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. It is one of the major diseases of chrysanthemums. So what morphological characteristics and control methods does chrysanthemum downy mildew have? Let us follow forestry experts to understand these issues.
I. What is chrysanthemum downy mildew?
The pathogen of chrysanthemum downy mildew (Peronospora radiide Bary) belongs to the Fungi, Mastigomycotina, Peronospora genus, and is one of the major diseases of chrysanthemums. The pathogen is prone to causing disease under low-temperature and humid environments. When disease occurs in spring, white frost-like mold 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, later the lesions gradually turn purple-black, and white frost-like mold layers appear on the lesions on the back of the leaves. Under high temperature, they easily develop into yellow-brown lesions, and 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 stalk swollen, size 225.0-412.0μm×7.8-11.8μm, the main stalk is 1/2 to 1/4 of the total length, the crown is 3-7 times dichotomously branched, the apex is 2-3 times dichotomously branched, at right angles or acute angles, terminal branches 7.8-11.8μm long, slender at the end, slightly thicker at the base, the tip of the terminal branch bluntly rounded, slightly swollen, or hyphae white, sporangiophores branched 3-5 times, the first branching asymmetrical, size 286.0-707.0μm×9.0-16.0μm, main stalk 192.0-473.0μm long, terminal branching nearly at right angles, 7.8-15.7μm long, straight or curved, pointed at the end. Sporangia light brown, oval, 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 Calendula officinalis, Helichrysum bracteatum, and Tagetes erecta.
2. Seed treatment: Before sowing, seed 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 600 times dilution, and the control effect reaches 70%; spray with 60% Mieke wettable powder 800-1000 times dilution and 65% zineb wettable powder 500 times dilution, and the control effects reach 85% and 90% respectively; spray with 69% Anke · mancozeb wettable powder 800 times dilution, once every 10d, and the control effect reaches 80%.
The article comes from "Jilin Forestry Science and Technology", Volume 38, Issue 6, "Morphological Characteristics and Control Techniques of Chrysanthemum Downy Mildew" Xue Junhua, Deng Zhigang, Guan Shuwei, Zhou Shengli