New Zealand Journal of Crop and Horticultural Science abstracts
Control of powdery scab of potatoes with chemical seed tuber treatments
M. BRAITHWAITE
Plant Protection Centre
MAF Quality Management
P.O. Box 24
Lincoln, New Zealand
R. E. FALLOON
R. A. GENET
A. R. WALLACE
J. D. FLETCHER
W. F. BRAAM
New Zealand Institute for Crop & Food
Research Ltd
Private Bag 4704
Christchurch, New Zealand
Abstract Powdery scab, caused by
Spongospora
subterranea (Wallr.) Lagerh. f. sp.
subterranea Tomlinson, has
become an increasingly important problem on potatoes grown in New Zealand in
recent seasons. During the 1992/93 season, the efficacy of 25 chemical seed
tuber treatments against tuber-borne inoculum of
S. subterranea was
tested in a field trial. Four treatments (stored treatments) were applied 6
weeks before planting whereas 21 were applied within 24 h of planting.
Treatments were applied to tubers of cultivars `Agria' (which had severe
powdery scab infection) and `Rua' (light infection). Plant emergence was
assessed and tubers from the subsequent crop were harvested and scored for
powdery scab infection. Yield parameters were also determined. Mancozeb,
formaldehyde solution, fluazinam, propineb, dichlorophen-Na, and mixtures of
maneb + zinc oxide, mancozeb + zinc oxide, propineb + zinc oxide, fluazinam +
zinc oxide, and tolclofos-methyl + cupric hydroxide, applied to `Agria' tubers
just before planting, reduced the proportion of diseased tubers from 95% at
planting to an average of 29% in the subsequent crop compared with the mean for
controls of 70%. Inclusion of zinc oxide in these mixtures did not improve
disease control. Stored treatments of zinc sulfate and zinc oxide reduced
infection in the subsequent crop compared with untreated controls. For `Rua',
only dichlorophen-Na, maneb + zinc oxide dust, fluazinam + zinc oxide, and the
stored zinc oxide treatment reduced the proportions of diseased tubers.
Phytotoxic effects were observed with: formaldehyde solution (reduced plant
emergence, tubers harvested per plot and total tuber yield); zinc sulfate
stored (reduced emergence); tolclofos-methyl + cupric hydroxide (reduced
emergence and tubers per plot); tolclofos-methyl + zinc oxide (reduced tubers
per plot); and dichlorophen-Na (reduced tubers per plot).
Keywords potatoes; Solanum tuberosum; powdery scab;
Spongospora subterranea f. sp. subterranea; fungicides; seed
tuber treatments; control
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