Bacterial Disease Control on Ornamentals using Aliette, Kocide, Greenshield and ASC-66825

University of Florida, IFAS
Central Florida Research and Education Center - Apopka
CFREC-Apopka Research Report, RH-92-10

Bacterial diseases of ornamentals are difficult to control due to unavailability of efficacious and nonphytotoxic bactericides. In the past, plant producers have relied on use of antibiotics such as Agri-Strep 21.2% (streptomycin sulfate) and copper compounds such as Kocide 101 77WP (cupric hydroxide). New compounds have been tested whenever available but none have shown activity equal to or surpassing that of the antibiotics or copper compounds (1). Since 1987, several reports have been published regarding the potential use of Aliette 80WP for bacterial disease control (2,3,4,5). These reports indicated that diseases caused by Xanthomonads could be partially controlled by preventative sprays of fosetyl aluminum (Aliette 80WP) at rates between 1 and 5 lb/100 gal (2,3,4). Aliette significantly reduces severity of some but not all of the diseases caused by Xanthomonads which were tested. The degree of control is approximately equal to that achieved with Kocide, which has been the best compound for controlling some Xanthomonas diseases of ornamentals (1). Aliette applications prior to symptom development and rates similar to those labeled for control of pythiaceous fungi should give the best response.

The following report summarizes tests comparing two formulations of Aliette (80WP and 80WDG) with Kocide 101 77WP for control of four Xanthomonas diseases. In addition, an experimental compound from ISK Biotech (ASC-66825) and a quaternary ammonium compound (Greenshield) from Whitmire was used against Pseudomonas and Xanthomonas on at least one plant species. A total of seven tests was performed between June 1991 and April 1992. Rates of each bactericide are given in appropriate tables. In each test, plants were sprayed once or twice prior to inoculation and then on the indicated interval. Inoculation with a suspension of the appropriate pathogen occurred 1 to 3 days after the initial chemical spray. Disease ratings consisted of number of lesions per plant except for anthurium which were rated for disease severity as the number of symptomatic leaves per plant.

Pseudomonas leaf spot of Impatiens is caused by Pseudomonas syringae and has been reported from both California and Florida. The bactericides used in this test were two rates of cupric hydroxide (Kocide 101 77WP at 16 and 32 oz per 100 gal), two rates of ASC-66825 (4 and 16 oz per 100 gal), and three rates of Greenshield (1, 2, and 4 oz per 100 gal).

Water treated controls (inoculated and noninoculated) were included. The Greenshield treatments were sprayed daily from 21 November to 1 December 1991. The other treatments were applied on 21 and 27 November 1991. Plants were inoculated on 25 November and the number of lesions per plant was recorded on 2 December. In addition, the height of the plants was recorded on 2 December. Plants receiving the Greenshield treatments were stunted with the 4 oz per 100 gal rate causing the most stunting (Fig. 1). Other bactericides did not affect plant height or cause any other signs of phytotoxicity. Disease control was significant only for those plants treated with Kocide (Fig. 1).

Xanthomonas blight on anthuriums is caused by Xanthomonas campestris pv. dieffenbachiae which also causes leaf spot and blight diseases of many other aroids. Treatments which were included in this test on A. andraeanum were water treated controls (inoculated and noninoculated), two rates of fosetyl aluminum in two formulations (Aliette 80WP and Aliette 80WDG at 2.5 and 5 lb per 100 gal each), and two rates of cupric hydroxide (Kocide 101 77WP at 16 and 32 oz per 100 gal). The 5 lb rate of the two Aliette formulations were applied 5 times on a biweekly interval. All other treatments were applied weekly from 8 August to 3 October for a total of 9 applications. Plants were inoculated on 20 August and again on 23 September and the number of leaves with blight symptoms was recorded on 20 September and 7 October. Only data from the initial rating are given. The Aliette treatments gave approximately equivalent control when used at the 5 lb rate but the WDG gave better control when used at the 2.5 lb rate (Table 1). The 1 lb rate of Kocide gave similar control to the high rates of Aliette but the 2 lb rate of Kocide gave the best disease control in this test. No signs of phytotoxicity were noted for these plants.

