How to prevent and treat downy mildew in zinnias? A detailed guide to practical methods

Zinnia is also known as zinnia and step-up-high, among other names, and is an annual herbaceous flower of the genus Zinnia in the Asteraceae family. It originated in Mexico. The flowers are relatively large, richly colored, distinctive in shape, and have a long flowering period, and it is now cultivated in various places. In zinnia breeding research and cultivation production practice, one of the most important diseases newly discovered is zinnia downy mildew, now reported as follows:

1. Symptoms

The pathogen of zinnia downy mildew belongs to the phylum Mastigomycotina fungi, and it can occur at the zinnia seedling stage, adult plant stage, and flowering stage. When the disease occurs at the seedling stage, it causes the seedlings to turn yellow and then die. When true leaves are affected, it mostly starts on the underside of the lower leaves, initially producing water-soaked light yellowish-brown spots with inconspicuous edges; after the water-soaked lesions persist for a relatively long time, white mold grows on the diseased parts when humidity is high or dew is present, or angular lesions form. Generally, light green spots first appear on the leaf surface and gradually expand into water-soaked yellowish-brown areas, turning brown after withering and death; the lesions are restricted by the leaf veins and appear irregular or angular. Zinnia downy mildew is spread by sporangia (or zoospores) through wind and rain, airflow, or irrigation water, and spreads rapidly. In severe cases, or if timely and effective control is not obtained after onset, the entire field and all seedlings can become infected, resulting in no harvest.

2. Prevention and control methods

1) First, select disease-resistant varieties.

2) Carefully select seeds and disinfect seeds. Keep seeds from disease-free plants, or before sowing, dress seeds with 25% metalaxyl wettable powder at 0.3% of seed weight.

3) Implement crop rotation on the plot for more than 2 years.

4) After harvesting the previous crop, remove diseased leaves and clean the field.

5) When applying additional fertilizer and water, do not flood-irrigate so that it overflows and flows everywhere.

6) Nutrient pots used again can be soaked in a 200-fold solution of 58% metalaxyl? mancozeb wettable powder.

7) After finding central diseased plants in the field, the first choice is spraying for control with 800-fold solution of 25% ridomil wettable powder, 200-250-fold solution of 40% fosetyl-aluminum wettable powder, 700-fold solution of 75% Shuangba wettable powder, 500-600-fold solution of 72% Shuangyiqing or 56% Shuangmeiqing wettable powder, 500-fold solution of 58% metalaxyl? mancozeb wettable powder, or 500-fold solution of 70% mancozeb wettable powder, once every 7-10 days, for 2-3 consecutive treatments.