March 2003

Painted-Pot Technology: A Novel Method of PGR and Pesticide Application By Steve Nameth and Claudio Pasian

Managing plant height, insects and mites, and the manydiseases that affect greenhouse-grown bedding and potted plants are some of themany challenges that face today’s growers. Most pest and plant growth problemsare controlled by using a variety of methods, both cultural and chemical. Someinsects and diseases respond very well to cultural controls, and in thesecases, minimal or no chemicals need to be applied. However, plant growth iscommonly regulated with the application of chemical-based plant growthregulators (PGRs). Even though today’s grower takes a more integrated approachto controlling problems by employing a combination of cultural, biological andchemical controls to produce a high-quality product, the use of chemicals forgreenhouse bedding plants, potted flowering plants and perennial production isstill necessary. Though vital to successful production, most growers are awarethey need to reduce the amount of chemical pesticides and PGRs that are appliedto their crop. Less chemical equals less expense and less “headache.”The issue of pesticide-breakdown products and where those products willeventually end up after they leave the greenhouse is something more and moregrowers have to address. In the very near future, growers will have to knowexactly how much pesticide they have applied to their crops, as well as howmuch of the active ingredient is leaving the greenhouse through the drainagesystem. Whether the product eventually ends up in the grower’s catch basin orthe city sewer system, this information will need to be known. Too much runoffof a particular product could result in a fine or some other type of penalty.

Because of this, growers are going to have to pay closerattention to the amounts of pesticides and PGRs they apply to their crops. Theless they use, the better. However, it’s not that simple. The grower will haveto balance using less product with the reality of reduced disease and insectcontrol and plant quality. For this reason, the development of novel methods ofpesticide delivery that will achieve the same degree of disease, insect andmite control, and plant growth quality is being explored by universityresearchers worldwide.

This article will address some of the latest research concerningthe 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 OhioState 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 interiorsurfaces were covered with a mixture of flat latex paint and a variety of PGRconcentrations. 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 ingredientper container. The growth of the mums in the painted pots was compared to thosethat received a standard drench of 0.24 mg of active ingredient (as per labelinstructions).

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

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

Insecticides

In 1997, Drs. Pasian, Lindquist and Struve publishedground-breaking research in the journal HorTechnology. In this paper, “ANew Method of Applying Imidacloprid to Potted Plants for Controlling Aphids andWhiteflies,” the researchers described the effectiveness of twoapplication methods of this insecticide in controlling the melon aphid on mumsand whiteflies on poinsettias. Like the other experiments, plants were grown incontainers with their interior

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

All imidacloprid treatments effectively reduced aphidsurvival for at least eight weeks, with the two most effective aphid treatmentsbeing the 1-percent granular application and the 88 mg/L (0.26 mg activeingredient) (see Figure 1, page 29). For the whiteflies, all insecticidetreatments reduced whitefly nymph survival, with the 42 and 88 mg/L and the1-percent granular treatments being equally effective in reducing whiteflynymphs on the lower poinsettia leaves (see Figure 2, page 29).

The importance of this work is very clear and highlysignificant: effective control with less active ingredient.

Fungicides

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

The pathogen used in this study was Pythium ultimum. Thisparticular fungus was isolated from a poinsettia with severe symptoms of rootrot 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. Thisfungicide was chosen because of its systemic nature in the target plant, forits high degree of control efficacy against Pythium, and its widespread usehistory in the greenhouse industry. For this project, three different rates ofmetalaxyl were used: one-half the manufacturer’s recommendedrate, the recommended rate and twotimes 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 inthis experiment: 1) minus Pythium, minus paint and minus fungicide; 2) plusPythium, minus paint, minus fungicide; 3) minus Pythium, plus paint, minusfungicide; 4) plus Pythium, plus paint, minus fungicide; 5) plus Pythium minuspaint, plus fungicide; and 6) plus Pythium, plus paint, plus fungicide. Thesepaint treatments were compared to the standard method of fungicide drenchingusing 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 drencheswere applied to the potted poinsettias at one and five weeks after planting.There were five replications of each treatment and experiments were arranged ina completely randomized block design. The rate response to the fungicide wasdetermined by regression analysis using SAS.

Poinsettia plants were planted in Scotts Metro Mix 360 in4-inch plastic pots that had been painted on the inside with 100 ml of whiteinterior flat latex paint into which the metalaxyl had been mixed at the ratesdetailed above. The painted pots were allowed to dry for 24 hours beforeplanting. Immediately following planting, the plants were fertilized with a14-14-14 slow-release fertilizer. Potted plants were inoculated with Pythiumusing a method described by Pasian, Varela-Ramirez and Nameth (in “Digitalvideo technology as a means of quantifying root rot,” published in a 1999issue of HortScience), and placed in a greenhouse under a controlledenvironment.

The amount and severity of Pythium Root Rot was assessedvisually in each plant using a disease severity index from 1-6, where 1 = noroot 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 crowninfection and 6 = plant death. The amount and severity of root rot were alsodetermined using a digital imaging method developed by Pasian in the papermentioned above.

The results

Based on the results of two complete experiments, there wereno significant differences in the control of Pythium-induced root rot of poinsettiaswhen either method of fungicide application was employed. In other words, theincorporation of the fungicide into the paint was just as effective as using astandard fungicide drench. These results are important in that root rot diseasecontrol was not compromised by employing the painted-pot method. This comparesfavorably to the previous painted-pot research with growth regulators andinsecticides. In this research there were also no significant differencesÁ

between fungicide rate treatments (one-half, versus full,versus twice the labeled rate) in controlling Pythium Root Rot. However, inboth experiments the manufacturer’s recommended rate (full rate) resulted inthe best control. Since the same amount of active ingredient was applied to theplant’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 beused 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 ofapplication were collected and analyzed with high-pressure liquidchromatography (HPLC) to determine the amount of metalaxyl coming out of thebottom of the pot. These results indicated that there were no significantdifferences in the amount of metalaxyl in the leachate of the two types ofapplication methods.

A basis for further research

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

Imagine that as a grower, you could purchase pots that werealready coated with PGR and/or pesticide at the effective rate of activeingredient.This has the potentialto be much safer, particularly when pesticides are used that confer a high degreeof danger when handled in the conventional manner.

Further work will need to be conducted that takes a look atsignificantly reducing the rate of chemicals in the paint but still maintainsefficacy. This, in turn, will allow for less product to be leached out of thebottom of the container. And in this day and age, that can only be a goodthing.