Re: first treatment with OA
The problem with using OA to try to control varroa in a hive with an actively laying queen is that the vast majority of varroa in the hive (I have heard estimates of up to 85%) are contained in sealed brood. Daniels suggestion of treating every 7 days is certainly better than a treatment every 10 days from a mite killing standpoint but it really only marginally helps the overall picture. His statement that an application lasts for 10 minutes, though a bit exaggerated, is a pretty good synopsis for how OA works and why it is virtually impossible to get any type of varroa control with brood present in the hive. Oxalic has virtually no residual effect and bees are constantly emerging with varroa that will almost immediately move into larvae that is within 24 to 48 hours of being capped. I have experimented with using OA throughout a summer to see if control can be achieved but could never really see much progress being made in reducing overall mite counts. My conclusion is to stick with the accepted and very effective practice of a single application well timed late in the fall when there is little or no sealed brood in the hive but before temps drop too low. If a treatment is needed earlier then I would recommend thymol, Hopguard or MAQS.
"Ve are too soon olt und too late schmart."- A nameless German philosopher