Compatibility of herbicides and insecticides for tank mix application in wet seeded rice

Abstract

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.