Group Title: CFREC-Apopka research report - Central Florida Research and Education Center-Apopka ; RH-90-19
Title: Effect of Osmocote rate on growth of Impatiens wallerana and severity of Pseudomonas leaf spot
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 Material Information
Title: Effect of Osmocote rate on growth of Impatiens wallerana and severity of Pseudomonas leaf spot
Series Title: CFREC-Apopka research report
Physical Description: 2 p. : ; 28 cm.
Language: English
Creator: Chase, A. R ( Ann Renee )
Central Florida Research and Education Center--Apopka
Publisher: University of Florida, IFAS, Central Florida Research and Education Center-Apopka
Place of Publication: Apopka FL
Publication Date: 1990
Subject: Impatiens wallerana -- Fertilizers -- Florida   ( lcsh )
Impatiens wallerana -- Diseases and pests -- Florida   ( lcsh )
Pseudomonas -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
Statement of Responsibility: A.R. Chase.
General Note: Caption title.
 Record Information
Bibliographic ID: UF00065859
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 70294524

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6,8-/. Effect of Osmocote rate on growth of Impatiens Wallerana
and severity of Pseudomonas leaf spot

A. R. Chase1

University of Florida, IFAS -! 2
Central Florida Research and Education Center Apopka
CFREC Apopka Research Report, RH-90-19 -- .

Impatiens Wallerana (common impatiens) are popular bedding plants
throughout the United States. Impatiens are not cold tolerant but can be grown year
round in Florida when shade and water conditions are appropriate. During the past
two years Pseudomonas leaf spot has been found and described on impatiens. The
cause of this disease has been identified as Pseudomonas syringae. The disease may
be present throughout the year although symptoms may only develop when
temperatures reach an optimum. New Guinea impatiens have also been found
infected with P. syringae. The following paper describes research performed to
evaluate the affect of fertilizer level on growth of impatiens and development of
Pseudomonas leaf spot.

Materials and Methods

Plugs of Impatiens Wallerana (common impatiens) were obtained from
commercial producers and planted in 5-inch round pots containing a steam-treated
medium consisting of Canadian peat and pine bark (1:1, by volume). Plants were
irrigated from overhead at least three times/week through the trial period. Light
levels ranged from 2600 to 3000 ft-c. with temperatures between 650 and 95 "F. Ten
pots were used for each of six rates of Osmocote 19-6-12 (a 3-4 month release term
formulation applied as a top-dressing): 3, 6, 9, 12, 15, and 18 g/5 inch pot. Plant
height and leachate soluble salts (using the pour-through method) were recorded
every 2 weeks after fertilizer was applied. Plant quality was rated after 4 weeks using
the following scale: 1 (dead), 2 (poor, unsalable), 3 (marginal, salable), 4 (good,
salable), and 5 (excellent, salable). Plants were inoculated with a bacterial
suspension of P. syringae after top quality was evaluated. The number of lesions per
plant was recorded 5 7 days after inoculation. Three tests were performed between
15 May and 31 July 1990.

Results and Discussion

Results from the three tests were similar and only those from test 2 are
presented. Leachate soluble salts increased as fertilizer rate increased and ranged
from 375 (for plants without fertilizer) to 3200 gmhos/cm after 2 weeks and 100 to
750 Amhos/cm after 4 weeks. Increasing the Osmocote rate increased final height

'Professor of Plant Pathology, Central Florida Research and Education Center -
Apopka, 2807 Binion Road, Apopka, FL 32703.

and plant quality with best plants produced with rates between 9 and 18 g Osmocote
19:6:12 (Table 1). Number of lesions caused by Pseudomonas syringae increased as
amount of fertilizer increased (Table 1).


The rapid decrease in leachate soluble salts indicates problems many growers
and homeowners face in supplying an adequate amount of fertilizer when plants are
produced under overhead irrigation during hot weather. Since all rates above the 3
g rate gave equivalent responses, the lowest rate (9 g should be used) and possibly
applied more frequently than every 90 days to avoid limiting the growth of the crop
due to lack of fertilizer. Use of higher rates is not recommended since the excess
fertilizer was apparently leached from pots and was lost. If Pseudomonas leaf spot
is a problem use of the 9 g rate may reduce development of this disease on

Table 1. Effect of fertilizer rate on growth of Impatiens Wallerana and
susceptibility to Pseudomonas syringae.
Osmocote 19:6:12 Height Top Number
g/5 inch pot (inches) quality lesions
3 6.0 3.5 4.4
6 7.0 4.1 7.9
9 7.4 4.4 12.3
12 7.7 4.7 13.4
15 7.8 4.8 19.7
18 7.7 4.7 21.1
Fertilizer rate significantly affected each parameter recorded.

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