage of adult phototaxis, hang black lights or frequency-vibration lights near camphor tree seedling sites to trap and kill adults. In the young larval stage, taking advantage of their gregariousness, for low camphor tree seedlings, manually remove leaves with dense larvae and kill them in a centralized manner; alternatively, during the larval damage stage, spray 90% trichlorfon crystal at 800 times dilution, or 2.5% fenvalerate at 1500 times dilution; when cocoons are found on miscellaneous shrubs, promptly prune and burn them, which can greatly reduce the occurrence of pest damage the following year.

Short-winged Rice Grasshopper

Because the male adult mates on the back of the female, it gets the name "negative grasshopper." It is mainly distributed in the Yangtze River basin, damaging flower species such as scarlet sage, pansy, Chinese rose, gardenia, chrysanthemum, and iris, chewing leaves and petals, causing notches and holes and reducing the ornamental value of plants. In the Yangtze River basin, it has 2 generations per year, overwintering as eggs in soil. Second-generation nymphs begin to hatch and cause damage from late June to mid-to-late August, emerge as adults from mid-August to mid-to-late October, and lay eggs to overwinter from late November to mid-December. Adults and nymphs mostly feed on branches and leaves and prefer to cause damage in groups; eggs are laid in masses in soil with fewer weeds in wasteland, wrapped in gelatinous material.

Control Measures

1. Clear weeds around flower plants, and plow nursery land in late autumn and early winter to kill eggs;

2. During the period when larvae gather to cause damage, manually capture and kill them in the morning; they can serve as high-quality protein feed for poultry;

3. When occurring over a large area, spray 90% trichlorfon crystal at 800 times dilution, or 75% dimehypo emulsifiable concentrate at 1500 times dilution to kill them.

Slug Moths

The high-temperature and drought environment of September is the period of rampant damage by slug moth larvae. Second-generation larvae of the yellow slug moth damage the leaves of cherry, crape myrtle, osmanthus, white magnolia, Chinese elm, ornamental peach, Japanese apricot, camphor tree, Elaeocarpus, and other flowering trees from mid-to-late August to late September. Second-generation larvae of the brown-edged green slug moth have their peak damage period from mid-August to September, mainly damaging the leaves and young shoots of ornamental plants such as cherry, Chinese rose, crabapple, Japanese apricot, white wax, holly, Chinese tallow, redbud, and Chinese elm. Second-generation larvae of the mulberry brown slug moth damage the leaves of camphor tree, French holly, Chinese tallow, soapberry, ginkgo, horse chestnut, Eucommia, ornamental peach, cherry, and other flowering trees from late August to September. Second-generation larvae of the flat slug moth and beautiful green slug moth damage the leaves of crabapple, Japanese apricot, redbud, crape myrtle, Chinese rose, osmanthus, pomegranate, tree peony, and other flowering trees from August to mid-September. When larval density is high, they can completely devour the leaves and young shoots of entire flowering trees.

Control Measures

1. Use black lights or frequency-vibration traps to kill adults;

2. For severely affected nursery land or garden green spaces, in the newly hatched larval stage, spray 25% chlorbenzuron No. 3 at 2000 times dilution, or 90% trichlorfon crystal at 1000 times dilution, or 40% omethoate emulsifiable concentrate at 1000 times dilution to kill larvae.

3. Pests commonly occurring in September also include bagworms, spider mites, rose sawflies, elm three-section sawflies, lace bugs, planthoppers, and scale insects, and control should continue to be strengthened.