A killing frost in sunflowers is considered to be –4C to –5C for 6 or more hours.
Although we have had a frost, we have not experienced a killing frost yet in Manitoba. So, the current cold nights have not been cold enough to substitute for a desiccation.
A desiccant may still be considered, if no other frost is is the forecast, but as we have now gotten cooler, plant metabolism has slowed down. The plants are not metabolizing the harvest aid desiccant products as quickly and dry-down will take longer.
To optimize the benefits of applying a desiccant, it is necessary to look at the weather forecast for the next week.
How cold will it get? If a frost below –4C is expected, a desiccant might not be required
How warm will it get? Desiccants perform much better if applied in temperatures >20 C
Applications to healthy green plants will provide optimum results. Since we have had a lack of morning dew lately, it is extremely important of maintain water volumes to get proper coverage.