Analysis of common rose pests and diseases: as midsummer arrives, detect early and treat early
Gardeners who love growing roses know that the rose is famously the "medicine bottle" of the flower family, especially in the muggy environment of summer, when it can easily pick up all kinds of pests and diseases during cultivation. Once attacked by pests or diseases, spray promptly to treat them and prevent the source of the disease from spreading.
1. Powdery mildew. It is the fungal disease that roses are most susceptible to. It easily infects roses for the first time in mid-to-late May each year, and spreads gradually in June and July as temperatures rise. It mainly shows as a layer of white powdery substance on the leaf surface and young shoots, which is the typical feature of powdery mildew. It can cause leaves to curl and scorch; when the infection is severe, young shoots die and leaves turn yellow and drop, seriously affecting plant growth and flowering. The main causes of powdery mildew are a growing environment that is relatively warm and dry or damp and muggy, and when the plant's branches and leaves are too dense and ventilation and light penetration are poor, the disease is severe. Long-term excessive application of nitrogen fertilizer, or soil lacking calcium or potassium fertilizer, also easily triggers powdery mildew.
Control methods: Place the plant in a position with good light and ventilation, prune and shape it in good time, thin out overly dense branches and crossing, overlapping branches to increase the plant's airiness. At the same time, spray 70% thiophanate-methyl 1000x solution, or Guoguang triadimefon, etc., all of which have good control effects. When spraying, note: it is generally recommended to spray from 8 to 10 a.m. and from 4 to 7 p.m., and the effect is best on a sunny, windless day.
2. Black spot. Rose black spot is a worldwide disease and occurs commonly in China. It mainly attacks leaves, followed by leaf stalks, leaf tips, young tender branches and flower stalks. When it first appears, there are small purple-brown to brown spots on the leaves, which then spread into round spots, and the lesions are often surrounded by a yellow halo. Large areas of the leaves around the diseased part turn yellow, and in severe cases all the leaves on the lower and middle parts of the whole plant drop off, leaving only a few new leaves at the top.
Rose black spot is a fungal disease, and it is severe in rainy seasons. Black spot can spread by rain or splashing irrigation water, and insects can also transmit it. In rainy seasons, newly transplanted plants with damaged roots and weak growth are generally prone to this disease. July to September is the outbreak period of this disease. Control methods: Remove diseased leaves promptly when found, usually avoid the potting soil being too wet, and when watering, choose the morning of a sunny day as far as possible and avoid spraying water over the plant. Chemical control can also be used: spray Nativo or Bordeaux mixture once every 7 days, spraying three times in a row, which has an obvious control effect.
3. Red spider mite. It is the pest that roses are most susceptible to. It shows as follows: starting from the lower leaves, adult mites or young mites gather on the underside of the leaves and suck the sap, forming small grayish-white dots on the leaves; afterward the leaves become yellow and weak, as if scorched dry by fire, so that the leaves cannot carry out normal photosynthesis, and when the damage is severe it can cause early leaf drop.
Red spider mites mostly occur from May to October when the weather is dry and the temperature is relatively high, and they are a very common rose pest that gives gardeners headaches. If red spider mites are found, in the early stage you can, along with pruning, remove and burn the leaves with grayish-white spots, and you can rinse the plant's leaves. Chemical control can also be used: you can use 20% dicofol EC 1000x solution, or 73% propargite EC 2000x solution, Abamectin, pyridaben, etc. It is recommended to alternate the two chemicals, spraying once every 7 days, three times in a row, which can achieve a relatively good effect.
4. Aphids. They are one of the most destructive pests in the world, green or gray. They usually gather on the young shoots and flower buds of roses. They do harm by sucking plant sap. They not only hinder the normal growth of roses, but also cause deformities in the flowers, leaves and buds of roses.
If a small number of aphids are found, you can catch them by hand, or spray with imidacloprid once a week, and generally 2 to 3 times is enough to clear them.
Besides the above several diseases, yellow leaf disease, rust disease, etc. are also common rose diseases. Yellow leaf disease is usually yellowing of leaves caused by overwatering and soil that is too alkaline. You can choose loose, breathable, slightly acidic soil, appropriately reduce the frequency of watering, and water only after the soil has dried out completely. Rust disease is also a disease that roses are easily infected by. It shows as brownish-yellow spots appearing on the branches and leaves, after which the whole leaf turns yellow. The main cause is that the rose growing environment is relatively dark and damp, and the ventilation is poor. When rust disease is found, promptly remove the diseased leaves, and spray fungicides such as chlorothalonil or thiophanate-methyl solution, either of which can control it.