Strategies to Control Powdery Mildew: Part 2

This blog is Part 2 of two blogs written on Strategies to Control Powdery Mildew: Part 1, largely extracted from an article written by Wayne Wilcox in the March, April 2003 issue of Practical Winery and Vineyard Journal called Strategies to Control Powdery Mildew.¹
Compounds used to control powdery mildew can be classified into the following groups as illustrated in this figure from the Dow AgroSciences website, and the PDF Managing Powdery Mildew in Grapes (CA).²

The above figure contains an acronym, FRAC which stands for Fungicide Resistance Action Committee and the following link provides information regarding FRAC Code List ©*2013: Fungicides sorted by mode of action (including FRAC Code numbering.) The following table is a summary of the chemicals available to control powdery mildew:^1,3

FRAC CODE	Pros	Cons
M i.e.Sulfur	Generally considered as a low risk group without any signs of resistance developing to the fungicides Cheap and effective Is a contact fungicide Protects existing foliage	Acts largely through the vapor phase and is temperature sensitive Inactive below 65 oF Phytotoxic at temperatures above 85 oF
3 i.e.DMI (DeMethylation Inhibitors)	Provides significant post infection activity PROTECTIVE and CURATIVE activity on powdery mildew	Declining efficacy due to increased resistance
11 i.e.Qols (Quinone outside Inhibitors)	Excellent protectant fungicides Best when present on the foliage or fruit before a spore lands and tries to infect Show significant “anti-sporulant” activity Provides some post-infection control against PM	Possibly more dangerous in terms of future resistance development High risk
13 i.e. aza-napthalene; Quintec is the only member of this class	Ability to redistribute across expanding leaf and berry tissues after application Can protect parts of the leaves and bunches that may not have received direct spray coverage Can protect grapes from powdery mildew for up to 21 days	Resistance to quinoxyfen known Medium risk
NC i.e. biologicals	Uniquely susceptible to topical applications of numerous alternative products (oils, potassium salts, hydrogen peroxide)	Appear to act primarily as temporary eradicants, with little or no protective activity against new infections Resistance not known

This is a lot to process and I'll be looking at more online information to get a better understanding of all of the available powdery mildew control agents, how to use them and what is the best chemical(s) to use for a vineyard trying to be organic.

References:
1. Wayne Wilcox, Strategies to Control Powdery Mildew, Practical Winery and Vineyard Journal, March, April 2003.
2. Managing Powdery Mildew in Grapes (CA).
3. FRAC Code List ©*2013: Fungicides sorted by mode of action (including FRAC Code numbering.)