Now entering the 'No DMI Zone'

Every year, we see a lot of golf course superintendents get into trouble by applying DMI fungicides to bentgrass or Poa annua putting greens during periods of hot weather. These products can cause severe damage to stressed cool-season grasses, and our general rule of thumb is that they should not be applied to putting green turf when temperatures above 90 are expected in the next two weeks. After a nice break in the weather late last week, temperatures are ramping up into the high 90's and I don't think we can count on seeing temperatures below 90 for quite some time.

There are few good reasons to apply a DMI fungicide during July and August anyway. Most of our summer diseases can be controlled very well with other chemistries that do not have these negative side-effects.

So, if you are considering an application of a DMI fungicide, ask yourself two questions: "Are my greens stressed? Are temperatures above 90 in the forecast?" If the answer to either of these questions is "Yes", then leave the DMIs on the shelf!

One exception is anthracnose; if you have Poa annua greens or older bentgrass varieties that are prone to anthracnose, a DMI application could be justified. The new-generation DMIs like metconazole, tebuconazole, and triticonazole have less injury potential on cool-season grasses and provide very good anthracnose control. Keep the rates low and tank-mix with chlorothalonil to minimize the chances for injury, thinning of the turf, and algae invasion.

Hit two birds with one stone using the DMIs

Although it's not yet officially spring, temperatures across North Carolina are becoming conducive to two common spring diseases: dollar spot and fairy ring. Now's the best time to initiate preventive fungicide programs for these diseases.

The dollar spot pathogen becomes active when low temperatures are consistently above 50ºF, especially when combined with heavy dew formation during the night. Looking at the forecast for the next week, low temperatures will remain in the low- to mid-50s for about another week in Wilmington, Raleigh, Greensboro, and Charlotte.

For greens established with creeping bentgrass, we recommend initiating preventive fungicide treatments for fairy ring when 5-day average soil temperature reaches 55ºF. Most of North Carolina will be hitting that mark over the next week as well.

Our recent research shows that the DMI fungicides, like Bayleton, Torque, Tourney, and Triton, are very effective for fairy ring prevention. These treatments, even though they are watered into the soil, will also provide excellent dollar spot control because the DMIs are translocated upward in the plant. So, in the current environment where everyone is looking to save money, the DMIs are an excellent way to control both dollar spot and fairy ring with one application!

For more information, please visit our disease profiles on dollar spot and fairy ring, or the Disease Management Utility for assistance in selecting a fungicide and application rate.

The best time for fairy ring prevention is near

Average daily soil temperatures in NC on March 6, 2011

The time for preventative fungicide applications for fairy ring control will be approaching over the next couple of weeks. Based on our field research, two applications of a DMI fungicide beginning when soil temperatures reach a 5 day average of 55F provides excellent control.

If you would like to monitor soil temperatures on your own, you can do so using the NC State Climate Office Advanced Map. For sandy soils or sand-based putting greens, the average daily soil temperature will be very close to the average daily air temperature, so you don't necessarily need a website or fancy weather station. Just take the average of today's high and low temperature, and when that number is at or above 55F for 5 straight days, it's time to pull the trigger!

For more information about fairy ring, including control recommendations, click here.