How can BT insecticide be used for the best results?
BT insecticide, namely Bacillus thuringiensis microbial insecticide, contains parasporal crystals and spore toxins that kill pests. It has good pest-killing effects, is safe for humans and livestock, causes no harm to natural enemies, and is relatively difficult for pests to develop resistance to, so it has been widely used to control crop pests. However, in practical application, because the methods are not mastered, ...
BT insecticide, namely Bacillus thuringiensis microbial insecticide, contains parasporal crystals and spore toxins that kill pests. It has good pest-killing effects, is safe for humans and livestock, causes no harm to natural enemies, and is relatively difficult for pests to develop resistance to, so it has been widely used to control crop pests. However, in practical application, because the methods are not mastered, the results are not satisfactory. To improve the control effect of BT insecticide, the following requirements must be mastered:
Master a reasonable application concentration. Different pest species have different degrees of sensitivity to BT insecticide, so the application concentration differs. Only by choosing a suitable concentration according to pest sensitivity can a good control effect be achieved. For sensitive pests such as rice skipper, rice leaf roller, and imported cabbageworm, a 500-1000 times dilution can be used; for less sensitive pests such as yellow stem borer and cotton bollworm, a 100-200 times dilution should be used.
The spores of BT insecticide have the highest activity and the best application effect when the temperature is 20°C-25°C and the relative humidity is above 85%; under environmental conditions such as temperatures below 20°C, long periods of sunlight, strong winds, and heavy rain, the activity is lower and the application effect is poorer, so these unfavorable weather conditions should be avoided when applying it. Under strong light and temperatures above 25°C, it is best to apply around 5 p.m., and on cloudy days it can be applied all day. When applying, spray both the front and back of the leaves thoroughly to improve the effect. Powder formulations should be applied when there is dew in the morning and evening or after light rain, so that the agent can adhere to the crop stems and leaves and exert its toxic effect.
Determine the suitable application time. The effect of BT insecticide is slower than that of chemical insecticides, so the application time should be 2-3 days earlier than that of chemical insecticides. The best effect is achieved when applied from the peak egg-hatching stage to the 1st-instar larval stage. For example, when imported cabbageworm is controlled during this period, the control effect can reach 92%.
Mix with chemical insecticides. To improve the control effect of the agent, especially when pests break out heavily and multiple pests occur together, it is advisable to mix it with chemical insecticides such as bisultap, monosultap, methamidophos, triazophos, dichlorvos, and trichlorfon. For example, if BT emulsion is used alone at 200 milliliters per mu, the control effect on rice leaf roller is only 70%-80%, and the control effect on striped stem borer is only 60%. If 100 milliliters of BT emulsion plus 100 milliliters of 18% bisultap aqueous solution is used per mu, the control effect on rice leaf roller can reach about 95%; if 200 milliliters of BT emulsion plus 100 milliliters of bisultap is used per mu, the control effect on striped stem borer can reach 95%.
At present, pesticides sold on the market such as Bishuangling, Lüshaming, Tesharming, and Bisharming are all BT powder or emulsion formulations, or compound formulations with monosultap powder or bisultap aqueous solution, and should be given priority for selection.