Lactic acid is an organic treatment against Varroa. It is applied by spraying directly onto bees on the comb.

How it works

It is a contact treatment: it reaches only the mites sitting on adult bees. Mites in sealed brood are unaffected.

From that follows the same rule as for oxalic acid: it works properly only in a broodless colony, or on bees that carry no brood at all.

Where it fits best

• Newly collected swarms: No brood, all mites on the bees
• Newly made nucs before brood is sealed
• Small units where spraying a few frames is quick
• Broodless colonies in the winter period

The swarm case is where it is most useful: one treatment before the first comb is drawn removes nearly the whole mite load.

Application

• Each side of every occupied frame is sprayed lightly and evenly
• The bees should be moist, not wet
• Frames are lifted one by one — which is why it is labour-intensive

Advantages

• Mild for bees and queen when correctly applied
• Less temperature-dependent than formic acid
• No lasting residue in wax
• Suitable for small units

Disadvantages

• Labour-intensive: Every frame must be handled, which makes it impractical at scale
• No effect on brood, so repeat treatments may be needed
• Opening the colony repeatedly is itself a disturbance

Safety

Lactic acid is corrosive to skin and eyes. Wear gloves and eye protection, and avoid inhaling the mist.

Rules

• Only approved preparations at the prescribed concentration
• Do not treat with supers on
• Record product, date, dose and colonies treated
• Observe withdrawal periods

Afterwards

Measure again. Without a follow-up measurement there is no way to know whether the treatment achieved anything.