Evaluating the Interaction of PGRs …

Evaluating the Interaction of Plant Growth Regulators and Lance Nematodes on Creeping Bentgrass Putt

By M. Aaron Tucker, Jon D. Eisenback, and David S. McCall, Ph.D.

The lance nematode, Hopolaimus galeatus, is a plantparasitic nematode (PPN) that is commonly identified as problematic in warm-season golf course putting green samples. We have noticed an increase of high lance populations in Virginia’s cool-season putting greens with limited options of control. Plant growth regulators (PGRs) are commonly used in putting green management for greater surface consistency and reduced mechanical stress. Numerous golf course superintendents who have used PGRs either currently or in the past have suggested to us that creeping bentgrass damage associated with high counts of PPN may be related. To date, there is no information available to validate or refute this relationship. Finally, the product fluopyram is a great management option for most PPN but has little to no efficacy against lance nematodes. Exclusive use of this product may lead to problematic populations of lance nematodes in putting greens. The objectives of this work were to determine whether the addition of fluopyram to PGR applications impact creeping bentgrass quality and how fluopyram combined with PGRs impact lance nematode populations.

FIGURE 1. The male (left) and female (right) lance nematode (Hoplolaimus galeatus) under magnification. Photo credit: Jon D. Eisenback.

A 5x2 factorial study was conducted at five locations across Virginia for 16 weeks to assess the impact of fluopyram, PGRs, and their interaction on putting green quality and nematode populations over time. The five locations consisted of Heron Ridge Golf Club (Virginia Beach), Golden Horseshoe Golf Club Gold Course (Williamsburg), The Club at Viniterra (New Kent), The Foundry Golf Club (Powhatan), and The Club at Glenmore (Keswick).

Five PGR treatments consisted of Primo Maxx (trinexapacethyl, 0.125 fl oz/1000 ft2, 14 days), Anuew (prohexadione calcium, 8 oz/acre, 14 days), Cutless (flurprimidol, 24.6 fl oz/acre, 28 days), Trimmit (paclobutrazol, 10 fl oz/acre, 42 days) and a no PGR control. Fluopyram was applied every 28 days at 0.2925 fl oz/ 1000ft2 and compared against a non-treated control. Assessments were collected every 14 days and consisted of visual estimations of creeping bentgrass quality, % phytotoxicity, and % visual damage, along with aerial image analysis. Percent phytotoxicity was measured as uniform damage across a treatment plot associated with chemical applications, and % visual damage was measured as non-uniform damage associated with plant stress or potential nematode damage. Root samples were also collected for nematode populations and root length at initiation, midseason, and final ratings.

FIGURE 2. Suspected lance nematode damage often shows up in the clean-up lab of many creeping bentgrass putting greens. Photo credit: Aaron Tucker

Differences in % phytotoxicity for all treatments were significant at four of five locations on some assessment dates but were well below the acceptable damage threshold of 30%. The most commonly rated phytotoxicity was a mild regulation that many associate with improved overall quality by PGR applications. Visual damage associated with lance thinning was highly sparse in 2021 across all locations and were not different at any location. Differences in creeping bentgrass quality were significant at one location for PGRs and fluopyram, with relative root length reduced by fluopyram at one location. Relative change in lance populations were not different at any location from initiation to mid-season sampling.

To date, there is little evidence to suggest that applications of fluopyram with PGRs has an impact on creeping bentgrass quality or lance nematode populations. While temperatures across Virginia were roughly 3°F warmer than average in 2021, there was also adequate and timely rainfall for much of the state. Overall, the summer was relatively mild with limited reports of creeping bentgrass damage during peak stress and may have been a factor in not seeing many treatment differences in our studies. Damage caused by lance nematodes is most severe in conjunction with environmental or mechanical stress. While our data did not show an impact of the PGR/fluopyram interaction, it is worth noting that this may not always be the case with other stressors involved.

FIGURE 3. Field testing location in mid-summer immediately after core removal for nematode and root sampling. Photo credit: Travis Roberson

Future work will consist of more field work across years as well as greenhouse studies to validate the current work by reducing variability of lance populations through controlled experiments. We also plan to conduct a survey among Virginia golf course superintendents to understand more information about historical lance populations and PGR use on creeping bentgrass putting greens at their respective facilities. These studies are part of a larger focus within the Virginia Tech turfgrass pathology and nematology labs to gain a better understanding about the role of lance nematodes on creeping bentgrass putting green health. Please reach out to us with any feedback that you think may benefit our studies.