Rose Disease and Pest Control

Common diseases, powdery mildew

1. Pathogen and Symptoms: Powdery mildew belongs to the subphylum Ascomycota, order Erysiphales, and genus *Dictyophora*. The cleistothecia contain one colorless, oval-shaped ascospore, each containing eight unicellular, colorless ascospores. Asexual conidia are . This disease primarily affects young shoots, leaves, and flowers. The most obvious symptom is the appearance of a white powdery substance on infected areas. Initially, chlorotic yellow spots appear on the leaves, later developing into white spots on the underside, gradually expanding into irregular shapes. In severe cases, the white spots merge into larger patches. Young shoots curl and wrinkle. Flower buds are covered with a white powdery substance, resulting in deformed flowers. The powdery layer on petioles and prickles is thick and difficult to remove, causing leaf drop and preventing flower buds from opening.

2. Disease Development Pattern: The pathogen mainly overwinters as cleistogamous spores on diseased leaves and buds. After spring rains, ascospores are released, initially infecting the roots . The resulting conidia are spread by air currents and cause repeated infections. The peak disease period is from May to September , and the disease ceases in October . Dry years and weakened plants are more severely affected.

3. Control methods: A. Remove diseased leaves , and prune diseased buds, branches, and leaves in early spring, and bury or burn them. Improve cultivation conditions, increase ventilation and light penetration, reduce nitrogen fertilizer, and increase phosphorus and potassium fertilizer. B. Spray with 5 % sulfur mixture before sprouting ; at the initial stage of disease, spray with 25% wettable powder of triadimefon at 1500 times dilution; or spray with 70 % wettable powder of methyl thiophanate at 1000 times dilution; or spray with 15 % wettable powder of triadimefon at 1000 times dilution; or spray with 0.02-0.03% potassium permanganate solution.

Common diseases, black spot disease

1. Pathogen and Symptoms: This pathogen belongs to the Deuteromycetes, Order Melanopsiales, genus Actinobacillus. Conidia are oblong-ovate or elliptical , colorless two-celled, slightly constricted at the septum, and can break into two cells. This disease is a global and very common one, causing extremely serious damage during the main growing season. It can occur on leaves, flowers, and new shoots. Initially, black spots of varying sizes appear on the leaves, with radiating brown mycelial lines and small black dots (conidiophores) beneath the cuticle . These spots later enlarge and turn yellowish-brown or dark purple, eventually becoming grayish-brown. In severe cases, new shoots die back, and all lower leaves fall off, leaving the plant bare.

2. Disease Development Pattern: The black spot fungus overwinters as mycelium or conidiophores on diseased plant debris and spreads via rain splash and insects . In warm, humid environments, especially during the rainy season, the fungal spores spread and multiply. Spores that land on damp leaf surfaces begin to germinate within 8 hours, penetrating the cuticle cells to grow new mycelium. This process continues, producing a large number of new spores. The disease typically occurs in July and August .

3. Prevention and Control Methods: a. Pay special attention to removing fallen leaves and dead branches in winter and spraying with lime sulfur mixture. Thoroughly branches to reduce the source of infection. b. Strengthen cultivation management, apply more phosphorus and potassium fertilizer to improve the plant's disease resistance. During the disease period, minimize watering; if necessary, only water in the morning when the weather is sunny and temperatures are rising, avoiding prolonged wetting of the leaves. c. In the early stages of the disease, spraying with 50 % carbendazim wettable powder at a 1000- fold dilution ; or 50 % mancozeb at a 1000- fold dilution ; or 70% thiophanate-methyl wettable powder at a 1000- fold dilution are all effective.

Common Diseases - Twig Die

1. Pathogen and Symptoms : This pathogen belongs to the Deuteromycetes, Order Spheroidales, and genus *Cladosporium*. The conidiophores are borne within the stroma, initially embedded under the host's septum epidermis, later breaking through the epidermal opening to become exposed. The conidiophores are flattened triangular flask-shaped. They are unicellular and colorless , producing septa upon maturity. This disease primarily affects the branches and trunks of roses, causing cankerous lesions. Initially, these are small red spots that enlarge and darken, turning brown at the center. In later stages, the lesions become sunken and crack longitudinally, with black spots appearing at the center of the affected area. Black . In severe cases, the lesions girdle the stem, causing the branches below the affected area to wither and die.

