Downy mildew diseases cause significant problems in nursery seedlings, if not controlled.
- They are prevalent in cool wet months, but can occur all year around.
- The diseases generally don’t kill the plant; they make it look ill, uncared for and therefore unsaleable.
- Downy mildew diseases are found on many nursery seedling lines e.g. stock, brassicas, viola, anemone, onion and lettuce.
- The diseases are estimated to cause economic losses of 10-12% in production of ornamental and vegetable seedlings in nurseries, which are valued at $60 million nationally (32 million punnets).
- Crop loss estimates, made by growers suggest that losses due to downy mildews account for about $4 million in retail sales nationally.
This 28 page detailed publication, is designed to assist nursery managers better control downy mildew.
Control Strategies for Downy Mildews :
To control downy mildew on seedlings and in nurseries, integrate management strategies with fungicide sprays.
Keep all areas clean and weed free. Rogue out heavily infected seedlings as these provide a source of spores for subsequent infections.
Avoid watering seedlings in the mornings, when spores are released and available for infection.
Space trays of seedlings to improve ventilation. This will dry leaf surfaces off quickly to reduce leaf wetness and thus infection.
Maintain a balanced program of nutrition as a deficiency of potassium (K) will make seedlings (cauliflowers) more susceptible to the disease.
Apply fungicide protocols developed by Projects NY406 and NY97011 or
maintain a fungicide spray program consisting of registered fungicides when the
downy mildew disease is expected.
Monitor seedlings on a regular basis to detect downy mildew (at least once a week).
Isolate stock plants, especially when first introduced into the nursery.
The author thanks the following for their contributions to Downy Mildews on Nursery Plants.
Gray Harrison – Chemical Standards Branch
Ian Pascoe – Manager Crop Health Services
Bob Taylor – Nursery Consultant
Dr Peter Ridland – Research Scientist