Common pests and diseases of roses and prevention methods

The main diseases of roses are black spot, powdery mildew, downy mildew, rust, leaf blight, gray mold, black stem disease,etc.

• Black spot disease

Black spot disease of roses mainly occurs in summer with high temperature and heavy rain. Rain or water splashing on leaves can cause infection. In early stage, small purplish-brown spots appear on leaves. Later, leaves turn yellow and spots become dark brown or black until all leaves fall off. Prevention is mainly to reduce leaf wetting chances. If disease occurs, isolate in time, pick off diseased leaves and spray with fungicides like DuPont Fuxing Gaozhao diluted as per proportion.

• Downy mildew

In the early stage of downy mildew of roses, it mainly occurs on newly grown branches and leaves in the middle and lower parts. The leaves have light green irregular patches, like fading of normal green. There is sparse white downy mildew on the back. In the later stage, it spreads from bottom to top. Leaves have dark purple water-soaked patches. Finally, it turns into irregular brown mildew layers like burned ones until leaves fall off and die. Downy mildew mainly occurs in humid environments. Prevention is ventilation to reduce humidity and maintain illumination. If infected, use propamocarb hydrochloride to spray and irrigate roots in proportion with water to cure.

• Leaf blight

If the rose plants are too dense and grow in a high-temperature and high-humidity environment, leaf blight is prone to occur. In the initial stage of leaf blight infection, the leaf tips or leaf edges will turn purple and there will be small yellow spots. Later, the small spots will invade the middle of the leaves and gradually expand and connect to form irregular large yellowish patches with distinct boundaries like those burned by fire. There will also be sparse small black spots. The prevention of leaf blight mainly includes reducing the density of rose plants and avoiding being rained on. After infection, it needs to be treated by watering the roots with carbendazim diluted in water and spraying the leaves with chlorothalonil diluted in water.

• Gray mold

In early spring or late autumn, when temperature is relatively low and there’s more rain, roses are prone to be infected by gray mold fungus in low-temperature and high-humidity environment. In the initial stage of infection, leaf tips or edges show small water-stained spots of different colors. Gradually, they become larger, softer and rot. Gray mold can be seen in high-humidity environment. Flower buds or petals are also easily infected. To prevent gray mold, reduce environmental humidity. If the disease has occurred, remove diseased leaves in time and use Hymexazol mixed with water for root irrigation and spraying treatment.

• Rust disease.

Rust disease of roses mainly occurs during the rainy season from June to September. After the disease occurs, small spots will appear on the surface of the leaves until the back. The spots are orange-yellow or orange-red powder. Later, white spots will appear on the front of the leaves. In severe cases, the leaves will be scorched and withered, and the back will be covered with yellow powder until the leaves fall off. The prevention of rust disease also requires a dry and ventilated environment. If the disease occurs, diseased leaves should be cleaned up in time, and chlorothalonil should be sprayed and treated with water in proportion.

• Powdery mildew

If roses are infected with powdery mildew, there will be irregular small yellow-green spots in the initial stage. Then the spots will expand until a layer of white powder appears on the leaf surface and tender shoots. Eventually, the leaves will turn yellow and fall off, affecting the normal growth and flowering of roses. Powdery mildew can be treated by spraying drugs such as chlorothalonil and mancozeb with water. It should be noted that this layer of white powder has a waterproof function. If the spraying is not in place, it will not work. It must be sprayed carefully.

• Black stem disease

Black stem disease of roses mainly occurs in an environment with insufficient light and excessive humidity. The pruned branches will gradually turn from yellowish-brown to black from top to bottom, eventually leading to the withering and death of the whole plant. The prevention of black stem disease mainly includes maintaining sufficient light, increasing the air permeability of the potting soil, and not pruning branches on rainy days. If pruning is done, seal it with wax to prevent moisture from seeping in and causing black stems. If the disease occurs, directly cut off the diseased stems completely in a sunny and dry environment. It is a non-pathogenic disease.

• Withered branch disease

The pathogen of rose withered branch disease belongs to Deuteromycotina, Sphaeropsidales, and Coniothyrium. Pycnidia are located in stromata. Initially buried under epidermal septum, later break through and open. When climbing roses are infected, first small red spots, then expand and deepen to brown. Later, spots are sunken and cracked. Severe cases girdle stems, causing upper branches to wither. For ulcers or tumors, disinfect or prune in time. If infected, prune and destroy diseased parts. Spray fungicides for prevention. During growth, spraying urea solution can enhance growth and reduce disease occurrence.

The main pests of roses are spider mites, whiteflies, aphids, thrips.

• Spider Mites

Those who grow roses should be clear about what pests roses may have, as this can help roses grow better. Spider mites are no strangers to many people. They have extremely strong reproductive ability and are easily infected in a high-temperature and high-humidity environment. This pest can cause the leaves of roses to form webs and have many spots on the surface.

• Whiteflies

It is one of the common pests of roses. They mainly live by sucking nutrients from the leaves. They can reproduce all year round, with about 8 to 9 generations per year. If whiteflies are not dealt with in time, the leaves of roses will turn yellow and wilt. In severe cases, the plant may die directly. The best drug for preventing and controlling whiteflies is imidacloprid.

• Aphids

It is also a very harmful pest. It mainly lives by sucking the nutrients in rose buds, tender leaves and twigs. Its reproductive ability is even more astonishing. If not dealt with in time, the whole plant will be overrun by aphids. The places sucked by aphids will turn black. Generally, the incidence rate is highest in summer and autumn.

• Thrips

It mainly suck the juice in rose flowers. Rose flowers damaged by thrips are extremely prone to falling. Some roses still in the bud stage will fall before blooming. This kind of pest is very small and can fly and run. The leaves of the infested plant will turn yellowish-green and various parts will grow abnormally. In severe cases, the rose will stop growing.