Abstract Phosphonic (phosphorous) acid (Fol

M F Wachtel

P A Magarey

T J Wicksb

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Phosphonic (phosphorous) acid controls Plasmopara viticola 
the cause of downy mildew of grapevines 
P.A. Magarey*, T.J. WicksB and M.F. Wachtel* 
ASouth Australian Department of Agriculture, Loxton, South Australia 5333 
=South Australian Department of Agriculture, Northfield, South Australia 5085 
Abstract 
Phosphonic (phosphorous) acid (Foli-R-Fos 200) has been 
extensively evaluated in glasshouse and field trials since 
1986. This new fungicide (at 600 mL1100L) demonstrated 
a high level of efficacy in the post- but not pre-infection 
control of Plasmopara viticola. Control equivalent to Ridomil 
MZ 720WP was achieved up to 17 days post-infection 
reducing sporulation and hastening oilspot necrosis. A 
tank-mix with copper oxychloride offers potential to com- 
plement existing fungicides in Australian anti-resistance 
management strategies. 
Until recently the only fungicide registered in Aust- 
ralia for post-infection control of grapevine downy 
mildew (caused by Plasmopara viticola (Berk. & 
Curt.) Berl, and de Toni) was the phenylamide 
metalaxyl (Ridomil Plus). Tests of the efficacy of 
phosphonic acid (H3P03 on P. viticola were of in- 
terest because another phosphonate fungicide, 
fosetyl-Al was an effective inhibitor of P. vitticola (Co- 
hen and Coffey 1986). Also H3P03 had shown high 
levels of efficacy against Phytophthora species, a 
related pathogen (Pegg et al. 1985; Cohen and 
Coffey 1986). 
Glasshouse and field evaluation of H3P03 began 
in South Australia in 1986 and is summarised here. 
Phosphonic acid was applied as a foliar spray of Foli- 
R-Fos 200 (UIM Agrochemicals (Aust.) Pty Ltd, Bris- 
bane, Qld) at 600 mL f.p.1100 L. 
Post-infection efficacy Phosphonic acid reduced 
disease incidence when a single spray was applied 
up to 3 days after infection and reduced the area 
of leaf affected when applied up to 13 days after 
infection. A single application at least 7-9 days post- 
infection significantly reduced sporulation in numer- 
ous experiments (Magarey and Wachtel 1987; 
Magarey et al. 1987; Wicks et a/. 1990). In three 
experiments when the incubation period for downy 
mildew was 10 days, the disease was controlled 
when sprays were applied as late as 17 days post- 
infection. The efficacy in these experiments was 
mainly through significant reduction in sporulation 
and hastening of necrosis of oilspots which dried out 
and died more quickly, thus more effectively eradi- 
cating the disease (Magarey and Wachtel 1987; 
Magarey et a/. 1987; 1990). 
Sporangia that developed from foliage sprayed up 
to 17 days post-infection were reduced in viability, 
resulting in further reduction in the potential for 
epidemics to develop (Magarey et a/. 1987; 1990). 
Spread of P. viticola from active lesions sprayed 4 
days post-infection, was prevented (Magarey and 
Wachtel 1987). 
GeneraUy, in post-infection application Foli-R-Fos 
200 has performed as well as, if not better than 
recommended rates of Ridomil MZ 720 WP (metal- 
axyl + mancozeb, Ciba Geigy (Aust.) Ltd). 
Pre-infection efficacy In 16 experiments, H3PO3 
alone gave poor pre-infection (protectant) control of 
downy mildew, controlling the disease only if applied 
1 to 7 (usually 3) days before infection (Magarey et 
a/. 1989). These experiments failed to confirm previ- 
ous glasshouse tests (Magarey and Wachtel 1987). 
Weekly applications did not improve the efficacy of 
H3P03. 
The hydrolysis product of H3PO3 in plants is 
phosphonate (Ouimette and Coffey 1988) and is 
extremely mobile within vine tissues moving from 
leaf to leaf, both up and down shoots. Phosphonate 
residue levels in leaf tissues were determined effici- 
ently and quickly (Glenn etal. 1990). Levels declined 
rapidly within the first 5 days from application. This 
rapid movement of phosphonate probably accounts 
for the lack of pre-infection control of P. viticola by 
H3P03. 
In glasshouse experiments H3P03 was taken up 
by the roots of potted vines and controlled infection 
by P. viticola but application of the fungicide to the 
soil via drip-irrigation systems for control in vineyards 
was not successful. 
Foli-R-Fos 200 can be mixed with mancozeb, cop- 
per oxychloride, the powdery mildew fungicides 
Bayleton, Tilt, and sulphur, and with the foliage 
nutrients zinclmanganese (proprietary mixture) and 
nitrogen (as urea), without affecting its activity. Tank 
mixes with copper oxychloride were effective. They 
both eradicated existing infection and provided pro- 
tection, demonstrating the potential to increase 
growers' spray efficiency with a single tank-mix 
application. Fermentation and wine taste studies 
showed Foli-R-Fos 200 was safe to use on wine 
grapes and should leave no harmful residues to 
cause concern on export markets. 
Rates of Foli-R-Fos 200 above 5 LllOO L were 
phytotoxic and until low volume and other methods 
