Beware of the DMI Fungicides

As temperatures climb in the southeast US, it is time to put the DMI fungicides on the shelf until fall. All of them.

The DMIs can cause significant damage to bentgrass and bermudagrass putting greens if temperatures exceed 90 degrees after an application is made. Note that the temperature at the time of application is not important, it is the weather in the days and weeks after an application that leads to problems.

The DMI fungicides include Banner, Bayleton, Eagle, Rubigan, Tourney, Trinity, and Triton.

All of the DMIs have growth regulating properties. The effects are minimal when the turf is healthy and actively growing, but significant thinning of the canopy can occur during hot weather, even on otherwise healthy turf. Combine a DMI application, hot weather, and severely stressed turf and the consequences can be disastrous.

Several new DMI fungicides have been released in the last two years, and many of them are promoted as "safe". Admittedly, they are safer, but by no means are they safe. Severe damage has been observed where these new DMIs were applied to stressed cool-season grasses prior to or during hot weather. We have also observed that these new DMIs are more injurious to bermudagrass than the older DMIs. Tourney, Trinity, and Triton are not labeled for application to bermudagrass greens for this reason.

Most golf course superintendents in the southeast don't need DMIs during the summer anyway. Effective alternatives are available for control of most diseases, but anthracnose is an exception. Many superintendents with older bentgrass varieties or Poa annua greens battle this disease, and most anthracnose populations have become resistant to the QoI and benzimidazole fungicides. If you are in this situation, you pretty much have to use a DMI. The newer DMIs (Tourney, Trinity, and Triton) are very effective against anthracnose and should be worked into a preventative anthracnose program. Just be sure to use low rates, tank-mix with chlorothalonil to prevent algae invasion, and do not apply more than once a month to minimize the potential for injury.