278 V. N. Ghante et al.
considered as possible causative agents for red-
dening. As many as 40 reasons were documented
as factors influencing reddening in Bt cotton
(Ghante et al. 2010 ). Thus, a concerted effort in-
volving physiological, biochemical, nutritional
and biotic factors is required for diagnosing, con-
firmation and management of red leaf symptoms
in Bt cotton (Praharaj and Sankaranarayanan
2010 ). Survey work and field experiments for
reddening management on Bt cotton were un-
dertaken with the aim to understand (a) sucking
pests (b) multinutrient management for Bt cotton
reddening and (c) identification of tolerant Bt hy-
brids for reddening.
Material and Methods
Surveys were carried out across different Bt cot-
ton-growing belts of North Karnataka to know
the causes for reddening in Bt cotton through a set
of questionnaire. Thereafter, experiments were
designed and executed to validate the biotic and
abiotic factors known to cause the problem. Pot
culture experiments were conducted to know the
role of biotic factors such as insects and disease-
causing pathogens in symptom manifestation.
Field experiments with Bt hybrids, susceptible
to sucking pests were conducted with and with-
out sucking pest management and red leaf index
(RLI) at 60 and 100 DAS to know the role of
sucking insects, especially green leafhopper. RLI
is the manifestation of all the factors responsible
for reddening in leaves in cotton. RLI indicates
the degree of leaf reddening quantitatively (Das-
tur et al. 1952 ). As the performance of Bt cotton
hybrids depends on the interaction of hybrids and
environment, a total of 14 Bt cotton hybrids with
one non-Bt check (DCH-32) (most preferred by
farmers) was screened for reaction to reddening
under recommended package of practices and
unprotected conditions.
Integrated module includes (1) use of leaf red-
dening–tolerant cotton hybrid, namely Jackpot,
MRC 7351, MRC 7347 and Marvel; (2) balanced
and timely soil application of macro- and micro-
fertilizers; (3) threshold-based management of
sucking pests, especially leafhopper, using effec-
tive systemic insecticides like Acephate 75 SP at
1 g/L, Clothianidin 50WG at 0.07 g/L and Thia-
methoxam at 0.25 g/L; (4) seed treatment with
Trichoderma 4 g/kg seeds against wilt and foliar
application of Mancozeb 75WP at 2 g/L against
leaf spot diseases; (5) three foliar applications of
water-soluble multinutrient mixtures at 4 ml/L
during 60, 75 and 90 DAS; (6) recommended
plant density was adopted for variety/hybrid to
avoid competition for light, moisture and nutri-
ents; and (7) weeding during first 40 DAS.Results and Discussion
Comprehensive studies conducted for 3 years on
reddening in Bt cotton revealed that it is a com-
plex phenomenon caused due to multiple factors.
Reddening is of two types: in the first, the change
in colour is from green to yellow and then to red;
in the second type, the change is directly from
green to red (Fig. 1 ). Reddening was seen irre-
spective of the crop stage (Fig. 2 and 3 ), and in
most of the cases, the reddening at the early phase
of the crop was attributed to severe incidences of
cotton leafhopper. The reddening noticed during
the later phase of the crop was specifically due to
nutrient deficiencies.
The role of sucking pests in Bt cotton leaf red-
dening was confirmed by an experiment of suck-
ing pest management in leafhoppers susceptible
to non-hairy cotton hybrid RCH-2 Bt. The crop
treated for effective control of leafhoppers was
free from reddening compared to the untreated
one (Table 1 ). Reddening with change in the shape
of the leaf (curling/cupping) was observed under
field conditions due to desapping by leafhopper,
while reddening caused by nutrient deficiencies
usually have normal leaves without any change
in the shape of the leaf (Fig. 4 ). Leafhopper plays
a major role in the manifestation of reddening
symptoms under field conditions. Yield losses of
60–75 % were seen due to occurrence of redden-
ing in the early stages of squaring to flowering,
and losses of about 10–25 % were recorded in
the fields when reddening was observed at post-