Fanping, Saturday. July 26, 1997 Corn By Degree (Days) (Continued from Pago A 1) nies use and provide GDDs with other data about varieties they offer, though historically the “rela tive days to maturity” have been the mainstay of farmers. But days to maturity is not a very good help to predicting when a plant variety will actually reach that stage. Using GDD estimates can nar row down maturity very closely, without having to go the field every other day to check for other plant indicators of maturity. Starting at 50 degrees Fahrenheit the bottom threshold temperature for com activity the accumulated amount of energy usable by a plant to achieve certain stages of maturi ty, including maturity, can be fol lowed during the year to help pre dict field woik requirements for optimum harvest GDDs can also be used as a gen eral indicator of which varieties of corn (and other crops that have been shown to have growth changes that closely correlate to GDD) may be most suitable for a specific location, harvest window, and use. Dr. Greg Roth, a Penn State Extension agronomy specialist stated in a several-year-old Exten sion publication, “Hybrid maturi ties for com are rated either by a ‘days to maturity* system or by a ‘growing degree day’ system." That publication, “Latest Plant ing Dates For Com Hybrids In Pennsylvania.” referred to the last possible dates in the year for plant ing a com variety so that it would mature before frost It discusses GDDs and the for mula for calculating them. A farmer who knows his daily high and tow temperatures can cal cualte the GDDs on his farm, track and anticipate the growth of plants. “The days to maturity system is a relative measurement of hybrid maturity and is based on the grain moisture content of hybrids at harvest compared with check hybrids,” Roth wrote. “For example, under similar conditions, a 75-day hybrid will generally have a tower grain mois ture content at harvest than a 100-day hybrid. “The days to maturity expressed in these ratings do not actually rep resent the number of days needed for a hybrid to mature, since a 100-day hybrid may require 95 days to mature in a warm season and 115 days in a cool season.” With GDDs, if it requires 2.450 GDDs to attain maturity, that doesn’t change, regardless of cool or warm season. In fact, by using GDDs, a grow er can know fairly well what kind of season he is experiencing while it is happening, not a month or more later. Though the information about GDD has been around for years, its use has not been that great Voight wants to change that because he said he believes those who use them can better plan optimum times for harvest and also because they can be used to predict insect emergences. Two weeks ago Voight said that some of the com in test plots he was involved in planting this spring should start tasselling this week. At the time, with unseasonably high and dry weather, with com leaves curled tightly and brown bottom leaves, and with plants stunted and looking about ready to die instead of advancing into a reproductive stage, his prediction based on GDD seemed as though he was putting too much reliance on an estimate. Perhaps with the long cool spring/summer seasons, and the heat only picking up relatively recently, it didn’t seem as though corn was developing to have much maturation. He made the prediction and it came through. What it means is that for dairy producers who need to build up feed stocks for their herd, there is a tot of short com and silage and grain production should be cut dra matically from last year. While com pices are currently relatively tow,' several people this week suggested that dairy produc ers may want to purchase grain needs now in advance of any price increases, in order to cover their shortness in home-grown feed. But what Voight’s come-true prediction also means is that using GDDs actually works well, much better than days to maturity in nar rowing down when things will happen with the plants. Cora growers who haven’t been in their fields in die area should also be interested to know that com rootworm beetles have infested many fields, and their emergence and activities can also be tracked and predicted using GDDs. As more and more research is done to correlate GDDs with plant and insect activities, the ability to monitor them at home should help farmers better plan their activities. The publication that Roth helped to author was mostly con cerned with helping farmers figure out which com hybrids would fit in their fields so as to reduce the risk of frost-kill before maturity. Color-coded maps of Pennsyl vania are included in the publica tion that correlate colors to weeks in the spring during which a hybrid could be planted with only a 25-percent chance of frost before maturity. If the weeks when frost kill his torically hits a farm field can be determined, and a farmer has access to historic daily tempera ture variations for his area, he can calculate GDDs for his farm fields and what varieties will mature before frost The formula for determining GDD is simple: the daily high temperature is added to the daily tow temperature and divided by two; SO is then subtracted from that number. “SO” is used in the equation because at 50 degrees, com plants are basically dormant Any temp erature below SO is considered effectively to be SO. Likewise, a com plant generally doesn’t grow any faster at temper atures above 86 degrees, so for any recorded daily high temperatures above 86 should be considered as 86 degrees in the equation. GDDs are cumulative. For accumulation of growing degree days for com, SO or less would equal zero accumulation. Likewise 86 or above would equal 86. In the seed company literature, the GDDs are generally reported along with the relative days to maturity. For most varieties of 85 days to 120 days, the GDD is usu ally above 2,000 and less than 2,800. Some ate very close in terms of relative days, but the decision of whether to harvest or not to harvest on a specific day can be deter mined if GDDs are tracked. Voight** prediction of tasselling (Turn to Pago A2l) Delbert Voight, Lebanon County Extenelon agronomy agent, stands In between com variety test rows to show the difference in growth and response to growing degree days. Based on his recording of growing degree days for the area, he is able to predict within a day or so when certain stages of growth should occur. By tracking GDDs, and knowing the research determined levels for physiological changes, as weH as following the weather reports, he was able to predict about two weeks in advance about what day the com would be In tassel. By continuing to collect and record GDDs, he will be able to predict maturity of com for harvesting. The pratical application of using GDDs as a farm management tool is that it can significantly help plan work, and provide a belter sense of control over activities on the farm. From tho loft, Del Volght, Lebanon v Extension agronomy agent, shows a com rootworm beetle to farm owner Tom Krali, and howto determine the difference In sexes. By using growing degree days, K is possible to predict ineect activity tar better anticipation and preparation tor control.
Significant historical Pennsylvania newspapers