Preventive Use of DMI Fungicides on
Golf Putting Greens (Article 3)
The HOW is NOW
Another weekend warm-up has most of Missouri into the appropriate soil temperature range for applying the first preventive DMI application to golf putting greens. Soil temperatures are crashing with the moderation to more spring-like temperatures. For our studies, we will be going out next week as a forecasted cool down should keep CoMO in the 55-60°F soil temperature range. On another note, models are indicating crabgrass germination in southern Missouri, so the time for pre-emerge applications is also definitely now. This is also a fantastic time to fertilize cool-season grasses.
THE WHO = Diseases targeted – Fairy Ring, Take-all Patch, Summer Patch, potentially Dollar Spot
THE WHAT – Low rates of fungicides in the DMI class including the 4 T’s (Triton, Trinity, Torque, Tourney) and Bayleton.
THE WHEN - First application when 2” soil temperatures average 55-60°F for five consecutive days. Second application 28 days later.
Next two weeks - (4/11-4/20).
THE WHERE - Golf putting greens
THE WHY – DMI fungicides are plant growth regulators, and should not be utilized in the summer heat on bentgrass putting greens. Curative applications may need to be applied repeatedly, and often result in more fungicide use.
THE HOW - Two applications 28 days apart. Do not tank-mix preventive fungicide with a wetting agent. Water in the application with 1/8” (preferably 1/4”) of irrigation immediately after application (preferred) or at least that night. Remember the pathogens we are targeting are in the soil, so put the fungicide there.
Two applications 28 days apart.
See last week’s report. I have gotten some questions regarding the label stating 21 d instead of 28 d intervals. We can only go on what we have tested, so I am not particularly sure if 21 days is too short an interval between the two sprays. If 21 d intervals are used, it may be prudent to make three applications instead of two to make sure you are not too early with the second dose. Keep an eye on the heat for the last application though, and don’t let the last application slip into June.
Without a doubt, this is the most confusing aspect of this fairy ring preventive strategy. The standard recommendation has always been to apply fungicides with a wetting agent to ensure delivery to the target zone. But this is a recommendation for curative applications. In figure A below, data from Dr. Bruce Martin at Clemson University shows that fungicides applied curatively without a wetting agent provide inadequate control as compared to those with a wetting agent. This makes sense as fairy ring fungi produce a hydrophobic mat layer, which restricts the movement of water and fungicide through the soil profile. The wetting agent helps break through this hydrophobic layer and puts the fungicide in the target zone.
Our research at North Carolina State suggests the direct opposite for preventive applications. Tank-mixing a wetting agent consistently reduced the efficacy realized from the two preventive applications. Why? The preventive fungicide is being applied before the hydrophobic mat layer is produced by the fairy ring pathogen. The theory is that tank-mixing a wetting agent with the preventive application may move the fungicide too far through the target zone, and potentially diminish fungicide adherence to soil particles or organic matter. On two rating dates (out of two years of study), we also noted some minor, short-lived phytotoxicity with the two Bayleton applications. This phytoxicity was significantly higher in plots where Bayleton was tank-mixed with the wetting agent than in plots where Bayleton was applied alone.
An additional, important note regarding wetting agent applications. This absolutely does not mean to forego wetting agent applications during spring. In figure B above, you’ll notice two control plots that did not receive a fungicide application; one a true untreated control and the other that had two applications of the wetting agent Revolution. Note how much lower the fairy ring severity is in the Revolution alone plots as opposed to completely untreated. I don’t have a true explanation, but the data clearly suggests that wetting agents should still be applied on their normal schedule, just not tank-mixed with the preventive fungicide applications. The suggestion is to apply the initial preventive application, 14 d later wetting agent, 28 d later second preventive fungicide application. This is also true for PGR applications like Trimmit, since the DMIs are related to some of these chemistries and can have regulating properties.
Irrigation Amount & Timing
In all of our trials, we standardized the irrigation amount to 1/4", which definitely soaks in the preventive fungicide (see picture above). It may be possible to use 1/8” to deliver the preventive fungicide since most fairy ring pathogens are in the top 2” of the green profile where the organic matter (food source) is most abundant. However, this has not been determined in a replicated research trial.
After the initial release of our preventive recommendation, we repeatedly got the question of whether to irrigate immediately or if it was possible to negate the effect on play and wait until the night irrigation cycle. So, we added an irrigation factor to the study above to examine the effects of 1/4" of immediate irrigation vs. 1/4" of irrigation 10 hours later. The results were surprising in that there was no difference in either year between the two treatments. Our hypothesis was that the turf foliage would take up the fungicide, and consequently watering in later would reduce fungicide efficacy. So, we modified our recommendation to highly suggest the application be watered-in immediately but if necessary could be watered-in that night.
This should be taken with a good grain of salt. Upon releasing our recommendation, I have gotten a few calls from supers that complained of the preventive applications not working. In most of these cases, it came down to not watering the fungicide in until the next night’s irrigation cycle. From these experiences, it is obvious that not watering-in the fungicide negates the advantage of using this application strategy.
Make plans to join us at the University Missouri Turf & Ornamental Research Farm on July 26th for our annual field day! We will be presenting the latest research on cultivar evaluations, pest controls, and management considerations for turf, trees, and woody ornamentals. It’s a fine day and a fine way to interact with colleagues and your local Mizzou research team.