Xanthomonas leaf spot of Dieffenbachia is caused by the same pathogen as the disease on Anthuriums. Two tests were conducted in 1991 using the same treatments as described above for the anthurium test. In this first test, applications were made between 7 June and 5 July 1991. Plants were inoculated on 11 June and rated for the number of lesions per plant on 10 July. The lower rate of Aliette 80WP gave the same degree of control as both the higher rate of Aliette WDG and both rates of Kocide (Table 1). Disease severity was relatively low in this test and it was repeated later in the year. In the second test, treatments were applied between 31 October and 19 December 1991. Plants were inoculated on both 12 November and 9 December and the number of lesions per plant was rated on 30 December 1991. None of the bactericides tested gave a high degree of disease control in this test. The higher rate of Kocide, both rates of Aliette 80WP, and the higher rate of Aliette 80WDG gave the best disease control in this test (Table 1).

Xanthomonas leaf spot of English ivy is caused by Xanthomonas campestris pv. hederae which also causes disease on aralia (Polyscias spp.) and scheffleras (Brassaia and Schefflera spp.). The first of two tests conducted in 1991 used the same treatments as described above for the anthurium test. Treatments were applied between 7 and 21 June 1991. Plants were inoculated on 11 June and the number of lesions per plant was recorded on 24 June 1991. Best control was achieved with both rates of Aliette 80WDG and Kocide at the 1 lb per 100 gal rate (Table 2). The second test on English ivy employed the treatments described for the Pseudomonas test on Impatiens. In this test, treatments were applied between 15 November and 1 December 1991. Plants were inoculated on 19 November and the number of lesions per plant was recorded on 2 December 1991. ASC66825 gave good control of Xanthomonas leaf spot of English ivy and was equivalent to Kocide in efficacy (Fig. 2). Greenshield did not give significant disease control on English ivy at the rates tested.

Xanthomonas leaf spot of geranium (Pelargonium hortulanum) is caused by Xanthomonas campestris pv. pelargonii The same treatments as described above for the anthurium test were used. Treatments were applied between 8 and 22 August with inoculation on 20 August and rating on 28 August 1991. None of these treatments gave any significant degree of disease control although most treated plants had fewer lesions than the water sprayed inoculated controls (Table 2).

Aliette 80WP and Aliette 80WDG gave approximately the same degree of control but were not very effective when compared to Kocide in these tests. The difference between the low and high rates of the Aliette formulations was not consistent and use of the lower rate would probably be desirable to reduce pesticide costs. ASC-66825 (fluazinam) gave good control of Xanthomonas on English ivy but failed to control Pseudomonas on impatiens. Further testing is needed to determine if the degree of control is affected by the pathogen, the plant or both. Finally, daily applications of Greenshield were able to reduce severity of Xanthomonas on English ivy but not Pseudomonas on impatiens, again indicating the need for further testing. Kocide 101 77WP continues to provide the best control available for bacterial diseases of ornamentals. When disease pressure is relatively high, the degree of control may be correspondingly poor. Current tests involve use of a variety of copper compounds as well as ASC-66825 and Greenshield.

Table 1. Effect of Aliette 80WP, Aliette 80WDG, and Kocide 101 77WP on severity of Xanthomonas leaf spot and blight of aroids.

