Pest and Disease Control Methods During Zinnia Cultivation
Zinnia white star disease
Symptoms: The disease occurs on leaves. Initially small dark brown spots appear, which later develop into lesions with dark brown margins and grayish-white centers, 2 to 4 mm in diameter. It mostly occurs on lower leaves, and in severe cases the leaves curl and wither. The surface of the lesions bears dark green mold-like growth.
The pathogen CercosporazinniaeEllisetMartin is the zinnia cercospora fungus, belonging to the Deuteromycotina subdivision of the fungi.
Transmission route: The fungus overwinters as mycelial masses on seeds or diseased plant residues, and can also overwinter on diseased plants in greenhouse cultivation, becoming the source of primary infection. The pathogen on the lesions can also spread through wind, rain, and horticultural operations.
Conditions for zinnia disease development: High temperature and high humidity conditions favor disease occurrence. The suitable temperature for this disease is 22 to 28°C, with relative humidity above 85%. However, under conditions of high temperature and drought with nighttime dew formation, the disease is also prone to occur. In addition, lack of fertilizer, lack of water, or flood irrigation, and poor growth all make the disease more likely to occur.
Zinnia control methods
1. Strengthen management: Apply sufficient fertilizer, cultivate strong seedlings, provide rain protection and shade, water timely after planting, and avoid flood irrigation. Strengthen ventilation in sheds and greenhouses to reduce humidity. Promptly remove diseased plant residues.
2. Chemical control: In the early stage of disease, promptly remove diseased leaves, then immediately spray for control. You can use 1:0.5:200 dilution of Bordeaux mixture plus 0.1% sulfur powder, or 65% zineb wettable powder at 500 times, or 75% chlorothalonil wettable powder at 500 to 800 times, or 50% amobam at 800 to 1000 times.
Zinnia black spot disease
Zinnia black spot disease is also called brown spot disease. It occurs throughout the country. The leaves of infected plants turn brown and dry up, and the petals shrivel, affecting ornamental value.
Symptoms: Leaves, stems, and flowers can all be harmed by this disease. On leaves, small black-brown spots first appear, which soon expand into large irregularly shaped spots, 2 mm to 10 mm in diameter, reddish-brown. As the spots expand and increase in number, the entire leaf turns brown and dries up. On stems, the disease starts from the base of the petiole and develops longitudinally, forming dark brown elongated streaks. The symptoms on flowers are similar to those on leaves, and soon the petals shrivel and dry up. At the seedling stage, when the base of the stem is affected, dark brown sunken canker spots with depressed centers form, and the lesions gradually encircle the stem, causing the seedlings to show damping-off symptoms.
Pathogen: The fungus AlternariazinniaePa-pe.
Infection route: This pathogen overwinters on diseased leaves, diseased stems, and other residues. Infected material can also become the source of primary infection. The pathogen spreads by wind and rain and can infect throughout the entire growth period of zinnia. It is most severe under high temperature and high humidity climatic conditions.
Control methods:
1. Choose well-drained areas for planting. Planting density should be appropriate. Avoid continuous cropping. Seeds should be disinfected before sowing (soak seeds with 50% carbendazim wettable powder at 1000 times dilution for 10 minutes). After autumn, diseased leaves, diseased stems, and other materials should be collected and destroyed to eliminate the source of infection for the next year. Save seeds from disease-free healthy mother plants.
2. Spray with 50% zineb or mancozeb at 5000 times dilution, or 80% Xinwansheng wettable powder at 600 times dilution. When spraying, pay special attention to spraying the leaf undersides evenly.
Zinnia mosaic virus disease (CMV)
It occurs throughout the country and often causes plants to become stunted and degenerate, reducing ornamental value.
Symptoms: In the early stage of disease, the leaves show slight mottling, which later becomes light and dark green mottling. The symptoms are more obvious on new leaves.
Pathogen: The virus causing zinnia mosaic disease is mainly cucumber mosaic virus CMV.
Transmission route: This viral disease can be transmitted by many kinds of aphids. Cucumber mosaic virus has a very wide host range, and the zinnia growing season is also the active period of aphids, so aphids are highly correlated with the occurrence of the disease.
Control methods: Eliminating aphids to prevent disease has a certain controlling effect on zinnia mosaic disease. In addition, attention should also be paid to field sanitation management, eradicating diseased plants, and clearing other hosts of CMV to reduce sources of infection.