Disease Resistance Strategies

Three strategies exist for using fungicides, each with different potential for resistance. The first strategy is the continuous use of a fungicide or ones with the same mode of actions. If the fungicide is site-specific, as most fungicides are, continual use will result in strong directional pressure toward a resistant population. The more applications the quicker resistance will develop.


Figure 1.  Fungicides are a critical component for maintaining quality plying surfaces on golf courses.

The second strategy is alternating fungicides of different modes of action. Alternating fungicides can delay the appearance of resistance. The lack of a single fungicide mode of action reduces the selection pressure and depending on the resistant population fitness may allow for a recovery of the wild type population between subsequent applications. Alternating fungicides with similar modes of action has no advantage because once resistance occurs a fungicide it will also occur to the fungicide with a similar mode of action.

The third strategy is mixing, which is the combing fungicides from different mode of actions together. In delaying resistance, fungicides used in a mixture should each be an effective control of the targeted disease if used alone. Advantages to mixing include disease control is not left to one mode of action, and the chance of resistance are less compared to continuous or alternating strategies if total pathogen population levels are kept low.

Whether alternating or mixing fungicides, a key component is keeping the disease population low. In a small wild-type population, it more difficult for a resistant population to establish and dominate. Integrated management practices like resistant species and cultivars and cultural practices targeted to reducing the disease severity help reduce populations. Fungicides applied at dosages effective for disease control and where possible preventatively are less likely to seat lower disease population levels help maintain low disease population levels.

Effective turfgrass disease control and fungicide resistance strategies depend on an integrated management strategy. Below are the steps important in helping to develop a fungicide use and resistance program.

1. Identify the diseases of concern. Which of those diseases require a fungicide application(s) to control?
2. Of the diseases of concern, has research shown the disease(s) becomes resistant? For example, anthracnose, dollar spot, gray leaf spot, Microdochium patch, and Pythium blight are common turf diseases that have become resistant to certain families of fungicides
3. The fungicides available in the table below are broad spectrum controls except for Subdue MAXX^® fungicide which is specific for Pythium blight. Identify which products are labelled for control of the disease(s) you have identified that will require fungicide(s) treatment
4. From the products selected, outline a treatment program. From a resistant management perspective use mixtures or alternate fungicides with different mode of actions. Where appropriate mix or alternate with Medallion^® SC fungicide. Risk of resistance is relatively low
5. Practice good management practices both genetically and culturally, which helps reduce the number of fungicide applications needed. Additionally, reducing the pathogen population makes it more difficult for the resistant population to dominate
6. Where possible apply preventatively

Fungicide	Common Name	Family	Resistance	FRAC# - mode of action
Banner Maxx® II fungicide	Propiconazole	Sterol Inhibitor (DMI)	High	3 - C14- demethylation in sterol biosynthesis
Heritage® Action™ fungicide	Azoxystrobin	Strobilurins (Qol)	High	11 - Complex III of fungal respiration: ubiquinol oxidase
Headway® fungicide	Azoxystrobin + Propiconazole	DMI + Qol		11 + 3
Medallion	Fludioxonil	Phenlpyrrole	Low to moderate	12 - MAP protein kinase in osmotic signal transduction
Subdue MAXX	Mefenoxam	Phenylamide	High	4 - RNA polymerase I
Secure® Action fungicide	Fluazinam	Pyridinamine	Low	29 Uncoupler of oxidative phosphorylation
Ascernity® fungicide	Benzovindiflupyr + Difenoconazole	Succinate dehydrogenase inhibitors (SDHI) + DMI	Moderate to high	7 + 3

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