Nematodes that feed on turfgrass roots can be problematic and damaging, especially in warmer climates where a lack of freezing soils allows greater populations to develop over time. One of the better new nematicides, fluopyram, was registered for turf and golf course use in 2016. An interesting thing about this product is that it is in the SDHI class of chemistry. That’s right, a fungicide that controls nematodes. Other SDHIs used in turfgrass have not been found to be nematicidal but their impact on nematode populations or sensitivities is not well understood. What is known is that this class of chemistry has a history of being vulnerable to fungicide resistance. The chemicals in this class can also have a very long soil residual.
During USGA Course Consulting Service visits to golf courses in Florida, observed nematode control with fluopyram was excellent initially – especially for sting and root-knot nematodes. As this chemical also has fungicide benefits, nematode-riddled putting greens seem to respond almost immediately with improved roots, surface coverage and density during the first few years of use. Some of this could be attributed to the strong fungicidal activity of this chemical. Shortly after fluopyram was released, the level of control seemed to wane. Sting and root-knot nematodes did not appear to respond as they previously had to applications of fluopyram – even after four spot-treatment applications in one year. The USGA Davis Program received and approved a grant proposal in 2020 to look into this issue – the study was titled “The Effects of Long-Term Fluopyram Use in Turfgrass Systems.”
Dr. Billy Crow and graduate student Christian Kammerer at the University of Florida collected samples from golf courses across the state. They separated putting green soil samples with a history of frequent fluopyram use and those with no history. They also collected samples from research field plots that were treated for four years with fluopyram, one year with fluopyram, or that had never received fluopyram. Preliminary results against root-knot nematodes indicated that fluopyram residues remain in the soil many months after application, lending activity on nematodes that were never directly exposed to the chemical. Secondly, there seemed to be a notable loss in sensitivity where treatments had been made for multiple years versus where fluopyram had never been used.
What does this mean?
- Nematode resistance to any nematicide on any crop has not been documented prior to these results.
- Whether this is resistance or loss of sensitivity, this preliminary research suggests there is a risk of decreased nematode control with use of this product and possibly this class of chemistry.
- This nematicide and its long-term efficacy and sensitivity to sting and other nematodes beyond root-knot nematodes is not known at this time but does justify monitoring nematode populations and root health prior to and after making applications.
As with fungicides, there are different levels of resistance and target sensitivity with nematicides. Hopes are that by using the guidelines for resistance management, limiting applications to when they are most necessary and utilizing different nematode management methods – including both cultural practices and rotating product modes of actions – the utility of this valuable mode of action will be preserved for both nematodes and diseases.
Southeast Region Agronomists:
Chris Hartwiger, director, USGA Course Consulting Service – chartwiger@usga.org
Steve Kammerer, Ph.D., senior consulting agronomist – skammerer@usga.org
Jordan Booth, Ph.D., agronomist – jbooth@usga.org