4. Symptoms:
o Initially, reddish spots of 0.5mm to 1cm diameter may
appear on the margin of the leaves.
o Disease symptoms are lesions with concentric
necrotic rings, with salient structures(sporodochia)
irregularly distributed.
o The affected portions fall off leaving irregular shot
holes on the leaves.
o The symptoms are observed on the petioles, bracts,
leaves and bolls.
6. Isolation:
o The pathogen was isolated and extracted in Potato-
dextrose-agar medium.
o Thirteen isolates of M. roridum were tested, which
includes 8 from cotton and 5 from soyabean.
o Fungal structures were evaluated by using light
microscope with ocular micrometer.
o The MA-75 was the most aggressive strain.
o Spores from cotton isolates are 5,1µm × 1,5µm.
o This is the first report on Myrothecium leaf spot from
Brazilian cotton fields.
7. Pathogen:
o Myrothecium roridum Tode ex Fr.
o Conidia are hyalines due to dilute olivaceous, single-
celled, abundantly produced in a dark green to black
aggregate mass.
o Spores from cotton isolates are 5,1µm × 1,5µm.
10. Favourable condition:
o In vitro studies show that the maximum disease
development was reported at 25ºC±1 in both Bt cotton
and non Bt cotton crops.
o Average humidity: 84.7%.
o Rain: 11.4mm.
o pH : 6.
o Heavy during June – October.
o Dense crop canopy.
o The leaf spot incidence increased with delay in sowing
date at 15 days interval from 1-April to 1- june.
12. Biological management:
By medicinal plant extract:
Maximum inhibition ia obtained at 5% solvent
extract of Datura metal followed by Alium sativum and
Eucalyptus citriodora.
By bioagent:
Apply Trichoderma harzianum, Pseudomonas
fluorescens.
13. Chemical management:
o Spray Mancozeb or Copper oxychloride at 2kg/ha at
the intimation of the disease.
o Two to three sprays may be given at 15 days interval.
o In vitro studies indicated that propiconazole and cobalt
chloride at 100 and 1000 ppm conc gave 100 and
87.9% growth inhibotion of M. roridum.
o Foliar spray of propiconazole and salicylic acid at
0.1% and 0.01 % effectively controls disease.
