Late Fall Final Varroa Mite Treatments

Lat Fall Varrao Mite Testing

Performing a late fall Varroa mite test and treatment (if warranted) will help ensure the health and survival of your colony through winter and will improve the chances of a strong spring buildup. When performing your final Varroa mite treatments, consider these two key factors:

• Population

  – Are you dealing with a decreasing population (some brood) or a dormant (broodless) colony? This largely depends on your geographic location. In temperate zones, you might still see some brood rearing through November and early December, while bees in northern areas may already be in a dormant stage.

• Temperature

  – Fall temperatures can fluctuate significantly. If temperatures fall outside the recommended range for your treatment, you could face reduced efficacy or, worse, cause your bees to abscond.

Here is a list of products suitable for use as temperatures cool down, for either population decrease or dormant (broodless) colonies:

• Apiguard: 59°F–105°F
• Apivar: No temperature restrictions
• Formic Pro: 50°F–85°F
• HopGuard III: >50°F
• Oxalic acid (EZ OX, Api-Bioxal): No temperature restrictions

Oxalic acid is frequently chosen for late fall treatments. When used as directed, it provides very effective results. Though the exact mechanism isn't fully understood, it's believed that oxalic acid is absorbed through the mite's feet and enters its bloodstream, leading to its death. It's crucial to remember that oxalic acid kills only phoretic mites, meaning it must come into contact with the mites to be effective. It cannot penetrate wax cappings to kill mites inside capped cells.

There are two methods for administering oxalic acid: the dribble method and the sublimation (vapor) method. The sublimation method is preferred by some as it doesn’t tend to harm brood like the dribble method can in some instances. The dribble method involves a single treatment, while vaporizing requires multiple treatments (one every five to seven days for three weeks, with some recommending up to four weekly treatments). For more details on using oxalic acid, refer to “Treating with Oxalic Acid.”

Photo Credit: Jennifer Scott - Varroa Mites In Cell