Identification of Rose Gray Mold Symptoms and Control Methods

Roses are a relatively common ornamental flowering plant in China, native to China. Through long-term hybridization and breeding by horticulturists, they have now developed to more than 20,000 varieties. Although roses are relatively easy to cultivate, we should not overlook the common diseases of roses. The editor will now provide a detailed introduction to rose gray mold, and friends who like roses can study it together.

Rose

I. Symptom Characteristics

The pathogen is Botrytis cinerea. This pathogenic fungus infects the flowers, flower buds and tender stems of roses, with disease spots mainly occurring on the flowers. Initially, they are water-soaked irregular small spots, slightly sunken, then turning brown and rotting. When buds are affected, water-soaked irregular small spots also appear, and the spots can expand to cover the entire flower bud, ultimately causing the whole bud to soften and rot. After the diseased buds wither, they hang on or near the diseased tissue. In warm and humid environments, a large amount of gray mold layer can be produced on the diseased parts.

II. Disease Occurrence Patterns

The pathogen overwinters as mycelium or sclerotia lurking in the disease source.

The following year, it produces conidia that cause infection, and a gray moldy substance appears on the surface of the diseased parts. High temperature and abundant rain favor the massive formation and spread of conidia. After conidia come into contact with the host, they germinate and produce germ tubes to invade. When planting is too dense, humidity is high, light is insufficient, or nitrogen fertilizer is applied excessively, and plants grow weakly, the disease is prone to occur.

III. Control Measures

In autumn, do not use dead branches and fallen leaves to protect the roots, to avoid excessive moisture at the base of the stems, which favors the survival of the pathogen. When cultivating in a greenhouse, attention should be paid to ventilation and light transmission, avoiding excessively high humidity; avoid sprinkler-type watering, do not apply excessive nitrogen fertilizer, and do not plant too densely. Remove infected diseased flowers; for diseased buds, they should be cut off together with several cm of stem below the bud and destroyed.

During the disease period, spray 75% chlorothalonil wettable powder at 700 times dilution, or 1:1:120 to 160 Bordeaux mixture, or 50% meimeiling wettable powder at 900 times dilution, or 65% jiameiling wettable powder at 1000 times dilution, or 70% thiophanate-methyl wettable powder at 1500 times dilution.

Rose Gray Mold Symptoms and Control Measures

Gray mold mainly harms flowers and tender branches. After flower buds are infected, initially there are water-soaked irregular small spots, and the spots continuously expand until the whole bud softens and rots. After the diseased buds wither, they hang on the diseased tissue. The pathogen also attacks branch tips after flowers have been picked. Under warm and humid conditions, a large amount of gray mold layer develops on the diseased parts.

Disease Symptoms:

Rose gray mold mainly harms leaves, buds, flower buds and flowers, and can also harm young stems. When it occurs on leaf margins and leaf tips, initially there are water-soaked light brown spots, smooth and slightly sunken, then expanding and rotting. When flower buds are affected, the spots are grayish-black, which can prevent the flowers from opening, and the diseased buds turn brown and die. When flowers are infected, some petals turn brown, shrivel and rot. The gray mold pathogen also attacks branch ends after flower cutting, and the black diseased part can extend several cm downward from the infection point. In warm and humid environments, the gray mold layer can completely cover the infected parts.

Control Measures:

1. Remove diseased flowers promptly, remove withered old flowers, and burn them in a centralized manner.

2. When cultivating in a greenhouse, pay attention to ventilation, reduce air humidity, so that the roses indoors have a good growing environment, and prevent excessively high humidity.

3. During disease occurrence, spray 65% zineb wettable powder at 600 times dilution, 75% chlorothalonil wettable powder at 700 times dilution, or 70% thiophanate-methyl wettable powder at 1500 times dilution.

Symptoms and Control Methods of Rose Downy Mildew

Symptoms:Downy mildew harms leaves, tender shoots, flower stalks and flowers. In the early stage, irregular light green spots appear on the leaf surface, then expand and turn yellowish-brown and purple, later grayish-brown, with the edges being darker in color and no obvious boundary with healthy tissue. Eventually, it causes leaf curling and deformity. When the weather is humid, sparse grayish-white downy mildew layers can be seen on the diseased spots on the leaf underside. Leaflets often turn yellow, and some disease spots are purplish-red with grayish-white centers, similar to pesticide damage and fertilizer burn. When new shoots and flowers are infected, the spots are similar to those on leaves, but the spots on tender shoots are slightly sunken. In severe cases, leaves shrink and fall off, and new shoots die.

Pathogen:Rose downy mildew is caused by infection by Peronospora sparsa, a type of fungus. The pathogen overwinters as oospores or mycelium in the diseased tissue. When temperatures are low, relative humidity is high, and water droplets exist on the plant surface, the disease is prone to occur and spread. When greenhouse ventilation is poor, plants are too dense, humidity is high, and nitrogen fertilizer is excessive, the disease is severe. This fungus only infects roses.

Disease Occurrence Patterns:The pathogen overwinters and oversummers as oospores, and infects via conidia. The spore germination temperature is 1-25°C, with the optimum being 18°C. Above 21°C, the germination rate decreases; above 26°C, germination completely stops; at 26°C for 24 hours, the spores die. Spore transmission requires 100% air humidity and a temperature of 10-25°C. Spore germination requires the presence of water droplets. In open-field cultivation, it mostly occurs during the rainy season; in greenhouses, it mainly occurs in March to April and September to October, occurring in greenhouses. When seedling beds are dense, ventilation is poor, there is excessive moisture, and nitrogen fertilizer is excessive, the disease is severe.

Control Methods:Avoid high temperature and high humidity, reduce the time of leaf surface moisture retention, control air humidity, and open windows more for ventilation; use 20,000 times diluted amobam; spray 500 times diluted mancozeb or maneb for control, but the latter easily contaminates the leaves.