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Douglas Bailey, Professor, and Brian Whipker, Extension Horticulture Specialist - page 4 / 16

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not require the use of an additional wetting agent. If a wetting agent is needed to allow a spray material to more thoroughly cover plant surfaces, such as with a Cycocel spray on poinsettias, use as little as possible to avoid phytotoxic side effects. Start off using a very low concentration and by experimenting with water on test plants, slowly increase the wetting agent concentration. Add only enough wetting agent to prevent droplets from beading up on the leaves; a higher concentration is unnecessary and could cause leaf burning.

Environmental Conditions: The efficacy of a

PGR can be affected by

the environment at

time of application,

the status of the plant at

application, and the plant.

post-application treatment of

A good example of an environmental factor affecting PGR efficacy is the effect substrate components can have on CGR’s. A bark- containing substrate will reduce the efficacy of A-Rest and triazole growth retardants like Bonzi and Sumagic, when applied as a drench. Therefore, drenching may not be the application method of choice for these PGR’s if using a bark- based substrate; or growers should account for the presence of bark when deciding on the concentration of PGR to use.

Another environmental factor of concern is the time of day selected for applying PGR’s. Research with foliar sprays of nutrients has shown that the time of day chosen for an application can affect a plant’s ability to absorb a chemical. Morning applications, when evaporation rates are low, are more desirable than later in the day. The longer the solution wets the tissue, the greater the chance for chemical uptake. If possible, make spray applications on a cloudy day to allow the chemical solution even more time to be absorbed prior to evaporation of the water from the surface of leaves and stems.

Plant water status can affect chemical efficacy. Plants should not be wilted or stressed at application. A turgid plant is more able to absorb and translocate a PGR than a wilted plant.

4

With respect to post-application handling of treated plants, B-Nine has been shown to require a long period of time (up to 4 hours) for complete absorption after a spray application. If the plants are watered (wetting the foliage) too soon after a B-Nine application, the unabsorbed chemical will be washed off and the efficacy of the B-Nine will be reduced. This is not true for rapidly absorbed PGR’s such as A-Rest, Bonzi, and Sumagic, and plants either drenched or sprayed with these chemicals can be watered as soon as 1 hour after application without a reduction in chemical efficacy. The effects of post-application watering on Florel and GibGro efficacy are not known.

Best

Management

Practices

for

plant

growth

regulators do not end with the guidelines given above. For a total program, growers should always monitor the effectiveness of applied treatments to assure that the treatments are working and to help “fine-tune” the amount of chemical needed. Monitoring treatment effectiveness may indicate that less chemical is

needed.

Always

mixed in

with the

leave a few untreated controls treated population. This allows

comparisons

for

effectiveness

of

the

PGR

treatment.

For

growth for

the

growth treated

retardants, monitor plant plants regularly to know

when

plants

begin

to

“grow

out”

of

the

treatment

and to help in deciding application is needed.

if

and

when

another

When used properly, chemical plant growth regulators are effective tools to help produce a high quality crop. When misused, they can reduce crop quality and increase production costs. Uniformity and consistency in application are crucial to attain predictable and desirable results.

Table 1 does not contain reference to Accel or Pro-Shear. Unfortunately, re-registration for both of these products will not be pursued, and neither will be available once current supplies are used. Benzyladenine (BA; the active ingredient of Pro-Shear) at 100 ppm is highly effective on

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