We almost always encounter various diseases and pests affecting roses. We used to be at a loss when faced with them, but after figuring out some prevention methods, we gradually became more accepting of them.

Today, we will share some of our experiences without reservation, providing a comprehensive analysis of common diseases and pests in rose cultivation, helping you to grow flowers easily and enjoy the true pleasure of planting.

I also hope that in the new year, taking advantage of the opportunity to prevent and control pests and diseases, we can look forward to driving away the dirt of the past year.

We will discuss common diseases and pests affecting roses from two aspects: diseases and pests.

— Powdery mildew—

Symptoms: Powdery mildew typically affects the upper and middle parts of young leaves and branches. In the early stages, small red or reddish-brown spots appear on the upper or lower surface of the leaves. These spots become distorted and contain fine white granules. Later, the white granules increase in number and gradually form a powdery layer. In severe cases, the branches, tender tips, and young leaves are covered with white powder.

Disease pattern: It is more common in spring and autumn, mainly due to dry weather, poor ventilation in the microenvironment, and insufficient sunlight.

The plant is over-nourished (mainly due to excessive nitrogen fertilizer, resulting in overly succulent leaves).

Exposure to direct sunlight after heavy rain can also increase the risk of powdery mildew infection.

— Black Spot Disease —

Symptoms: The disease mainly affects the lower and middle older leaves, especially those near the ground. Initially, reddish-brown/dark brown spots appear on the upper surface of the leaves. These spots gradually enlarge, and yellowing occurs around them. In severe cases, the entire plant loses all its leaves, growth is severely affected, and the plant may even die.

Disease pattern: It occurs more frequently in the summer when there is excessive rainfall and in late summer and early autumn. The combination of a continuous long period of humid environment and relatively high temperature will cause the black spot fungus to multiply rapidly and spread.

— Downy mildew —

Symptoms: These brown patches are not black spots, nor are they a sign that the leaves are preparing for dormancy after the weather gets cold. Instead, they are a disease called downy mildew.

Disease pattern: High humidity and low temperature create the ideal environment for downy mildew to develop. Poor ventilation further increases the likelihood of downy mildew outbreaks.

— Gray mold —

Symptoms: Ulcers suddenly appear at the base of leaves and the upper middle part of young branches, or the leaves of the entire plant clump together when the disease occurs at the base of the seedling. Flower buds are severely deformed, and gray fungal spores appear on the petals.

Disease pattern: The main seasons for the disease are early spring, late autumn, and winter. The environment in which the disease occurs is characterized by low temperature, high humidity, and low light.

— Black Rot —

Symptoms: Black rot, also known as black stem disease, indicates a serious condition. In the early stages, leaves lose their luster, plant growth slows, and new shoots become watery and pale. In severe cases, the entire plant wilts uncontrollably, and the basal branches turn black and die.

Disease pattern: Poor soil aeration, excessive moisture, coupled with low temperature and insufficient sunlight, lead to rapid bacterial growth.

— Blighted Twig Disease —

Symptoms: Brown or purple lesions appear on branches and trunks, and longitudinal cracks appear on the stem epidermis; in the later stages of the disease, the lesions become sunken, and black patches appear on young stems. In severe cases, the branches and leaves above the diseased area wither and die.

Causes of disease: ① Prolonged high temperature and heavy rainfall in the environment with poor air circulation; ② Insufficient fertilizer and water, resulting in weak plant growth;

Disease pattern: The disease occurs during hot and rainy seasons, mainly affecting older seedlings, plants with few new shoots, and malnourished plants. Healthy plants rarely develop the disease.

Soil diseases —

The main diseases are root rot (which can be understood as root decay), including damping-off and other diseases in the soil or diseases on the soil surface near the soil.

Symptoms: This type of disease is often identified by abnormalities in the leaves, such as the sudden wilting of normally healthy leaves. Generally, this type of disease develops slowly and is easy to recognize.

Treatment: Bright Shield is recommended as a treatment. Bright Shield is a soil-borne fungicide produced by Syngenta, Switzerland, primarily designed to ensure the safety and health of crop roots.

— Red Spider —

Symptoms: Numerous tiny yellowish-white spots appear on the upper surface of the leaves, eventually causing the leaves to turn yellow and fall off. Red or white insects/insect secretions can be seen on the underside of the leaves.

