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 that are smooth and slightly sunken, later expanding and rotting. 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, with black lesions extending several centimeters below the infection point. In warm, humid environments, the gray mold layer can completely cover the infected area.

Pathogen: Botrytis cinerea Pers, a fungus belonging to the class Hyphomycetes and order Hyphomyales.

Transmission route: The fungus overwinters as mycelium or sclerotia in diseased parts, producing conidia the following year. These conidia are spread by wind and rain, entering through wounds or directly through the epidermis. Gray mold is prone to occur in greenhouses with high humidity. When withered flowers and pedicels are not removed in time, the disease often first spreads from these decaying tissues to healthy flowers and buds.

Prevention and control methods: 1. Promptly remove diseased parts to reduce the source of infection. Wilted rose petals should also be pruned promptly. 2. Ensure proper ventilation in the greenhouse to avoid excessive day-night temperature differences and high humidity. Leave adequate space between rose pots. Water from the rim of the pot, avoiding water retention on leaves and flowers. Cutting flowers on sunny days promotes wound healing. 3. Chemical control: Spray protective agents at the initial stage of disease. When using a 1:1:100 Bordeaux mixture, spray once every two weeks. 4. Spraying method: Use 50% iprodione wettable powder at a dilution of 2000 times, or 50% procymidone (iprodione) wettable powder at a dilution of 1000-1500 times, or 50% thiophanate-methyl (methyl thiophanate) wettable powder at a dilution of 500 times, or 50% carbendazim at a dilution of 500 times, or 70% mancozeb at a dilution of 500 times, spraying 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 preventive effect of the above agents is better than the curative effect, and attention should be paid to alternating 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 10% iprodione smoke agent at a dilution of 200-250 grams per 667 m2, or 45% chlorothalonil smoke agent at a dilution of 250 grams per 667 m2, and fumigate for 3-4 hours. 2. Dust method: In the evening, spray 10% carbendazim dust, 5% chlorothalonil dust, or 10% cymoxanil dust at 1 kg per 667 m2, once every 9-11 days, and use continuously or alternate with other control methods for 2-3 times.

Black spot disease of roses

Rose black spot, also known as brown spot disease, is a global rose disease.

Symptoms: Rose leaves, young shoots, and flower stalks can all be affected. Initially, leaf spots appear as small purplish-brown to brown dots, later expanding into round spots 1.5–13 mm in diameter, black or dark brown with fibrous edges, although some varieties may have smooth, even edges. A yellow halo often surrounds the spots. Under a magnifying glass, small black pustular granules can be seen on the affected area. Several spots often merge, and the surrounding leaves turn yellow over a large area, making the spots appear as "islands" with green edges. Infected leaves easily fall off, but some rose varieties do not. Purple to black streaks appear on young shoots and flower stalks, slightly sunken. In severe cases, the entire lower and middle leaves of the plant fall off, leaving only a few new leaves at the top.

Pathogen: A fungus of the genus *Actinonema* [*Actinonema rosae* (Lib.) Fr.]. Conidiomata are borne beneath the host's plasmid layer and later protrude from the epidermis. They measure 108–198 μm in size, with short, inconspicuous conidiophores. Conidia are oblong or swim-bladder-like, measuring 18–25 x 5–6 μm, two-celled, smaller at the apex and larger at the base, with slight constriction at the septum. The apex is beak-like and often deviates to one side.

Transmission route: The mycelium overwinters as diseased branches, leaves, or fallen leaves. In early spring of the following year, it forms conidiophores, which then spread and cause damage. Conidia are also the primary source of infection. Conidia are spread by wind, rain, and splashing water droplets, thus the disease is more likely to occur in rainy, foggy, and dewy conditions. Experiments have shown that spores can germinate and invade within 6 hours when there is residual moisture on the leaves. The optimal temperature for germination and invasion is 20-25℃, with a pH of 7-8. The incubation period is 10-11 days, slightly longer on older leaves (13 days). The pathogen can cause repeated infections throughout the growing season. Disease is generally more severe during the rainy season and typhoon season, while its spread is slower during the hot, dry summer months. Weak plants are more susceptible to the disease. There are differences in resistance among varieties, but there are no immune varieties.

Prevention and Control Methods: 1. Regularly sweep up fallen leaves and remove diseased leaves to reduce sources of infection. In winter, heavily prune severely diseased plants to remove overwintering pathogens from diseased stems. 2. When potting, avoid overcrowding and ideally, do not place directly on the ground to prevent excessive soil wetting when the ground is flooded. Place them on a tiered planting platform. Improve watering methods and timing; water from the edge of the pot, avoiding spraying. Do not water at night, as water on the leaves cannot dry quickly, facilitating pathogen invasion. 3. Chemical control. Begin spraying when new leaves just unfold in summer, generally every 7-10 days. Suitable pesticides include 50% carbendazim wettable powder at 500-1000 times dilution, or 75% chlorothalonil wettable powder at 500 times dilution, or 80% zineb wettable powder at 500 times dilution, or a 1:1:100 Bordeaux mixture, or 70% thiophanate-methyl at 1000-1200 times dilution. After winter pruning, you can also spray lime sulfur solution at 3-5 Baume degrees to eliminate pathogens.

