Spider Mites: My Lessons Learned and Varietal Differences Noted

Like many growers and crop consultants if I don’t see spider mites for another 24 years it will be too soon. As we transition into physiological maturity and put this season behind us it is always a good idea to reflect back on what we have experienced and learned so a documented record is present for the next time these infrequent events occur. So here is what I learned battling spider mites in 2012.

1. There are product efficacy differences. I sprayed our Janesville, East Troy, Fond du Lac, and Arlington (twice) sites in 2012 for spider mites. All of the locations were sprayed with Dimethoate except Fond du Lac which received bifenthrin. For the most part I was pleased with control at all locations. 
2. I waited too long to spray. I am a strong proponent of IPM guidelines and follow them religiously with excellent success. My mistake was that I did not effectively scout the large border areas surrounding our Arlington research trials. This did not lead to any significant plot loss or impact my research but it did lead to a continuous re-supply of spider mites due to egg numbers that I had to manage.
3. Rain did not help. Rain did knock down populations for a couple days but they quickly rebounded and required chemical control.
4. Varietal differences are evident. Plot to plot variability was noted at our Janesville and Fond du Lac sites so we took plot notes to quantify (0-10, where 0 = no plot damage and 10 = 100 of plot injured. this variability. Analysis of the data indicated significant varietal differences (0 to 8 at Janesville and 0 to 3 at Fond du Lac). It is unclear whether these differences where due to initial selection, preferential feeding, or increased fecundity (more eggs) but they were real. Given the infrequency of spider mites for Midwest growers I would not select varieties based on this criteria, but it may help explain infestation or control variability for 2012.