Disease pattern: The disease is more likely to occur in hot and dry environments, with a high incidence rate in greenhouses or indoors, and very rare in the open air. It is difficult to detect in its early stages, and treatment becomes extremely difficult once it spreads, and drug resistance is easily developed.

— Whiteflies —

Whiteflies, also known as greenhouse whiteflies, are small white winged flying insects.

Harm: Whiteflies suck sap from the undersides of leaves, causing yellowing and wilting, and even death. They also secrete large amounts of honeydew, creating sooty mold, and can spread viruses. However, there's no need to worry too much, as whitefly infestations on roses are not very severe.

Treatment: Generally, only manual treatment is needed. If you are concerned, you can use yellow sticky traps or spray with imidacloprid or Bayer's Abamectin.

— Aphids —

Symptoms: Aphids gather on the buds, tender leaves, and flower buds of roses and suck the sap. When there is a large infestation, there is a honey-oil-like black secretion, which affects both the growth of roses and the quality of the flowers.

Disease pattern: Aphids are more likely to occur in winter and early spring.

Prevention: In autumn, prune branches infested with insects and promptly remove weeds and fallen leaves. During the peak hatching period of overwintering eggs, imidacloprid and abamectin can be used alternately.

Treatment: Small numbers can be crushed by hand or sprayed off with water. For medication, using an insecticide like fenbendazole will suffice. For those who don't want to use medication, yellow sticky traps can be used.

— Thrips —

The leaves that have been eaten by thrips are wrinkled.

Symptoms: Young leaves and branches become twisted and deformed; tender tips and flower buds wither and become deformed, forming scars after development. Affected leaves lose their green color, dry out, become hard and brittle, and the entire plant grows slowly, resulting in impaired growth.

Prevention and control: Imidacloprid or Bayer's acetamiprid can be used. After spraying, be sure to prune diseased leaves.

— Caterpillars, caterpillars —

Damage: Green caterpillars and caterpillars mainly damage the tender leaves, tips, buds, and petals of roses.

Treatment: If a small number of these insects appear, you can simply crush them by hand. If a large number appear or if you are worried, you can use pesticides (DuPont Odten and chlorantraniliprole are recommended, as they are both effective at killing insects) .

Prevention: No prevention is needed. Just pay attention to the eggs and small insects when you see butterflies flying around on the flowers. They are relatively easy to deal with when they are small.

— Scale insects —

Symptoms: Small white, gray or black insects densely clustered on the old branches of the plant. Often, a group of insects form a hard shell inside and gnaw on the plant, which can severely damage the plant's growth.

Treatment: These insects are quite small and difficult to deal with, so chemical extermination is generally used. For small numbers, wiping with alcohol is sufficient, but for large numbers, chemical pesticides (such as Muwangte) are required .

— Cut leaf bee —

Leaves gnawed by leafcutter bees

Harm: Leafcutter bees use their mouthparts to gnaw off leaves for nest building. This can affect the appearance of roses, but it does not have a significant impact on their health.

Prevention and control: Since leafcutter bees collect leaves not for consumption, chemical control is not very effective. Physical control methods, such as using yellow sticky traps, are generally preferred. For those who don't want to kill the bees, moving the rose bush to a different location will eliminate the presence of these "single-minded" leafcutter bees.

— Stem bee —

Harm: Causes rose branches to suddenly wilt, droop, and die. Stem borers lay their eggs on the tender branches of roses, which then hatch into a large number of green, soft-bodied insects. The upper part of the branches bored by these insects wilts and dies, causing significant damage to the roses.

Prevention and control: The most direct way to kill stem wasps is by spraying insecticides. In spring, about a week after the rose bushes sprout, start regularly spraying with broad-spectrum insecticides  (such as high-efficiency cypermethrin)  . This method is effective for both contact killing and prevention.

— Sawfly —

The rose leaf beetle, also known as the yellow-bellied beetle.

Damage: The larvae bite and feed on the leaves of roses. Dozens of them often eat all the leaves off the plant together, causing great damage to the roses.

Prevention and control: When pests occur, conventional insecticides can be used for control and good results can be achieved.

Regular observation, preventative measures before flowering, and mastering pest and disease treatment methods are all crucial. Immediate treatment upon discovery of pests or diseases are also essential. To enjoy the beauty of roses, hard work is always necessary.