MSc

Weeds and insect pests are the major biotic constraints in rice production.
Chemical methods of control of insects as well as weeds is very common in rice
production. Separate application of the chemicals is expensive and labour
intensive with the result that many farmers of Kerala adopt tank mix application
of different chemicals without due consideration to efficacy and compatibility.
The present study entitled “compatibility of herbicides and insecticides for
tank mix application in wet seeded rice” was conducted in a farmer’s field at
Alappad Kole lands of Thrissur district, from August 2016 to January 2017. The
experiment aimed at studying the compatibility of two commonly used herbicides
(bispyribac sodium and cyhalofop-butyl) with two new generation insecticides
(flubendiamide and imidacloprid) for tank mix application in wet seeded rice.
Another objective of the study was to assess the pest control efficiency of
herbicides and insecticides. Out of 14 treatments, four treatments in the trial
included sequential and mixed application of bispyribac sodium with two
insecticides separately. The next four included cyhalofop-butyl substituted for
bispyribac sodium. The remaining treatments were application of herbicides
alone, hand weeding with and without application of insecticides and unweeded
control.
Weed spectrum of the experimental field included barnyard grass
(Echinochloa crus-galli), hippo grass (Echinochloa stagnina) and red sprangletop
(Leptochloa chinensis) among grasses. Major broad leaf weed was water primrose
(Ludwigia parviflora). Yellow nut sedge (Cyperus iria) was the only sedge
species which was the major weed of the experimental plot.
Treatments were studied for their phytotoxic effects on rice and no toxicity
symptoms were observed in tank mix or sequential application. Weed counts,
weed dry matter production and weed control efficiency were estimated at
different stages of crop growth.
Comparing sequential application and tank mix application of bispyribac
sodium and flubendiamide, the mixed application resulted in high weed dry
weight and low weed control efficiency. Yield parameters and yield were
recorded low in this treatment. For sequential and combined applications of
bispyribac sodium and imidacloprid, weed control efficiency, weed dry weight,
yield and yield attributes were on par. Weed dry weight was low and weed control
efficiency was high for mixed application of cyhalofop-butyl and flubendiamide.
Yield and yield attributes were also high for this treatment. Weed dry weight,
weed control efficiency, yield attributes and yield were comparable for sequential
and mixed applications of cyhalofop-butyl and imidacloprid.
Insect pest infestation was very low in the experimental field. Rice leaf
folder (Cnaphalocrocis medinalis), white backed plant hopper (Sogatella
furcifera), red spotted earhead bug (Menida versicolor) and yellow stem borer
(Scirpophaga incertulas) were the insect pests noted. Observation on insect count
showed that there was no significant difference among treatments with respect to
insect pest counts at 5, 7 and 11 days after spraying which was comparable to
unweeded control. Hence efficacy of insecticides when tank mixed with
herbicides could not be interpreted.
Hand weeding was the best treatment in terms of weed control efficiency,
yield and yield attributes. However, the highest B: C ratios were registered by the
treatments
cyhalofop-butyl
+
flubendiamide
and
bispyribac
sodium
+
imidacloprid. Highest net return was recorded in bispyribac sodium +
imidacloprid. Unweeded control recorded lowest values for yield and B: C ratio.
With respect to efficacy of herbicides used, the study indicated that the
two insecticides tried were compatible with cyhalofop-butyl. In the case of
bispyribac sodium, the insecticide imidacloprid appeared to be compatible, but
mixing of flubendiamide cannot be recommended since weed control efficiency
was very low.