EPIDEMIOLOGY AND MANAGEMENT OF ALTERNARIA LEAF SPOT IN COTTON
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Date
2017
Authors
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Publisher
Acharya N.G. Ranga Agricultural University
Abstract
Alternaria leaf spot/blight of cotton caused by Alternaria macrospora
Zimmermann is the most commonly occurring disease in Andhra Pradesh.
A. macrospora is found to be an aggressive pathogen which can attack all crop growth
stages starting from seedling stage to harvesting manifesting in seed rot, damping off,
seedling blight, mummification of bolls etc. Under severe conditions it causes severe
defoliation, cracking, breaking of stems and reduction in boll formation.
Epidemiological studies indicated that irrespective of different dates of sowing,
Alternaria leaf spot occurred at its first peak intensities (17.5%, 18.25% and 18.33%) in
44th meteorological week (Oct 29-Nov 4) and its second maximum intensities (39.25%,
33% and 33.5%) in 1
st standard meteorological week (Jan1- Jan7). Among the weather
parameters sunshine significantly influenced the disease progress in susceptible Jadoo
BG II hybrid.
Fungicides viz., mancozeb, carbendazim, hexaconazole, propiconazole and
carbendazim 12% + mancozeb 63%; botanicals viz., neem leaf, garlic clove extracts
and biocontrol agents T. harzianum strain 1, P. fluorescens strain 1 and B. subtilis
significantly inhibited the growth of A. macrospora in vitro. Interactions with all the
Trichoderma strains in dual culture revealed lysis of A. macrospora with evidence of
protoplast aggregation, wrinkling of mycelium and germination of Trichoderma
conidia on Alternaria mycelia.
Field evaluation of seed treatment and foliar spray of selected fungicides,
botanicals and biocontrol agents against Alternaria leaf spot of cotton showed that ST
with carboxin + thiram (vitavax power) at 2 g kg-1
of seed and 0.1% carbendazim +
mancozeb sprays, three times, at 15 days interval recorded the lowest per cent disease
index (6.8), the highest yield (1571.4 kg ha-1
) and the highest benefit cost ratio (1.61)
compared to per cent disease index (35), yield (1013 kg ha-1
) and benefit cost ratio
(0.69) in control.
Description
D5444
Keywords
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