Research Articles continued
Early Detection of Stress on Annual Bluegrass on Putting Greens Virginia Tech Researchers: David S McCall, Dept. of Plant Pathology, Physiology, and Weed Science; and Valerie A. Thomas and Laura Lorentz, Dept. of Forest Resources and Environmental Conservation
A
nnual bluegrass is considered both a desirable turfgrass species and problematic weed on golf putting greens in our region. Its growth attributes make it desirable because of its density and ability to withstand close mowing, although management requirements are much greater than with creeping bentgrass. Both annual and perennial biotypes are found on golf putting greens. Despite its perennial nature, however, the latter often suffers from numerous stresses during the summer months, frequently resulting in widespread plant death. Advanced stress detection of annual bluegrass could be highly beneficial for timing key management events, such as fungicide applications or irrigation.
Our research
We are currently exploring a unique method — hyperspectral radiometry — for early stress detection of annual bluegrass. Since herbicide injury typically produces expected (predictable)
results, this approach was used as an initial screen for stress detection. Two herbicides known to injure annual bluegrass — bispyribac-sodium and amicarbazone — were chosen for this initial experiment. We conducted our trials on a research golf putting green at the Virginia Tech Golf Course in October 2011. The site consisted of a mixed stand of annual bluegrass and creeping bentgrass. Bispyribac-sodium and amicarbazone were applied at 30 grams ai/A and 100 grams ai/A, respectively, on October 3, 2011. For each plot, ten distinct colonies of annual bluegrass were selected for daily data collection before and after herbicide application. Reflectance data were collected and analyzed from each subsample. Three hundred spectrum data were pooled and analyzed to provide one spectral signature for each treatment per day. Plots were also monitored daily for injury that was visible to the human eye alone.
26 | Virginia Turfgrass Journal May/June 2012 www.vaturf.org
Research results
In bispyribac sodium-treated plots, a mild chlorosis was first visually noticed five days after application and remained through the duration of data collection. Injury from amicarbazone was less pronounced. Using spectral analysis software, reflectance data were graphed for each day. Temporal effects were evident with each herbicide throughout the study at 715nm using second derivative analysis. Days zero and one, days two and three, and days four and five, were clustered together, respectively. Amicarbazonetreated plots were analyzed similarly. While visible symptom development was not as obvious, the analysis also detected change two days after application.
Conclusion
Results from this experiment provide evidence that physiological changes may be detected with spectral analysis as early as two days after application with two herbicides, before damage symptoms can be seen visually. It is not known at this time whether the same spectral features used for this analysis will be present when exposed to other biotic or abiotic stresses. For outbreaks of many diseases to occur, annual bluegrass and other species must be predisposed to abiotic stresses, such as heat or drought. If the spectral feature described in this report is consistent for all stresses of annual bluegrass, this information could prove highly beneficial for turf managers attempting to control diseases preventatively with adequate application timing. Additional research is ongoing. c