Bud Mite Damage on Hazelnuts

Bud mites are widespread pests of hazelnut production worldwide. Bud mites are very small mites that feed on leaves during summer and within flower buds during dormancy. Two species of bud mite are known to cause damage to hazelnuts, Phytoptus avellanae and Cecidophyopsis vermiformis, which can be found alone or may be present in buds together. P. avellanae is the more harmful bud mite, but both can reduce yield. In recent weeks, we have observed bud mites in significant numbers and bud damage in Ontario hazelnut plantings.

Symptoms

Bud mites belong to the mite family Eriophyidae, a group of extremely small, slow-moving, four-legged mites that are difficult to see with the naked eye. Adult bud mites are white and cigar-shaped. Bud mite feeding causes buds to swell and die, with damage appearing as abnormally enlarged buds.

Life Cycle and Period of activity

Bud mites overwinter inside dormant buds and often kill female flower buds in spring before the flower has a chance to open. As the surviving buds open in spring, female mites move to the young leaves and lay eggs. After egg hatch, the nymphs develop on the leaf surface and change into adults by summer. In late summer and early fall adults move inside new dormant buds of the current year's growth. The adults breed in fall and overwinter inside buds. Feeding occurs inside the buds in fall and spring. Feeding causes female flower buds to enlarge and swell larger than normal. Female flower buds suffer more damage than vegetative buds or male catkin buds. In late spring, damaged swollen buds die and dry up but remain fixed to the stem. Variable amounts of damage can occur each year, from mild injury to complete crop loss.

Monitoring

Monitoring for damaged buds can be done in fall and spring. Damaged buds are easy to identify as enlarged dry pea-sized buds. Monitoring for adult activity can be difficult due to the small size of bud mites. In mid-May, place Tanglefoot on twigs that surround damaged, swollen buds. Check for extremely small adult mites using a 20× hand lens on the surface of bark near the buds as the mites emerge in spring. Swollen buds can also be opened and check for the presence of bud mite adults using a 20x hand lens.

Management notes

Due to the life cycle, and from experience gained from hazelnut production in Oregon, it is believed that control of bud mite is most effective when miticide is applied in spring or early summer as bud mites are feeding on leaves, and before they move into new dormant buds in the fall, where they are protected from the effects of controls. However, at present there are no pest control products registered for bud mite control on hazelnuts in Ontario.

Bud mites can be more damaging to cultivars of European origin or in native hybrids having a European blend, so selection of resistant cultivars may reduce the impact of this pest. New hazelnut cultivars are being screened for tolerance to bud mite, as well as eastern filbert blight disease, a significant disease of hazelnuts.

Additionally, beneficial predatory mites can provide some biological control of pest mites, including the bud mite. Many species of predatory mites exist, and predatory mites have been observed feeding on bud mites in Ontario hazelnuts this spring.

Figure 1. The swollen flower bud on the left is killed by bud mite. The healthy female flower bud on the right is swelling normally in spring.

Figure 2. Infested female flower opened to reveal tiny white cigar-shaped adult bud mites.

Figure 3. Tiny white adult bud mites (and one aphid) feeding inside a female hazelnut flower.