Alternaria
After a prolonged cool and damp (but not wet) period, temperatures are about to rise dramatically. Combined with some frost damage and canopy stunting due to the long, cool period, this will greatly increase the risk of Alternaria leaf and stem blight. Hot and humid conditions are ideal conditions for infection and spread of the disease. The keys to good Alternaria control include:
- Apply a rotation of effective products. Using products with multiple modes of action or tank mixing effective products with different mobility in the plant (if permitted on the label and compatible) can help with disease control and resistance management.
- Ensure good spray coverage of all leaf surfaces and the stem. For more information, consult Spraying Ginseng on Sprayers101. The post rows, where coverage is often the poorest, are often the start of a disease outbreak. In 2-year-old gardens without a thick canopy, alternating the direction of travel of the sprayer can ensure areas that are difficult to reach may get at least some protection. Doing this in older gardens may cause damage to the canopy between the beds.
- Reduce plant stress by ensuring adequate ventilation of heat (raise side shades, open up vents at the top of hills within the garden) and timely irrigation to avoid drought stress. Delhi has only had 8 mm of rain in the past four weeks, so soil moisture may be an issue if there are no thunderstorms tonight or tomorrow before the heat arrives.
