{"id":43,"date":"2019-02-20T12:49:11","date_gmt":"2019-02-20T17:49:11","guid":{"rendered":"http:\/\/site.extension.uga.edu\/vidaliaonion\/?p=43"},"modified":"2019-02-21T10:33:00","modified_gmt":"2019-02-21T15:33:00","slug":"downy-mildew-forecast-model","status":"publish","type":"post","link":"https:\/\/site.extension.uga.edu\/vidaliaonion\/2019\/02\/downy-mildew-forecast-model\/","title":{"rendered":"Downy Mildew Update"},"content":{"rendered":"
\"\"
Downy Mildew sporulation on a Vidalia Onion leaf in 2018.<\/figcaption><\/figure>\n

It’s that time of year again when we start to worry about Downy Mildew (Peronospora destructor<\/em>) on our onions.\u00a0 As of this time, none has been reported to me in the Vidalia area.\u00a0 Growers need to be vigilant in protecting their onions against this disease.\u00a0 We have used a “Forecast Model” for the past several years to help warn growers when conditions are favorable for disease development.\u00a0 This model is paid for by the growers and tracks weather conditions at several locations in the Vidalia Onion growing region.<\/p>\n

Last week, the week of February 11th-15th, the forecast model gave us a “warning” that conditions were favorable for Downy Mildew development.\u00a0 This does not necessarily mean that Downy Mildew is present, but if it was, conditions are favorable for it to reproduce and spread rapidly.<\/p>\n

So what does this mean to you as a grower?\u00a0 It means that we need to take precautions for this disease.\u00a0 If you haven’t already, you may want to make sure you have products to spray that will protect against this disease, and make sure you are using them in your spray program.<\/p>\n

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Here is a graph showing what the model is predicting. Anything over a “7” triggers a warning that conditions are favorable for disease development.<\/figcaption><\/figure>\n

So what do we need to be using to protect our onions from Downy Mildew?\u00a0 Below is a summary of last year’s research trials, conducted by Dr. Bhabesh Dutta.\u00a0 He shared this information at the last grower production meeting:<\/p>\n

\"\"
This is a summary of Dr. Dutta’s Downy Mildew research trials in 2018 at UGA. In the column to the far right, the lower the number, the lower the disease incidence for that treatment.<\/figcaption><\/figure>\n

Let’s explain your options, based on the most recent (2018) UGA research data.\u00a0\u00a0I want to provide some options and how I rank them in terms of potential.\u00a0 I use these as a TIER system of better products to somewhat beneficial.\u00a0 Below are the products and a brief justification.\u00a0 Hopefully this information can be utilized to help you make a decision for your spray program.\u00a0 Remember, a good downy spray program includes rotating chemistries\u00a0 and not relying solely on one product.\u00a0 A good spray program can include products from all of these “tiers”.<\/p>\n

TIER 1: (Most reliable,based on UGA data)<\/strong><\/em><\/p>\n

Orondis Ultra<\/strong>:\u00a0 Active ingredients are Oxathiapiprolin + Mandipropamid (Revus). In last year’s trial it was a top performer.\u00a0 This product would be a good fit if you have an active outbreak, or for preventative use.\u00a0 It has curative activity.<\/p>\n

Bravo<\/strong>:\u00a0 Active ingredient chlorothalonil.\u00a0 This product also did really well in last year’s trial.\u00a0 Bravo does not have curative activity, but it has good protectant<\/strong><\/em> qualities.<\/p>\n

***Note about Bravo:\u00a0 I don’t want there to be any confusion about our Bravo recommendation.\u00a0 Bravo has been used for many years on onions and other crops and has a lot of value in a fungicide spray program.\u00a0 While Bravo performed very well in this test, keep in mind that it was sprayed each week on those onions.\u00a0 I like to think of Bravo as a “coat of paint” or “protective barrier” that keeps disease from developing on the leaves.\u00a0 However, this protective barrier is only as good as your spray coverage and only lasts so long.\u00a0 It gets washed off and broken down by rain, irrigation, and sunlight.\u00a0 In this trial a constant “coating” of Bravo was maintained on the leaves during the test, and it worked well.\u00a0 However, most growers may not be able to spray their onions every week and may only apply Bravo every 14 or 21 days.\u00a0 Bravo works as a protectant\/preventative for disease.\u00a0 Do I think Bravo is a good option use in downy prevention? Yes.\u00a0 And it can be applied with some of the other products, such as a Phosphoric acid, for an economical preventative spray.\u00a0 Am i saying that we should rely on Bravo solely for downy prevention?\u00a0 No.\u00a0 If we had an active outbreak of downy, I would recommend using the Orondis or Zampro or Omega 500 as a go to.\u00a0 However, it could be tank mixed with some of these products.<\/p>\n

 <\/p>\n

TIER 2: (Moderate\/Good)<\/strong><\/em><\/p>\n

Orondis Opti<\/strong>:\u00a0 Active Ingredients\u00a0Oxathiapiprolin + chlorothalonil (Bravo).\u00a0 Showed good results, did not do as well as Orondis Ultra or Bravo alone.\u00a0 Contains curative and protectant active ingredients<\/p>\n

Zampro<\/strong>:\u00a0\u00a0 Active ingredients Ametoctradin + Dimethomorph.\u00a0 Showed good efficacy last year.<\/p>\n

Omega 500<\/strong>: Active ingredient\u00a0Fluazinam.\u00a0 Showed good efficacy last year, also good for other diseases as well.<\/p>\n

 <\/p>\n

**Reason<\/strong>:\u00a0 In the past, Reason was a top tier product.\u00a0 Last year’s data does not support this recommendation.\u00a0 We are changing our ranking of the product based on the most recent UGA data.<\/p>\n

 <\/p>\n

TIER 3 (Some benefit):<\/strong><\/p>\n

Phosphoric Acid<\/strong>:\u00a0\u00a0Phosphoric 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.<\/p>\n

Maneb<\/strong>:\u00a0 \u00a0Dithane, Pencozeb, etc\u2026 the maneb products are listed as somewhat effective.\u00a0 I wouldn\u2019t count on much help if we get to the point of seeing downy, but they may be offering some prevention.<\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

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