NEW HAMPSHIRE NEWS 



Grow^ing Degree Days 



A management tool for the horti- 

 cultural industry! 



UNH Cooperative Extension is 

 working together with the NH 

 Department of Agriculture and 

 the New England Agricultural 

 Statistics to bring you weekly 

 growing degree day (GDD) infor- 

 mation throughout the summer 

 months. This pilot year will be a 

 learning experience for us all. . . 

 so, please be patient as we work 

 out the details. 



What is a growing degree day? 

 Insects are cold-blooded animals 

 whose activity and development 

 are controlled by the temperature 

 of the surrounding environment. 

 It has long been recognized that 

 growth could be measured indi- 

 rectly by tracking temperature 

 over time once the lower 

 (baseline) and upper threshold 

 temperatures for a particular in- 

 sect were known. This would al- 

 low us to predict events in an 

 insect's life cycle during the sea- 

 son by measuring growth in 

 terms of temperature over time. 



This measurement is called a 

 "growing degree day". Currently, 

 50°F is used as a standard 

 baseline for all insect and mite 

 pests of woody plants. 



Why a lower threshold num- 

 ber of 50 degrees? This tem- 

 perature was chosen as plant 

 and insect growth in the north- 

 east is thought to start between 

 45°F and 55°F. Obviously, the 

 further an insect or mite's true 

 baseline is from 50°F, the less 

 accurate these range numbers 

 are. Unfortunately, accurate 

 baseline threshold temperatures 

 are known for only a relatively 

 few insect species. 



How are growing degree days 

 measured? The simplest calcula- 

 tion of a degree day starts with 

 the recording of maximum and 

 minimum temperatures. These 

 two numbers are added together 

 and divided by two to determine 

 an average temperature for the 

 day. This average number is then 

 subtracted from a lower threshold 

 number of 50°F. The result is 

 the GDD for that day. (Negative 

 numbers are not counted!) These 



Summer Horticulture Courses at the Thompson School 



numbers are accumulated through- 

 out the growing season and may 

 number in the thousands by 

 summer's end. 



How will I receive and use 

 GDD information? As you would 

 expect, GDD data will vary 

 greatly throughout the state. For 

 this reason, New England Agri- 

 cultural Statistics is supporting 

 GDD data from 19 NH sites. 

 Fortunately, handy charts have 

 been developed which list par- 

 ticular insects and the GDD 

 needed for their development. 

 Beginning May 3, 1999, this in- 

 formation will be disseminated 

 weekly to the public through a 

 variety of means: 



• Web page (http://ceinfo.unh.edu): 

 UNH Cooperative Extensions web 

 site will devote an special projects 

 area to this project and will list all 

 GDD sites as well as a comprehen- 

 sive breakdown of expected insect 

 emergence and action tips for that 

 particular pest. When you arrive at 

 our Cooperative Extension home 

 page, click on the "Special 

 Projects" icon. This will lead you 

 a page which includes a listing 

 entitled "Growing Degree Days" — 

 click on this and you'll be ready 

 to receive information. 



The Thompson School at UNH offers six courses in ornamental 

 horticulture this summer. These are listed below. Some may re- 

 quire prerequisites; all have a $10.00 special fee. 



HT236 Pest Management: Insects 5/24-7/30 T 5-8pm 



HT237 Pest Management: Weeds 6/28-7/30 MW 5-8pm 



HT239 Pest Management Control Applications 5/24-6/25 MW 5-8pm 



HT254 Water Management 5/24-7/30 M 9-12 



HT257 Woody Landscape Plants 5/24-7/30 Th 4-8pm 



HT263 Landscape Construction and Maintenance 5/24-7/2 Tli 5-8:30pm 



You can enroll by phoning the Division of Continuing Education at 

 603-862-2015. For information on credit, content, the part-time 

 associate's degree program, or the diploma in landscape horticulture, 

 call 603-862-1035. Additional courses are offered at the UNH De- 

 partment of Plant Biology. 



• Telephone Message at 862-4800: 

 A recorded message will be up- 

 dated weekly listing GDD for se- 

 lected sites as well as anticipated 

 insect emergence. 



• Weekly Market Bulletin: 

 Selected GDD sites will be pro- 

 filed each week and insect alerts 

 will be highlighted. 



For more information, contact 

 Nancy Adams, Agriculture Educa- 

 tor, Cooperative Extension, Rock- 

 ingham County, at 603-679-5616. 



APRIL / MAY 1999 



