MSc

The most important biological constraint to rice production is weed
infestation. Echinochloa spp. are the most devastating and serious graminaceous
weeds associated with rice. Herbicides which selectively kill Echinochloa are
commonly used by rice farmers, as hand weeding is often ineffective due to its close
morphological similarity to rice. Of late, some new types of Echinochloa are seen
in the major rice tracts of Kerala, and farmers report that these new types are tolerant
to most herbicides used by them. The present study was conducted to study the
diversity of Echinochloa spp. in the rice tracts of Palakkad and to test the efficacy
of select herbicides against them. The efficacy of herbicides was evaluated for the
major Echinochloa species collected from Kuttanad and Kole lands too.
Surveys were conducted twice in the major rice tracts of Palakkad, once
during January-February, and the other during August-September in 2016. Three
major Echinochloa types were identified infesting rice fields, leading to severe crop
competition. The three types were E. colona, with awnless spikelets and two types
of E. crus-galli viz., E. crus-galli (type A) having short awns and E. crus-galli (type
B) having long awns. Other than the length and arrangement of awns, there were no
other significant differences in the morphological characters of the latter two types.
There was no specific association between the Echinochloa types and soil
nutrient parameters, probably as there were no drastic differences in the chemical
properties among the different locations. Saturated soil moisture regime was
observed in all the rice fields of surveyed areas.
The major species in Kuttanadu and Kole area was E. stagnina, which was
found only in flooded soils. This species differed morphologically from the other
three types collected from Palakkad rice tracts.
All the types, except Echinochloa crus-galli (type B) exhibited seed
dormancy. Pre-treatment with ethanol (1M) for three days under darkness was most
effective for promoting germination of Echinochloa.
The efficacy of pre and post emergence herbicides on various species of
Echinochloa was evaluated as pot culture study. The pre emergence herbicide
treatments included pretilachlor, oxyfluorfen, pyrazosulfuron ethyl, pendimethalin,
pretilachlor + bensulfuron methyl and oxadiargyl, and all were applied to both
puddle sown and dry sown condition. All the herbicides except pyrazosulfuron ethyl
were completely effective against all the four types of Echinochloa.
Post emergence treatments were applied at the four leaf and eight leaf stages
of Echinochloa spp. and the treatments included cyhalofop butyl, bispyribac
sodium, penoxsulam, fenoxaprop-p-ethyl, ethoxy sulfuron and metamifop.
Bispyribac sodium and metamifop were effective against E. colona at both
four leaf and eight leaf stages, whereas penoxsulam was effective only at the four
leaf stage. Bispyribac sodium at the eight leaf stage was highly effective against E.
crus-galli (type A). Echinochloa crus-galli (type B) was effectively controlled by
metamifop when sprayed at the four leaf and eight leaf stages, fenoxaprop-p-ethyl
at the four leaf stage and penoxsulam at the eight leaf stage. This indicated that
though the two types of E. crus-galli were morphologically similar except in awn
characters, they had varying response to herbicides. E. stagnina was tolerant to all
the herbicides tried. However, cyhalofop butyl and fenoxaprop-p-ethyl although
effective at the four leaf stage in reducing the survival percentage, resulted in highly
persistent survivors.
The study showed the importance of optimal use of the correct herbicide
against each species of Echinochloa at the most susceptible stage of the weed.
Constant monitoring of the Echinochloa population in the field is important so that
appropriate control strategy can be adopted.