Bt – Rotation Considerations

Bt - Rotation Considerations

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Bt - Rotation ConsiderationsYears of data from scores of trials support the use of Bt as a partner with conventional pesticides for control of lepidopteran pests. The efficacy and affordability of Bts combined with their resistance management properties, make it a front line solution for worm control. But is it better to tank mix Bt with other products, or deliver it in rotation? And if rotation, in what order should the rotational partners be applied?

When you make a living growing produce, these are critical questions that demand answers. While it’s true that any of the scenarios mentioned will provide control, it’s the level of control that’s going to impact your bottom line. Insect populations and the resultant levels of crop damage can vary greatly from one approach to another.

Researchers will tell you that each of these strategies has to be evaluated on a case by case basis. Key variables include region, time of year, the pesticide(s) being partnered with Bt, and most importantly, the pest complex you’re up against. As a general rule, however, tank mixes often provide the best control but wind up being the most expensive option. So if you apply Bt products in rotation, which partner should come first?

That’s where resistance can play a big factor. Whatever the conventional partner, it’s generally accepted that some portion of the existing population is already resistant. If you partner Bt with a pyrethroid, for example, and apply the pyrethroid first, you’re going to select out the resistant population with the first application before coming back in with the Bt. By the third application, your level of resistance in the resultant population will be proportionally higher because the pyrethroid was used first.

Conversely, using Bt as the first partner will delay this effect – a result that can have significant effect on marketable yield. Bt will knock down the entire population and only upon the second application – with the conventional product – will the selection take place. Coming back in with Bt as the third application means that two of the first three applications have sidestepped the onset of resistance. By the end of the season, the ordering of these early applications can bring about a dramatic effect on the pest population and marketable yield.

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Avatar for Anonymous Anonymous says:

What other pests can be controlled using Bts? Thrips, Aphids, Whitefly, Leafminers ?

Avatar for Anonymous Anonymous says:

For 40 weeks of the year we have mange tout and sugar snap peas in the ground planted weekly. The other 12 weeks have a green bridge of bean and chillies and our helicoverpa armigera population is always around. We use a lot of Bts in conjunction with beauvaria bassiana and conventional pesticides ranging from pyrethroids to lufenuron, spinosad and indoxicarb. However whilst having a 0 day pre harvest interval, the Bts are ineffective during harvest as the caterpillars on hatching go straight into the pod rather than eating leaf which is where the bulk of the Bt is sitting. Any ideas to increase the intake would be much appreciated.

Avatar for Anonymous Anonymous says:

What other pests can be controlled using Bts? Thrips, Aphids, Whitefly, Leafminers ?

Avatar for Anonymous Anonymous says:

For 40 weeks of the year we have mange tout and sugar snap peas in the ground planted weekly. The other 12 weeks have a green bridge of bean and chillies and our helicoverpa armigera population is always around. We use a lot of Bts in conjunction with beauvaria bassiana and conventional pesticides ranging from pyrethroids to lufenuron, spinosad and indoxicarb. However whilst having a 0 day pre harvest interval, the Bts are ineffective during harvest as the caterpillars on hatching go straight into the pod rather than eating leaf which is where the bulk of the Bt is sitting. Any ideas to increase the intake would be much appreciated.