Oxalic dribble is not as effective when colonies contain brood (as during spring or summer), but colonies at that time do appear to tolerate stronger or repeated doses due to the rapid turnover of the adult population at that time of year.
I don’t have data on efficacy, but I’ve treated colonies once a week for three consecutive weeks in late summer without noticing adverse effects (although we prefer thymol or formic acid at that time of year).
I've never noticed any effect on using in the summer on open brood. OAV does not work as well in the summer either.
Mixing correctly is important, Downsizing the dose is confusing.
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