Primula spot disease

Symptoms: mainly harmful to plant leaves. The disease spread from the lower part of the plant to the upper part. The spot is usually 3 to 4 mm in diameter, brown, and in severe cases, the diseased leaves die, resulting in fallen leaves (see figure 2). The disease is caused by Alternaria alternata. The pathogen overwintered on the diseased residue by mycelium or conidium, and the seeds could also carry bacteria, which became the source of initial infection in the second year. The disease is mainly spread by conidia in the air and Rain Water. Re-infection is frequent in the growing season. Plants are usually prone to disease in warm and humid weather and partial application of nitrogen fertilizer. The disease usually begins in July and is prevalent from August to October.

Control methods: select disease-resistant varieties, strengthen fertilizer and water management, increase the application of organic fertilizer and phosphorus and potassium fertilizer, and avoid partial application of nitrogen fertilizer. At the initial stage of the disease, 70% methyl topiramate was sprayed with 1000 times solution plus 75% chlorothalonil wettable powder 1000 times solution, or 1 ∶ 1 ∶ Bordeaux solution.