Economic threshold for treating Varroa mites, mite load

[Wisnewbee]

It seems the infestation level (mite load) at which treatment should be applied has changed over the years. The information depends on the time of season, migratory or stationary operation and the county or country giving the recommendation. I've read in the past that if you have a 10% mite load (adjusted for mites under cappings, not just mites on bees) you should be treating. The information I've come across lately has a much lower threshold for treatment, in the 2-3% range (adjusted for brood mite load). In a perfect world we would endevor to always keep the mite load as low as possible, but in the real world at what mite load do you feel the need to take action? 1%, 2%, 5%? Spring, summer, fall treatments and loads.

Wisnewbee

[gmcharlie]

Well the number I like is 5% but I can tell you I had several hives last AUG hit 20% and were just starting to show signs of problems.

[Wisnewbee]

How are you testing? Are you just counting mites knocked off bees or are you adjusting your number for mites on brood?

[jim lyon]

I think its really hard to arrive at a definitive threshold number for treating for varroa. Here are the general rules that I go by. Using a 300 bee 1/2 cup sample size I think you want to see something in the 1% or under range in the late spring if you expect them to make it through a honey season untreated. Late summer numbers ideally are something under 4% and in my opinion getting much over 5% can be dangerous. Post treatment going into the winter you would like that number to be back under 1% and maybe even see a few negative readings. All I can really say for sure, though, is less is better than more. Another reason its difficult to be real definitive on numbers is that viruses are a variable that can compound the problem.

[squarepeg]

wis, how do you adjust the number for mites on brood?

[squarepeg]

never mind, saw it in the other thread.

[jim lyon]

Yeah this is confusing, I thought my earlier post had disappeared.

[Mbeck]

Jim do you randomly sample hives in a yard or test them all ?
Do you test before and after treatments?
How many hive and how often do you test ?
Example: x amount per 100 3x per year

[Wisnewbee]

Squarepeg, glad you saw it. The formula that I've been using is from the University of Minnesota Bee Lab. They use a 300 bee sample also. Count the mites and divide by 3 to give you a mite count per hundred bees. Then multiply this number by 2 if brood is present. This would give you the mite load percentage. Their old information is for hives that don't migrate, and are situated in Minnesota or a similar northern climate, so there is a large break in the brood cycle. They previously recommended treating at around the 10% level. I have talked to beeks in Canada that say they're told to treat around the 2% or less level.

Wisnewbee

[jim lyon]

I just try to analyze a yard of 35 to 40 hives by sampling a few bees from 4 or 5 hives to make a single sample and doing that a couple times per yard. If there is a wide variation I might do a third sample. But frankly we dont even attempt to sample every yard just a few here and there to get an idea of what is going on. The results may not really change what we do that much only ease our mind or give us more of a sense of urgency since there are so few good treatment windows. The only sampling that really affects our management decisions are the spring numbers which determine whether or not they should be treated.

[Mbeck]

So fall treatment is a given?

If you make the decision to treat in the spring do you treat all hives or yard by yard?

I have hives that where treated and "rolled" low numbers this winter that may reach a threshold by mid summer.

I ask because here in Florida I'm getting the impression that the feeling is that it's better to error on the side of treating a little too often as opposed to letting them go longer. I'm sure our mite cycles are different.


Treat heavier or more often?
Thanks

[jim lyon]

As things stand now I really can't imagine not knocking your mite numbers back in that critical late summer early fall treatment window, it is just so important to wintering success. I don't worry too much about varroa again until our nucs are up and running and then making a decision based on mite counts. Personally I think it's more about treatment timing than it is about how often you do it.

[Wisnewbee]

I'd like to thank everyone who provided valueable information on an evolving topic.

Wisnewbee