Rose mosaic disease

Symptoms: Rose mosaic virus is characterized by small chlorotic spots, sometimes exhibiting polygonal patterns. The leaves around the lesions are often somewhat deformed. Some symptoms present as ring-shaped, irregular wavy patterns, as well as oak-leaf-type chlorotic spots. Generally, it has no effect on growth vigor, or it may have a slight impact leading to severe dwarfing.

Pathogen: The pathogen of rose mosaic virus is Rose Mosaic Virus (RMV). The virus has a spherical structure, approximately 25 nanometers in size. The lethal temperature is 54°C, the dilution endpoint is 1:125, and the in vitro survival time is 6 hours (room temperature).

Transmission route: Rose mosaic virus overwinters in the living tissue of the host and spreads through diseased buds, scions, and rootstocks, causing infection and disease during budding and grafting.

Prevention and control methods: 1. Avoid using infected roses as propagation material. 2. Keep them at 38℃ for one month; this heat treatment method can inactivate and eliminate the virus.

Lunar wrinkle disease

Symptoms: This is a systemic virus infection, meaning symptoms can appear on all parts of the plant, including leaves and flowers. Yellow necrotic spots appear on the leaves, causing them to wrinkle. The sepals sometimes become leaf-like, and the stamens turn green, somewhat resembling the leaves. Even if the flower manages to bloom, it is withered and loses its ornamental value. Branches sprouting from the base of the plant also wither, and the leaves have dark brown necrotic spots.

Pathogen: May be a mycoplasma or a virus.

Transmission route: Possibly through grafting. The natural transmission route is currently unknown.

Prevention and control methods: Diseased plants should be treated promptly. Do not obtain propagation material from diseased plants.

Rose powdery mildew

Powdery mildew is a common disease affecting roses. In some areas, it can cause quite serious damage.

Symptoms: The disease can affect leaves, petioles, flower buds, and young shoots. Initially, chlorotic yellow spots appear on the leaves, gradually expanding and developing a layer of white powdery substance. In severe cases, the entire leaf is covered with a white powdery layer. Infected young leaves curl back, wrinkle, and thicken, sometimes turning purplish-red. When petioles and young shoots are infected, the affected parts swell and bend backwards. Infected flower buds are covered with a white powdery mold layer, resulting in deformed growth and abnormal or absent flowering.

Pathogen: The sexual stage of the pathogen is a fungus of the genus *Sphaerotheca pannosa* (Wallr.) Lev., with cleistothecia that are spherical to pear-shaped, 85–120 μm in diameter. The appendages are filamentous, few in number and short, dark brown, and septate. Each cleistotheca contains one ascus, which is broadly elliptical to spherical, measuring 88–115 × 69–75 μm. There are eight ascospores, measuring 20–27 × 12–15 μm, broadly elliptical. The asexual stage is *Oidium leucocnium*, with conidia occurring in chains.

Transmission routes: The pathogen of rose powdery mildew overwinters as mycelium on diseased buds, leaves, or branches. In some areas, it can overwinter in cleistothecia. The following year, it causes primary infection via ascospores or molecular spores. It spreads by wind, directly invading the epidermis or stomata. The disease develops rapidly in warm, humid seasons. Different rose varieties exhibit varying resistance to powdery mildew. Generally, sparse, climbing, and multiflora varieties are more resistant, but this resistance is often lost due to the development of new physiological races. Excessive nitrogen fertilizer and insufficient potassium fertilizer in the soil exacerbate the disease.

Control methods: 1. Prune and destroy all dead, diseased branches and shoots in early spring to reduce the source of infection. Remove diseased leaves as early as possible. 2. In greenhouse cultivation, increase ventilation to prevent excessive humidity. Avoid excessive nitrogen fertilizer and appropriately increase phosphorus and potassium fertilizer. 3. When using chemical control, spray thoroughly and protect tender parts. Increase the frequency of spraying during the peak growth period of new shoots and the rainy season. At the initial stage of the disease, you can choose 15% wettable powder of triadimefon at 1500 times dilution, or 20% emulsifiable concentrate of triadimefon at 2000 times dilution, or 50% polysulfide suspension and 75% wettable powder of chlorothalonil at 600 times dilution, etc., spray once every 7-10 days, for 2-3 consecutive sprays.