Review of Spring Dead Spot and Large Patch Trials From 2021-22

— Written by Jim Kerns — Contributors: Lee Butler | May 31, 2022

Each year our program conducts 60 to 75 fungicide trials on various turfgrass diseases. Fall disease management trials focus on diseases of warm-season grasses and those diseases include spring dead spot and large patch. As promised from social media, this post will detail the results from our spring dead spot and large patch trials from fall 2021 into spring of 2022. However, before focusing in on the details of these 8 trials, we should spend a minute discussing application strategies for these two diseases.

For spring dead spot, we suggest making preventative applications when soil temperatures decline to 70^oF, which typically has been late September to early October in Raleigh, NC. Follow up applications should be made 21 to 28 days after the initial application. Based on some of our trials, it seems like 21 days is the more appropriate re-application timing. All of our spring dead spot treatments are irrigated in immediately with 1/8 inch of water to ensure that the fungicides are getting to where the pathogens reside.

Preventative large patch applications for St. Augustinegrass and centipedegrass should be initiated when soil temperatures decline to 80^oF which is typically in late August or early September in Raleigh, NC. For zoysiagrass, the preventative applications should start when soil temperatures decline to 70^oF. In order for these fungicides to be successful, they need to be applied in at least 88 gallons/acre (2 gallons/M). The large patch pathogen attacks the leaf sheath, therefore more water in the spray tank is necessary to ensure the fungicide is getting on target. Our research continues to indicate that fall applications are most critical for suppression of large patch in the Carolinas. Spring applications may be necessary in cool-wet springs and can compliment a strong fall based application program.

2021-22 Spring Dead Spot & Large Patch Trials

Line graph "Large Patch 2021-2022" showing percent large patch over dates for four treatments — In zoysiagrass, Densicor under extreme large patch pressure reduced large patch severity. Mirage performed better in this trial. Do note that this trial area was severely affected with large patch, so this trial like many of the trials we conduct, was a worse case scenario. Both fungicides are labeled for golf course turf only.

Large Patch 2021-2022: bar charts comparing area under disease progress curve and turf quality curve — In St. Augustinegrass, Densicor under extreme large patch pressure reduced large patch severity. The 0.20 rate of Densicor was significantly better than the 0.13 rate. Mirage performed better in this trial. Do note that this trial area was severely affected with large patch, so this trial like many of the trials we conduct, was a worse case scenario. Both fungicides are labeled for golf course turf only.

Line chart titled "Large Patch 2021-2022" showing % Large Patch over dates for multiple treatments — In zoysiagrass, we tested experimental granular formulations of fungicides that suppress large patch as well as the sprayable formulations. Hopefully, these products will be on the market in the near future and available to all turf application sites.

Chart "Large Patch 2021-2022" showing % large patch by date; non-treated control peaks ~32% — In St. Augustinegrass, we tested experimental granular formulations of fungicides that suppress large patch as well as the sprayable formulations. Hopefully, these products will be on the market in the near future and available to all turf application sites.

Bar chart "Spring Dead Spot 2021-2022" showing % spring dead spot by treatment on 04/20/22 and 05/03/22 — In fairway height bermudagrass on native soil, all treatments suppressed spring dead spot compared to the non-treated control on 4/20/22. However, on our rating on 5/3/22, statistical separations weren't as clear, but the trends were very similar to the 4/20/22 rating date. This was likely due to the cool-dry April slowing the green-up of bermudagrass at the trial location. Conditions such as these present challenges when rating this disease. Take home message ... treatments containing Maxtima or Navicon performed well.

Spring Dead Spot 2021-2022 bar chart; Area Under Disease Progress Curve; Non-treated Control 1800 — On a sand based ultradwarf bermudagrass putting green, all treatments suppressed SDS when compared to the non-treated control throughout this study. Maxtima (0.8) and Kabuto (1.2) provided the best suppression of SDS in this trial.

Bar chart "Spring Dead Spot 2021-2022" showing % spring dead spot by treatment on 04/20/22 and 05/10/22 — On a sand based ultradwarf bermudagrass putting green, all treatments suppressed SDS when compared to the non-treated control on both rating dates. Kabuto and Maxtima have perennially been excellent performers for suppression of SDS. This trial is interesting because it documents that a single rate of Kabuto (3.2) provides excellent suppression of SDS. Moreover, an experimental granular formulation of a fungicide provided excellent control of SDS as well.

Spring Dead Spot 2020-2022 bar chart: Non-treated Control large AUC; Posterity 0.24 treatments near zero — On a sand based ultradwarf bermudagrass putting green, all treatments suppressed SDS when compared to the non-treated control throughout this study. Regardless of application timing, Posterity performed very well during this 2-year study.