Filbert aphid (Myzocallis coryli)
Hazelnut aphid (Corylobium avellanae)

Pest description and crop damage Medium to small aphids that feed on leaves and husks and produce honeydew. Filbert aphid is typically more problematic in Willamette Valley hazelnut orchards. It is primarily found on undersides of leaves where it feeds on phloem along marginal leaf veins, while hazelnut aphid is primarily found on nut husks. Early in the season before nut clusters develop, both species are found on leaves and shoots, with hazelnut aphid tending to dominate on shoots and leaf midribs. Filbert aphid is typically light green or pale yellow and lacks well-developed cornicles, which are tube-like projections that emerge from the abdomen. Hazelnut aphid by contrast has well-developed cornicles, longer legs, and is a darker green color and may also have reddish coloration. Experimental evidence indicates that heavy infestations of aphids should be controlled to prevent reduced kernel fill and smaller nut size. Damage caused by aphids is cumulative; benefits of control might not be seen during the first season, but they become evident after two years or more of aphid control. Honeydew produced by aphids is colonized by sooty mold fungus. Sooty mold fungus can impede photosynthesis and severely devitalize plants and retard growth. Honeydew also attracts pollinators, so use caution when managing severe aphid infestations with insecticides. These aphid species are specific to hazelnut, they are not found on other plants.

Biology and life history Both aphid species overwinter as eggs in crevices in bark and on twigs, and around buds and leaf scales. Eggs turn from a greenish color to black as they mature. In early spring, eggs hatch in synchrony with budbreak, and the aphids feed on swelling buds and leaflets before moving to the leaves. The winged 'stem mothers', or fundatrices that develop from these first nymphs are capable of dispersing by flight, and they give live birth to nymphs that also give live birth when mature (viviparae). The population can increase rapidly, and there are 8 to 10 generations per year. In the fall, winged sexual males and wingless females (oviparae) are formed. These mate and the oviparae females lay overwintering eggs.

Pest monitoring The sampling period is April 1-Sept 30. Check three terminal branches per tree and three leaves per terminal. Count the number of aphids per leaf and treat when the following thresholds for filbert aphid are reached: April: 20 per leaf, May: 30/leaf, June: 40/ leaf, and July: 40/ leaf with an increasing population. Because hazelnut aphid is a relative newcomer, action thresholds based on its density have not been developed. If there are signs of the parasitoid, Trioxys pallidus, hold off on treatment and check back on population levels in a week. Mummified aphids indicate that the parasitoid is active. Aphid mummies appear swollen, rounded, and darker and may have an exit hole chewed by the wasp. Note that populations of aphids typically peak by June and will decrease substantially by July regardless of management action. An increase in aphid populations tends to occur in the late growing season when conditions are cooler and the period of egg laying approaches.

Management-biological control

An introduced parasitoid wasp (Trioxys pallidus) that attacks both aphid species is well established in the Willamette Valley. This wasp makes aphid sprays unnecessary in many hazelnut orchards. Learn to recognize mummies and the wasps, and avoid treating when biological control is active. The aphid has a lower temperature threshold for development than the wasp, which typically emerges about two weeks after the aphids. As a result, there is lag time between population increase of aphids and the response of the wasp. Pest management practices that are detrimental to the wasp population can aggravate aphid problems. Note also that broad-spectrum insecticide applications made against aphids or other orchard pests that harm natural enemies can free the aphid populations from biological control, causing populations to surge. There are a number of important predators of aphids that occur in hazelnut orchards including: ladybird beetles (both larvae and adult beetles are predaceous), syrphid fly larvae, Geocoris (big-eyed bugs, Geocoridae family), Deraeocoris (plant bugs, Miridae), Orius (minute pirate bugs, Anthocoridae) and lacewing larvae. Yellow jackets and paper wasps also prey on aphids.

Management-cultural control

Aphid populations tend to be higher in plants that are fertilized liberally with nitrogen. Home orchardists: Wash aphids from plants with a strong stream of water or by hand-wiping. Avoid excessive watering which, together with nitrogen applications, produces flushes of succulent growth. Control ants, which "farm" the aphids for their honeydew and protect them from predators.

Management-chemical control: HOME USE

  • acetamiprid-Do not make more than four applications per season. PHI 14 days.
  • azadirachtin (neem oil)-Some formulations are OMRI-listed for organic use.
  • bifenthrin (as a mix with other ingredients)
  • esfenvalerate-PHI 21 days
  • gamma cyhalothrin
  • imidacloprid-PHI 7 days.
  • insecticidal soap-Some formulations OMRI-listed for organic use.
  • Kaolin-Some formulations are OMRI-listed for organic use.
  • mineral or vegetable oils-Dormant or delayed dormant applications can kill aphid eggs. Use caution not to interfere with active pollination.
  • plant-derived essential oils-Some formulations are OMRI-listed for organic use and have shown efficacy against aphids.
  • pyrethrins (often as a mix with other ingredients)-Some formulations are OMRI-listed for organic use.
  • zeta-cypermethrin-PHI 7 days

Management-chemical control: COMMERCIAL USE

  • acetamiprid (Assail 70WP) at 0.57 to 1.0 oz/100 gal water (2.3 to 4.1 oz/A). PHI 14 days. REI 12 hr. No more than 4 applications per season.
  • azadirachtin (neem oil)-Some formulations are OMRI-listed for organic use.
  • Beauveria bassiana (Bioceres WP)-Biological, entomopathogenic fungi. 1 to 3 lb/A. PHI 0 days. REI 4 hr. OMRI-listed for organic use.
  • clothianidin (Belay) at 3 to 6 oz/100 gal water. Use the low rate for smaller infestations or smaller trees. Apply no more than 0.2 lb ai/Acre per year.
  • diazinon (Diazinon AG 500) at 1 pint/250 to 400 gal water/A. No more than one application per season. PHI 45 days. REI 18 days. Washington and Oregon only.
  • flupyradifurone (Sivanto) at 7.0 to 10.5 fl oz/A. PHI 7 days. REI 4 hr. Use no more than 28 fl oz/Acre/year.
  • flonicamid (Beleaf 50 SG) at 2.0 to 2.8 oz/A. Use low rate for building population, high rate for damaging population. PHI 40 days. REI 12 hr.
  • imidacloprid (Admire Pro, generics) at 3.4 to 7 fl oz/A. PHI 7 days. REI 12 hr. Can be ground-applied or chemigated. See label details.
  • imidacloprid+beta-cyfluthrin (Leverage 360) at 2.8 oz/A. PHI 14 days. REI 12 hr.
  • imidacloprid+cyfluthrin (Leverage 2.7) at 3.8 to 5.1 oz/A. PHI 14 days. REI 12 hr.
  • kaolin-Some formulations are OMRI-listed for organic use.
  • oils-Various vegetable (non-mineral) oils are registered and may be useful as postharvest and delayed dormant sprays. Essential oil sprays can also be useful in-season. Many of these are OMRI-listed for organic use.
  • spirotetramat (Movento) at 6 to 9 fl oz/A. PHI 7 days. REI 1 day.
  • sulfoxaflor (Closer SC) at 1.5 to 2.75 oz/A. PHI 7 days.