Dollar spot is on a rampage! If you’ve noticed an increase in dollar spot severity and persistence this year as compared to previous years, you’re not alone. Throughout New England, there have been numerous complaints of pesky dollar spot outbreaks that just can’t seem to be controlled with products that worked well in the past. Why is that?
As has been known, plant pathogenic fungi, including dollar spot, thrive under sufficient moisture and proper temperatures that promote mycelial growth and reproduction via spore germination. Thinking back to the Disease Triangle Concept, disease occurs when a susceptible host, virulent pathogen and favorable environment interact simultaneously. The more favorable the environment to the pathogen, the higher the disease pressure. Where disease pressure is high, management often becomes tricky.
There is no doubt that the New England region has been experiencing favorable environmental conditions for disease this year, with extended and frequent periods of rain and optimal temperatures. In fact, we haven’t seen dollar spot pressure this severe and persistent in quite a long time. While this increase in dollar spot has been exciting for scientists who aim to better understand the biology of this disease, golf course superintendents tasked with managing diseases to maintain good-looking turf are not having a very good time. Even with the availability of so many fungicide classes and products for dollar spot control, this beast is giving superintendents a run for their money. Fungicides that were working in previous years are now breaking through at much sooner intervals. But why?
One explanation is that under higher disease pressure than normal, dollar spot populations with resistance to one or more fungicide classes (DMIs, SDHIs, Dicarboximides, and/or Benzimidazoles) become increasingly more difficult to manage. For example, in a study being conducted at a golf course in CT, where dollar spot pressure is frequently severe and resistance to DMIs and SDHIs has been confirmed, this has certainly been the case. Out of 10 treatments applied (single DMI’s and multi-active ingredient mixture), only one three-way a.i. treatment (Posterity XT®: pydiflumetofen, azoxystrobin, propiconazole) provided acceptable control (highlighted in picture). During these situations, where pressure is high and fungicide resistance is in play, here are some recommendations:
- Incorporate multiple cultural practices (dew/guttation removal, no drought stress predisposed, balanced fertilization, dethatching) for decreasing favorable conditions
- Avoid application of any fungicide class where qualitative resistance has been observed (SDHIs, Dicarboximides, and Benzimidazoles)
- Use contact and multi-site, low-risk fungicides (chlorothanonil, fluazinum)
- If DMI fungicides are the only option available, use higher rates and shorter intervals
- Use tank mixtures of Insignia® (QoI) or Pinpoint® (QoI) with multi-site fungicides
- Use tank mixtures of SDHIs (except for Emerald®) with the two QoIs,
- Use tank mixtures of DMIs (Banner Maxx®, Torque®) with the two QoIs
- Use tank mixtures of DMIs (Banner Maxx®, Torque®) with SDHIs (except for Emerald®).
Unsure if you have a fungicide resistant dollar spot population? Send us a sample! We offer fee-based fungicide resistance testing. For more information, please contact Dr. Geunhwa Jung (jung@umass.edu).
Submitted by: Dr. Geunhwa Jung and Michaela Elliott, Research Associate
