MSc

Experiments were conducted in the laboratory, pots and field during 1986-88 to ascertain the compatibility of insecticides and fungicides commonly used for the control of insect pests and diseases of rice. Standard bioassay technique and poisoned food technique were adopted in the laboratory studies using N. lugens and R. solani as test organisms. Based on these, concentrations to give 25, 50 and 75 per cent mortality of insect and 50, 75 and 100 per cent inhibition of the fungus were selected. The interaction of the insecticides and fungicides when mixed in the above doses, in all possible combinations, was studied with reference to their fungicidal and insecticidal effect assayed with the above test organisms.
Pot culture experiments were conducted for the assessment of effect of (i) combining insecticides and fungicides on the control of sheath blight and BPH, (ii) applying fungicides and insecticides in sequence and in combination on the control of sheath blight and N. Lugens and (iii) spraying fungicide – insecticide in combinations at different intervals after preparing the mixture, on the control of sheath blight and N. lugens.
A field trial was also laid out for assessing the efficacy of fungicide – insecticide combinations for the control of sheath blight.
The insecticidal effect of monocrotophos on N. lugens was not significantly altered when used in combination with captafol, ediphenphos or carbendazim in widely varying proportions. A synergistic effect was observed when quinalphos was combind with captafol or ediphenphos. Enhancement of action of lower dose of quinalphos when combind with captafol and ediphenphos was observed in pot culture study also.
Enhancement in the insecticidal activity of quinalphos in the laboratory in combination with carbendazim (at 1 ppm, 2.5 ppm and 5 ppm) was limited to lower doses of the insecticide. With higher dose of the insecticide there was no significant synergism. This favorable ratio of insecticide fungicide combination is not possible in the field since the dose of fungicide required in the field for the control of R. solani ranges from 500 – 1000 ppm.
Laboratory studies showed that the insecticidal effect of HCH 0.2% was significantly reduced when combined with captafol. But at 0.071 and 0.026% the combinations showed no antagonistic effect. In the pot culture experiment the insecticide and its combinations with two doses of captafol came on par. The lower dose of HCH and ediphenphos combinations were superior to the treatment with insecticide alone. The same result was obtained when HCH was combined with carbendazim in the laboratory. In pot culture studies the combinations did not show any difference with the use of HCH alone for the control of N. lugens.
Laboratory studies showed feirly high fungicidal effect for monocrotophos. Monocrotophos used in combination with fungicides showed antagonistic effect at higher levels of captafol, ediphenphos and carbendazim. But with lower concentrations there was an enhancement of fungicidal effect.
In the laboratory the fungicidal effect of quinalphos was observed to be high. While no antagonistic effect was observed when it was used in combination with higher levels of captafol and carbendazim, the combinations with lower levels of all the three fungicides showed synergistic effect. In the case of ediphenphos, combination of quinalphos with the higher level of fungicide showed antagonistic effect.
The fungicidal effect of HCH was very high in the laboratory at all the three doses tried. The three doses of HCH in combination with varying doses of fungicides gave 100% inhibition of the fungus in the laboratory.
In the pot culture experiment among the treatments, captafol 1500 ppm and monocrotophos 0.05% alone was found to be better in fungicidal action compared to the treatments with fungicides alone. Antagonistic alone was found to be better in fungicidal action compared to the treatments with fungicides alone. Antagonistic effect in disease control was observed where HCH 0.2% was combined with carbendazim 1000 ppm and ediphenphos 1000 ppm.
In the field experiment, higher control of the disease was obtained in combinations of monocrotophos 0.05% with captafol 3000 ppm, or 1500 ppm, ediphenphos 500 ppm and quinalphos combined with captafol 3000 ppm and ediphenphos 500 ppm. Combination of HCH with captafol did not show any antagonistic effect, but antagonistic action was observed in combination with ediphenphos and carbendazim.
Overall assessment of the data obtained from the laboratory, pot culture and field experiments showed that monocrotophos and quinalphos could be combined with captafol and ediphenphos without any antagonistic effect or even with synergistic effect. With carbendazim, monocrotophos alone is compatible. The synergism will be more in combinations in which higher proportion of insecticides were used. The possibility of lowering the quantity of fungicide in treatments when compatible insecticides and fungicides were used in combination for the control of diseases also was indicated in the experiment.
When the application of fungicides and insecticides in sequence (fungicide followed by insecticide and vice-versa) was compared to the combined application, it was found that in general the treatments were all on par. It was further seen that keeping of mixtures up to 24 hours after formulation did not affect the insecticidal and fungicidal properties of the mixtures and hence they can be kept for the required length of time after preparation to finish the spraying operation in the field without any adverse effect on toxicity.