Date August 25, 1993

Title of Project Managing Fungal Diseases of Ornamentals and Determining Their Mode of Action

Institution where work is being conducted Cornell University

Amount of Endowment Grant$ 20,000
Covering Period 03/01/93 to 08/31/93

Anticipated Date of Project Completion/Final Report 31 December 1994

Researcher did not apply for funding the final year

Individual(s) Conducting Project:

(List Project Leader First)

R. K. Horst - Title Professor

Telephone Number 607/255-7894

H. W. Israel - Title Senior Research Associate

Managing Fungal Diseases of Ornamentals and Determining Their Mode of Action

R. K. Horst and H. W. Israel

Cornell University

Final Report to the American Floral Endowment, 8/25/93

A. Project Objectives:

1. Which consequential diseases of ornamentals can be managed with

bicarbonates?

2. What is the minimal effective bicarbonate treatment necessary for

management of rose powdery mildew?

3. What is the mechanism(s) by which bicarbonate antagonizes Sphaerotheca

pannosa var. rosae?

B. Summary of Work Since Project’s Inception (1 January 1992):

Efficacy Studies: Our research has shown that bicarbonate solutions and horticultural oils

are excellent candidates for biocompatible control of plant disease.

Moreover, we now have formulations which contain bicarbonates as active

ingredients along with non-petroleum oil spreader-sticker supplements which

are more efficacious in control of rose powdery mildew and less phytotoxic.

Mechanistic Studies: Experimental methods previously described have determined bicarbonates to

be both preventive and eradicative in their activity. Viability and

germination percentages of powdery mildew conidia are strikingly reduced (99-100%)

within 1h submersion in KHCO3 at concentrations of 0.08M (0.5%

concentration).

C. Results to Date:

Efficacy Studies: Weekly sprays of 0.08M aqueous solutions of KHCO3 or NaHCO3 significantly

reduce mean disease severity of rose powdery mildew when combined with 0.5%

v/v Sunspray Ultrafine Spray Oil. Formulations containing both KHCO3 and

NaHCO3 as active ingredients and fatty acids as inactive ingredients are

equally efficacious and are less phytotoxic. Furthermore, the bicarbonate

formulations are more efficacious than commercially available agrichemicals

such as Pipron, Milban, and Banner.

Mechanism Studies: To learn how bicarbonates adversely affect established powdery mildew

infections of rose by S. pannosa var. rosae, the causal agent, we contrasted

paired leaflets, attached or detached, of the susceptible rose cultivar Sonia

after one postinoculation adaxial runoff spray of .08 M KHCO3 or of water.

Both intact and sectioned samples were examined by light and electron

microscopy. Superficial parasite structures and haustoria disappeared within

four days on adaxial surfaces where penetrated host epidermal cells recovered

but, with contiguous cells, exhibited phenolic-rich contents. Because abaxial

infection sites on the same leaflets flourished, as did all sites on water

sprayed leaflets, we infer that bicarbonate impacts the fungus directly, and

is not mediated by host tissues.

D. Future Plans Covered by the Endowment Grant:

1. In vitro tests in our laboratory show bicarbonates to be effective

against species of Fusarium, Colletotrichum, Alternaria, Botrytis,

Rhizoctonia, and Pythium. Our search will continue.

2. We are continuing our thorough investigations on the mechanism of

activity.

E. Anticipated Benefits for Floral Industry:

The bicarbonates which we term biocompatible chemicals will have an

exciting impact on disease control. An application will be made to EPA to

register a formulation we now have as soon as all the appropriate tests

required by EPA are completed.

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