14 CityTREES
(top left) Accumulated
growing degree days
as of Jun 15, 2017.
(top right) Plot of
accumulated growing
degree days in 2017
(blue line) and the
long-term average
(black line) for a
location in northern
Michigan. The red
line shows the six-
day forecast. This
plot can be generat-
ed for any location in
the continental U.S.
via the USA-NPN
visualization tool.
(bottom right) Regions
with 500-1,000 accu-
mulated GDDs as of
Jun 15, 2017.
Within the online visualization tool, it is also
possible to evaluate where a par ticular thresh-
old has been met, or estimate the date the
threshold will be met, if it has not yet been met.
The Accumulated Growing Degree Days graph
(page 15, top) also accessed via the USA-NPN
visualization tool, shows the temperature accu-
mulation at the location in nor thern Michigan
marked by the pin in the maps above in 2017
(blue line) compared to the long-term average
accumulation (black line). The six-day forecast
is shown via red line. As of Jun 15, this site
was predicted to reach 500 GDDs on Jun 19,
providing a 4-day advance warning for initiating
pesticide treatment.
Tutorials for using the USA-NPN visualization
tool are available. In addition, growing degree
day thresholds have been established for many
life cycle events in hundreds of plants and
insect species. These thresholds are commonly
found in University Extension publications and
websites. Some of the most comprehensive lists
of GDD thresholds are offered by Ohio State
University,
Michigan State University, and Utah
State.
Any of the thresholds can be applied to the
Growing Degree Day data available by the USA-
NPN to anticipate the timing of specific events
at a par ticular location. Caution should be exer-
cised, however, when applying a threshold to
accumulated temperature for a location far from
the place where it was developed. Many thresh-
olds have been developed using data from a
single location or region; it is generally unknown
how well thresholds developed at one location
perform at predicting events at other locations.
Map products are available for the continen-
tal U.S. and Alaska, spanning Jan 1, 2016 to
present. In addition to the USA-NPN's online
visualization tool, these maps are available both
as image and raster data files through an online
interface as well as through web services. Learn
more about these maps
here.
