New Zealand Journal of Crop and Horticultural Science abstracts
Assessment of seed tuber, in-furrow, and foliar chemical treatments
for control of powdery scab (Spongospora subterranea
f.sp. subterranea) of potato
R. E. FALLOON
A. R. WALLACE
New Zealand Institute for Crop & Food
Research Limited
Private 4704
Christchurch, New Zealand
M. BRAITHWAITE
Plant Protection Centre
MAF Quality Management
P.O. Box 24
Lincoln, New Zealand
R. A. GENET
H. M. NOTT
J. D. FLETCHER
W. F. BRAAM
New Zealand Institute for Crop & Food
Research Limited
Private 4704
Christchurch, New Zealand
Abstract Two field trials were carried out (at different
sites at Lincoln, Canterbury, New Zealand) to test the efficacy of chemicals
for control of powdery scab (caused by Spongospora subterranea (Wallr.)
Lagerh. f. sp. subterranea Tomlinson) of potato (Solanum
tuberosum L.). In Trial 1, at a site where potatoes had not been previously
grown, 17 seed tuber treatments and eight in-furrow treatments were applied
just prior to, or at, planting, to seed tubers of `Agria' infected with powdery
scab, and six foliar treatments were later applied to plants grown from
infected tubers. In Trial 2, seven in-furrow treatments were applied at the
time of planting healthy seed tubers of `Rua' or `Agria' into a field site
heavily infested with S. subterranea, and one foliar treatment was later
applied to plants of `Rua'. Both trials were irrigated to provide soil
conditions likely to encourage development of powdery scab. The trials were
harvested at crop maturity, when all tubers were assessed for powdery scab
infection, and yield parameters were determined. In Trial 1, treating
scab-infected seed tubers with fluazinam, mancozeb, dichlorophen-Na,
dichlofluanid, or a mixture of fluazinam + mancozeb before planting reduced the
incidence of powdery scab in harvested tubers. All of these chemicals, except
dichlofluanid, increased the yield (kg/plot) of "marketable" tubers (those with
<5% tuber surface infected with powdery scab) by up to 36%. In-furrow
applications of fluazinam, mancozeb, or a mixture of zinc oxide + zinc sulfate
also reduced the incidence of the disease, and fluazinam and mancozeb in-furrow
treatments increased yields of marketable tubers by up to 20%. Seed tuber
treatments with zinc oxide or tolclofos-methyl + cupric hydroxide, in-furrow
treatment with zinc oxide, or foliar treatments with phosphorous acid, did not
control the disease. Few effects of different rates of chemicals were detected,
and seed tuber and in-furrow treatments with both fluazinam and mancozeb gave
equivalent levels of powdery scab control. In Trial 2, in-furrow treatments
with fluazinam reduced powdery scab incidence, and increased yield of
marketable `Rua' tubers by up to 55%, and `Agria' tubers by 140%. High rates of
mancozeb also reduced incidence of the disease and increased marketable yield
of `Rua' by 34%, and of `Agria' by 68%. Effective treatments had no effect on
numbers of tubers produced but increased total yield, suggesting that severe
attack by S. subterranea may have affected plant growth and tuber
development. In-furrow treatment with zinc oxide and foliar treatments with
phosphorous acid did not control the disease. A low rate in-furrow mancozeb
treatment increased powdery scab incidence. These results confirm that
chemicals from several different classes can control powdery scab of potatoes.
In-furrow chemical treatments, both for infected seed tubers planted into
disease-free soil and for healthy seed tubers planted into soil infested with
S. subterranea, may provide an alternative to seed tuber treatment for
applying chemicals to control the disease. Minimum rates of fluazinam and
mancozeb for effective control of powdery scab were: for seed tuber treatment,
25 g fluazinam/100 kg seed tubers or 40 g mancozeb/100kg; and for in-furrow
application, 2 kg fluazinam/ha or 7.5 kg mancozeb/ha. Chemical treatments are
recommended as part of an integrated disease management strategy for powdery
scab, along with the use of resistant potato cultivars and appropriate cultural
practices.
Keywords potatoes; Solanum tuberosum; powdery scab;
Spongospora subterranea f. sp. subterranea; chemical control;
seed tuber treatments; in-furrow treatments
New Zealand Journal of Crop and Horticultural Science, 1996, Vol. 24:
341-353
0114-0671/96/2404-0341 $2.50/0 (c) The Royal Society of New Zealand
1996
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