Filbert bud mite (Phytoptus avellanae)
Pest description and crop damage Microscopic mites damage hazelnut leaf and flower buds, and sometimes catkins. Filbert bud mite is the official recognized common name for Phytoptus avellanae, but Cecidophyopsis vermiformis also damages hazelnut buds, and the two species are often collectively and familiarly known as big bud mite or simply bud mite. Mite feeding forms galls in the buds, which swell to an abnormally large size. The blasted bud often dies, or if it survives, it will produce a shoot with abnormal growth. Definitive studies linking yield loss to bud mite infestation are lacking for different cultivars, but it has long been known that there is heritable genetic resistance and a spectrum of susceptibility among different hazelnut cultivars. The tightness of bud scales may be related to susceptibility. Up to 30% infested buds have been observed in some orchards. Chronic bud mite infestation at this level can lead to trees with reduced fruiting wood in canopies. The OSU hazelnut breeding program selects against bud mites so blasted buds are not an issue in the most recent releases with genetic resistance to eastern filbert blight. The exceptions are 'Yamhill' and 'McDonald'. Other cultivars known to be highly susceptible to big bud mite include Ennis, Lewis, Clark, and Casina.
Biology and life history Phytoptus avellanae belongs to the Phytoptidae mite family and C. vermiformis belongs to family Eriophyidae. The two mite species have different life histories, but are similar in that they both spend months inside the buds. This limits pest management options, because the swollen buds can protect the mites from insecticides. Bud mite infestations become most apparent in late winter and early spring as bud break approaches. At this time, both mite species are present in the buds and their populations are at a maximum, with some buds containing thousands of mites. As bud break and shoot elongation begins, the mite nymphs (immatures) migrate from blasted buds to the new axillary buds. During the growing season, P. avellanae remains relatively inactive in the buds, but buds infested by C. vermiformis swell and ultimately drop in the late growing season. The mites from these blasted buds migrate to the buds occupied by P. avellanae, and infested buds begin to swell during fall and winter. Mites spread via wind and phoresy (hitch-hiking on other animals), so re-infestation can easily occur.
Pest monitoring The best time to scout and evaluate bud infestation rates is in the spring near the onset of bud swell when blasted buds will be most apparent. Most growers time sprays to intercept mites as they migrate from blasted buds to new buds in early spring. Sprays applied at the peak migration timing will be most successful. Recent research suggests the peak migration typically occurs from late March/early April to mid-May in the Willamette Valley. Monitoring is accomplished by placing double-sided sticky tape or tacky insect glue on branches below blasted buds and counting trapped mites under magnification at regular intervals. A microscope or 10x to 20x hand lens is useful for counting mites on tape traps that are clipped or removed from the tree. With magnification, mites can also be sampled by counting or estimating number of mites observed staging on the outside of blasted buds in anticipation of migration. The tree provides clues about the timing of the migration of mites. New axillary buds must be present for the mites to migrate to. The infested bud increasingly becomes inhospitable to the mites as bud break advances and the bud is increasingly blasted and necrotic Warm days are also associated with migration activity, and depending on the weather conditions, migration can occur over a short time or a prolonged period lasting multiple weeks.
Releases of predatory mites (Galendromus spp.) is thought to be impractical in commercial settings, but may be effective for home use. Predatory mites cohabitate in blasted buds with bud mites during winter. Mite flaring may be linked to excess use of broad-spectrum insecticides impacting predatory mites in the orchard.
Sanitation is not practical in commercial orchards, but home orchardists could remove and destroy blasted buds ahead of the spring mite migration.
Management-chemical control: HOME USE
- azadirachtin (neem oil) (Azera Gardening, EcoGarden)-Some formulations are OMRI-listed for organic use.
- kaolin (Surround At Home Crop Protectant)-Some formulations are OMRI-listed for organic use. Deters mites from feeding, full coverage of foliage and repeated applications are needed to be effective.
- insecticidal soap-Some formulations are OMRI-listed for organic use.
- pyrethrins (Pyganic Gardening, Bug Buster-O)-Broad spectrum insecticide. Some formulations are OMRI-listed for organic use.
Management-chemical control: COMMERCIAL USE
Note: Most materials labeled for bud mite cannot be applied by air.
- abamectin (gri-Mek, others) at 0.5 to 4.24 oz/A. PHI 21 days. REI 12 hr. Do not exceed two applications per season.
- calcium polysulfide (Sulforix) at 3 gal/A. REI 2 days.
- fenpyroximate (Fujimite XLO) at 2 to 4 pints/A in minimum of 100 gal water. No more than two applications per season.
- lime-sulfur (BSP) at 12 gal/A. REI 2 days.
- micronated sulfur (multiple SLN labels)-Use caution if hot weather is expected. Low rates are recommended.
- Auron DF at 5 to 25 lb/A in 50 to 400 gal water. See 24(c) SLN label. Do not apply when air temperatures will exceed 90°F within 3 days of application. REI 24 hr.
- Kumulus DF at 5 to 25 lb/A in 50 to 400 gal water. See 24(c) SLN label. Do not apply when air temperatures will exceed 90°F within 3 days of application. REI 24 hr.
- Microthiol Disperss at 10 to 20 lb/A in 50 to 400 gal water. See 24(c) SLN label. Do not apply when air temperatures will exceed 90°F within 3 days of application. REI 24 hr.
- Sulfur DF at 5 to 25 lb/A in 50 to 400 gal water. See 24(c) SLN label. Do not apply when air temperatures will exceed 90°F within 3 days of application. REI 24 hr.
- Sulfur WG at 5 to 25 lb/A in 50 to 400 gal water. See 24(c) SLN label. Do not apply when air temperatures will exceed 90°F within 3 days of application. REI 24 hr.
- pyridaben (Nexter) at 2.67 oz/100 gal water (10.67 oz/A). PHI 7 days. Do not exceed two applications per season.
- spirodiclofen (Envidor 2SC) at 16 to 18 fl oz/A. PHI 7 days. REI 12 hr.
- tolfenpyrad (Bexar) at 27 oz/A. PHI 14 days. REI 12 hr. See 2(ee) label for hazelnut (OR/WA only).