What are the common pest and disease control methods for roses?
Roses have beautiful blooms, come in a myriad of forms, are richly fragrant, and flower in all four seasons. In particular, they have a great many varieties and are easy to propagate and cultivate. They are praised as the "queen of flowers" and are one of China's ten most famous flowers. However, rose pests and diseases often cause poor growth and even death, seriously affecting their ornamental value. Let us take a look below at the common pest and disease control methods for roses.
Rose powdery mildew
[Symptoms] In the early stage, diseased leaves show chlorotic yellow spots, which then enlarge and become covered with white powder, curling backward, wrinkling, and thickening. After the petioles and young shoots are infected, they swell slightly and bend backward. After flower buds are infected, the flower form becomes deformed. In severe cases, the leaves turn yellow and withered, and the plant becomes weakened.
[Occurrence pattern] The pathogen overwinters on buds, leaves, and branches and spreads by wind. The optimal temperature for disease development is 17-25°C, with peak periods in May-June and September-October. It is prone to occur when there is too much nitrogen fertilizer or too little potassium fertilizer in the soil.
[Control methods] ① Choose disease-resistant varieties. ② Fertilize reasonably and avoid nitrogen fertilizer. ③ Remove and burn diseased leaves in early spring. ④ Prune moderately to keep the plant well ventilated and exposed to light. ⑤ Spray triadimefon, chlorothalonil, and other chemicals before and after disease onset for control.
Rose black spot
[Symptoms] Rose leaves, pedicels, and young branches can all be affected. In the early stage, the lesions are seed-brown to brown small spots, which then expand and turn black or dark brown, often surrounded by a yellow halo. In severe cases, all the leaves on the middle and lower parts of the whole plant drop off, and branches die back.
[Occurrence pattern] The pathogen overwinters in diseased branches, leaves, or fallen leaves and spreads through wind and rain. It is most severe after late summer. Under high temperature and drought, the disease spreads slowly. Weak plants are prone to infection.
[Control methods] ① Remove diseased leaves promptly and heavily prune diseased plants in winter. ② Prune often during the growing season to maintain good ventilation. ③ Chemicals such as chlorothalonil, carbendazim, zineb, and thiophanate-methyl can be used for control.
Rose leaf blight
[Symptoms] It occurs on rose leaves. In the early stage, yellow-green needle-point spots appear on the leaf surface. Later, the lesions expand into round or irregular shapes with purple edges, and after expansion they merge into patches. The boundary between diseased and healthy tissue is obvious. In the later stage, small black spots appear on the diseased areas, and the edges of diseased leaves look scorched.
[Occurrence pattern] The pathogen overwinters in diseased leaves or soil and spreads through wind and rain. Old leaves, weak branches, rainy seasons, and extensive management lead to severe disease.
[Control methods] ① Remove and destroy diseased leaves promptly. ② Choose disease-resistant varieties, plant at a reasonable density, and strengthen care. ③ Spray 3-degree lime sulfur mixture during the dormant season. ④ Spray chlorothalonil and other chemicals before disease onset for prevention. ⑤ Spray carbendazim and other chemicals in the early stage of disease for control.
Rose crown gall
[Symptoms] Tumors of varying sizes and shapes appear on the roots and stems of roses. The plant grows poorly, with short branches and leaves, yellowing and early falling leaves, and small flowers or no flowers.
[Occurrence pattern] The pathogen survives in the soil and spreads through water and tools. In the early stage, the galls are small and soft, white, and later gradually enlarge, turn dark brown, with a rough, cracked surface, and become hard and woody.
[Control methods] For open-field planting, try as much as possible not to grow continuously on the same land. Improve grafting standards, change grafting methods, reduce wounds, and avoid transmission.
Rose mosaic disease
[Symptoms] It mainly manifests as mosaic patterns, with some showing ring spots or oak-leaf patterns, and others showing chlorotic spots, yellow veins, or stunting.
[Occurrence pattern] It is a viral disease and can be transmitted by using diseased plants as propagation material, through sap contact, and by piercing-sucking insect pests. Strong light and drought in summer favor symptom expression and spread.
[Control methods] ① Avoid using diseased plants as propagation material. ② Pull out and destroy diseased plants promptly when found. ③ Choose disease-resistant varieties or tissue-cultured seedlings. ④ Pay attention during the growing season to controlling aphids and other transmission vectors. ⑤ Spray amino-oligosaccharin aqueous solution in the early stage of disease to inhibit virus spread.