I got a call from a consultant in regards to keeping Botrytis (gray mold of vegetables) in onion under control. The pictures below show some symptoms of white leaf spots on the onion leaves.
All of the rain we have had has made it optimal conditions for rapid disease spread by way of increased moisture and humidity. Botrytis also has other symptoms such as, stem cankers, bulbs and tuber rots. Botrytis colonizes on weakened and dead tissue and survives on decaying plant material. Severe symptoms of Botrytis as shown on these leaves can lead to reduced bulb size.
It is very important that we stay timely and implement sound fungicide programs since we are dealing with favorable disease spreading conditions. Based off of these field symptoms, Dr. Bhabesh Dutta with UGA recommended these products: Inspire Super, Omega 500, and Luna Tranquility.
Attached is the 2019 Onion fungicide program. (Dr. Bhabesh Dutta, Extension Vegetable Pathologist)
The effective management of onion diseases begins prior to planting. By using integrated
methods such as disease-free seed and transplants, proper crop rotation, disking and deep
ploughing of plant debris, and use of resistant varieties, growers can minimize the amount of
disease epidemic by either reducing the amount of initial inoculum or the rate of disease
development. Integrated use of management practices reduces the weight on individual
management option and provides growers disease management options at lower risk. Chemical
management using fungicides should be the last resort after using the other management options.
Most of the fungicides are effective when used as protectants, only handful of fungicides have
curative actions.
Spray Schedule = 7 day
Two weeks after transplanting: Overhead drench application of Fontelis/RHIZ, WM, PR + Copper fungicide (foliar pathogens)
1 2Chlorothalonil/BNR, BLB, PB/ BLB, PB
2 Pristine or Merivon or Fontelis/BLB, BNR, SLB, PB
3 Chlorothalonil/BNR, BLB, PB/ BLB, PB
4 Pristine or Merivon or Fontelis or Scala/BLB, BNR, SLB, PB; (Scala do not
have activity against SLB)
5 Chlorothalonil/BNR, BLB, PB/ BLB, PB
6 Pristine or Merivon or Fontelis/BLB, BNR, SLB, PB
7 Chlorothalonil/BNR, BLB, PB/ BLB, PB
8 Scala or Luna tranquility or Inspire super or Omega 500 or Quadris top or
Switch or Zing!/BLB, BNR, SLB, PB (Omega 500 and Scala do not have SLB
activity)
9 Chlorothalonil/BNR, BLB, PB + ManKocide (bacterial blight)
10 Scala or Luna tranquility or Inspire super or Omega 500 or Quadris top or
Switch/BLB, BNR, SLB, PB (Omega 500 and Scala do not have SLB activity)
11 Chlorothalonil/BNR, BLB, PB + ManKocide (bacterial blight)
12 Scala or Luna tranquility or Inspire super or Omega 500 or Quadris top or
Switch/BLB, BNR, SLB, PB (Omega 500 and Scala do not have SLB
activity)+ Pristine or Merivon or Fontelis or Scala/BLB, BNR, SLB, PB;
(Scala do not have activity against SLB)
13 Chlorothalonil/BNR, BLB, PB + ManKocide (bacterial blight)
14 Scala or Luna tranquility or Inspire super or Omega 500 or Quadris top or
Switch or Zing!/BLB, BNR, SLB, PB (Omega 500 and Scala do not have SLB
activity)
15 Chlorothalonil/BNR, BLB, PB + ManKocide (bacterial blight)
2
16 Scala or Luna tranquility or Inspire super or Omega 500 or Quadris top or
Switch/BLB, BNR, SLB, PB (Omega 500 and Scala do not have SLB activity)
The fungicide spray for downy mildew (DM) will be based on a forecasting model. Alerts for
the DM spray will be communicated by the Vidalia Onion and Vegetable Research Center and
the UGA, Tifton. Fungicides with some degree of efficacy on DM are: Reason, Zampro,
Orondis Opti and Omega 500.
1Please use the labeled rate of recommended fungicide. Rotate fungicides for good disease
control.
2Chlorothalonil (Bravo, Echo, Equus etc)
Disease acronyms: BNR=Botrytis neck rot; BLB=Botrytis leaf blight; PB=Purple blotch;
RHIZ=Rhizoctonia root rot; WM=White mold; PR=Pink root; SLB=Stemphylium leaf blight;