A Detailed Explanation of the Morphological Characteristics and Control Methods of Chrysanthemum Downy Mildew

Chrysanthemum downy mildew mostly occurs in mountainous areas with an average temperature of 16.4°C-19.0°C, annual rainfall of about 1500mm, and low-temperature, rainy springs, and is one of the main diseases of chrysanthemums. So what are the morphological characteristics and control methods of chrysanthemum downy mildew? Let us follow forestry experts below to understand these issues.

I. What is chrysanthemum downy mildew?

The pathogen of chrysanthemum downy mildew (Peronospora radii de Bary) belongs to the Fungi, Mastigomycotina, Peronospora, and is one of the main diseases of chrysanthemums. The pathogen is prone to causing disease in low-temperature and humid environments. When disease occurs in spring, white frost-like mildew appears on the stems and leaves of seedlings, growth vigor weakens, or seedlings wither and die; after plants are infected in autumn, the lesions on the leaves are light green, and the lesions later gradually turn purple-black, with white frost-like mildew layers appearing on the lesions on the back of the leaves, and under high temperature they easily develop into yellow-brown lesions. In severe cases, the lesions merge and the plants die.

II. Morphological characteristics of chrysanthemum downy mildew

Sporangiophores are solitary or clustered, emerging from stomata, without septa, with the base of the main trunk swollen, size 225.0-412.0μm×7.8-11.8μm, the main stalk being 1/2 to 1/4 of the total length, the crown with 3-7 times fork-like branching, the apex with 2-3 times fork-like branching, at right angles or acute angles, terminal branches 7.8-11.8μm long, thin at the end, slightly thicker at the base, the tips of the terminal branches bluntly rounded, slightly swollen, or hyphae white, sporangiophores branching 3-5 times, the first branching asymmetrical, size 286.0-707.0μm×9.0-16.0μm, main trunk 192.0-473.0μm long, terminal branching nearly at right angles, 7.8-15.7μm long, straight or curved, with pointed ends. Sporangia light brown, elliptical, size 24.5-31.2μm×14.7-24.5μm; or sporangia without papillae, size 23.0-33.0μmX17.0-27.0μm.

III. Control methods for chrysanthemum downy mildew

1. Agricultural measures: select disease-resistant chrysanthemum varieties, such as pot marigold (Calendula officinalis), strawflower (Helichrysum bracteatum), and marigold (Tagetes erecta).

2. Seed treatment: before sowing, seeds can be dressed with 50% thiram wettable powder.

3. Strengthen field management: strengthen fertilizer and water management, and prevent water accumulation and moisture retention.

4. Chemical control

In the early stage of disease, spray with 72% Kelu wettable powder at 600 times dilution, and the control effect reaches 70%; spray with 60% Mieke wettable powder at 800-1000 times dilution and 65% zineb wettable powder at 500 times dilution, and the control effects reach 85% and 90% respectively; spray with 69% Anke · mancozeb wettable powder at 800 times dilution, once every 10d, and the control effect reaches 80%.

The article comes from "Jilin Forestry Science and Technology", Vol. 38, No. 6, "Morphological Characteristics and Control Techniques of Chrysanthemum Downy Mildew"  Xue Junhua, Deng Zhigang, Guan Shuwei, Zhou Shengli