Fungicide mode of action table. 29

Turf Fungicide Mode of Action Table

Turf fungicide resistance refers to the ability of fungal pathogens that infect turfgrass to survive exposure to fungicides that would normally kill or inhibit their growth. This can occur when a population of fungal cells develops genetic mutations that allow them to tolerate the fungicide. These resistant cells are able to survive and reproduce and over time, the proportion of resistant cells in a fungal population can increase, making it more difficult to control the fungus with the fungicide. This fungicide mode of action table is to help delay the onset of fungicide resistance.

Turf fungicides are commonly used to control diseases such as dollar spot, brown patch, and fairy ring. The same principles of disease control apply to both professional turf managers and home lawn owners. However, the overuse or improper use of fungicides can lead to the development of fungicide resistance in fungal populations. This is managed by rotating fungicides with different modes of action, using fungicides in combination, and using cultural practices to reduce fungal populations. Cultural practices include irrigation management, fertilization, mowing, and aeration.

Fungicide Rotation.

Fungicide rotation is a strategy used to manage fungicide resistance in which different fungicides with different modes of action are used to prevent the build-up of resistance in fungal populations. The IGFH Guide to Australian Turf pesticides goes into more detail on this topic but the following is a summary.

Fungicides have different modes of action, which refers to the way in which they kill or inhibit the growth of fungal pathogens. So for example azoxystrobin fungicide mode of action differs from that of chlorothalonil.

By rotating fungicides with different modes of action, the likelihood of a fungal population developing resistance to a single fungicide is reduced. This can be achieved by alternating between fungicides with different modes of action during a single season, or by using fungicides with different modes of action in successive seasons. 

Fungicide rotation can be used in combination with other resistance management strategies, such as using combination fungicides like Lexicon Intrinsic and cultural practices to reduce fungal populations. It’s important to keep track of the fungicides that you use and the timing of their application to ensure that rotation is effective.

Fungicide resistance can develop quickly, so use fungicides responsibly and in rotation with other products and management practices. It’s also important to monitor for resistance and to adjust management strategies accordingly.

Australian turf fungicide mode of action table

Fungicide Resistance management plan for turf.

Single site turf fungicides are at a medium to high risk of developing resistance. Being single-site means they act at a specific point in the pathogen. Multi-site fungicides are mostly contacts such as Squadron Weatherace and have a variety of different target sites. This means there is less of a resistance risk as more changes are required in the pathogen for resistance to occur.

Rotate.

Do not use site specific fungicides from the same group more than twice in a row. This also applies if your are using premix combination fungcides such as QualiPro Enclave.

In an ideal situation aim to use multisite fungicides as often as possible, as they have low to no risk for resistance.

Interestingly, CropLife has published the following resistance guidelines specific to turfgrass.

1. Groups classified as medium to high risk for fungicide resistance development; Groups 1, 2, 4, 7 (N3), 11 and 21 should be rotated as a key means to reduce the development of resistance.
2. Do not apply consecutive sprays from the same activity group, unless mixed with a registered fungicide from a different mode of action group with no known resistance.
3. Group N3 nematicides are also classified as Group 7 fungicides and consecutive application should be avoided, even if targeting different pests/pathogens.
4. If consecutive sprays are applied from a high-risk fungicide group (i.e. Group 1, 2, 4, 7, 11 or 21) they must be followed by at least the same number of applications of fungicide(s) from a different group(s) before the same high-risk fungicide is used again.

Apply the correct rates.

On so many occasions we have seen turf managers change the rates of application as it “didn’t work last time”. This is a big no no. Stick to the label rates.

Practice integrated disease management (IPM).

Don’t just say you do it. Actually do do it! IPM practices will break any disease cycle. Increasing air flow, reducing turf stress and using resistant cultivars of bentgrass or ryegrass can save you a lot of money in the long term. I would also consider products such as salicylic acid into any IPM plan as these will also counter any resistance issues. This product is contained in the turf pigment Vertmax Duo.