A.R. Chase |
1. Why is downy mildew a particular problem this winter? 2. So is downy mildew one of the worst diseases that growers face? 3. What are the symptoms of downy mildew? In some cases the flower spots (on rose) can easily be confused with Botrytis on flowers. On roses, downy mildew also can cause stem infections which appear as tiny red spots. Leaf drop overnight can be a clue that downy mildew is involved. This is common on some roses. 4. And the conditions that promote downy mildew? The optimal temperatures are wide for some downy mildew pathogens (snapdragon downy mildew), narrower for others (pansy downy mildew) and even relatively warm (coleus and salvia downy mildews). In general, the optimal temperature range is between 50°F-75°F (same as Botrytis). Poor air circulation which can occur in the closed winter greenhouse leads to very rapid downy mildew outbreaks. It is critical to never water late in the day, extend mist into the night unless absolutely necessary or spray fungicides more than twice a week. Each of these activities can result in immediate outbreaks. 5. What are common sources of downy mildew?
Fenamidone (FenStop) is not a strobilurin, but should not be rotated with a strobilurin due to potential for cross-resistance. Phosphonates (i.e., Aliette) remain very good choices for downy mildew control. Subdue MAXX has been used for years to eradicate downy mildew and is now legal for this use on ornamentals. Adorn provides very good control and it must be mixed with another downy mildew fungicide when used for this disease. FYI:
Have a question? You can write Ann at archase@chaseresearch.net. |
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