Mar 29, 2016

Broad spectrum insecticide use can flare spider mites

Broad spectrum insecticides, including materials like pyrethroids (IRAC Group 3 materials), organophosphates (IRAC Group 1B), and carbamates (IRACvGroup 1A) have been demonstrated by our laboratory and lots of other entomologists to flare spider mite populations following their use.  The reasons each of these classes of insecticides flare mites differ, but the result is the same–more mites following treatment than you start out with.

Unfortunately, many of these materials are also recommended for spotted wing drosophila (SWD) management.  As I wrote two years ago, at the beginning of the SWD invasion in NC:

“…A good rule of thumb is to observe at least 10 leaves or leaflets per acre or per variety block, if they are smaller than an acre. Spider mites can be observed and counted with a 10x hand lens. If spider mites are present, the planting should be treated with a miticide before beginning organophosphate or pyrethroid (update: or carbamate) treatments.

Spider mites may not be the only non target (unintentional) pest made worse by SWD treatments. Organophosphates and pyrethroids are broad spectrum materials, meaning they kill many different types of insects, including beneficial predators. The insects these predators may control could increase in their absence, but we cannot necessarily predict which insects these may be. Growers treating for SWD should be vigilant and scout their fields at least weekly to assess whether any new or unexpected insect or damage is present.”

In our 2012 SWD experiments in strawberries, we tanked mixed all our intial SWD treatments with a miticide, Acramite.  This tank mix was effective against the large spider population present and did not damage plants.  I do not have first hand experience with tank mixing other miticides with insecticides, so I would be cautious. When tank mixing two materials, be sure to test for compatibility (a jar test is one way) and treat a small area first before treating your whole field.

— Hannah Burrack, North Carolina Cooperative Extension

Source: North Carolina State University