Walnut-Aphid

Includes

Dusky winged aphid (Callipterus juglandis)
Walnut aphid (Chromaphis uglandicola)

Pest description and crop damage Walnut aphids are pale yellow, much smaller than the dusky-veined aphid, and feed on the lower surface of leaves. Dusky-veined aphids have dark banded spots on their backs and are found feeding along the mid-vein on the top surface of leaves. Both aphids suck plant juice and deposit honeydew. Feeding of the dusky-veined aphid causes the leaf midrib to turn black. The honeydew is toxic to the husk of some varieties and turns it black. High populations may lead to leaf drop and a loss of nut yield and quality. Aphid populations are most damaging in spring and early summer when nuts are developing rapidly.

Pest monitoring Begin observing shoots prior to budbreak, as management is best undertaken early while the aphids are small.

Management-biological control

In the 1980s, a parasitic wasp was introduced (Trioxys pallidus) which has reduced problems with the walnut aphid substantially. In addition, aphids have many natural enemies including ladybeetles, syrphid fly larvae, and green lacewings. Avoid broad-spectrum insecticide applications when parasitoids are active against aphids.

Management-cultural control

Aphid populations tend to be higher in plants that are fertilized liberally with nitrogen. Home orchardists: 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

Dormant-season spray

Apply only during dormant or delayed-dormant period. Use enough water to cover tree thoroughly including small limbs and shoots.

  • superior-type oil

Growing-season spray

Predators usually reduce aphid populations. Apply pesticides only when predators are few and aphid population is heavy.

  • acetamiprid-Do not apply until after trees have flowered or when bees are actively foraging. Do not make more than one application a year. PHI 7 days.
  • azadirachtin (neem oil)-Some formulations are OMRI-listed for organic use.
  • Beauveria bassiana-Some formulations are OMRI-listed for organic use.
  • bifenthrin
  • carbaryl
  • esfenvalerate
  • gamma-cyhalothrin
  • horticultural oil-Some formulations OMRI-listed for organic use.
  • imidacloprid-Do not apply until after trees have flowered or when bees are actively foraging. Do not make more than one application a year. PHI 7 days.
  • insecticidal soap-May require several applications to be effective. Some formulations are OMRI-listed for organic use.
  • kaolin clay (Surround® at Home®)-Some formulations are OMRI-listed for organic use.
  • lambda-cyhalothrin
  • permethrin
  • plant-derived essential oils (clove, garlic, peppermint, rosemary oil, etc.)-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.
  • sulfur
  • sulfur/oil/pyrethrins (Natria insect, disease and mite control)
  • zeta-cypermethrin

Management-chemical control: COMMERCIAL USE

Aphids seldom warrant control. Predators usually reduce aphid populations. Pesticide applications are advised only when predators are few and aphid population is heavy.

  • acetamiprid (Assail 30SG) at 0.047 to 0.18 lb ai/a. No more than 4 applications and a maximum of 0.72 lb ai/a per growing season. Retreatment interval 14 days. PHI 14 days.
  • alpha-cypermethrin (Fastac EC) at 0.02 to 0.025 lb ai/a. Retreatment interval 7 days. Maximum 0.075 lb ai/a. PHI 7 days.
  • azadiracthtin (Azasol, Azatin, others)-See label for rates. Some formulations are OMRI-listed for organic use. REI 4 hr.
  • Beauvaria bassiana (Mycotrol ESO)-See label for rates. OMRI-listed for organic use.
  • beta-cyfluthrin (Baythroid XL) at 0.19 to 0.022 lb ai/a. Maximum per 14 day and per season: 0.022 lb ai/a. PHI 14 days.
  • bifenthrin (Brigade WSB) at 0.05 to 0.2 lb ai/a. PHI 7 days. REI 12 hr.
  • bifentrin/abamectin B1 (Athena) at 7.5 to 20 fl oz/a. Retreatment interval 21 days. Maximum of 2 applications per season. PHI 21 days.
  • chlorpyrifos/gamma-cyhalothrin (Cobalt) at 26 to 57 fl oz/a. PHI 14 days. Do not make more than 2 applications per season of Cobalt or other product containing chlorpyrifos for walnuts.
  • clothianidin (Belay) at 0.05 to 0.1 lb ai/a. Maximum 0.2 lb ai/a. PHI 21 days.
  • cyantraniliprole (Exirel) at 13.5 to 20.5 oz. Retreatment interval 7 days. PHI 5 days. REI 12 hr.
  • deltamethrin (Delta Gold) at 0.02 to 0.033 lb ai/a. Maximum 0.165 lb ai/a. Retreatment interval 7 days. PHI 21 days.
  • esfenvalerate (Asana XL) at 0.05 to 0.1 lb ai/a. PHI 21 days. REI 12 hr. Do not exceed 0.2 lb ai/a per season. Do not feed or graze livestock on treated orchard floors. Extremely toxic to fish and aquatic habitat.
  • horticultural oil-Some formulations OMRI-listed for organic use.
  • imidacloprid (Admire Pro) at 7 to 14 oz for soil application or 1.2 to 2.4 oz for foliar application. PHI 7 days. REI 12 hr. Generic formulations of imidacloprid are available.
  • insecticidal soap (M-Pede) at 2% solution. PHI 0 days. Some formulations are OMRI-listed for organic use.
  • lambda-cyhalothrin (Warrior II) at 0.02 to 0.04 lb ai/a. PHI 14 days. REI 1 day. Do not exceed 0.16 lb ai/a per season or 0.12 lb ai post bloom.
  • malathion (Malathion 57% EC) at 0.2 to 0.4 oz/a. PHI 7 days. REI 12 hr.
  • methidathion (Supracide 25W) at 4 to 12 lb/a. PHI 7 days. REI 2 to 14 days depending on the rate. Apply as a cover spray when aphids appear. Do not tank-mix with oils, which can injure trees. Do not graze.
  • pyriproxyfen (Esteem 35WP) at 4 to 5 oz /a. PHI 21 days. REI 12 hr. Do not exceed two applications per season.
  • spinosad (Success 2L) at 4 to 10 fl oz/a. PHI 14 days. REI 4 hr. Allow at least 7 days between treatments. Do not exceed 29 fl oz/a per year.
  • spinosad (Entrust SC) at 4 to 10 oz/a. PHI 14 days. REI 4 hr. OMRI-listed for organic use.
  • spirotetramat (Movento) at 6 to 9 fl oz. PHI 7 days.
  • sulfoxaflor (Closer SC) at 1.5 to 2.75 oz. PHI 7 days. REI 12 hr.
  • tolfenpyrad (Bexar) at 17 to 27 oz. PHI 14 days. REI 12 hr.
  • zeta-cypermethrin (Mustang, Mustang Max, Mustang Maxx) at 0.02 to 0.025 lb ai/a. Maximum of 0.125 lb ai/a per seaon. PHI 21 days.