Painted-Pot Technology: A Novel Method of PGR and Pesticide Application

February 28, 2003 - 08:01

One of these days, you could be purchasing pots pre-treated with all the PGRs and pesticides you need to grow quality plants while causing less harm to the environment.

Managing plant height, insects and mites, and the many
diseases that affect greenhouse-grown bedding and potted plants are some of the
many challenges that face today's growers. Most pest and plant growth problems
are controlled by using a variety of methods, both cultural and chemical. Some
insects and diseases respond very well to cultural controls, and in these
cases, minimal or no chemicals need to be applied. However, plant growth is
commonly regulated with the application of chemical-based plant growth
regulators (PGRs). Even though today's grower takes a more integrated approach
to controlling problems by employing a combination of cultural, biological and
chemical controls to produce a high-quality product, the use of chemicals for
greenhouse bedding plants, potted flowering plants and perennial production is
still necessary. Though vital to successful production, most growers are aware
they need to reduce the amount of chemical pesticides and PGRs that are applied
to their crop. Less chemical equals less expense and less "headache."
The issue of pesticide-breakdown products and where those products will
eventually end up after they leave the greenhouse is something more and more
growers have to address. In the very near future, growers will have to know
exactly how much pesticide they have applied to their crops, as well as how
much of the active ingredient is leaving the greenhouse through the drainage
system. Whether the product eventually ends up in the grower's catch basin or
the city sewer system, this information will need to be known. Too much runoff
of a particular product could result in a fine or some other type of penalty.

Because of this, growers are going to have to pay closer
attention to the amounts of pesticides and PGRs they apply to their crops. The
less they use, the better. However, it's not that simple. The grower will have
to balance using less product with the reality of reduced disease and insect
control and plant quality. For this reason, the development of novel methods of
pesticide delivery that will achieve the same degree of disease, insect and
mite control, and plant growth quality is being explored by university
researchers worldwide.

This article will address some of the latest research concerning
the use of painted-pot technology as a novel method of delivering PGRs,
insecticides and fungicides to greenhouse potted crops.

Plant growth regulators

In 1998, Drs. Claudio Pasian and Daniel Struve, The Ohio
State University, published a paper in the journal PGRSA Quarterly entitled,
"Paclobutrazol/Paint-Treated Containers Control Dendranthema grandiflora
(Ramat) Height." Mum plants were grown in containers in which the interior
surfaces were covered with a mixture of flat latex paint and a variety of PGR
concentrations. The concentrations of paclobutrazol used were 0, 5, 10, 20, 40,
80, 100, 150, 160 and 200 mg/L of solution. These concentrations represented 0,
0.015, 0.03, 0.06, 0.12, 0.24, 0.3, 0.45, 0.48 and 0.6 mg of active ingredient
per container. The growth of the mums in the painted pots was compared to those
that received a standard drench of 0.24 mg of active ingredient (as per label

Results of this study showed that this method of application
was just as effective as a traditional drench application in controlling plant
height. In a follow-up paper, Dr. Pasian looked at how paint/

paclobutrazol-coated containers controlled poinsettia
growth. As with the mums, a highly significant linear relationship between the
PGR/paint dosage and poinsettia plant height was observed. Both of these
studies indicate the potential to use paint/PGR as a novel method of PGR


In 1997, Drs. Pasian, Lindquist and Struve published
ground-breaking research in the journal HorTechnology. In this paper, "A
New Method of Applying Imidacloprid to Potted Plants for Controlling Aphids and
Whiteflies," the researchers described the effectiveness of two
application methods of this insecticide in controlling the melon aphid on mums
and whiteflies on poinsettias. Like the other experiments, plants were grown in
containers with their interior

covered with a mixture of flat latex paint plus several
concentrations of the insecticide (0, 10, 21, 42 and 88 mg/L) or treated with a
granular Á application of the insecticide at a rate of one percent
active ingredient (10 mg active ingredient).

All imidacloprid treatments effectively reduced aphid
survival for at least eight weeks, with the two most effective aphid treatments
being the 1-percent granular application and the 88 mg/L (0.26 mg active
ingredient) (see Figure 1, page 29). For the whiteflies, all insecticide
treatments reduced whitefly nymph survival, with the 42 and 88 mg/L and the
1-percent granular treatments being equally effective in reducing whitefly
nymphs on the lower poinsettia leaves (see Figure 2, page 29).

The importance of this work is very clear and highly
significant: effective control with less active ingredient. style="mso-spacerun: yes"> 


With the excellent results of the PGR and insecticide
research, it was only logical to explore the possible use of this technology as
a method of fungicide delivery. For the fungicide project I cooperated with Dr.
Pasian. This project was in partial fulfillment of the requirements necessary
for our graduate student to receive a Ph.D. degree in Plant Pathology. Like the
PGR and insecticide work, we used poinsettias. They were chosen for this study
because of their high value as potted plants as well as their susceptibility to
Pythium Root Rot disease. Plant material was kindly donated by the Paul Ecke
Ranch, Encinitas, Calif.

