We have confirmed Downy Mildew of Vidalia Onion today in the growing region today. I am urging growers to please take precautions and protect their crop from this disease! Here are your control options, based on the most recent (2018) UGA research data. I want to provide some options and how I rank them in terms of potential. I use these as a TIER system of better products to somewhat beneficial. Remember, a good downy spray program includes rotating chemistries and not relying solely on one product. A good spray program can include products from all of these “tiers”.
TIER 1: (Most reliable,based on UGA data)
Orondis Ultra: Active ingredients are Oxathiapiprolin + Mandipropamid (Revus). In last year’s trial it was a top performer. This product would be a good fit if you have an active outbreak, or for preventative use. It has curative activity.
Bravo: Chlorothalonil alone has done well in UGA trials at preventing/and protecting from downy. However, due to the active find of downy in the area, growers should not rely on it alone. It can be tank mixed with the other fungicides to increase protection.
TIER 2: (Moderate/Good)
Orondis Opti: Active Ingredients Oxathiapiprolin + chlorothalonil (Bravo). Showed good results, did not do as well as Orondis Ultra or Bravo alone. Contains curative and protectant active ingredients
Zampro: Active ingredients Ametoctradin + Dimethomorph. Showed good efficacy last year.
Omega 500: Active ingredient Fluazinam. Showed good efficacy last year, also good for other diseases as well.
**Reason: In the past, Reason was a top tier product. Last year’s data does not support this recommendation. We are changing our ranking of the product based on the most recent UGA data.
TIER 3 (Some benefit):
Phosphoric Acid: Phosphoric acids such as Phostrol, ProPhyt, KPhite, and others have shown to be slightly effective at preventing downy in some studies. They are a cheaper option, and have some benefit to the overall fungicide program.
Maneb: Dithane, Pencozeb, etc… the maneb products are listed as somewhat effective. I wouldn’t count on much help if we get to the point of seeing downy, but they may be offering some prevention.
Take a look at these recent blog posts to find out more on downy mildew of onion:
UGA Onion Downy Mildew Control