Not much info on DIF for poinsettia PGR does it work?

Let's review the concept of using DIF for those that aren't familiar with it, them we'll discuss its effectiveness.

DIF refers to the difference between day and night temperatures. Day temperatures - night temperatures = DIF. As the DIF becomes more positive stem elongation increases, and as it becomes more negative stem elongation decreases. Stem elongation increases as day temperatures increases. When night temperatures are cool stem elongation decreases. Warm days and cool nights equal a positive DIF while warm nights and cool days equal a negative DIF. For most parts of the country is very difficult and expensive to use an actual negative DIF so most growers run what is called a "zero" DIF. A zero DIF occurs when the night temperature equals the day temperature. Morning temperatures are dropped at or before sunrise (to 60-62F/15-17C) for two four hours until the greenhouse begins to naturally heat up. This technique provides a moderate negative DIF response.

The way poinsettias respond to a DIF depends on different factors. The effect on stem elongation will be greater if the plants go from a positive DIF environment than from a zero DIF to a negative DIF environment. Using DIF to control height is also most effective during the vegetative growth phase when the plants are most actively growing. Unfortunately this phase is usually in late August and September when the days are still very warm in the greenhouse. The technique is easier to achieve in October and November when only slight height control is needed and to reduce the amount of growth regulating needed. Growers must also be careful during this time because the temperature reduction also reduces the average daily temperature which has an impact of the rate of bract development and expansion.