The high temperature season in summer is the peak period for diseases and pests of paeoniarockii. The high temperature and high humidity environment is particularly prone to induce a variety of diseases and pests. The following types of problems need to be focused on:
- Main diseases (mainly fungal, induced by high temperature and high humidity)
- Root rot:
Cause: Heavy rains or excessive watering in summer lead to waterlogging in the soil, lack of oxygen in the roots, and high temperature, and fungi such as Fusarium and Phytophthora multiply and infect the root system.
Symptoms: The plant grows slowly and wilts (especially obvious at noon on sunny days), and the leaves turn yellow and fall off. Digging up the roots shows that the roots turn brown, black, and rot. In severe cases, the whole plant dies.
Key prevention period: After continuous rain or improper watering. - Gray mold:
Cause: In high temperature and humidity (especially hot and humid after rain), Botrytis cinerea infects. Mainly harms flowers, buds, tender stems, and leaves.
Symptoms: Water-soaked brown spots appear on the affected parts (especially withered petals and injured tissues), which quickly expand and are covered with gray-brown or gray-white mold layers. The affected buds cannot open or open abnormally. The affected tender stems are prone to bend.
Key prevention period: flowering period and after flowering, especially after rain. - Anthracnose:
Cause: In hot and rainy seasons, anthracnose bacteria infect leaves, petioles, and stems.
Symptoms: Nearly circular or irregular brown, reddish-brown or dark brown spots appear on the leaves. The color of the central part of the spots becomes lighter in the later stage, and sometimes ring patterns or small black spots (conidia) can be seen. In severe cases, the spots are connected, and the leaves turn yellow and fall off.
Key prevention period: The whole summer, especially the rainy season and typhoon season. - Powdery mildew:
Cause: Although it is more common in spring and autumn, it may also occur in the alternating environment of high temperature, dryness and high humidity in summer.
Symptoms: A layer of white powdery mold covers the surface of leaves, tender shoots, and buds. In the later stage, small black particles (closed asci) may appear in the mold layer. The affected leaves are twisted, deformed, yellowed and fall off.
Key prevention period: In summer, when ventilation is poor, dry and hot. - Integrated pest and disease control strategy in the high temperature season in summer
- Environmental regulation (the most fundamental and most important):
Shading and cooling: During the high temperature and strong light period (10 am to 4 pm), appropriate shading (50%-70% shading rate of shading net) is carried out to reduce the surface temperature and transpiration of the plants and relieve heat stress.
Strengthen ventilation: Avoid dense planting in the planting area to ensure good air circulation between plants and reduce humidity. Potted plants should be placed in a ventilated place.
Shelter from rain: If conditions permit, a simple shelter can be built, especially during the flowering period and continuous rainy period, to effectively reduce the high humidity environment and the spread of pathogens caused by rain.
Scientific watering: Strictly avoid water accumulation! In summer, watering should be done in the early morning or evening, avoiding the high temperature at noon. Adopt the principle of “see dry and see wet”, and water thoroughly after the soil surface is slightly dry. Avoid watering the leaves and try to water the roots.
Improve soil drainage: Choose a high and dry plot with good drainage for ground planting. For potted plants, ensure that the drainage holes at the bottom of the pot are unobstructed and use loose and breathable culture soil. You can cover the soil surface with pine scales, ceramsite, etc. to help cool down and retain moisture and reduce rain splashing on the soil. - Gardening management:
Clean up diseased and damaged bodies in time: Remove diseased leaves, diseased branches, and withered petals at any time, and take them away from the garden for destruction, which can effectively reduce the source of pathogens.
Reasonable pruning: Remove overcrowded branches and inner branches to increase ventilation and light transmission. Cut off diseased and weak branches.
Avoid damage: Reduce plant wounds, which are an important way for pathogens to infect. - Chemical control (as an auxiliary, timely and accurate use):
Preventive spraying: Before the rainy season, after continuous rain, or when sporadic disease spots are observed, spray broad-spectrum protective fungicides (such as mancozeb, thiophanate-methyl, methyl thiophanate, etc.) in time for prevention.
Targeted treatment:
Root rot/blight: When early symptoms are found, root irrigation can be carried out with agents such as benomyl, metalaxyl·mancozeb, and cymoxanil hydrochloride. Severely diseased plants need to be dug out, rotten roots removed, disinfected, replanted or destroyed after soil replacement.
Gray mold/anthraquinone: Use therapeutic fungicides such as azoxystrobin, pyraclostrobin, isoproton, and boscalid.
Powdery mildew: Tebuconazole, myclobutanil, difenoconazole, and kresoxim-methyl can be used.
Red spider: Choose specific miticides such as avermectin, pyridaben, etoxazole, spirodiclofen, bifenazate, etc., and be sure to spray the back of the leaves, and use them alternately to avoid resistance.
Aphids/thrips: Insecticides such as imidacloprid, acetamiprid, thiamethoxam, dinotefuran, and high-efficiency chlorflucythrinate can be used. Note that thrips are mostly in the flowers and on the back of the leaves, and the spraying should be meticulous.
Scale insects: The nymph stage (when the wax shell has not formed or is thin) is the key to prevention and control, and buprofezin, spirotetramat, chlorpyrifos, etc. can be used. The adult stage is protected by the wax shell and the efficacy is poor, so it can be scraped off manually or combined with pruning.
Underground pests: Phoxim granules, clothianidin granules, etc. can be mixed with soil or spread on the soil surface and then hoe shallowly.
Summary of key points
Prevention first, comprehensive prevention and control: Environmental control (shading, ventilation, rain shelter, water control, and drainage) is the core and basis for the prevention and control of purple peony diseases and pests in summer.
Observe frequently, discover early, and deal with it early: Check the plants frequently in summer (especially after rain). Once a small number of diseased leaves, insects or abnormal symptoms are found, remove/catch them immediately and take corresponding measures.
Keep the plants strong: Apply fertilizers reasonably (avoid concentrated fertilizers in high temperatures in summer, and apply thin phosphorus and potassium fertilizers to enhance resistance) to enhance their own resistance.
Clean the garden: Clean up diseased and fallen leaves and flowers in time to reduce the source of diseases and insects.
Use medicines scientifically: Use medicines accurately when necessary, pay attention to safety and rotation.
Through the above comprehensive management measures, the pressure of diseases and insect pests on purple-spotted peonies caused by high temperature and high humidity in summer can be effectively reduced, ensuring their healthy growth and safe summer.