Scientists at the LSU AgCenter are attempting to understand the primary factors influencing the die-offs and the implications of the roseau cane scale invasion.
State-wide census to determine the geographic extent of the scale in Louisiana: By inspecting roseau cane populations in parishes where the plant is known to occur over the 2017 growing season, researchers have developed a map indicating where the scale is known to occur. This will help agencies monitor the spread and help the public prevent unintentional introduction of the scale to un-infested parishes.
Update February 2018: Statewide sampling has yet to resume. Many stands of cane are still recovering from the harsh winter weather and have new growth is only just starting to appear. AgCenter lead sampling efforts will resume later in the spring once roseau stands have had an opportunity to put up new shoots and overwintering scales have emerged and dispersed. We do encourage interested members of the public to help contribute to our sampling by submitting information on infested or un-infested stands to our web-based survey.
Monitoring of scale populations at sample sites across the lower Delta: In addition to the statewide survey, periodical sampling of reference points across the lower delta are providing how scale populations change and how infestations affect Phragmites stands over the course of the growing season. With this data we can monitor changes in roseau stand density, growth, and changes in vegetation cover.
Update February 2018: The first round of sampling is currently underway. There are still some sites which need to be sampled, and the data are still being entered and analyzed. It won’t be until this summer that we have a full years’ worth of data on scale population dynamics in the Delta; however, we are beginning to see some trends in our preliminary data. Total scale counts and percentage of infested stems were relatively low as of May 2017, but reached a mean of approximately 100 scales per stem and almost 100 percent of stems were infested. Recent data from spring 2018 shows scale populations have drastically declined, but whether this is part of a natural cycle or is due to unusually harsh winter weather remains to be seen. Data collected in 2018 will give researchers a more complete picture of how the scale populations grow and change in the marsh.
Dr. Jim Cronin measuring roseau cane at a sample site in Plaquemines parish (Photo: Rodrigo Diaz)
Stand of resistant European invasive (near right) adjacent Delta variety (far center) (Photo: Ian Knight)
Testing roseau varietal resistance to scale infestations: Louisiana has several genetic lineages of roseau cane distributed across the state. Initial surveys have found that while the dominant ‘Delta’ variety of roseau in the lower delta appears to be susceptible to the scale, while an invasive ‘European’ variety appears less susceptible to the scale and does not show the die-off symptoms. Additionally, an experiment is being designed to address how abiotic stressors like prolonged inundation and increased salinity interact with infestations of the scale on susceptible and resistant varieties from the delta. The scale is also being assessed for the risk of infesting other Louisiana natives and agriculturally important grass species.
Update February 2018: Rhizome clippings from sites across the delta were collected in summer and fall of 2017 and are currently being propagated in a greenhouse for use in controlled trials to assess the effect of the scale on roseau cane under controlled settings. Initial propagation attempts resulted in suboptimal plants; however, current efforts have yielded a healthy crop which will subjected to experimental treatments later this spring. Results from paired plot experiments in the Delta early in the year had suggested that scale population were lower in stands of the ‘European’ cane variety, however results from fall sampling suggest that these differences disappear late in the season. The factors behind this delay in infestation are currently being investigated, and will be compared to results from sampling efforts scheduled for 2018.
Leslie Lopez (left) and Dr. Rodrigo Diaz (right) sample scales occurring in a roseau cane common garden at LSU (Photo: Madeline Gill)
Dr. Blake Wilson testing different insecticides for scale control on infested roseau cane (Photo: Madeline Gill)
Investigation of chemical management solutions: While options for chemical treatments in wetland habitats are likely to be limited, in case the scale is found to be an agricultural pest, various insecticides are being tested on infested populations of roseau cane.
Update February 2018: Insecticide trials conducted in naturally occurring roseau stands and in the LSU roseau common garden have yielded poor results for chemical management of the scale. Topical insecticides may be limited in effectiveness due to the concealed nature of the scale, though systemic insecticides also have little-to-no effect on scale counts. Further trials will be conducted in the summer of 2018, to find an effective insecticide.
Longitudinal population dynamics: In addition to the projects listed above, a new experiment is underway sampling sites along a North-to-South gradient. By visiting easily accessible sites on a biweekly basis over the season, we will get a fine temporal scale resolution of how scale populations emerge and change throughout the year.