made from cardboard, wood, or metal and will have a 

 slot to slide over the yardstick at a 90° angle (i.e., 

 the crossbar is horizontal to the bench). A carpenter's 

 level attached to the crossbar will further improve ac- 

 curacy. With the yardstick placed on the bench, the 

 crossbar can be slid gently down to just touch the 

 top of the plant without disturbing leaves. 



Step 3. Plot heights on the graph. 



Calculate the average height of the five sample 

 plants and enter it onto the graph, in the example 

 {Figure 1), the grower measured plant height twice a 

 week and plotted them on the curve (shown as rect- 

 angles), and also recorded growth retardant applica- 

 tions ('G' symbols). 



4. Make height-control decisions. 



Graphical tracking will show you whether your crop is 

 too tall or short, but it does not tell you what the best 

 management decision is The biggest advantage is that 

 the method gives you a consistent basis for deciding 

 whether to apply a growth retardant or change your DIF 



temperatures. 



The aim is to keep plant height between the maxi- 

 mum and minimum target heights throughout the crop. 

 If plant height is above the maximum target curve, ap- 

 ply a growth retardant if plants do not show bract color 

 and/or run negative DIF temperatures (warmer night 

 temperature than day temperature). Use positive DIF 

 temperature (cool night, warm day) if plant height is 

 below the minimum target curve 



In the example crop (Figure 1), the grower applied 

 Cycocel 1500 ppm growth retardants when the crop was 

 near or above the upper target curve, until the crop 

 showed first bract color 



For those interested in more details about graphical 

 tracking and height control, Dr. Heins and I are writing 

 an in-depth series on graphical tracking in Greenhouse 

 Grower, which started in the |une 1997 issue. 



Paul fisher is assistant professor in the Department of Plant 

 Biology, University of New Hampshre, Durham. He can be 

 reached by phone at 603-862-4525 or fax at 603-862-4757; 

 his e-mail address is <prf@hopperMnh.edu>. 



Figure 2. A screen from UNH FloraTrack showing a poinsettia graphical tracking chart. 



UNH FloraTrack: Graphical Tracking for Poinsettia. Version 1.0 for Excel 7 



Copyright University of New Hampshire 1997 Developed by Paul Fisher, Dept of Plant Biology, UNH, Durham. NH 03824 



V17 Crop 1 (Angellka Red, Pot size 6 Inches) 



9 ° s z z z 



