Prevention and treatment of Primula spot

The symptoms occur on the leaves. The spot is usually 3-4 mm in diameter, brown, and in severe cases, the diseased leaves die, resulting in fallen leaves. The disease spread from the lower lobe to the upper lobe.

The pathogen RamulariaprimulaeThumen is Alternaria alternata. It belongs to a subphylum of semisciferous fungi. Conidiophores protruding from stomata, several branches clustered, extremely short, unbranched, colorless, slightly curved at the end; conidia cylindrical or short rod-shaped, unicellular or bicellular, colorless, 16-24 × 3-4 microns in size.

The transmission route and disease conditions were that the mycelium or conidia overwintered on the diseased remains, and the seeds could also carry bacteria, which became the source of infection at the beginning of the next year. The conidia produced from the disease department were spread by airflow and Rain Water sputtering, and re-infected frequently in the growing season. Usually warm and humid weather and partial application of nitrogen fertilizer, the plant growth is too dense, which is conducive to the disease. The disease usually begins in July and is prevalent from August to October.

Control methods 1) breeding disease-resistant varieties. 2) strengthen the management of fertilizer and water, increase the application of organic fertilizer and phosphorus and potassium fertilizer, and avoid excessive application of nitrogen fertilizer. 3) after the onset of the seedling disease, spray 70% methyl thiophanate wettable powder 1000 times plus 75% chlorothalonil wettable powder 1000 times, or 50% mixed thiophanate suspension or 36% methyl thiophanate suspension 500600 times, or 1RV 100 Bordeaux solution.