of application are evaluated, care should be taken 
to avoid rates approaching 5 L Foli-R-Fos 2001100 L 
of water. 
Summary 
Foli-R-Fos 200 is a safe and effective fungicide for 
Australasian Plant Pathology Vol. 19 (4) 1990 
post-infection control of downy mildew. It is now 
registered for use in south-eastern Australian viticul- 
ture, but its use should be restricted to applications 
made as soon as possible after infection, preferably 
within 7-10 days. 
The addition of copper oxychloride in a tank-mix 
should give good pre- and post-infection control of 
downy mildew. This mix offers significant potential 
to complement existing phenylamide fungicides in 
anti-resistance strategies for Australian viticulture. 
Acknowledgements 
We thank Australian Grape and Wine Research 
Council and Mr Clyde Waugh, UIM Agrochemicals 
(Aust.) Pty Ltd, for financial assistance. 
References 
Cohen, Y. and Coffey, M.D. (1986)-Systemic fungicides 
and the control of Oomycetes. Annual Review of 
Phytopathology 24: 31 1-338. 
Glenn, T.J., Biggins, M.R. and Magarey, P.A. (1990)- 
Rapid, quantitative detection of phosphite by simple ion- 
exchange chromatography using post-separation sup- 
pression. Proceedings of the Phosphonic (Phosphorous) 
Acid Workshop, 7th Australasian Plant Pathology 
Society Conference, Brisbane, Qld 3-7 July 1989, Aust- 
ralasian Plant Pathology 19: 139-1 40. 
Magarey, P.A. and Wachtel, M.F. (1987)-Control of grape- 
vine downy mildew with phosphorous acid. Proceedings 
6th Australasian Plant Pathology Society Conference, 
Adelaide, SA, May 1987, p. 45. 
Magarey, P.A., Wachtel, M.F., Frensham, A.B. and 
McHenry, W. (1987)-Strategic use of acylanilide and 
phosphonate fungicides against grapevine downy mil- 
dew. Proceedings 6th Australasian Plant Pathology 
Society Conference, Adelaide, SA, May 1987, p. 46. 
Magarey, P.A., Wachtel, M.F. and Newton, M.R. (1990)- 
Evaluation of phosphonic (phosphorous) acid, phosethyl- 
Al and several phenylamide fungicides for post-infection 
control of grapevine downy mildew caused by Plas- 
mopara viticola. Australasian Plant Pathology (in press). 
Magarey, P.A., Wicks, T.J. and Wachtel, M.F. (1989)- 
Field evaluation of phosphorous acid for the control of 
grapevine downy mildew. Proceedings 7th Australasian 
Plant Pathology Society Conference, Brisbane, Qld, 3-7 
July 1989, p. 113. 
Pegg, K.C. Whiley, A.W., Saranah, J.B. and Glass, R.J. 
(1985)--Control of Phytophthora root rot of avocado with 
phosphorous acid. Australasian Plant Pathology 14: 
25-29. 
Wicks, T.J., Magarey, P.A., Wachtel, M.F. and Frensham, 
A.B. (1990)-Effect of post-infection application of phos- 
phorous (phosphonic) acid on the incidence and sporul- 
ation of Plasmopara viticola on grapevine. Plant Disease 
74: (in press). 
The control of black pod, canker and seedling blight of 
cocoa, caused by Phytophthora palmivora, with potassium 
phosphonate 
R.D. AndersonA and D.I. GuestB 
ACocoa Black Pod Research Trust of Papua New Guinea, P.O. Box 71 1, Madang, Papua New Guinea 
BSchool of Botany, University of Melbourne, Parkville, Victoria 3052 
Abstract 
Trunk injected potassium phosphonate (8 or 16 g a.i. per 
tree every 6 months) controls ljlack pod and stem canker 
of cocoa. Foliar sprays of potassium phosphonate (20 g 
a.i. per tree every 6 months) or Ridomil Plus 72WP (0.72 g 
a.i. per tree every 6 weeks during the wet season) do not 
control black pod. Trunk injection is less weather depen- 
dent than foliar sprays, and is a more effective application 
method for mature trees in the cocoa growing areas of 
Papua New Guinea. Single Ridomil Plus 72WP (0.8%) or 
potassium phosphonate (4%) sprays control artificially 
inoculated seedling blight more effectively than either a 
lower rate of potassium phosphonate (0.5%) spray or a 
soil drench of potassium phosphonate (1 010). 
Introduction 
Phytophthora palmivora (Butl.) Butl. is the most des- 
tructive pathogen of cocoa (Theobroma cacao L.) in 
Papua New Guinea. The disease affects all parts 
of the plant, but the major losses are due to fruit rot 
(black pod), bark canker and seedling blight. Yield 
losses of up to 39% have been attributed to black 
pod, and canker and blight cause further losses in 
PNG (McGregor 1982). In this paper we present the 
results of three experiments using potassium phos- 
phonate and Ridomil Plus 72WP to control these 
diseases. 
Methods 
All trials were conducted on Kar Kar Island, Madang 
Province in Papua New Guinea, a cocoa growing 
area with high rainfall and black pod incidence. 
Fungicides Potassium phosphonate was pre- 
pared by titrating a solution of phosphonic acid 
Australasian Plant Pathology Vol. 19 (4) 1990 


Phosphonic (phosphorous) acid controls Plasmopara viticola the cause of downy mildew of grapevines

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Phosphonic (phosphorous) acid controls Plasmopara viticola the cause of downy mildew of grapevines

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