Temperatures and GDD Tracking

This is a blog I track written by the most respected entomologists in the nation.  I know eyes begin to glaze over when I speak of Growing Degree Days (GDD) but here is the interesting take away from this:  If you were to ask me, I would have said that this past spring was by far warmer than last year, or any year in recent memory.  However, the high temperatures may have been above average but from the perspective of a grass plant, we are a full 4-7 days behind last year when the temperatures are analyzed from the GDD model.   

Wavering Weevils

• May 27, 2016
• by Dr. Rick Brandenburg/Terri Billeisen

 

 

If you have been following the WeevilTrak blog, you know that fluctuating temperatures have made this a strange year for annual bluegrass weevil (ABW) life stage timings, not just in North Carolina, but everywhere.

 

In the southwestern corner of the state (Cashiers), consistently low temperatures have continued to keep us approximately 4-7 days behind in degree day accumulations from last year. In fact, during nearly a whole week in early May, no degree days were accumulated at all! This did not seem to have much of an impact on the number of adults recovered from soap flushes. For the last three weeks, adult numbers have been consistently higher than in 2015 despite the delay in initial incline. This week, however, we have started to see a slight reduction in adult numbers, indicating that now is a good time for an early-instar larval application if necessary. In the southern U.S., we have been relying on life cycle timing, rather than the presence or absence of larvae, to estimate the most effective application dates. This approach differs from that of our northern colleagues because of the difficulty of finding larvae following a peak in adult activity. Consistent soil sampling has not yielded ANY larvae unless conducted in an area with considerable turfgrass damage. This is most likely due to much smaller populations of ABW with a much more patchy distribution within a fairway, which makes it difficult to find larvae even in areas of past damage.

 

This recommendation does not necessarily extend to turfgrass managers in the southern part of the state but further east of Cashiers. We have collected 1st-2nd instar larvae in damaged turfgrass around the greater Asheville area this week. In areas east of the mountains or at an elevation less than approximately 3,200 ft., managers should be actively scouting for larger larvae and applying products with more contact activity.

 

At the Beech Mountain and Blowing Rock sites, a consistent increasing of temperatures throughout the month of May have allowed degree day accumulations to approach the last year’s level. Overall adult activity in these areas is much more consistent compared to 2015. Each week, at least SOME adults are recovered from soapy water flushes each week rather than a single adult emergence date followed by weeks of no activity (see graph). In general, there is a stronger overall ABW presence compared to last year and it is worthwhile to monitor each life stage rather than relying on an early-season application for season-long control when necessary. That being said, adult numbers in these areas are still way below threshold (1-2 adults/4 sq. ft.) and unless you see damage, treatment is not recommended. 

 

 

One thing to note is that these current observations and recommendations are region-specific and should not be interpreted to work for outside the sampling area. Based on the knowledge provided by our cooperators and what you know about the ABW life cycle and behavior, you may have to think about how both are affected by environmental conditions in your region.
- Terri Billeisen