An apparent new strain of dollar spot has reared its ugly head across parts of the upper Midwest this season. It looks like any other dollar spot, but it seems to be very aggressive and it does not respond well to the more traditional control fungicides. Fungicides like Iprodione and Chlorothalonil, either used separately or in combinations, have been the old standbys for dollar spot, but neither chemical has been effective in battling this apparent new strain. The cost of applying these two chemicals is around $80 per acre according to most superintendents. However, they have now been forced to go to more expensive chemicals that cost up to $140 per acre to get even minimal control.
That is the bad news. The good news is that the disease has been either relatively easy to control or nonexistent on turf that has been on a regular Nature Safe program. In some instances, Nature Safe turf that did not receive any fungicide applications had much less disease than nearby turf that had received applications of fungicide. At one golf course in Michigan, the superintendent had divided one fairway to trial Nature Safe next to his standard synthetic product. He applied Iprodione fungicide at the rate of three ounces per thousand to the side of the fairway that was fertilized with the synthetic product. On the Nature Safe side he made two applications (June and August) of 10-2-8 and did not apply any fungicide. As you can see from the pictures taken in early October, the Nature Safe side suffered very little damage from dollar spot while the side that had synthetic fertilizer plus Iprodione was severely infested.
While dollar spot is a problem almost every year, it seems to intensify every two or three years and becomes a major problem. This seems to be the year it is gearing up to cause major problems and it seems to have acquired some resistance to the fungicides. That could mean that we are going to have continuing problems next year and beyond. A regular Nature Safe program, even at lower rates, is the best way to combat this problem and to help insure quality turf in the future. While pathogens can develop immunities to fungicides they cannot develop immunity to the beneficial organisms that compete with them. It is the high level of amino acids in Nature Safe that feed the beneficial organisms and helps them to fight the pathogens and suppress the various diseases. Now is the time to get started on a Nature Safe program. If you wait until this resistant strain of dollar spot catches up with you, it will be too late to avoid some turf damage.