In response to this disease outbreak, it may be advisable for growers and landscapers to limit impatiens orders for spring sales and use begonias or New Guinea impatiens as replacement plants as these are not susceptible to infection. If plugs are coming from Florida growers, supplies of impatiens may be limited. We don’t know how the disease will progress during our hot, summer months; however, past experience with this disease in a few states suggests that the pathogen stops producing spores and infecting plants during hot weather. One of the main concerns for growers is that although they may be able to reduce infection and symptom development within their operation through preventive fungicide applications, once these plants go out into the landscape, the disease may cause severe losses for their customers in the spring and fall as fungicide use is often not continued in landscapes. Impatiens downy mildew infection can be reduced through fungicide drenches (28-day interval) or sprays (7-day interval) of Subdue MAXX (mefenoxam), Adorn (fluopicolide), Vital (potassium phosphite), Protect T/O (mancozeb), Pageant (pyraclostrobin + boscalid), Disarm (fluoxastrobin), Segway (cyazofamid), Stature SC (dimethomorph), FenStop (fenamidone) and Heritage (azoxystrobin) plus Capsil as a surfactant. Aliette (fosetyl-Al) has not provided control of this disease in several trials. Fungicide resistance development is a real concern for downy mildew diseases, so rotate fungicides making no more than two consecutive applications of the same fungicide or a fungicide with the same mode of action (with the same FRAC code).
Since most downy mildew diseases are blown northward from southern regions during storms, it may be only a matter of time before this disease shows up in Georgia and other southeastern states. If you have questions, please contact me at jwoodwar@uga.edu.
