Treat for varroa mites in late summer and fall

Apply varroa mite treatments in August-September to ensure the generation of "winter bees" (long-lived bees raised in fall) develops with low mite pressure. Colonies with mite loads above 2-3% at this stage produce weakened winter bees that often die before spring.

Why It Works

Varroa destructor feeds on bee fat bodies and vectors deformed wing virus (DWV), Israeli acute paralysis virus (IAPV), and other pathogens. Winter bees need intact fat bodies to survive 4-6 months. Research from the University of Maryland shows that colonies with August mite loads above 3% suffer 2-3 times higher winter mortality than colonies treated below that threshold.

Tips

• Monitor mite levels with an alcohol wash or sugar roll -- count mites per 300 bees (half cup sample)
• Treat if mite wash exceeds 2 mites per 100 bees (6 per 300-bee sample)
• Common fall treatments: oxalic acid vaporization (broodless period), formic acid strips (temperatures 10-29°C), or amitraz strips (follow label timing)
• Do not wait until October -- winter bees are being raised in September, and late treatment cannot repair the damage to bees already parasitized
• Re-test 2-3 weeks after treatment to confirm mite levels dropped below threshold