2. Disease Development Pattern: This pathogen is a weak parasite that mainly overwinters on diseased branches and trunks. The following year, new shoots consume nutrients , and the pathogen thrives on weakened branches and trunks, allowing it to quickly spread and cause lesions to appear. Between June and July , a large number of fruiting bodies and spores produced on diseased branches are spread by wind and rain during the rainy season. The severity of this disease is closely related . Old, weak, damaged, and poorly watered/fertilized plants are severely affected; healthy, vigorous plants are not susceptible.

3. Prevention and Control Methods: A. Thoroughly prune and . Strengthen cultivation management and apply sufficient base fertilizer. During the growing season , spray with a 0.13% urea solution to enhance plant growth. B. Spray with lime sulfur mixture during dormancy ; spray with 25% carbendazim wettable powder at a 600- fold dilution in May and June ; or spray with 50 % thiophanate-methyl wettable powder at a 1000- fold dilution ; or spray with 50 % chlorothalonil wettable powder at a 500- fold dilution.

Common disease - root gall disease

1. Pathogen and Symptoms: The pathogen is *Nematodeus fasciculata*, whose eggs are oblong, slightly curved laterally, and clustered within the female adult, forming a fascicle. The larvae and males are thread-like; the females are pear-shaped, swelling and breaking through the root cortex to expose themselves as the white , tumor-like growths seen on the roots. Young tumors are white and elastic, later hardening. The surface of the tumor is rough, brown or dark brown, and in severe cases, the root nodules can extend above the ground . Roses with root nodules exhibit poor growth, yellowing leaves, reduced root numbers, and a significant increase in the number of root nodules.

2. Disease Development Pattern: The L- nematode has two , in spring and autumn . It overwinters and can survive in the soil or tumors for more than a year. After invading the rose roots, the nematode can stimulate the proliferation of root bark cells, leading to cancerous lesions.

3. Prevention and Control Methods: A. Before planting, soak the plant roots in a 500-1000 times diluted solution of concentrated streptomycin for 10 minutes. B. When grafting, sterilize the grafting knife with high temperature or alcohol to prevent nematodes from entering through the wound. C. Apply a mixture of methanol, glacial acetic acid, and iodine tablets (50:25:10 ) to the affected area ; or apply a mixture of sodium dinitrophosphate powder and lignin ( 20:80 ) to the affected area to make the galls disappear.

Common diseases - Rust

1. Pathogen and Symptoms: This pathogen belongs to the Basidiomycota, Rustales, and *Polycystis*. It is a syn-host rust fungus that produces five types of spores. Rust conidiophores accumulate as orange-red powder on the underside of leaves, surrounded by paraphyses, and are naked. Rust spores are borne in chains; urediniospores are borne in masses surrounded by club-shaped paraphyses; teliospores are black and scattered, naked. Rust disease affects the buds, leaves, young branches, petioles, receptacles, and pedicels of roses. It mainly occurs on buds and leaves. In spring, during budding, the base of diseased buds swells, and numerous orange-red powdery substances grow within 1-3 layers of scales, resembling small yellow flowers; some buds become bent and deformed, and die after 15-20 days. When young leaves are infected, clusters of small yellow dots of conidiophores first appear on the upper surface, later forming orange-red conidiophores on the underside. In autumn, axillary buds infected by the fungus often die after overwintering.

2. Disease Development Pattern: This pathogen mainly overwinters as mycelium within diseased rose buds. In late March of the following year , when the diseased buds sprout, the disease begins to manifest, producing urediniospores which spread and infect the leaves. Teliospores on diseased leaves can also overwinter, germinating the following spring to produce basidiospores , which infect young leaves and shoots, subsequently producing sex spores and aesiospores. The aesiospores then infect the leaves, producing urediniospores again. Urediniospores can be produced multiple times, repeatedly expanding the infection. The incubation period is as short as 7 days. Leaf infection begins in late April each year. The peak disease period is from late May to early July . In August , the disease progresses further. At average temperatures above 27 degrees Celsius, the disease does not develop; at temperatures above 28 degrees Celsius, urediniospores do not germinate. After September , only axillary buds are affected. Years with abundant and evenly distributed rainfall result in more severe disease.