The pathogen used in this study was Pythium ultimum. This
particular fungus was isolated from a poinsettia with severe symptoms of root
rot that was submitted to The C. Wayne Ellett Plant and Pest Diagnostic Clinic,
The Ohio State University.

The fungicide used in this study was metalaxyl. This
fungicide was chosen because of its systemic nature in the target plant, for
its high degree of control efficacy against Pythium, and its widespread use
history in the greenhouse industry. For this project, three different rates of
metalaxyl were used: one-half the manufacturer's recommended style="mso-spacerun: yes">  rate, the recommended rate and two
times the recommended rate. These rates amounted to the application of 5.6,
11.2 and 22.4 mg of active ingredient per potted poinsettia. Á

There were six disease/paint/fungicide treatments used in
this experiment: 1) minus Pythium, minus paint and minus fungicide; 2) plus
Pythium, minus paint, minus fungicide; 3) minus Pythium, plus paint, minus
fungicide; 4) plus Pythium, plus paint, minus fungicide; 5) plus Pythium minus
paint, plus fungicide; and 6) plus Pythium, plus paint, plus fungicide. These
paint treatments were compared to the standard method of fungicide drenching
using the same amount of active ingredient (one half the labeled rate = 5.6;
full rate = 11.2; and twice the labeled rate = 22.4 mg). The standard drenches
were applied to the potted poinsettias at one and five weeks after planting.
There were five replications of each treatment and experiments were arranged in
a completely randomized block design. The rate response to the fungicide was
determined by regression analysis using SAS.

Poinsettia plants were planted in Scotts Metro Mix 360 in
4-inch plastic pots that had been painted on the inside with 100 ml of white
interior flat latex paint into which the metalaxyl had been mixed at the rates
detailed above. The painted pots were allowed to dry for 24 hours before
planting. Immediately following planting, the plants were fertilized with a
14-14-14 slow-release fertilizer. Potted plants were inoculated with Pythium
using a method described by Pasian, Varela-Ramirez and Nameth (in "Digital
video technology as a means of quantifying root rot," published in a 1999
issue of HortScience), and placed in a greenhouse under a controlled

The amount and severity of Pythium Root Rot was assessed
visually in each plant using a disease severity index from 1-6, where 1 = no
root rot, 2 = mild root rot (less than one-third of the roots rotted), 3 =
intermediate root rot (one-third to two-thirds rotted), 4 = severe root rot
(greater than two-thirds of the roots rotted), 5 = severe root rot and crown
infection and 6 = plant death. The amount and severity of root rot were also
determined using a digital imaging method developed by Pasian in the paper
mentioned above.

The results

Based on the results of two complete experiments, there were
no significant differences in the control of Pythium-induced root rot of poinsettias
when either method of fungicide application was employed. In other words, the
incorporation of the fungicide into the paint was just as effective as using a
standard fungicide drench. These results are important in that root rot disease
control was not compromised by employing the painted-pot method. This compares
favorably to the previous painted-pot research with growth regulators and
insecticides. In this research there were also no significant differences

between fungicide rate treatments (one-half, versus full,
versus twice the labeled rate) in controlling Pythium Root Rot. However, in
both experiments the manufacturer's recommended rate (full rate) resulted in
the best control. Since the same amount of active ingredient was applied to the
plant's root system either by paint incorporation or by conventional drenching,
a comparison could not be made as to whether or not the painted method could be
used to reduce the amount of fungicide needed to get adequate disease control.
With the insecticide research this was shown to be the case.

Also, irrigation leachates collected from both methods of
application were collected and analyzed with high-pressure liquid
chromatography (HPLC) to determine the amount of metalaxyl coming out of the
bottom of the pot. These results indicated that there were no significant
differences in the amount of metalaxyl in the leachate of the two types of
application methods.

A basis for further research

In conclusion, novel methods of PGR, insecticide and
fungicide application will need to be continually explored as growers become
more and more accountable for what goes in and comes out of each pot.
Incorporating paclobutrazol, imidacloprid and metalaxyl into paint and painting
the interior of a pot proved to be just as effective in controlling plant
growth, insects and root rot when compared to the traditional drench method.
The potential for this method of PGR and pesticide application needs to be
investigated in greater detail.

Imagine that as a grower, you could purchase pots that were
already coated with PGR and/or pesticide at the effective rate of active
ingredient.  This has the potential
to be much safer, particularly when pesticides are used that confer a high degree
of danger when handled in the conventional manner.

Further work will need to be conducted that takes a look at
significantly reducing the rate of chemicals in the paint but still maintains
efficacy. This, in turn, will allow for less product to be leached out of the
bottom of the container. And in this day and age, that can only be a good

About The Author

Steve Nameth is professor in the Department of Plant Pathology and Claudio Pasian is associate professor in the Department of Horticulture and Crop Science at The Ohio State University, Columbus, Ohio. They may be reached by phone at (614) 292-8038 or via E-mail at

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