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Douglas Bailey, Professor, and Brian Whipker, Extension Horticulture Specialist - page 2 / 16

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be at Stage 5 of floral development (i.e., style elongated and open) when treatment is initiated. Applying prior to this stage could result in abnormal flower development.

For most plants, apply CGR’s such as A-Rest, B-Nine, Bonzi, Cycocel, Florel, and Sumagic after the plant has developed sufficient foliage (photosynthetic area, leaf area) to prevent excessive stunting of the plant’s development. For example, a Bonzi spray on pansy plugs should not be made until three true leaves are present on the plants. Earlier applications may stop plant growth completely rather than merely reduce elongation. Apply CGR’s just prior to rapid shoot elongation; e.g. after pinching and newly developing shoots are visible, but before shoot elongation has occurred. Remember that CGR’s are chemical growth retardants not chemical plant reducers--they cannot shrink plant

growth already present. application before the stage

Make your final when floral size will

be

reduced.

If

growth

retardants

are

applied

too

late,

the

size

of

the

flowers

can

be

reduced

and

floral development can be slowed. example would be bract size reduction

A and

good delay

of bract color in poinsettia due to late of A-Rest, B-Nine + Cycocel, Bonzi, Sumagic.

application Cycocel, or

Timing of a PGR application should be based on a physiological stage of plant development such as the number of leaves present, the length of shoots, or plant diameter, not chronological age such as 3 weeks after pinching. Recommendations given in terms of chronological age are merely guidelines that have been correlated to physiological stages and should only be used as rough estimates as to when to apply plant growth regulators. Also remember to read the label when deciding on timing for a PGR

application. plant stage application.

Many labels suggest the proper of development for chemical

Target: The target tissue or plant part to receive the chemical depends on the chemical and the plant species.

2

Foliage and Stems: Chemicals can be sprayed on, or shoots can be dipped into a chemical solution at time of transplanting. If dipping shoots into a solution, use a consistent soaking time, such as 10 seconds. For sprays, remember that areas are sprayed not individual plants. Imagine yourself painting a wall with a roller. You want uniform coverage over the entire area-

  • -

    not heavy clumps (every time you pass over a

plant). This is the only way to assure even coverage and consistent results. With many PGR’s such as A-Rest, Bonzi, and Sumagic, spraying different volumes of the same concentration spray over a given area gives different levels of control. If growers “spray to runoff” or “spray to glistening”, every grower will apply a different amount, and there is no way of predicting the results.

Proper coverage is essential for consistent results (see Application Technique section). For example, Bonzi and Sumagic are not very effective if only applied to plant leaves. Transport of Bonzi and Sumagic to the growing point in the plant is most effective if it is applied to the stem or if it is absorbed through the roots. If an insufficient application volume is used and stems are not wetted, poor height control will be the result. On the other hand, since root uptake is very effective, an over application of Bonzi or Sumagic using too large a volume will result in the excess spray dripping onto the substrate leading to root uptake of the chemical and causing too great a reduction in growth.

Substrate: PGR’s can be applied to the substrate (growth media or soil), if the root system is the target tissue. This is the same as a soil drench; drenches use larger volumes of solution per plant or pot, but usually at lower concentrations than a spray or dip. Drenches can take more time to apply than sprays, and require exact metering of volume delivered per pot for consistent control of elongation.

Roots: PGR’s can be applied directly to the roots or the underground portion of the plant such as bulbs, corms, or tubers, prior to planting.

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