Downy mildew is a fungus disease caused by Peronospora parasitica, and also cause damage to other crucifer crops such as broccoli, cauliflower, cabbage, and Brussel sprouts. Infection can be seen in any stage of crop development. Cool, high humidity, fog, drizzling rains, heavy dew and moist weather gives an invitation to the disease. Fungus spore production increases by temperatures cooler than 12-27 C i, e in the early spring-fall or in prewinter season. and neutral to acidic soil 5-7.0 ph. Downy mildew causes poor growth and reduces yield and quality of produce at later stages.
Downy Mildew Identification.
The symptoms start appearing on the upper surface of the leaves. On the upper side of the leaves, you can see irregular yellow patches while in the lower side grey molds can be visible during the moist and cool condition but in the dry condition, it becomes brown and papery. Generally in the mature crop, the symptoms are more visible in the lowermost leaves which are near to the ground. In the moist condition, the patches grow faster & larger and joints with other patches and appear as large dead patches. The common stage of symptoms development is on seedbed. Leaf wetness of 4-6 hours at 20°C and 6-8 hours at 15°C are necessary for significant infection and development of downy mildew.
Downy Mildew Spreading Agent.
Insects, wind, rain or garden tools.
Cabbage Downy Mildew Damage.
As the disease grows you can see brown to black, sunken, angular, pepper-like on the upper leaves. Heavy lose can be seen on the seedlings, cotyledons and hypocotyls i e the early stage of development. The small, angular, irregular lesion develops on the mature plant's leaves and flowering branches. Infected heads have pale brown to grey discoloration occurs on the surface of the head and it deteriorates rapidly. On the stem areas, black streaks can be visible. Infected tissues become susceptible to attack by secondary rotting organisms. Infected organs develop a black, epidermal blotch and an internal discoloration.
Control/Prevention for Cabbage Downy Mildew.
- Use resistant varieties for planting
- Keep nurseries free from weeds.
- Early morning irrigation helps in the low moisture contents.
- Use the correct amount of seedlings per bed for better airflow.
- Use the infected free seedling and remove the infected one as soon s you notice.
- If symptoms are seen, spray all the seedlings with a systemic fungicide.
- Chemical control Apply first spray as soon as seedlings appear the symptoms; apply 3 times a week until completely covering the plant.
- Remove the weeds (wild mustard, etc.)
- Intercrop culture with auriferous family crops.
- Remove the infected crop debris.
- Give 1- 2 ploughs after each harvest.