Approaches on Herbicide - Herbicde Interaction - a Review

Herbicide mixtures are commonly used in agriculture to broaden the spectrum of weed control. The interactions or the combinations may be desirable or undesirable. Acetachlor at 150g/ha applied and ready mix application of anilofos and ethoxysulfuron at 780 g /ha provide effective control of weeds with higher grain yield. Tank mix application of metribuzin with isoproturon at 1.0 kg/ha, clodinofop (60g/ha) and fenoxyprop (120g/ha) applied at 3 leaf stage marginally increase the mortality against the resistant biotypes and susceptible biotypes of Phalaris minor with the corresponding increase in the dose of metribuzin. Tank mixing of MON 12000, CGA 152005 with atrazine or bentazon reduces the weed control of these post emergence herbicides, in controlling velvetleaf. Chlorimuron is compatible with glyphosate, but aciflurofen antogonise glyphosate activity. Thus the interaction effect of herbicide molecule differed. Herbicide technology is an alternative to traditional hand weeding to manage the greater menace in Agriculture ‘the weeds’. But continuous use of a single herbicide may lead to build up of herbicide resistance in weeds. Hence, there is need to focus our attention on herbicide mixtures to enhance the weeding efficiency, broadening the spectrum of weed control and saving the herbicide and labour requirement. Though, it is widely practiced in the developed countries, the basis behind the combination among herbicide molecules should be known for the advancement. Thus an attempt has been made to compile the interactional effects of herbicides. Classification of herbicide interactions Herbicide interactions are generally classified as Additive, Synergistic, Antagonistic and Enhancement. Additive The combined effect of two herbicides applied in combination is additive, if over a range of rates and ratios, the plant response is same as that obtained when one chemical is substituted for the other at rates based on the activity of each herbicide used singly. Synergism The combined effect of two herbicides applied in combination is synergistic, if over a range of rates and ratios, the plant response is greater than that obtained when one chemical is substituted for the other at rates based on the activity of each herbicide used singly. Antagonism The effect of two herbicides applied in combination to plant is antagonistic, if over a range of rates and ratios, the response is less than that obtained when one chemical is substituted for the other at rates based on the activity of each chemical used singly. Enhancement The effect of a herbicide and a non-toxic adjuvant applied in combination on a plant is an enhancement, if the response is greater than that obtained when the herbicide is used at the same rate without the adjuvant. 33 Vol. 30, No. 1, 2009 Experimental results of herbicide herbicide interactions The predominant herbicides used in rice provide the control of grassy weeds alone and their application window is narrow, i.e. 0 to 3 DAT (Days after transplantation) generally. Acetachlor and anilofos + ethoxysulfuron are the new herbicides which can be effective for both the type of weeds. Narwal et al. (2002) inferred that acetachlor at 150g /ha and ready mix application of anilofos and ethoxysulfuron at 780 g /ha provided effective control of weeds and recorded higher grain yield. Weed shift from grasses to non grasses and annual sedges is being observed in continuous use of butachlor and pretilachlor in major rice growing areas. This undesirable ecological change forces us to go for alternate chemicals where herbicide mixtures are gaining momentum in providing a wide spectrum of weed control. The effect of almix and butachlor alone and in combinations on transplanted rice and associated weeds was studied by Singh et al. (2004) and they found that almix 4g/ha was compatible with butachlor as tank mix application, which increased the weed control spectrum and produced higher grain yield than alone application of almix or butachlor. Evolution of resistance in little seed canary grass against isoproturon in wheat was considered as one of the most serious cases of herbicide resistance in the world resulting in the total crop failure under severe infestation. Tank mix application of metribuzin with isoproturon at 1.0 kg/ha, clodinofop (60g/ha) and fenoxyprop(120g/ ha) applied at 3 leaf stage marginally increase the mortality against the resistant biotypes and susceptible biotypes with the corresponding increase in the dose of metribuzin. The same with diclofop (700g/ha) and tralkoxydim(300g /ha). However increase in the dose of metribuzin enhanced the phytotoxicity in wheat, thus the herbicidal mixture would be a futile exercise against the Phalaris minor in resistance affected areas of rice wheat cropping system. (Yadav et al., 2004). Tralkoxydim is more effective against wild oat than against the wild canary grass. But broad leaved weeds are not controlled by this herbicide. Thus herbicide mixture of broad leaved herbicides would increase the spectrum of weed kill. Tank mixture of tralkoxydim @ 300g/ha and isoproturon @ 250 or 375 g/ha were more effective against the complex weed flora and also recorded higher grain yield of wheat than application alone and with other herbicidal combinations (Panwar et al., 1995). Synergism Pyridate , a phenyl phyridazine herbicide, non-translocating pyridate inhibits photosynthesis by blocking electron transport through photosystem II. Pyridate is hydrolysed in tolerant crop like crop resulting in removal of the S octyl group. This process produces 3phenyl 4-hydroxy 6-chlorpyridiazine which is the only active form of pyridate, which is subject to conjugation by some species, which renders it herbicidally inactive. The experiment was conducted by Hicks et al. (1998) to study the interaction of pyridate and 2,4 DB in peanut, Desmodium and Senna (Table 2). Peanut was unaffected by even the highest rate of pyridate alone. The highest rate of 2,4 -DB applied alone resulted in nominal peanut injury and all pyridate plus 2,4DB found to be addit ive. Considering the translocation 14C absorbed in the treated leaf increased. Thus 2,4 -DB served to increase pyridate absorpt ion. Consequent ly the synergistic response observed in sicklepod can be partially attributed to enhance the herbicide entry in to leaf tissue. The tolerance of peanut and sickle pod relative to that of Desmodium is due to differential metabolism specifically to the ability of the plant to metoholise 3 phenyl 4 hydroxy 6 chlorpyridiazine into a benign metabolite. The improved control of sicklepod obtained into pyridate -2, 4 -DB tank mixtures is a synergistic response that can be partially attributed to enhanced pyridate absorption. 34 AGRICUTURAL REVIEWS Crop Herbide mixture Dose (g/ha) Weed population/m2 Grain yield (kg/ha) References Soybean Pursuit plus