Fungicides to Replace Benlate for some Diseases of Ornamentals

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A R Chase, Ph.D.

University of Florida, IFAS
Central Florida Research and Education Center - Apopka,
2807 Binion Rd., Apopka, FL 32703.

This work was supported in part through grants from the following chemical companies: Ciba-Geigy Corporation, Elf-Atochem North America, Grace-Sierra Crop Protection Company, ISK Biotech Corporation, Kincaid Enterprizes Inc., Rhone Poulenc Ag Company, Rohm and Haas Company, Sandoz Agro, Inc., and Uniroyal Chemical Company, Inc.

On September 11, 1991, Dupont deleted all ornamental uses from the Benlate 50WP label. Due to its range of activity against plant pathogenic fungi and its broad label including all ornamentals this fungicide was widely used for many diseases on ornamentals. Many growers have faced the problem of replacing Benlate 50WP with another efficacious compound. There are a number of potential candidates available for a replacement, but their spectrum of activity and/or label restrictions make simple substitution impossible.

The most likely compound to fill the Benlate 50WP gap is thiophanate methyl. Thiophanate methyl has the same mode of action as Benlate 50WP although the active ingredient differs. There are currently a number of flowable and wettable powder formulations of thiophanate methyl: Cleary's 3336 (flowable and wettable powder in prepackaged water soluble bags from Cleary's), Domain FL (flowable from Grace-Sierra), Fungo 50WP (wettable powder from Grace-Sierra), Systec 1998 (flowable from Regal), and Topsin M (flowable from Atochem).

In addition, there are a wide variety of other fungicides which could be used in place of Benlate 50WP including both registered and experimental compounds. The following research was conducted to fill some of the data gaps regarding the fungicides for diseases on a wide variety of ornamentals caused by Alternaria, Cylindrocladium, Fusarium, Helminthosporium, powdery mildew, Rhizoctonia, and Sclerotinia spp. Specific fungicides, plants and diseases are given in the tables as well as the results of the tests.

Alternaria and Helminthosporium Leaf Spots

Benlate was never an appropriate choice for control of either Alternaria or Helminthosporium leaf spot since it was not effective against these fungi. Since some growers used Benlate for these diseases, a number of tests were performed. The tests summarized in Table 1 showed that the thiophanate methyl compounds also failed to give a significant level of control (Fungo and Domain). Best disease control was consistently given with Chipco 26019, Daconil, fluazinam (experimental compound) and Manzate. Terraguard and Domain gave a limited amount of control in one trial. Phytotoxicity occurred in the Aechmea trial when plants were treated with either Daconil or fluazinam.

Cylindrocladium diseases

Benlate was routinely used on a number of crops to control Cylindrocladium diseases. Previous work has shown that Terraguard gives better control than alternatives for Cylindrocladium root and petiole rot of Spathiphyllum. The winter test also showed that under lower disease pressure all the thiophanate methyl compounds tested (Cleary, Domain and Systec) as well as fluazinam (experimental compound) can give good disease control.

Tests with Cylindrocladium cutting rot on azaleas and miniature roses showed that many compounds can give some disease control although none were excellent The experimental compounds bromuconazole, cyperconazole, and myclobutanil did not give any measurable control in these trials. Terraguard gave some control in one trial on azaleas but no control in the miniature rose trial.

Fusarium Leaf Spot on Dracaena

Fusarium diseases have long been targets for control with Benlate. Three tests were performed to evaluate fungicides for control of Fusarium leaf spot on red-edge dracaena. The only compound which did not give a significant degree of control was Terraguard. The thiophanate methyl compounds gave some to excellent control depending on disease severity. Zyban is a combination of thiophanate methyl and mancozeb (Manzate).

Powdery Mildew on Gerber Daisy

Although there are several fungicides which give better control of powdery mildew diseases Benlate was used on some crops for this disease. Our test identified a number of compounds were identified which gave excellent control of powdery mildew on gerber daisies, although many of them also caused phytotoxicity. Funginex caused the most severe phytotoxicity, while myclobutanil (experimental compound) was apparently safe at low rates but caused problems at the highest rates tested. Very slight phytotoxicity was seen on plants treated with either bromuconazole (experimental compound) or Chipco 26019. The two thiophanate methyl compounds (Fungo or Topsin M) gave a lesser degree of control.

Rhizoctonia Diseases

Some of the Rhizoctonia diseases were easier to control than others. The easiest disease to control was aerial blight of Boston fern. All of the chemicals tested gave excellent disease control including the two thiophanate methyl compounds (Domain and Fungo). Damping-off of China Doll seedlings was also controlled by Domain and Topsin M, but Terraclor and Terraguard gave only moderate control of this Rhizoctonia disease. Stem rot of Impatiens was controlled with four fungicides but again Terraclor and Terraguard gave a lesser degree of control. The pothos trials showed a reversal with the best control achieved when Terraclor or Terraguard were used and a lesser degree of control with the thiophanate methyl compounds (Cleary, Domain, Fungo, Systec, and Topsin M).

The final trial was performed on aerial blight of pittosporum which is caused by a binucleate type of Rhizoctonia (not R. solani). In this trial, Terraneb did not give any disease control, although it gave excellent control of aerial blight of Boston fern which is caused by R solani. Domain gave excellent control of aerial blight of pittosporum.

Sclerotinia Blight on Platycodon (Balloon Flower)

One trial was performed for control of Sclerotinia blight. Manzate gave the best control with Chipco 26019, Daconil, fluazinam (experimental compound), and myclobutanil (experimental compound), also giving some disease control. Both Sentinel and Terraguard failed to give any disease control in this trial.

Conclusions

These tests have established alternative fungicides which should effectively replace the use of Benlate for many diseases of ornamentals. Since none of these compounds is broadly labeled for all ornamentals, growers must consult labels to determine legal crops, rates and intervals for use. The widespread interest of the chemical companies which market products for ornamentals indicates that fungicides will continue to be available for control of our most serious diseases of these crops.

 

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References

1. Chase, A.R. 1990. Phytotoxicity of bactericides and fungicides on some ornamentals. CFREC-A Research Report, RH-92-5.
2. Simone, G.W. and A.R. Chase. 1989. Disease control pesticides for foliage production (Revision #4). Foliage Digest 12(9):1-8]

Pesticides should be applied according to label directions.

Regardless of the pesticide or mixture of pesticides used, it is
strongly recommended that the effects be evaluated on a few
plants, under your particular conditions before treating all plants.

Mention of a commercial or proprietary product in this paper
does not constitute a recommendation by the authors,
nor does it imply registration under FIFRA as amended.

Reference to University of Florida/IFAS Pest Control Guides