Managing Diseases of Ornamentals with Bicarbonates and Determining their Mode of Action Progress Report –September 1992
Date August 21, 1992
Title of Project Managing Fungal Diseases of Ornamentals with Bicarbonates and Determining their Mode of Action
Institution where work is being conducted Cornell University
Amount of Endowment Grant $ 20,000
Covering Period 1 January to 31 December 1992
Anticipated Date of Project Completion/Final Report 31 December 1994
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 with Bicarbonates and Determining Their Mode of Action
R. K. Horst and H. W. Israel
Cornell University
- 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. Concern over unimpeded fungicide application derives from a serious consideration of:(i) worker safety and reentry; (ii) glasshouse drainage water contamination; (iii) fungicide residue exposure of
product consumers; and (iv) crop photosynthetic/yield reductions. Review has shown that bicarbonate
solutions and horticultural oils, both “natural” substances with antifungal properties, are likely candidates for
the biocompatible treatment of diseased plants (and alarmed citizens). Our work has strengthened and
underscored the likelihood. We have now determined the minimum effective bicarbonate treatment necessary
for management of rose powdery mildew.
- Mechanism Studies. Four experimental near-optically ideal systems have been established to find thetime/space window in the rose powdery mildew cycle through which the mechanism(s) for bicarbonate efficacy
can be observed. The systems have been constructed in a way that permit microscopic and quantitative
determinations of: (i) whether bicarbonates function as eradicants and/or preventives; (ii) whether, when, and
at what rate bicarbonates adversely impact spore viability, germinability, and/or penetrability; (iii) bicarbonate
dose response levels; and (iv) adjuvant dose response levels.
- C. Results to Date:
- Efficacy Studies. Powdery mildew, caused by Sphaerotheca pannosa (Wall ex. Fr.) Lerv. var. rosae Wor.,the costliest disease of glasshouse grown Rosa spp. in the world, together with blackspot, caused by
Diplocarpon rosae Wolf, the most serious pair of diseases of nursery and garden grown roses, are significantly
managed by weekly sprays of 0.5% (w/w) aqueous solutions of either potassium or sodium bicarbonate plus
0.5% or 1.0% (v/v) SunSpray Ultra-fine Spray Oil. Bicarbonates with oil are more efficacious than either alone
in the apparent eradication of the pathogens from the host plants.
- Very recent studies on effective dose minima indicate that although 0.5% and 0.25% concentrations of bothsodium and potassium bicarbonate significantly reduce powdery mildew severity, 0.5% is the more effective.
The studies also show that ammonium bicarbonate is not as efficacious as sodium or potassium and that
0.05% bicarbonate sprayed weekly will not effectively control powdery mildew.
- Mechanism Studies. Work with naturally inoculated leaflets sampled 24 and 48 hours after treatment invarious ways has indicated noteworthy results with respect to conidial germination. These include striking
differences in efficacy among the bicarbonates and their concentrations, much enhanced efficacies of
bicarbonates over the organic fungicide Banner, and no effects whatsoever on germination by SunSpray oil
alone.
- Studies which made use of intact plants have revealed that after one adaxial foliar spray application ofpotassium bicarbonate (i) superficial pathogen structures are eradicated, (ii) host epidermal layers recover
completely from infection but contain phenolic-rich cells, and (iii) the bicarbonate and/or its effect(s) are neither
mediated nor translocated by the host tissues.
- Thus far it is inferred that bicarbonate either dessicates, plasmolyzes, ruptures, and/or devacuolates fungalpathogen cells, including pregerminated spores. Any or all of these effects, although ontogenetically
nonspecific, are judged presently to be markedly deleterious to the fungus.
- 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, and Alternaria. We will carry out experiments to more intensely explore these and other
pathogen sensitivities.
- 2. The mechanism(s) which we have developed provide us the means for thoroughly studying at the cellularlevel how the interactions between host and pathogen cells are affected by bicarbonates. We will thoroughly
study the mechanism(s) of activity.
- E. Anticipated Benefits for Floral Industry:
- The bicarbonates which we term biocompatible chemicals will have an exciting impact on disease controldue to increased public and commercial concerns about environmental quality. The breadth of effectiveness
in disease control and the mechanism(s) by which bicarbonates inhibit pathogens are important components
in developing the optimal bicarbonate systems approach in disease control.
