Jeffrey Hahn, Asst. Extension Entomologist
This past year saw a significant increase in the number of reported cases of cottony grass scale (CGS), Eriopeltis festucae, in Minnesota lawns. In 2007, we were only aware of one reported case of cottony grass scale. By 2008, that number had grown to about 6 newly reported cases with the one from 2007 disappearing entirely as there were no signs of infestation in 2008. However, by the end of September in 2009 the number of reported cases that we knew about rose sharply to between 75 and 100. While these were reported cases and not necessarily confirmed infestations, most recognized and described the symptoms, and ultimately the insect, as that shown in our previous article first describing this insect in Minnesota. (See the December 2008 YnG newsletter). Hence, it appears reasonable to assume that most identifications were likely correct.
In order to get a better feel for the scope and range of this insect in Minnesota, it was decided to conduct a survey of those reporting CGS infestations to us. The survey was conducted with SurveyMonkey.com with potential participants notified via email that the survey had been posted followed by a request that they take a few minutes to complete the survey. All respondents and responses were kept anonymous.
The survey covered a variety of topics ranging from symptoms observed, site conditions where most commonly found as well as cultural and pesticide practices employed to manage and control the pest. Sixteen respondents of about 18 receiving the questionnaire completed the on-line survey. This article summarizes those results as well as provides an update to last year's article concerning CGS In Minnesota.
While our awareness of this pest was first noted in 2007, one survey respondent reported seeing it in 2006 although we are not certain as to its location. In 2007 and 2008 all of the reported infestations were from around the greater Twin Cities metropolitan area. In the survey, CGS was reported in just two sites in 2007 and only nine sites in 2008. In 2009, reports of CGS infestation had expanded to include many Twin City municipalities as well as reports from border counties in western Wisconsin, Mankato, St. Cloud, Brainerd and Alexandria. There may be other locations as well. However, we only have confirmed documentation from those particular areas. In the survey, CGS was observed at 63 - 78 sites. It is unclear why this dramatic increase of reports occurred.
We were very interested to learn if CGS was successfully surviving winters. Of the single site in 2006, the 2 properties in 2007, and the 9 lawns in 2008, CGS was observed on all of same properties the following season. Although not reflected by the survey, we are aware of at least one property where CGS has not been found in two years since it was first found in 2007. Still, this suggests that CGS are capable of surviving winters in Minnesota.
Typically, CGS is observed in August or September, although in a few cases it was noticed in June and July. Late summer coincides with when CGS matures into adults and produces egg sacs. These stages are much more conspicuous as a white woolly material surrounds the insect, making them much easier to see in the grass. The life cycle is still not well understood but this species is reported in the literature to overwinter in Maine in the egg stage. That appears to be true in Minnesota.
As was noted last year, the most common symptom associated with CGS is the distinctive mower pattern in which the wheel tracks consistent with those of a commercial riding mower remain green and mostly non-infested. This creates a striped pattern where grass is mowed in only one direction or a checkerboard pattern where grass is mowed in two directions and at right angles to each other. See Pictures 2 and 3. The area below the mowing deck varied from light to very heavy infestations of CGS with the corresponding yellow to tan grass blades associated with their feeding. Only two of sixteen respondents reported an infestation that did not show-up in that same pattern. In one of those instances a walk behind rotary mower was used as opposed to a commercial riding type of mower.
While that sort of mowing pattern suggests that the insects may be being destroyed via a crushing action imparted by the riding mower, it remains uncertain as to whether or not, or how much of that really occurs. Further evidence gleaned from the survey that some type of crushing action is occurring was noted by three of the survey respondents. In one instance, a respondent noted that when the area was rolled using the roller on a lawn aerifier, the lawn improved dramatically within two to three weeks. In another instance, the infested area was rolled with (presumably) something like a sod roller where it was again noted that the lawn recovered 'rather quickly'. In this last case the rolling was done when the cottony, cocoon-like grass scales were present and visible on the grass blades. One respondent noted that by not mowing in the same wheel track pattern each time, thereby destroying another portion of the CGS infestation, recovery of the turfgrass was evidenced by improved green color. See picture 4.
To the best that we can interpret from survey information, all of the rolling/crushing activity would have occurred when the cottony, sac-like structures were clearly evident. While the above observations are very important in helping us better understand the potential vulnerability of CGS, it is hoped that further investigation and observation will help clarify the specific association with mower wheel tracks and the presence or absence of this pest in those specific, rather narrow areas.
