In my recent travels, I was able to see that spring has begun to arrive.  That being said, much of the landscape of the upper Mid-West and East Coast are still behind with regard to growth and development of turfgrasses (as well as other plants in the area).  The development and emergence of annual bluegrass seedheads is several days later than last year, so PGR suppression should be better this year.  Golf course superintendents continue to vary with regard to their PGR choice from Embark to Proxy to the combination of Proxy/Primo.  The pluses and minuses of any choice remain from year to year and are not consistent from place to place.  From a percent reduction perspective, Embark continues to provide the best suppression, but it does have some baggage that Proxy/Primo applications do not typically have (injury to off target species, discoloration, etc.). 

Remember that suppressing annual bluegrass seedheads conserves carbohydrate which makes the plant stronger and better able to withstand environmental stresses during the summer months.  Therefore, if reducing the amount of annual bluegrass in the stand is one of your objectives, it is better to let it produce the head and put all your cultural programming into promoting the creeping bentgrass or what ever species you are attempting to encourage.  For example, if you are trying to convert a mixed stand of annual bluegrass and creeping bentgrass to more creeping bentgrass by using Class B PGR's, the timing of application is best when the annual bluegrass seedhead is beginning to shatter (around the end of May). 

The American Society of Agronomy (Crop Science/C-5 Turfgrass Division) has a CD available that discusses in great deal the classification system now being used for PGR's.  It is authored by myself, Dr.Joe Dipaola, and Dr.Dennis Shepherd.  This CD contains the most comprehensive explanation and discussion of plant growth regulator use on turfgrasses.  Please understand that this is not a sales pitch as the authors do not receive any compensation (the proceeds go to the society.