The objective of early drenches is to achieve good size control with less effect on bract development compared to PGR sprays. The early drench is sometimes referred to as a low-dose drench because the rate used is much lower than late drench rates. An early drench is applied as needed using the same decision process as currently used for making spray applications. The low rate that is used does not stop elongation and only slows plant growth similar to the effect of a spray. The early drench can either replace some or all of the sprays. An important point is that there is not a cutoff date for early drenches and they can be applied in mid and late October. While, early drench applications are generally safer than sprays at the same time, problems can occur if too much is applied just like all PGR usage.
Any of the growth regulators that work as a drench can be used for an early drench, but rates will vary depending on activity of the chemical. We have the most experience with paclobutrazol (Paclo.) products (Bonzi, Paczol, Piccolo). Paclo. rates for early drenches are 1/10 to 1/5 ppm (0.1 – 0.2 ppm) for medium to very vigorous varieties and depending on the amount of control desired. At this time, we do not suggest using this technique on low vigor varieties like Chianti and Pepride without extensive testing to determine the optimum rates. In the past couple of years, this technique has been used by growers in both the north and south with very good success.
In cool climates I suggest using 1/10 to 1/8 ppm on all crops.
In warm climates use 1/7 to 1/5 ppm for varieties like Snowcap, Santa Claus and Monet. Use 1/10 to 1/8 for varieties like Freedom, Prestige and Orion.
Note for those outside North America. The rates given above are for active ingredient rather than formulated product. 1 mg a.i./liter = 1 ppm