Previous information provided by people encountering this problem indicated that it was primarily found on more highly maintained lawns presumably dominated by Kentucky bluegrass and for the most part receiving full sun exposure. As a follow-up to that anecdotal information, the survey asked respondents to identify the lawn care situations where this pest was being observed. Their choices were as follows:
- Highly maintained lawns (e.g. regularly mowed, fertilized at 3 to 5 pounds of N per 1000 square feet annually, irrigated, kept green throughout the year)
- Moderately maintained lawns (e.g. regularly mowed, fertilized at 2 to 3 pounds of N annually, irrigated as needed to keep lawn basically green but some browning tolerated)
- Low maintenance lawns (e.g. mowed as needed, not irrigated at least with any degree of regularity, fertilized with 1 or 2 pounds of N annually, brown grass associated with summer dormancy is tolerated)
Twelve of the sixteen respondents indicated that this was a pest primarily infesting more highly maintained, Kentucky bluegrass lawns thus lending credence to what others were saying as well as our own observations. Only three indicated a presence on moderately maintained lawns and only one respondent noted CGS presence on a low maintenance lawn. While not asked directly in the survey, personal observation of infested sites along with input from others indicated that this pest is not as attracted to the fine fescue (only two reports) lawn grasses. While their presence was noted on the fine fescues it was in much smaller numbers than that observed on Kentucky bluegrass. In another sighting, it was observed that the creeping bentgrass growing in the same area as Kentucky bluegrass was not infested while the surrounding Kentucky bluegrass was heavily infested. See Picture 5.
From this limited amount of field observation, it would appear that well maintained, predominantly Kentucky bluegrass lawns, are more likely to be infested with CGS than those lawns receiving moderate to low levels of maintenance. With this being a relatively small sample size, further observation and monitoring will help confirm any turfgrass species preferences of this pest.
While the level of sunlight received by the infested areas was not specifically asked in the survey, it would generally be assumed that an otherwise healthy, more highly maintained Kentucky bluegrass lawn would be located in an area receiving full to mostly sunlight conditions. However, there are at least two reports, one from the survey and one not, that did observe CGS in partially (tree) shaded areas of the lawn. In light of where this pest appears to occur most frequently, it would appear that its preference would be for actively growing Kentucky bluegrass in mostly sunny areas. However, its occurrence in more shaded situations cannot be ruled out. Again, future monitoring and observation should help clarify site and plant material feeding preferences of CGS.
Another aspect of CGS management that the survey helped assess was whether or not the implementation of any particular cultural practice or change in cultural practice helped improve the turfgrass stand (i.e., symptoms abated and grass color and vigor improved). Ten of sixteen respondents tried making at least one cultural practice change compared to what was previously being done. Those cultural practices asked by the survey included:
- use of more or less water
- use of more or less nitrogen
- mowing heights increased or decreased
- mowing frequency less often or more often
- lawn dethatched only, lawn aerified only or, lawn dethatched and aerified.
Four of the ten respondents who indicated the implementation of at least one cultural practice change noted that the lawn improved following those practices during the same growing season. Two respondents reported no improvement.
There was no clear pattern of practices that seemed to be any more helpful than another. For example, the one respondent who indicated that they 'aerified only' reported improvement in the turfgrass similar to two respondents who utilized four different practices including the use of aerification. Of the two respondents that increased water or chose to mow less often, both indicated seeing no improvement in the turfgrass. A respondent who indicated an increase in N and mowing higher was uncertain as to whether or not the situation had improved. However, that same respondent did indicate that use of Merit alone or with cultural practice changes (presumably those mentioned above) resulted in improvement in the turfgrass stand. When changes in cultural practices were combined with the application of an insecticide, four of six respondents noted an improvement while two noted no improvement.
While there appears to be a clearer understanding as to this pest's preference for well maintained lawns, it is not as clear as to which cultural practices might be more important in either encouraging or discouraging the establishment of and/or maintaining an existing pest population. Also, there does not seem to be a clear cut pattern of control using pesticides alone or with a particular set of cultural practice changes. For example, of the two respondents who indicated that they reduced water and nitrogen amounts and used an insecticide (Merit), one noted improvement while the other did not.
Eight people applied insecticides to attempt to manage CGS. Two used Merit and both believed these applications decreased the population of CGS. One applicator also treated his lawn with Talstar (bifenthrin) but did not think it was effective. One respondent used both Merit and Talstar believing that this was effective management. Likewise, one person used Scimitar (lambda cyhalothrin) and thought he gained a reduction of CGS. There was also a single record of acephate although they did not record whether they thought it was effective. Another person used horticultural oil but didn't know whether it was effective.
It is interesting that the insecticide applications appeared to improve the turf in some cases. Although Merit should be effective, it would not be expected to have an impact on CGS numbers until the following spring. We would not expect any of the residual insecticides (Talstar, Scimitar, horticultural oil) to be effective on adults, although they would be effective against crawlers if you were able to time the application when they were present.
Eight out of nine people that did nothing did not see an improvement in the turf in the same season. There was one respondent that said the turf was looking good again by late October. It will be particularly interesting to observe infested lawns next spring to see whether they have recovered or not. It has been our observation to this point that turf does improve without any lasting injury. With many more properties to examine, this will help us determine if this generally true.
In summary, it is understood by the authors that this survey represents a relatively small number of respondents. Nonetheless, it is an attempt to gather rudimentary yet useful information about CGS presence, habits and control strategies being utilized in Minnesota to manage this pest. It is hoped that our own further observation and monitoring plus valuable input from the lawn care industry will continue to provide an expanding data base on CGS management. From that information, effective IPM strategies can be developed and refined to provide lawn care personnel as well as homeowners with a variety of effective management and control options for CGS.