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April 21, 2014

Growing degree days and Phenological Events

By José Fernández in | 0 Comments

I would like to start a series of blogs for the purpose of tracking growing degree days (GDD) and associated phenological events.
Without getting into a complex description of what growing degree days represent, simply be aware that organisms develop in a pattern strongly influenced by increasing temperatures accumulated throughout the season. As arborists, we keep track of growing degree days (that other people track for various other reasons) to know when certain harmful pests are about to emerge so we can time our treatments accordingly.

Phenological events or indicators are useful to easily determine when a specific pest is likely to be emerging because these are events that coincide with the event you wish to track. A great example which is commonly used to illustrate this is the coincidence of adult Emerald Ash Borer (EAB) emergence with the flowering of Black Locust. Black Locust typically reaches full bloom around 548 GDD and adult EAB emerges around 550 GDD. If we keep this in the back of our minds, we know we can expect to see EAB flying around soon after Black Locust is in full bloom. (For the record, we use the GDD chart created and maintained by The OSU OARDC Extension).
GDD vary from area to area, so make sure whatever resource you use to track GDD is specific to your zip code or at least close by. As an alternative, you can calculate the exact GDD for your microclimate by using the appropriate measurements (Tool: thermometer - easy) and formula (Tool: Mathematics – ugh).

To date, according to the OARDC website, we are at 127 GDD for Westerville OH. White Pine Weevil has emerged (84 GDD) and Eastern Tent Caterpillar has hatched (92 GDD). You may read TJ’s blog post on how he witnessed the Eastern Tent Caterpillars hatching before his very eyes last Saturday, which is probably when we were around the 92 mark.
What is coming up on the horizon? European Pine Sawfly at 144 GDD, so watch your Mugo Pines for creepy crawlies devouring the needles. Last year was a bad year for those – hopefully this year will not be.
That’s all I have time to cover for now. Please feel free to let me know what you would like to see on future postings covering this topic.

Your friendly neighborhood arborist,
José Fernández


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