Control of Some Fungal Diseases of
Ornamentals with Agribrom

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University of Florida, IFAS
Central Florida Research and Education Center - Apopka
CFREC-Apopka Research Report, RH-91-3

A. R. Chase*

Fungal diseases cause substantial losses in many floral, foliage and landscape crops. Losses may occur during any stage of production from rooting of cuttings to finishing the crop. Currently available fungicides have different levels of efficacy depending on each type of pathogen. In addition, considerations of labeling and phytotoxicity limit use of some of these products. Use of fungicides during the rooting process is not always successful due to the excessive amounts of foliar wetting needed during this time. A compound which can be added to the irrigation water which would restrict development of plant pathogens would be beneficial. Agribrom (Great Lakes Chemical Corp., West Lafayette, IN 47906) has been labeled for water treatment as an algicide for several years (5). Although some claims have been made regarding its effectiveness in controlling both fungal and bacterial diseases, little data have been developed in this area (1,2,3,4). The following research was conducted to partially evaluate its potential for fungal disease control on eleven different ornamental crops under a mist system.

Two benches in a fiberglass-covered greenhouse were used for all tests. One bench received the Agribrom treatment while the other bench served as the nontreated control. An Agribrom stock solution was prepared every three or four days by adding 10 g of the powder per gallon of hot tap water and placing on a hot plate until completely dissolved (usually 1 hour). The stock was then stored in a holding tank shielded from light exposure and added to the mist system by a Dosatron proportioner (Dosatron International, Inc. Clearwater, FL 34615) set at 4% which diluted the solution delivered to the leaf surface to about 50 to 60 ppm. The mist system operated for 35 sec every half hour for 12 hours per day. This treatment was started three days prior to inoculation and continued until test completion (up to one month).

Plants were obtained as seedlings or were rooted from cuttings. They were grown in Vergro potting medium usually in a 4-inch pot until they were well established. Fertilizer was applied once at planting at 1.5 g/pot of Sierra 17-6-12 controlled-release fertilizer (Grace-Sierra, Milpitas, CA 95035). A minimum of 10 plants was used for each of the following treatments: 1) noninoculated - control, 2) inoculated - control, 3) noninoculated - Agribrom treated, and 4) inoculated - Agribrom treated.

Inocula were grown for various periods of time on potato dextrose agar medium and adjusted to concentrations between 1 x 10⁴ and 1 x 10⁶ depending upon the pathogen and disease pressure desired. Plants were removed from mist, inoculated by spraying to drip with a conidial suspension and returned 2 hours later. Disease severity was determined after 2 days to 4 weeks according to its development and was reflected by the number of lesions per plant or the percentage of the foliage or flowers with symptoms. The plants and pathogens included are listed in Table 1.

Varying degrees of disease control were achieved with the Agribrom treatment (Table 1). Control ranged from 71 to 93% for the majority of the leaf spotting fungi (Alternaria, Corynespora, Drechslera, and Fusarium leaf spots). In addition, Rhizoctonia petiole rot of pothos (E. aureum) and Rhizoctonia aerial blight of Boston fern (N. exaltata) were controlled 88 and 93%, respectively. Botrytis blight of flowers on geranium (P. hortorum) and leaves on African violet (S. ionantha) showed some control but could not be expected to control disease significantly on all affected portions of these plants (Table 1). Although Myrothecium petiole rot was not controlled on nephthytis (S. podophyllum), Myrothecium leaf spot of creeping fig (F. pumila) showed significant reduction when treated with Agribrom (Table 1).

Phytotoxicity occurred on several plants during these trials and during similar trials with Agribrom to evaluate bacterial disease control. A summary of the plants affected and the symptoms which developed as a result of Agribrom treatment, presumably due to bromine toxicity, are given in Table 2. Earlier work showed that while 50-60 ppm of bromine could cause severe phytotoxicity on some crops, a reduced rate of 25 ppm was apparently safe (1).

Agribrom shows good activity against a number of important fungal and bacterial pathogens (1) of ornamentals. Although its use in mist systems seems warranted, one cannot expand this efficacy to weekly or even daily foliar sprays. Previous research has indicated that bromine should be available on the leaf surface almost continually to afford maximum control of plant pathogens.

*Professor of Plant Pathology, University of Florida, IFAS, Central Florida Research and Education Center-Apopka, 2807 Binion Road, Apopka, FL 32703-8504.

Literature Cited

1.Chase, A.R. 1990. Control of some bacterial diseases of ornamentals with Agribrom Proc. of the Fla. State Hort. Soc. 103: (in Press)

2.Chase, A.R. 1988. Controlling cutting rot of marble queen pothos. CFREC-Apopka Research Report, RH-88-4.

3.Nishijima, W. 1990. Chemical control. pp. 39-40 In. Proceedings of the Third Anthurium Blight Conference. A. Alvarez, editor.

4.Powell, C.C. and S. Ashley Smith. 1989. The use of Agribrom on Cyclamen. Ohio Florists' Assn. Bull. No. 716. pp- 1-3.

5.Rickard, D.A. and H.K. Tayama. 1990. Bring algae down and plug profits up with Agribrom. Grower Talks 54(8):82, 84, and 89.

^aPhytotoxicity occurred on these plants (see Table 2 for symptom descriptions).