PGR drenches for growth control

Trying to control the growth of all your different spring crops can be a challenge. With so much diversity in our greenhouses, heads can spin trying to keep all the requirements for different species and cultivars straight (Fig. 1), and plant growth regulator (PGR) strategies are no different.

There are several methods for applying plant growth regulators to your greenhouse crops, including foliar sprays, substrate drenches, liner dips, and bulb soaks. Each of these methods are effective for applying PGRs, but each have advantages and limitations.

Liner dips and bulb soaks are application techniques that are used during specific stages in production or for specific crops. Foliar sprays are the most widely used application technique, such as when young plants are transplanted into their final containers.

But, it is my belief that substrate drenches must have a spot in your PGR toolbox for controlling spring crop growth. This article is going to focus on maximizing the effectiveness of PGR drenches for controlling containerized crop growth.

Why drenches?

If foliar spray applications are so ubiquitous, why consider applying PGRs with substrate drenches? First, drenches are the application of a known volume of PGR solution to each container. This can aid in improving uniformity in growth control across the crop compared to foliar spray applications. Drenches can also provide growth control for a longer duration than sprays. While the increased duration of activity can increase the chances of overregulation if too much PGR is applied, this can be used to your advantage when applications are correctly applied.

PGR?

One of the most important aspects of applying substrate drenches is selecting the right chemical or active ingredient. When applying PGRs to substrate, you need to select PGRs that have substrate activity. Ancymidol (Abide, A-Rest) flurprimidol (Topflor), paclobutrazol (Bonzi, Paczol, Piccolo), and uniconazole (Concise, Sumagic) are the most commonly used active ingredients for substrate drenches. While chlormequat chloride (Citadel, Cycocel) does have some activity when applied to the substrate, it is not labeled for use in drenches for the United States. Ethephon (Collate, Florel) is also not currently labeled for substrate drenches, but with recent research reporting the effectiveness of ethephon drenches, labels will likely be changing in the near future.

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Source: Greenhouse Management