How to Correctly Manage Plant Growth Regulator

Plant growth regulators such as Shortstop® 2SC have a wide range of secondary effects; while their primary effect is to encourage more root growth, it also leads to thicker leaves, waxier leaves, increased fibrous roots, and healthier looking plants. With these secondary effects, we are observing trees with less leaf scorch due to drought, less damage after construction, and an increase in disease suppression.

It is important to follow the label and treatment guidelines with Shortstop, as each species of plant will have varying levels of sensitivity to the active ingredient, Paclobutrazol. There are other factors that also need to be accounted for when treating. For instance, the applicator can reduce the rate based on pre-existing conditions with the tree or environment.

With so many factors and variables to consider, it is not uncommon to accidently overtreat shrubs and get overregulated plants with unattractive stunted growth. Here are some things to look out for.

Symptoms of Over-Regulation

An overregulated plant may have atypically small and distorted leaves. Small flowers and delayed blooming and leaf-out may occur. Shortstop 2SC typically does not kill trees or shrubs, but at high rates will kill grass (If you notice white/dead turf, remove it, along with the soil).

Overregulation on a Japanese maple.
Overregulation on a Japanese maple.
Overregulated lilacs
Overregulated lilacs

How to Manage Overregulated Trees and Shrubs

  1. Immediately remove the soil that was treated with Shortstop 2SC. This will reduce additional uptake of the active ingredient into the tree or shrub.
  2. Replace with organic matter and new soil – this will help absorb any additional product.
  3. For trees, consider a trunk injection with PHOSPHO-jet™.This will trigger the plant’s natural defense and encourage strong cell walls. It will also improve new stem, root, and leaf growth. The plant should recover by the next growing season.
  4. For trees and shrubs, consider a soil application of a fertilizer/soil conditioner containing nutrients, seaweed extract, humic acid and humectants. We suggest NutriRoot® for optimum results and to encourage plant and soil health.

For additional questions or concerns, reach out to your local regional technical manager ( ).