If you are using pesticides on a regular basis (i.e. a weekly rotation), it’s vital that you rotate your chemicals in order to decrease the change of your pest becoming resistant.
Pesticide resistance is not uncommon among insects. According to “Global Pesticide Resistance in Arthropods” (Whalon et al., 2008), there have been over 7747 insecticide resistance cases reported! That same database (pesticideresistance.com/search.php) showed 56 cases of insecticide resistance within 2013 alone, and the silverleaf whitefly (Bemisia tabaci) having populations that were reportedly resistant to over 54 active ingredients.
By repeatedly spraying chemicals that target the same mode of action (i.e. method in which is kills) in the insect, resistant populations are encouraged and can emerge. This point is vital:
Using a product with a different trade name or using a different active ingredient isn’t the same as changing mode of action
Different products can share the same active ingredient (listed as active ingredient on the label; typically top on ingredient list), and different active ingredients can share the same mode of action. For example, both imidacloprid and thiamethoxam are neonicotinoids that target the acetylcholine receptors of the central nervous system, cause paralysis and death in the insect – in other words, they block the same nervous system receptor. Thus, by spraying both imidacloprid and thiamethoxam, we are putting selection pressure on the same mechanism in the insect! Eek!
So how do we ensure that we are rotating Modes of Action? Our great ally, the Insecticide Resistance Action Committee (or IRAC for short). Among many of their great resources is a newly updated Mode of Action chart, where you can search the different active ingredients and ensure that they are in a different mode of action group.
Check the products you are using on a regular basis and ensure that they belong to different mode of action groups. Note that they must belong to a different number; different letters within a number is not sufficient!
By selecting insecticides that belong to different modes of action in your rotation, you can feel more comfortable that you’re less likely to breed resistant insect populations that will cause you and your neighbors any headache.