To start i will say that i have never used hopguard. That said, I have used several other products. Not just with bees but with cows aswell. When a product is not used as labelled, problems can start to occur.
1. resistance. The residual mites will start to build a resistance to the product. It happens faster than one might think. Not using as specified could come back to bite in the not to distant future
2. Contamination. Test are done by the USA's drug and pesticide groups. In Canada it is the PMRA. They set out the guidelines for usage based on trials. Several factors go into the process...like leaving a product in longer than normal and testing the comb, left over honey, bees etc. One can run the risk of contaminated comb or honey or residuals in the products by not following the directions. Have you not heard all the commotion in the news from alot of activist groups about drug contaimation and the need to regulate livestock meds more than they are now? By not following the direction, you lend credence to these groups...That there are "people" who can not follow directions properly. Well done.
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3. Illegal. It is also against the law to use products like this against regulations and one can be heavily fined.
There are many reasons why we need to follow manufactures directions. Some reasons are for our protection, some for the bees health protection, and some because good management practices with livestock should be common sense.