3. Control methods: A. Promptly remove diseased buds. Check from late March to early April ; immediately remove and destroy any diseased buds found. Generally, the disease rate is less than 0.5% , and removal will prevent spore spread. B. Spray 1-2 times before the two peak disease periods in early April or late August to control disease development. Suitable pesticides include 50 % chlorothalonil at 600x dilution; or 50 % thiophanate-methyl at 500x dilution ; or 50 % thiram at 500x dilution; or 25 % carbendazim wettable powder at 1500x dilution . Alternatively, spray with 0.2% lime sulfur mixture before spring budding; or spray with 0.2% lime sulfur mixture at the initial stage of disease .

gray mold of roses

Symptoms

When gray mold occurs on the leaf margins and tips of roses, it initially appears as water-soaked, light brown spots, smooth and slightly sunken, which later expand and rot. When flower buds are infected, the lesions turn grayish-black, preventing the flower from opening; infected buds turn brown and wither. When flowers are affected, some petals turn brown, wrinkle, and rot. The gray mold fungus also infects the tips of branches after flowering; the black lesions can extend several centimeters . In warm, humid environments, the gray mold layer can completely cover the infected area. Pathogen

* Botrytis cinerea* Pers. is a fungus belonging to the class Hyphomycetes and order Hyphomyales. Its occurrence pattern...

The fungus overwinters as mycelium or sclerotia in diseased areas, producing conidia the following year. These conidia are spread by wind and rain, entering through wounds or directly through the epidermis. Gray mold is more likely to occur in greenhouses with high humidity. If withered flowers and pedicels are not removed promptly, the disease often first spreads to these decaying tissues before infecting healthy flowers and buds. Control methods .

1. Remove diseased parts promptly to reduce the source of infection. Withered rose petals should also be pruned in a timely manner.

2. The greenhouse should be properly ventilated to prevent excessive temperature differences between day and night and excessive humidity. There should be adequate space between the rose pots. When watering , pour water from the rim of the pot to avoid water remaining on the leaves and flowers. Cutting flowers on sunny days allows the wounds to heal more easily.

3. Chemical control : Spray protective agents at the initial stage of disease. When using Bordeaux mixture at a 1 : 1 : 100 ratio, spray once every two weeks . 4. Spraying method: Use 50% iprodione wettable powder at a 2000- fold dilution, or 50% procymidone (iprodione) wettable powder at a 1000-1500 - fold dilution, or 50% thiophanate-methyl (methyl thiophanate) wettable powder at a 500- fold dilution, or 50% carbendazim at a 500- fold dilution, or 70% mancozeb at a 500- fold dilution . Spray once every 7-10 days , for 2-3 consecutive times . Each spray should be no less than 50-60 kg of solution per 67 m² . The preventative effect of the above agents is better than the curative effect. It is important to alternate between agents to prevent the development of drug resistance.

When cultivating roses in greenhouses, the following application methods can also be tried:

1. Smoke method: Use 200-250 grams of 10% carbendazim smoke agent per 667m2 , or 250 grams of 45% chlorothalonil smoke agent per 667m2 , and fumigate for 3-4 hours .

2. Dust method: 10% carbendazim dust, 5% chlorothalonil dust, or 10% cymoxanil dust can also be sprayed in the evening at 1 kg per 667 m2 , once every 9 or 11 days, and used continuously or alternately with other control methods for 2 or 3 times.

downy mildew of roses

Downy mildew is a fungal infectious disease of roses. It spreads rapidly and causes severe damage, making it a devastating disease. It primarily affects the newly sprouted branches and leaves in the lower and middle parts of the plant. Initially, chlorotic spots appear on the underside of the lower leaves. These spots are irregular covered with a downy mold layer, later turning dark purple and water-soaked, eventually becoming brown. The spots are polygonal and gradually become scorched. In severe cases, all leaves fall off, and the plant dies.

Prevention and control measures

1. Plant at a reasonable density, with no more than 12 plants per square meter, and the leaves should not overlap.

2. Apply fertilizer rationally and in a balanced manner, using more organic fertilizer. With sufficient nitrogen fertilizer, apply more phosphorus and potassium fertilizer to enhance the plant's resistance. Also, spray with a flower-strengthening agent during the rose bud stage to promote strong buds, large petals, vibrant colors, rich fragrance, and extended flowering period.

3. Promptly remove and dispose of fallen branches and leaves. Apply a wound-healing and antiseptic film to pruning cuts to prevent bacterial infection and protect the wound.