Treatment^a	oz per 100 gal	Anthurium no.blighted leaves^b	Dieffenbachia no. lesions test 1^c	Dieffenbachia no. lesions test 2^c
Noninoculated	---	0.8 a	0 a	0 a
Inoculated	---	1.8 c	1.2 ab	19.1 c
Aliette 80WP	40	1.2 bc	0.3 a	10.2 b
Aliette 80WP	80	0.9 b	1.4 ab	10.8 b
Aliette 80WDG	40	1.2 bc	2.0 b	16.2 bc
Aliette 80WDG	80	1.8 c	0.2 a	8.5 b
Kocide 101 77WP	16	1.2 bc	0.1 a	15.0 bc
Kocide 101 77WP	32	0.4 ab	0.4 a	10.9 b

^aIn the Anthurium test, the 80 oz rates of Aliette 80WDG and Aliette 80WP were applied on 8 and 22 August and 5 and 19 September 1991. Other treatments were applied weekly from 8 August to 3 October 1991. In the first Dieffenbachia test, the 80 oz rates of Aliette 80WDG and Aliette 80WP were applied on 7 and 21 June and 5 and 18 July, 1991. Other treatments were applied weekly from 7 June to 25 July 1991. In the second Dieffenbachia test, the 80 oz rates of Aliette 80WDG and Aliette 80WP were applied on 31 October, 15 and 27 November and 12 December 1991. Other treatments were applied weekly from 31 October to 19 December 1991. b Anthurium plants were inoculated on 20 August and 23 September and the number of leaves with blight symptoms was recorded on 20 September 1991 (the second rating is not presented).
^c Dieffenbachia plants in test 1 were inoculated on 11 June and the number of lesions per plant was recorded on 10 July 1991. Dieffenbachia plants in test 2 were inoculated on 12 November and 9 December and the number of lesions per plant was recorded on 30 December 1991.

Table 2. Effect of Aliette 80WP, Aliette 80WDG, and Kocide 101 77WP on severity of Xanthomonas leaf spot of English ivy and geranium.

Treatment^a	oz per 100 gal	English ivy no.lesions^b	Geranium no. lesions^c
Noninoculated	---	0.3 a	0 a
Inoculated	---	14.5 b	113.0 b
Aliette 80WP	40	9.7 b	60.8 b
Aliette 80WP	80	13.3 b	99.6 b
Aliette 80WDG	40	7.6 ab	88.3 b
Aliette 80WDG	80	7.8 ab	72.9 b
Kocide 101 77WP	16	5.5 ab	61.6 b
Kocide 101 77WP	32	12.5 b	72.0 b

^aIn the English ivy test, the 80 oz rates of Aliette 80WDG and Aliette 80WP were applied on 7 and 21 June and other treatments were applied weekly from 7 to 21 June 1991. In the geranium test, the 80 oz rates of Aliette 80WDG and Aliette 80WP were applied on 8 and 22 August and the other treatments were applied weekly from 8 to 22 August 1991.
^bEnglish ivy plants were inoculated on 11 June and the number of lesions per plant was recorded on 24 June 1991.
^cGeranium plants were inoculated on 20 August and the number of lesions per plant was recorded on 28 August 1991.

Figure 1. Effect of Kocide 101, ASC-66825, and Greenshield on growth and severity of Pseudomonas leaf spot of Impatiens Wallerana caused by P. syringae.

Figure 2. Effect of Kocide 101, ASC-66825, and Greenshield on severity of Xanthomonas leaf spot of Hedera helix (English ivy caused by X campestris pv. hederae.

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

1.Chase, A.R. 1986. Effect of experimental bactericides on three bacterial diseases of foliage plants. Journal of Environmental Horticulture 4:3741.

2.Chase, A.R. 1987. Effect of fosetyl aluminum on severity of two Xanthomonas leaf spot diseases. Proc. of Symposium on Aliette. pp. 81-86.

3.Chase, A.R. 1987. Update on controlling three bacterial diseases of foliage plants. Foliage Digest 9(8):1-2.

4. Chase, A. R. 1989. Aliette 80WP and Bacterial Disease Control - Xanthomonas. Foliage Digest 12(11):1-3.

5. Chase, A. R. 1989. Aliette 80WP and Bacterial Disease Control - Pseudomonas and Erwinia. Foliage Digest 12(11):3-4.

6. Chase, A. R. 1989. Aliette 80WP and Bacterial Disease Control - Phytotoxicity. Foliage Digest 12(11):4-5.